湿法刻蚀调控形貌和暴露晶面及其性能研究

Considering the special effect of patterned r-plane sapphire substrate for the growth of nonpolar GaN, a model is proposed by introducing a modified Wulff- Joccodine method to identify the topography of structural facets. The r-plane sapphire etching field is obtained by rotating the c-plane sapphire etch rate hemisphere, resulting in different structural characteristics. The proposed model provides a reliable prediction of microstructure topography by key orientations etched on r-plane sapphire and explains their morphological evolution process.

Special surface plays a crucial role in nature as well as in industry. Here, the surface morphology evolution of ZnO during wet etching is studied by in situ liquid cell transmission electron microscopy and ex situ wet chemical etching. Many hillocks are observed on the (000 1 ¯ ) O-terminated surface of ZnO nano/micro belts during in situ etching. Nanoparticles on the apex of the hillocks are observed to be essential for the formation of the hillocks, providing direct experimental evidence of the micromasking mechanism. The surfaces of the hillocks are identified to be {01 1 ¯ 3 ¯ } crystal facets, which is different from the known fact that {01 1 ¯ 1 ¯ } crystal facets appear on the (000 1 ¯ ) O-terminated surface of ZnO after wet chemical etching. O2 plasma treatment is found to be the key factor for the appearance of {01 1 ¯ 3 ¯ } instead of {01 1 ¯ 1 ¯ } crystal facets after etching for both ZnO nano/micro belts and bulk materials. The synergistic effect of acidic etching and O-rich surface caused by O2 plasma treatment is proposed to be the cause of the appearance of {01 1 ¯ 3 ¯ } crystal facets. This method can be extended to control the surface morphology of other materials during wet chemical etching.

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The development of a technology for the microfabrication of Bi2Sr2CaCu2O8+δ (Bi2212) crystals is essential for realizing high-performance terahertz emitting devices based on Bi2212 single crystals. We developed an anisotropic wet-etching method using potassium hydroxide solution to improve the etching accuracy of Bi2212 crystal chips. Etching solutions with potassium hydroxide concentration of 10–13 wt. % and temperatures of approximately 40–45 °C are suitable for sample etching. The developed etching method enabled us to obtain crystal chips with sidewall angles of approximately 90°. In the case of a crystal chip with a thickness of ∼6 μm, the undercuts from the edges of the photomask were ∼1.5 μm, which were significantly shorter than those obtained in previous studies using acidic solutions (∼5–10 μm). The etching rate of the developed solution (0.1 μm/min) was lower than that of the acidic solutions (∼20 μm/min), which provided suitable etching conditions for the samples. Devices using Bi2212 crystal chips, fabricated using the developed technique, exhibited clear terahertz emissions, similar to those reported in previous studies. The enhanced accuracy of the proposed etching process is expected to improve the device characteristics of Bi2212 terahertz emitters, particularly in terms of the emission power and frequency.

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The dry etching of high crystal quality c-plane AlN grown by metal organic chemical vapor deposition was examined as a function of source and chuck power in inductively coupled plasmas of Cl2/Ar or Cl2/Ar/CHF3. Maximum etch rates of ∼1500 Å min−1 were obtained at high powers, with selectivity over SiO2 up to 3. The as-etched surfaces in Cl2/Ar/CHF3 have F-related residues, which can be removed in NH4OH solutions. The Al-polar basal plane was found to etch slowly in either KOH or H3PO4 liquid formulations with extensive formation of hexagonal etch pits related to dislocations. The activation energies for KOH- or H3PO4-based wet etching rates within these pits were 124 and 183 kJ/mol, respectively, which are indicative of reaction-limited etching.

Wet etching of quartz is an important microfabrication technique for etching and patterning structures by etching material surfaces using liquid chemicals. However, because of its complex anisotropy, the simulation of the etching results is often difficult to predict and control. In this paper, we propose a new modeling method based on Monte Carlo method by calculating the offsets between the cells of quartz atoms, and a new atomic coding method that can quickly determine the characteristic properties around each atom and distinguish between bonds with the same bond lengths but different types. Compared with the traditional modeling method, the algorithm reduces the amount of computation and computation time by avoiding a large number of computational processes during modeling and the need to traverse all other atoms to determine the configuration state of the target atom after the modeling is completed. The subsequent simulation results are basically consistent with the experimental graphical comparisons, providing a new modeling method and atom encoding approach for the simulation modeling of etched structure and morphology prediction of other cut types.

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This paper introduces a MEMS wet etching process simulation platform based on adaptive octree level set method (LSM). Under the limited memory, the mesh adaptive technique for octree can solve the level set simulation problem of MEMS wet etching with large scale, high aspect ratio and fine structure. The octree grid is nonuniform, and the advanced interpolation technology can accurately obtain the signed distance value of the neighbor grid. An advanced interpolation technology is also proposed to solving this problem. Finally, LSM based on adaptive octree technology is applied to the simulation of C-plane sapphire wet etching process. The simulation results indicate that this method can improve the calculation accuracy, reduce the calculation memory and reduce the calculation time in the process of MEMS wet etching simulation.

Understanding the device characteristics associated with the shape and size of crystal chips is a key requirement for developing high-performance terahertz (THz) wave-emitting devices made of high-temperature superconductor Bi2Sr2CaCu2O8+δ(Bi2212) crystal chips, because these parameters reflect the emission frequency, emission power, self-heating conditions, and impedance matching. Wet-etching techniques are beneficial for creating comparable emitting chips from the same crystal fragment to further understand the above points regarding using Bi2212-crystal chips. Using wet-etching techniques, we prepared rectangular crystal chips with the same area using three different width (w) and length (L) aspect ratios and compared their emission characteristics. The range of the observed emission frequencies tended to be less dependent on the w/L ratio. However, the three samples differed significantly in terms of the excitation modes expected from the w/L ratio. When the aspect ratio approached one, the results indicated a tendency to resonate in the higher excitation modes. The excitation modes along the width of the chip were suppressed by decreasing the w/L ratio owing to the increased resonance frequencies of the transverse magnetic TM(m,0) modes. Although further studies are required, especially in terms of output enhancement, the results obtained herein are expected to aid in producing devices that can operate in the desired excitation mode.

Wet chemical etching of silicon has been a topic of significant interest due to its importance in microelectromechanical systems (MEMS), nanotechnology, and semiconductor device fabrication. Many kinds of MEMS components (e.g., cavity, diaphragm, cantilever, etc.) are fabricated through wet anisotropic etching-based silicon bulk micromachining of {100} and {110} oriented silicon wafers. Wet anisotropic etching of silicon is primarily carried out using alkaline solutions such as potassium hydroxide (KOH), tetramethylammonium hydroxide (TMAH), etc. The etching rate of Si{111} crystal planes is significantly slower compared to other planes like Si{100} and Si{110} as a result of its atomic structure and surface properties. Therefore, the Si{111} crystal plane is of particular interest owing to its unique properties and potential applications. In this work, we report the wet anisotropic etching characteristics of Si{111} in KOH with addition of isopropyl alcohol (IPA). Surface morphology of the etched Si{111} surfaces was examined using confocal laser scanning microscopy (CLSM). In all experimental scenarios, the Si{111} crystal surface gives rise to triangular etch pits, the size and depth of these etch pits are contingent upon the etching time. Following your advice, we revised the abstract phrase “become more sharper” in the summary and quantified the angle data of the triangle. The entire statement has been specifically modified to Furthermore, when the additive IPA is incorporated into the etchant, the corners of these triangular etch pits on the surface transitions from rounded to sharp (with each angles of approximately 60°), indicating that the overall shape of these triangular etch recesses approaches that of an equilateral triangle. In addition, the theory of crystal cleavage is introduced to explain the formation mechanism of surface triangular flat-bottom etch pits during the etching process of Si{111} crystal planes. At the same time, the relevant experiments on Si{111} samples with a SiO2 mask layer on the surface have been completed, and the results verify the correctness of the analysis of the relevant mechanism. The relevant results and mechanism presented in this article are of large significance for engineering applications in both academic and industrial laboratories.

The development of low-resistance Gallium nitride (GaN) trench metal-oxide semiconductor (MOS) channels is required. Since the trenches are formed by dry etching, their surfaces are inevitably exposed to plasma, leading to plasma-induced damage. Therefore, wet etching to remove the damaged layer is an important surface treatment. Conventionally, tetramethylammonium hydroxide (TMAH) solution has been employed for this purpose, which forms a vertical trench sidewall defined by the 011¯0 m-face. Comparing the MOS properties on different crystal faces would be highly informative, so we invented a H3PO4 wet etching technique that forms tilted trench sidewalls. Using these two kinds of trench sidewalls, we investigated MOS channel properties. As a result, we revealed that refraining the GaN surface from being exposed to plasma during the SiO2 deposition is critically important on those crystal faces. A maximum channel mobility of 310 cm2/Vs was obtained on the m-face treated with TMAH, while 245 cm2/Vs was obtained for the tilted sidewalls treated with H3PO4. These results indicate that by paying enough attention to the GaN surface preparation process and the structure, the interface between SiO2/GaN sidewalls exhibits a high MOS channel mobility of >300 cm2/Vs.

The influence of alcohol as a solvent on the wet etching of GaN pillars formed by dry etching was investigated using tetramethylammonium hydroxide (TMAH) solutions. TMAH solutions diluted with de-ionized water (DIW), ethanol and isopropyl alcohol (IPA) were used in the wet etching. Pillars formed on the (0001) surface by dry etching were subsequently selectively etched toward their sidewalls in the TMAH solution rather than along the c-axis direction. The etching progression was the same regardless of the kinds of solvents in the TMAH solutions. However, the etch rates of TMAH solutions diluted with DIW and IPA were considerably faster than those with ethanol. Furthermore, it was found that the etch rate could be varied by changing the IPA concentration in the solutions. The difference in etch rates suggested that the adsorption of alcohol on the crystal surface depends on the type and the concentration of the alcohol.

The complex anisotropic nature of sapphire wet etching significantly impedes the preparation of patterned sapphire substrates. This paper investigates the measurement of wet etching rates and Level Set simulation of patterned sapphire substrates to advance their application. The study introduces a segmented hemispherical measurement method and corresponding experimental apparatus to measure the etching rates of complete crystal planes of sapphire. The accuracy of these measurements is analyzed using the Wulff–Jaccodine method. Subsequently, C-plane sapphire substrates with various masks undergo wet etching using a designed wafer insertion-type rotary experimental device, and the etched structures are simulated using the Level Set method. The findings demonstrate that the proposed measurement method effectively prevents shallow etching and over etching phenomena of the hemisphere, yielding accurate etching rates of complete crystal planes. The experimental device successfully prevents micro-mask etching and ensures proper wet etching of wafers. The simulated results closely align with experimental outcomes, potentially reducing the design and preparation cycle of patterned sapphire substrates while minimizing costs.

This paper presents an atomic structure method to calculate anisotropic wet etching rates of sapphire crystal planes for the first time. Each sapphire crystal plane can be regarded as composed of three crystal plane unit A0, B0 and C0 in different combinations based on the distribution of atom types on the surface sites of each crystal plane at $< 11\bar{2}0 >$ direction. The wet etching rates of each crystal plane can be calculated accurately by analyzing the wet etching process of sapphire crystal planes with the step flow mechanism. The wet etching rates calculated by this method is in good agreement with the experimental etch rates, which demonstrates the validity of the proposed method.

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We realize strongly confined quantum dots (QDs) in InAs nanowires (NWs) by combining epitaxial crystal-phase control with chemical wet etching. A strong axial confinement is first introduced by growing closely spaced wurtzite (WZ) tunnel barriers in NWs to enclose a zinc blende (ZB) QD. The NW cross-section is then reduced by isotropic etching to obtain very small QDs, with a maximum observed charging energy > 30 meV. Using low-temperature electrical characterization and finiteelement method simulations, we study how charging energies and the onset of electron filling scale with QD diameter. For extremely small diameters, we identify a regime where stray capacitances become non-negligible, limiting further increase in charging energy by diameter reduction alone. This approach to increasing confinement is particularly relevant for understanding the strong spin-orbit interaction observed in crystal-phase QDs, possibly linked to polarization charges at the WZ/ZB interfaces. Small diameter QDs allow considerably weaker interfering electric fields when studied, but the QDs cannot be realized with epitaxial growth alone due to a loss of crystal phase control.

Silicon carbide (SiC) is a promising material for a wide range of applications, including mechanical nano‐resonators, quantum photonics, and non‐linear photonics. However, its chemical inertness poses challenges for etching in terms of resolution and smoothness. Herein, a novel approach known as helium ion‐bombardment‐enhanced etching (HIBEE) is presented to achieve high‐quality SiC etching. The HIBEE technique utilizes a focused helium ion beam with a typical ion energy of 30 keV to disrupt the crystal lattices of SiC, thus enabling wet etching using hydrofluoric acids and hydrogen peroxide. The etching mechanism is verified via simulations and characterization. The use of a sub‐nanometer beam spot of focused helium ions ensures fabrication resolution, and the resulting etched surface exhibits an extremely low roughness of ≈0.9 nm. One of the advantages of the HIBEE technique is that it does not require resist spin‐coating and development processes, thus enabling the production of nanostructures on irregular SiC surfaces, such as suspended structures and sidewalls. Additionally, the unique interaction volume of helium ions with substrates enables the one‐step fabrication of suspended nanobeam structures directly from bulk substrates. The HIBEE technique is expected to facilitate and accelerate the prototyping of high‐quality SiC devices.

The processing of integral beam structures in quartz sensor devices is mostly done by wet etching, and the anisotropy of quartz etching makes the results of the etching process unpredictable, so it is necessary to predict the results of the process by simulation before the etching process. In this paper, a quartz beam structure wet etching simulation system is developed based on the hull method. The system can realise the simulation of beam structure of quartz crystal plate with different cutting type. By inputting the width of etching mask, offset distance and thickness of crystal plate, the etching samples of beams with different widths and thicknesses under different etching time are simulated, which provides guidance for the processing of quartz integral beam structure.

Sapphire crystal is extensively used in fabrication of advanced micro/nano devices. Due to its crystalline structure, sapphire shows more complicated properties in wet etching process. This paper for the first time investigates the measurement of the overall orientation dependence of the etch rate for sapphire under different etchant. The experiment shows that sapphire crystal has six high etch rate regions in etch rate distribution, which is quite different from other trigonal crystal materials. The change in surface morphology also strongly depends on the crystallographic orientation. We demonstrate etch rate distribution and texture of morphology as a function of orientation. The overall etch rate distribution successfully explains the transient and stable structural facets appearing on the sidewalls of trenches, cavities, mesas and complex structures during anisotropic etching, which is essential for the applications such as patterned sapphire substrates (PPS).

Anisotropic etching is a novel and effective means to modulate facets of metal-organic frameworks (MOFs) which deserves continuous exploration. Herein, we developed a facet-selective protection and etching method to achieve morphology control of MOFs. Our approach exploits the compositional differences between the facets of zeolitic imidazolate framework-67 and the moderate coordinating and etching properties of ethylenediaminetetraacetic acid disodium salt (EdtaH2Na2). The selected chelator, EdtaH22-, can specifically coordinate with unsaturated metal sites on the {100} crystal planes, protecting them from proton etching and meanwhile releasing protons. Moreover, the released protons with locally high concentration led to the etching of the unprotected {110} facets, ultimately forming nanocrystals with selectively exposed surfaces. This anisotropic etching strategy facilitates the precise modification of MOF surfaces, which is anticipated to play a crucial role in enhancing their properties in different application areas.

Crystalline thin films of LiGa5O8 have recently been realized through epitaxial growth via mist-chemical vapor deposition. The single crystal, spinel cubic LiGa5O8 films show promising fundamental material properties and, therefore, make LiGa5O8 a potential enabling material for power electronics. In this work, chemical resistance and etch susceptibility were investigated for the first time on crystalline LiGa5O8 thin films with various wet chemistries. It was found that LiGa5O8 is very chemically resistive to acid solutions, with no apparent etching effects observed when placed in concentrated acid solutions of HCl, H2SO4, HF, or H3PO4 at room temperature. In contrast, orthorhombic (010) LiGaO2 shows effective etching in HCl solutions at varying dilution concentrations, with etch rates measured between 8.6 [1000:1 (DI water: HCl concentration)] and 6092 nm/min (37 wt. % HCl). The inductively coupled plasma reactive ion etching (ICP-RIE) of LiGa5O8 using BCl3/Ar and CF4/Ar/O2 gas chemistries was investigated. The etching rate and surface morphology of etched surfaces were examined as a function of RIE and ICP power. Using a CF4/Ar/O2 gas chemistry with an RIE power of 75 W and an ICP power of 300 W resulted in smooth etched planar surfaces while maintaining an etch rate of ∼24.6 nm/min. Similar dry etching studies were performed for LiGaO2. It was found that the BCl3/Ar gas chemistry was better suited for LiGaO2 etching, with similar surface morphology quality being obtained after etching as prior etching when a RIE power of 15 W and an ICP power of 400 W is utilized.

The research designs a novel micrometer-level hemisphere structure and develops a focused ion beam process to fabricate the high-precision microsphere samples. The experiment successfully determines the overall distribution of the etch rate of Ga-face GaN in an anisotropic etchant for the first time. Subsequently, based on the level set method, an etching process model supporting a combined focused ion beam and wet etching process for GaN is established, successfully simulating the entire etching process of nanowire arrays.

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In this study, a kind of rectangular suspended single crystal Si nanowire with (001) planes and along <001> direction is developed via a CMOS-compatible top-down scheme. In this scheme, the nanowires are formed by anisotropic etching of TMAH on different silicon crystallography orientations. By designing the initial orientations of hard mask patterns, the rectangular suspended silicon nanowires can be successfully fabricated without any sacrificial epitaxial layers. Due to the damage-free process and the high mobility on (001) planes, this scheme will provide a high-quality channel for the future gate-alI-around silicon transistor technology.

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Ferroelectric domain walls, agile nanoscale interfaces of polar order, can be selectively controlled by electric fields for their position, conformation, and function, which is ultimately the key to realizing novel low-energy memory and computing structures. LiNbO3 single-crystal domain wall memory has the advantages of high operational speed, high integration density, and virtually unlimited endurance cycles, appearing as a good solution for the next generation of highly miniaturized low-energy memories. However, the etching process poses significant challenges in the nanofabrication and high-density integration of LiNbO3 domain-wall memories. Here, we employed a hybrid etching technique to achieve smooth sidewalls with a 90° inclined angle, leading to a 24% reduction in the coercive field and a 2.5-fold increase in the linear domain wall current density with a retention time of more than 106 seconds and endurance of over 105 writing cycles. Combined with the results of X-ray diffraction patterns and X-ray photoelectric spectra, it is concluded that the excellent electrical performance is related to the formation of an oxygen-deficient LiNbO3-x layer on the sidewall surface during the wet chemical etching process, which is a conductive layer that reduces the thickness of the "dead" layer between the side electrodes and the LiNbO3 cell and rectifies the diode-like wall currents with an onset voltage reduced from 1.23 to 0.28 V. These results prove the high-density integration of ferroelectric domain-wall memories at the nanoscale and provide a new strategy applicable to the development of LiNbO3 photonic devices.

GaN, as a representative of single-crystal group III nitride semiconductors, has excellent properties suitable for processing high-power devices, and anisotropic wet etching allows the preparation of complex and precise microstructures on GaN. In this paper, we propose a simulation method based on continuous cellular automata (CCA) to simulate the etching fabrication process of spoke structures on GaN (0 0 0 1) crystallographic plane. The metamerism rate in the CCA simulation is based on the removal rate of different types of atomic groups, which can be obtained from the step flow rate model established in the GaN <0001> crystallographic zone. The interfacial evolution is based on a step-flow mechanism, with the removal of metastable cells based on the change of metastable cell occupation values. The etching process of four spoke structures spaced at 10° from the (1 0 -1 0) crystallographic plane to the (1 1 -2 0) crystallographic plane is simulated under H3PO4(85%wt) solution conditions at 140°C. Comparing the results after simulated etching with experiments, the tip retraction length and the sidewall shortening distance show small errors, indicating the validity of the CCA simulation.

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A novel octagonal upright micro-pyramid structure was generated by wet chemical anisotropic etching on a monocrystalline silicon wafer (100). The primary objectives are to reduce front surface reflectance of silicon wafers, improve wettability, enhance surface morphology, and maximize the area coverage by generated octagonal pyramids. Under rigorous control and observation, the etching process’ response time was maintained precisely. The experimental outcomes show a significant decrease in the optical surface reflectance of silicon wafers, with the lowest reflectance of 8.98%, as well as enhanced surface structure, periodicity, and surface area coverage of more than 85%. The octagonal silicon pyramid was formed with a high etch rate of 0.475 um/min and a much shorter reaction time with the addition of hydrofluoric acid coupled with magnetic stirring (mechanical agitation) at 500 rpm.

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A micropyramid structure was formed on the surface of a monocrystalline silicon wafer (100) using a wet chemical anisotropic etching technique. The main objective was to evaluate the performance of the etchant based on the silicon surface reflectance. Different isopropyl alcohol (IPA) volume concentrations (2, 4, 6, 8, and 10%) and different etching times (10, 20, 30, 40, and 50 min) were selected to study the total reflectance of silicon wafers. The other parameters such as NaOH concentration (12% wt.), the temperature of the solution (81.5°C), and range of stirrer speeds (400 rpm) were kept constant for all processes. The surface morphology of the wafer was analyzed by optical microscopy and atomic force microscopy (AFM). The AFM images confirmed a well-uniform pyramidal structure with various average pyramid sizes ranging from 1 to 1.6 μm. A UV-Vis spectrophotometer with integrating sphere was used to obtain the total reflectivity. The textured silicon wafers show high absorbance in the visible region. The optimum texture-etching parameters were found to be 4–6% vol. IPA and 40 min at which the average total reflectance of the silicon wafer was reduced to 11.22%.

In this paper, we present the results of the study on the fabrication of inverted pyramids on n-type Si wafer by a single-step anisotropic copper-assisted chemical etching. The relationship between etchant composition, etching time and the surface morphology for n-type Si has been investigated. Different surface structures were obtained by adjusting molarity of H2O2, Cu(NO3)2, HF in the etching solution. Cu(NO3)2 amount promoted, while increasing H2O2 amount over optimum value reduced the etch rate. By optimizing etching duration, etching temperature and etchant composition, uniform distribution of inverted pyramids with dimensions around 2 μm was achieved. Surface average weighted reflectance was reduced to 5.67% in the wavelength range of 400-1000 nm with novel surface texturing method.

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Fabrication of plasmonic structures on a gold film is a well-established approach to improve the performance of surface plasmon resonance (SPR) sensors. However, traditional fabrication techniques, such as photolithography, electron beam lithography (EBL), and focused ion beam (FIB) milling, often involve complex procedures and costly equipment. In this study, we present a mask-free, convenient method to fabricate robust plasmonic structures on the surface of z-cut α-quartz by combining femtosecond laser-induced modification with chemical etching for high-sensitivity Kretschmann configuration SPR sensing. We find that the etching process of laser-modified α-quartz in ammonium bifluoride (NH4HF2) solution proceeds in two distinct stages: isotropic etching and anisotropic etching. By comparing the etching morphology of the craters ablated by femtosecond laser with wavelengths of 400 and 800 nm, we observe that due to the lower threshold fluence and steeper crater profile, the 400 nm laser can induce more pronounced anisotropic etching, leading to sharper inverted pyramid structures. A 5-nm-thick Cr film and a 50-nm-thick Au film are then deposited on the patterned quartz surface, which is used to detect the refractive indices (RIs) of glycerol solutions as an SPR sensor. The inverted pyramid structures can enhance the localized electric fields, causing a red shift of the resonance peak and thereby improving the sensitivity of the SPR sensor. The sensor demonstrates a sensitivity of 4662.21 nm/RIU, achieving a 21.51% improvement compared with a traditional SPR sensor with a plain Au film under the same light incident angle. The refractive index (RI) resolution reaches 2.7 × 10-5 RIU, and the figure of merit (FOM) is 85.36 RIU-1. Femtosecond laser-assisted chemical etching offers an efficient and convenient method for fabricating plasmonic structures on α-quartz. The high-sensitivity SPR sensors developed through this approach demonstrate promising potential for applications in fields such as medical diagnostics, disease detection, and environmental monitoring.

Despite considerable advancements in the synthesis of two-dimensional (2D) mesoporous nanomaterials, achieving precise control over their components, morphology, lateral dimension, and thickness remains a formidable challenge. Here, we report a rational interface-confined anisotropic assembly strategy that enables the synthesis of square-shaped 2D mesoporous nanosheets with finely tunable features including compositions (metal ion-doped mesoporous polydopamine or silica), lateral dimensions (100-200 nm), thicknesses (14-25 nm), and in-plane mesopore sizes (8-20 nm). In this strategy, truncated rhombic dodecahedral ZIF-8 metal-organic framework (MOF) nanoparticles serve as seeds to direct the selective assembly of mesoporous micelles onto their six {100} facets. The geometric confinement of these square facets guides the interfacial organization of micelles into 2D sheet-like structure, faithfully inheriting the square geometry. Following etching of the ZIF-8 seeds, the resulting nanosheets preserve their well-defined square-shaped 2D morphology and mesoporous architecture. This versatile approach enables the fabrication of diverse 2D mesoporous tunable structural attributes and metal-ion dopants. As a proof of concept, mPDA-Zn2+/Fe2+ nanosquares, featuring a uniform 2D architecture, near-infrared (NIR) photothermal properties, and Fenton-like catalytic activity, demonstrate synergistic therapeutic effects. Compared to conventional spherical analogs (1.08 × 10-8 M/s), these nanosquares (2.11 × 10-8 M/s) achieve nearly doubled maximum reaction rates and achieved remarkable tumor inhibition of up to 90%. Overall, this study establishes a novel approach for the precise engineering of 2D mesoporous nanosquares with controllable parameters, unlocking new opportunities for applications in biomedicine and beyond.

The morphology and size control of anisotropic nanocrystals are critical for tuning shape-dependent physicochemical properties. Although the anisotropic dissolution process is considered to be an effective means to precisely control the size and morphology of nanocrystals, the anisotropic dissolution mechanism remains poorly understood. Here, using in situ liquid cell transmission electron microscopy, we investigate the anisotropic etching dissolution behaviors of polyvinylpyrrolidone (PVP)-stabilized Ag nanorods in NaCl solution. Results show that etching dissolution occurs only in the longitudinal direction of the nanorod at low chloride concentration (0.2 mM), whereas at high chloride concentration (1 M), the lateral and longitudinal directions of the nanorods are dissolved. First-principles calculations demonstrate that PVP is selectively adsorbed on the {100} crystal plane of silver nanorods, making the tips of nanorods the only reaction sites in the anisotropic etching process. When the chemical potential difference of the Cl− concentration is higher than the diffusion barrier (0.196 eV) of Cl− in the PVP molecule, Cl− penetrates the PVP molecular layer of {100} facets on the side of the Ag nanorods. These findings provide an in-depth insight into the anisotropic etching mechanisms and lay foundations for the controlled preparation and rational design of nanostructures.

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The synthesis of nanoparticles with a hollow and anisotropic structure have attracted considerable interest in synthetic methodology and diverse potential applications, but endowing them with delicate control of the hollow structure and outer anisotropic morphology remains a significant challenge. In this study, anisotropic nanoparticles with hat-like morphology are prepared via a kinetics-controlled growth and dissolution strategy. Starting from forming solid polymer nanospheres with location-specific compositional chemistry distribution based on the distinct reactivity and growth kinetics of two reactants. After etching by acetone, the inhomogeneity nanospheres transformed to hat-like nanoparticles through the kinetics-controlled dissolution of two kinds of precursors. Due to chemical etching and repolymerization reactions occurring within a single nanospheres, an autonomous asymmetrical repolymerization and concave process are observed, which is novel at the nanoscale. Moreover, regulating the amount of ammonia significantly impacts the growth kinetics of precursors, primarily affecting the composition and subsequent dissolution process of solid polymer nanospheres, which play an important role in constructing polymer nanoparticles with varying morphologies and internal structures. The as-synthesized hat-like carbon nanoparticles with an open carbon structure, highly porous shell, and favorable N-doped functionalities demonstrate a potential candidate for lithium-sulfur batteries.

Rhombohedral polytype transition metal dichalcogenide (TMDC) multilayers exhibit non-centrosymmetric interlayer stacking, which yields intriguing properties such as ferroelectricity, a large second-order susceptibility coefficient χ(2), giant valley coherence, and a bulk photovoltaic effect. These properties have spurred significant interest in developing phase-selective growth methods for multilayer rhombohedral TMDC films. Here, we report a confined-space, hybrid metal-organic chemical vapor deposition method that preferentially grows 3R-WS2 multilayer films with thickness up to 130 nm. We confirm the 3R stacking structure via polarization-resolved second-harmonic generation characterization and the 3-fold symmetry revealed by anisotropic H2O2 etching. The multilayer 3R WS2 shows a dendritic morphology, which is indicative of diffusion-limited growth. Multilayer regions with large, stepped terraces enable layer-resolved evaluation of the optical properties of 3R-WS2 via Raman, photoluminescence, and differential reflectance spectroscopy. These measurements confirm the interfacial quality and suggest ferroelectric modification of the exciton energies.

Light-driven synthesis of plasmonic metal nanostructures has garnered broad scientific interests. Although it has been widely accepted that surface plasmon resonance (SPR)-generated energetic electrons play an essential role in this photochemical process, the exact function of plasmon-generated hot holes in regulating the morphology of nanostructures has not been fully explored. Herein, we discover that those hot holes work with surface adsorbates collectively to control the anisotropic growth of gold (Au) nanostructures. Specifically, it is found that hot holes stabilized by surface adsorbed iodide enable the site-selective oxidative etching of Au0, which leads to non-uniform growths along different lateral directions to form six-pointed Au nanostars. Our studies establish a molecular-level understanding of the mechanism behind the plasmon-driven synthesis of Au nanostars and illustrate the importance of cooperation between charge carriers and surface adsorbates in regulating the morphology evolution of plasmonic nanostructures.

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A 2D anisotropic photonic crystal (APC) of bowl-shaped nanoparticles has been fabricated using deformable spherical nanoparticles. The prepared 2D isotropic photonic crystal (IPC) of spherical nanoparticles is transformed into a 2D APC by a chemical etching process, in which the interiors of the spherical nanoparticles are preferentially dissolved to eventually form a bowl-like morphology. Due to the accurate and controllable deformability of the spherical nanoparticles, the arrangement and orientations of the bowl-shaped nanoparticles are highly ordered and uniform. The morphology, optical properties and surface wettability of the 2D APC are all distinct from those of the prepared 2D IPC. This facile strategy provides an easy and low-cost way to fabricate highly ordered and uniform APCs.

Silicon inverted pyramid (IP) structures, with lower reflectance and increased surface recombination, are one of the best choices for light-trapping structures of high-efficiency silicon solar cells. The solution process of IP generally goes through three main steps: porous silicon etched by metal-assisted chemical etching, acid etching, and alkali anisotropic etching. In this paper, the role that acid modification plays in IP preparation and the application of our optimized texture for passivated emitter and rear solar cells (PERC) were investigated. Experimental results show that acid plays a decisive role in optimizing and modifying the morphology of porous silicon; thus, the morphology of porous silicon has no direct influence on the morphology of IP. In addition, the opening size of IP is mainly determined by the size of silicon micron holes modified by the acid process. PC1D simulation results manifest that IPs can increase the short-circuit current density (Jsc) of devices by 1.04 mA/cm2 and power conversion efficiency by 0.55%; hence, our optimized IP-based PERC achieve the highest simulative conversion efficiency of 23.21%. This is an effective and important way to manipulate the structure of IP, which points out the direction of fabrication and application of high-efficiency IP textures.

In this paper, a three dimensional (3D) model was built to elucidate the formation mechanism of the dislocation line, the surface morphology evolution with changing of the cutting angle, and the shape of etched pits after the chemical-mechanical polishing (CMP) process of a (001) homoepitaxial film. The dislocation line of an angle at approximately 60° with respect to the (001) plane observed from the [100] direction originates from the intersection line between the principal (100) plane of the nanopipe and the (11-1) plane in the quasi-tetrahedron region of the (010) plane surface. The surface morphology transition from a groove to a triangular pit is related to inheriting the cutting shape of nanopipes on the (001) surface. The appearance of chevron-shaped etching pits on CMP processed (001) homoepitaxial film can be explained by exposing two lateral (111) and (1-11) facets as sidewall, with the (100) facet remaining as the central core in the defect position after anisotropic wet etching. The 3D model also provides the possibility to explain the different angles and the Burgers vector of dislocation lines in single-crystal substrates, which is due to diverse sidewall planes of the nanopipe intersection with the planes in the quasi-tetrahedron region of the (010) plane.

Biomolecular polymerization motors are biochemical systems that use supramolecular (de-)polymerization to convert chemical potential into useful mechanical work. With the intent to explore new chemomechanical transduction strategies, here we show a synthetic molecular system that can generate forces via the controlled disassembly of self-organized molecules in a crystal lattice, as they are freely suspended in a fluid. An amphiphilic monomer self-assembles into rigid, high-aspect-ratio microcrystalline fibres. The assembly process is regulated by a coumarin-based pH switching motif. The microfibre crystal morphology determines the monomer reactivity at the interface, resulting in anisotropic etching. This effect exerts a directional pulling force on microscopic beads adsorbed on the crystal surface through weak multivalent interactions. We use optical-tweezers-based force spectroscopy to extract mechanistic insights into this process, quantifying a stall force of 2.3 pN (±0.1 pN) exerted by the ratcheting mechanism produced by the disassembly of the microfibres. Disassembling molecular microcrystalline fibres produce mechanical work by dragging micro objects along their surface via biased diffusion.

In this work, ethanol vapor diode sensors based on silicon nanowires (SiNWs) were fabricated. SiNWs were obtained by metal-assisted chemical etching technique (MACE). Surface morphology, electrical and gas sensitive characteristics were studied. It was determined the influence of MACE synthesis parameters on sensor efficiency. Also we showed the effect of presence of textured surface of the silicon wafer and additional processing of it in the isotropic/anisotropic etchants on the device characteristics. The obtained sensors are characterized by a rectification ratio of 1836 and a response value to the gas analyte (ethanol) of 25, which are 11 and 6 times higher than for a silicon sensor without SiNWs, respectively.

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Surface texturing is one of the most important techniques for improving the performance of photovoltaic (PV) device. As an appealing front texture, inverted pyramid (IP) has attracted lots of research interests due to its superior antireflection effect and structural characteristics. In this paper, we prepare high-uniform silicon (Si) IPs structures on a commercial monocrystalline silicon wafer with a standard size of 156 × 156 mm 2 employing the metal-assisted chemical etching (MACE) and alkali anisotropic etching technique. Combining the front IPs textures with the rear surface passivation of Al 2 O 3 /SiN x , we fabricate a novel Si IP-based passivated emitter and rear cell (PERC). Benefiting from the optical superiority of the optimized IPs and the improvement of electrical performance of the device, we achieve a high efficiency of 21.4% of the Si IP-based PERC, which is comparable with the average efficiency of the commercial PERC solar cells. The optimizing morphology of IP textures is the key to the improvement of the short circuit current I sc from 9.51 A to 9.63 A; meanwhile, simultaneous stack SiO 2 /SiN x passivation for the Si IP-based n + emitter and stack Al 2 O 3 /SiN x passivation for rear surface guarantees a high open-circuit voltage V oc of 0.677 V. The achievement of this high-performance PV device demonstrates a competitive texturing technique and a promising prospect for the mass production of the Si IP-based PERC.

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Crystal facet engineering is considered as an effective way to improve photoelectrochemical (PEC) performance. Here, we have developed a nanoetching technology (TiO2 → TiO2/Bi4Ti3O12 → TiO2/BiVO4 → etching-TiO2) to treat rutile TiO2 nanorod films. Interestingly, the technology can induce the exposure of a large number of high energy (101) faces, and the etching-TiO2 film (E-TiO2) showed a significantly enhanced PEC performance. A dynamic study indicates that charge separation and transfer have been obviously improved by such a nanoetching technology. In particular, the charge transfer efficiency (ηtrans) of E-TiO2 reaches 93.4% at 1.23 V vs. RHE without any loaded cocatalyst. The mechanism of PEC performance enhanced by the strategy is experimentally and theoretically unraveled. The improvement of PEC performance is mainly attributed to the shorter distance between H and the neighboring O-b for the HO* intermediates of the rutile (101) facet, which can reduce the energy barrier for the OER. Besides, the driving force for spatial charge separation between the (110) and (101) facets can promote charge separation. This work offers a new and versatile nanotechnology to induce the exposure of the high energy crystal facets and improve the PEC performance.

The development of lithium sulfur (Li-S) battery is considerably limited due to the "shuttle effect" of the soluble lithium polysulfides (LiPSs). The introduction of modified separator at the cathode side...

Defining the redox activity of different surface facets of ceria nanocrystals is important for designing an efficient catalyst. Especially in liquid-phase reactions, where surface interactions are complicated, direct investigation in a native environment is required to understand the facet-dependent redox properties. Using liquid cell TEM, we herein observed the etching of ceria-based nanocrystals under the control of redox-governing factors. Direct nanoscale observation reveals facet-dependent etching kinetics, thus identifying the specific facet ({100} for reduction and {111} for oxidation) that governs the overall etching under different chemical conditions. Under each redox condition, the contribution of the predominant facet increases as the etching reactivity increases.

Shape control of nanocrystals (NCs) is crucial for tuning their assembly behavior and functional properties, yet the precise manipulation of facet composition remains challenging. Here, we present a nanocrystal reshaping strategy to control and modulate the facets of gold (Au) NCs. Our one-pot approach, conducted at room temperature, requires only initial Au NCs, Au3+ ions, and surfactants, distinguishing it from conventional reduction-mediated “etching-and-regrowth” methods. Detailed structural studies using electron microscopy, small-angle X-ray scattering (SAXS), and UV–vis spectroscopy reveal the surfactant-encoded pathway for NC transformation from shaped particles to spheres and then into various polyhedral shapes while preserving the individual particles' volume. The proposed reshaping mechanism involves the dissolution of surface Au atoms into Au+ complexes in the presence of Au3+ and surfactant, followed by surfactant-guided redeposition and formation of facets with different atomic planes. Using the ethanol oxidation reaction (EOR) as a probe, we observe a quasi-linear decrease in onset potential and an increase in activity with increasing {100} facet exposure. This work broadens synthetic strategies by offering precise NC reshaping and facet control.

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High-level control over the surface and interface of II-VI heterostructures is crucial for enhancing charge separation and optimizing active sites, thus improving photocatalytic performance. However, due to variations in surface energy and atomic arrangement among different crystal facets, achieving selective growth of specific facets remains a significant challenge. Herein, we have achieved the selective growth of CdSe or ZnSe dots on the lateral facets or basal facets of two-dimensional CdS or ZnS nanoplates by carefully selecting Se source precursors with different reaction activities. The lateral-ZnSe/CdS exhibit enhanced activity for photocatalytic hydrogen evolution compared to that of basal-ZnSe/CdS, attributed to the high exposure ratio of the basal facets and the effective modulation of photoinduced electron-hole pairs at the lateral-ZnSe/CdS interfaces. This work expands the structural diversity of II-VI heterostructures and also provides a viable strategy to enhance their photocatalytic performance by tailoring the surface and interface structures.

It is an important task to construct intelligent packaging for meat freshness monitoring with good color stability and indication function. Herein, cobalt-based metal-organic framework nanomaterials (Co-MOF, ZIF-67) with antimicrobial and ammonia-sensitive properties were successfully synthesized and added into gelatin/agar (GA) matrix to develop highly stable intelligent films (GA/ZIF67). The incorporation of ZIF-67 nanoparticles enhanced the hydrophobicity (water contact angle >90°) and UV-blocking properties (close to 0.3 % at T280) of the films and endowed the films with excellent antimicrobial activity. The GA/ZIF67 films exhibited outstanding ammonia-sensitive functionality and color stability. More crucially, the ammonia-sensitive color-changing mechanism of ZIF-67 may be attributed to the slow etching effect of its crystal facets upon exposure to ammonia. With the gradual spoilage of beef, the color of the GA/ZIF67 film changes from blue-violet to gray-yellow/orange-red. In addition, the RGB value of the film collected by a mobile device App was used to quickly determine the freshness of beef, reducing individual variability in color perception. Overall, this work offers novel insights into exploring Co-MOF as a new type of indicator for developing a rapid and real-time beef freshness monitoring system, which has great potential for application in the intelligent packaging field.

Single-crystal semiconductor-based photocatalysts exposing unique crystallographic facets show promising applications in energy and environmental technologies; however, crystal facet engineering through solid-state synthesis for photocatalytic overall water splitting is still challenging. Herein, we develop a novel crystal facet engineering strategy through solid-state recrystallization to synthesize uniform SrTiO3 single crystals exposing tailored {111} facets. The presynthesized low-crystalline SrTiO3 precursors enable the formation of well-defined single crystals through kinetically improved crystal structure transformation during solid-state recrystallization process. By employing subtle Al3+ ions as surface morphology modulators, the crystal surface orientation can be precisely tuned to a controlled percentage of {111} facets. The photocatalytic overall water splitting activity increases with the exposure percentage of {111} facets. Owing to the outstanding crystallinity and favorable anisotropic surface structure, the SrTiO3 single crystals with 36.6% of {111} facets lead to a 3-fold enhancement of photocatalytic hydrogen evolution rates up to 1.55 mmol·h-1 in a stoichiometric ratio of 2:1 than thermodynamically stable SrTiO3 enclosed with isotropic {100} facets.

The exposure of workers to propylene glycol monomethyl ether acetate (PGMEA) in manufacturing environments can result in potential health risks. Therefore, systems for PGMEA removal are required for indoor air quality control. In this study, core–shell zeolite socony mobil-5 (ZSM-5)/polyvinylpyrrolidone–polyvinylidene fluoride nanofibers were directly electrospun and partially wet-etched on a mesh substrate to develop a cover-free compact PGMEA air filter. The electrospinning behaviors of the core–shell nanofibers were investigated to optimize the electrospinning time and humidity and to enable the manufacture of thin and light air-filter layers. The partial wet etching of the nanofibers was undertaken using different etching solvents and times to ensure the exposure of the active sites of ZSM-5. The performances of the ZSM-5/PVDF nanofiber air filters were assessed by measuring five consecutive PGMEA adsorption–desorption cycles at different desorption temperatures. The synthesized material remained stable upon repeated adsorption–desorption cycles and could be regenerated at a low desorption temperature (80 °C), demonstrating a consistent adsorption performance upon prolonged adsorption–desorption cycling and low energy consumption during regeneration. The results of this study provide new insights into the design of industrial air filters using functional ceramic/polymer nanofibers and the application of these filters.

We explore the origin of inequivalent etching on equivalent crystal sites by developing a kinetic Monte Carlo model. This new model focuses on the effects of both the diffusion of reactants and ligands, factors that are ubiquitous in wet-chemistry experiments and yet often overlooked or oversimplified in conventional simulations, where the defaults are rapid reactant redistribution and rapid equilibration of ligand adsorption/desorption. Our results show the dramatic differences arising from non-equilibrium ligand control, which cause selective etching at the corners, edges, or facets of Au triangular nanoplates. Basically, the ligand effects provide a positive feedback when etching targets the ligand-deficient sites, and the newly exposed atoms are ligand-free. In contrast, slow reactant diffusion provides a negative feedback, as a reactive site cannot etch unrestrictedly due to the lack of reactants. The dynamic competitions are clearly manifested in the focused etching mode when ligand effects coincide with large diffusion rates. By appropriately setting these two crucial factors, we reproduce in silico a series of etching products that are fully consistent with previous experimental results, along with the details in the shape of notches at the edges and holes on the plane. We believe that our simulation model could be expanded to many other systems and provide detailed inner workings for the mechanisms of abnormal crystal morphologies.

Mg is a low-cost, earth-abundant, and biocompatible plasmonic metal. Fine tuning of its optical response, required for successful light-harvesting applications, can be achieved by controlling Mg nanoparticle size and shape. Mg's hexagonal close packed crystal structure leads to the formation of a variety of unique shapes in colloidal synthesis, ranging from single crystalline hexagonal platelets to twinned rods. Yet, shape control in colloidal Mg nanoparticle synthesis is challenging due to complex nucleation and growth kinetics. Here, we present an approach to manipulate Mg nanoparticle shape by one-pot synthesis followed by colloidal etching with polycyclic aromatic hydrocarbons. We demonstrate how tips and edges in faceted Mg nanoparticles can be preferentially etched to produce quasi-spherical nanoparticles with smooth surfaces. The developed approach provides an essential shape control tool in colloidal Mg synthesis potentially applicable to other oxidising metals.

Tuning the facet exposure of Cu could promote the multi-carbon (C2+) products formation in electrocatalytic CO2 reduction. Here we report the design and realization of a dynamic deposition-etch-bombardment method for Cu(100) facets control without using capping agents and polymer binders. The synthesized Cu(100)-rich films lead to a high Faradaic efficiency of 86.5% and a full-cell electricity conversion efficiency of 36.5% towards C2+ products in a flow cell. By further scaling up the electrode into a 25 cm2 membrane electrode assembly system, the overall current can ramp up to 12 A while achieving a single-pass yield of 13.2% for C2+ products. An insight into the influence of Cu facets exposure on intermediates is provided by in situ spectroscopic methods supported by theoretical calculations. The collected information will enable the precise design of CO2 reduction reactions to obtain desired products, a step towards future industrial CO2 refineries. Regulation of Cu facets to promote electrocatalytic CO2 reduction is interesting and challenging. Here the authors describe a deposition-etch-bombardment synthetic approach to prepare Cu(100)-rich thin film electrodes for CO2 electroreduction with over 50% ethylene Faradaic efficiency at a total current of 12 A.

Designing polyanionic cathodes that simultaneously deliver structural stability and fast Na + transport remains a key challenge for sodium‐ion batteries. Here, we present a facet‐directed lattice engineering strategy that enables controlled crystallographic orientation, defect chemistry, and ion‐transport kinetics in Na 2 FeSiO 4 (NFS). Solvent coordination coupled with thermodynamically guided calcination yields a cubic P 2 1 3 phase with preferential exposure of the (210)/(211) facets. Structural analyses and density functional theory identify these planes as dominant Na + migration highways with ultralow barriers (0.21–0.25 eV) and reversible elastic lattice breathing, supporting near‐zero‐strain operation during cycling. The optimized cathode delivers a high reversible capacity of 173.6 mAh g − 1 at 0.2 C with 92.3% retention, minimal voltage hysteresis, and excellent rate capability. Beyond facet effects, the engineered lattice environment stabilizes the Fe 2 + /Fe 3 + redox balance and an optimized oxygen‐vacancy landscape, while the nanosheet architecture shortens diffusion lengths and buffers interfacial strain; concurrently, in situ–derived carbon forms a percolating conductive network that promotes electron transport and stabilizes the cathode–electrolyte interface (CEI). In pouch‐cell configuration, the material retains >80% capacity with the lowest charge‐transfer resistance among all variants, underscoring scalability and durability. This facet‐governed design concept links atomic‐scale crystal engineering with practical electrodes, offering a general route to high‐rate, long‐life sodium‐ion batteries.

Dental implantation is the most reliable method for replacing missing teeth. Success rate of dental implants is influenced by osseointegration. Surface roughness of implants influences osseointegration by altering surface area and texture, providing stimulation to cells. Sandblasting and acid-etching are common methods for making implant surfaces rough. Main goal of this study was to investigate effects of sandblasting and acid-etching variables, that is, blasting-pressure and acid-temperature, on surface roughness of implants to find the controlled values of variables for a favorable surface roughness. An acceptable surface roughness was assumed to have an arithmetic average height (Sa) between 1 and 2 µm, and an area developed ratio (Sdr) over 50%. Seventy-two titanium-made analogs were sandblasted with three different pressures, that is, 4, 5, and 6 MPa, and three different durations, that is, 15, 30, and 45 s, and then were etched with two different etching temperature, that is, 60°C and 80°C, and two exposure-time, that is, 5 and 10 min (two repetition for each combination). Surface roughness parameters were then measured using a profilometer. Multi-factorial ANOVA was used as statistical analysis method. Results showed that 14 groups demonstrated favorable Sa (1–2 µm), among which just four groups had acceptable Sdr (Sdr > 50%). Among four parameters stated above, which affect sandblasting and acid-etching processes, it was found that blasting duration is the most effective variable on implants roughness. This work highlights the importance of sandblasting and acid-etching parameters for a controlled titanium dental implant surface, which can achieve surface roughness parameters that correspond to those previously reported in the literature as favorable ones for osseointegration.

Magnesium metal batteries (MMBs), recognized as promising contenders for post-lithium battery technologies, face challenges such as uneven magnesium (Mg) plating and stripping behaviors, leading to uncontrollable dendrite growth and irreversible structural damage. Herein, we have developed a Mg foil featuring prominently exposed (002) facets and an architecture of nanosheet arrays (termed (002)-Mg), created through a one-step acid etching method. Specifically, the prominent exposure of Mg (002) facets, known for their inherently low surface and adsorption energies with Mg atoms, not only facilitates smooth nucleation and dense deposition but also significantly mitigates side reactions on the Mg anode. Moreover, the nanosheet arrays on the surface evenly distribute the electric field and Mg ion flux, enhancing Mg ion transfer kinetics. As a result, the fabricated (002)-Mg electrodes exhibit unprecedented long-cycle performance, lasting over 6000 h (> 8 months) at a current density of 3 mA cm-2 for a capacity of 3 mAh cm-2. Furthermore, the corresponding pouch cells equipped with various electrolytes and cathodes demonstrate remarkable capacity and cycling stability, highlighting the superior electrochemical compatibility of the (002)-Mg electrode. This study provides new insights into the advancement of durable MMBs by modifying the crystal structure and morphology of Mg.

Spiral inorganic perovskite nanowires (NWs) possess unique morphologies and properties that allow them highly attractive for applications in optoelectronic and catalytic fields. In popular solution-based synthesis methodology, however, challenges persist in simultaneously achieving precise and facile control over morphological twisting and fantastic carrier lifetimes. Here, a cooperative strategy of concurrently employing selective etching and ligand engineering is applied to facilitate the formation of spiral CsPbBr3 perovskite NWs with an ultralong carrier lifetime of ≈2 µs. Specifically, a novel amine of 1-(p-tolyl)ethanamine is introduced to functionalize as both a selective etchant and the source of forming an effective ligand to passivate the exposed facets, favoring the structural twisting and the enhancement of carrier lifetimes. The twisting behaviors are dependent on the etch ratios, which are essentially associated with the densities of grain boundaries and dislocations in the NWs. The ultralong carrier lifetime and long-term stability of the spiral NWs open up new possibilities for all-inorganic perovskites in optoelectronic and photocatalytic fields, while the cooperative synthesis strategy paves the way for exploring complex spiral structures with tunable morphology and functionality.

The confirmation and regulation of active sites are particularly critical for the design of methanol oxidation reaction (MOR) catalysts. Here, an acid etching method for facet control combined with defect construction was utilized to synthesize Co3O4 nanoparticles on nickel foam for preferentially exposing the (311) facet with enriched oxygen vacancies (VO). The acid-leached oxides exhibited superior MOR activity with a mass activity of 710.94 mA mg-1 and an area-specific activity of 3.390 mA cm-2 as a result of (i) abundant active sites for MOR promoted by VO along with the highly active (311) facet being exposed and (ii) phase purification-reduced adsorption energy (Eads) of methanol molecules. Ex situ X-ray photoelectron spectroscopy proved that highly active CoOOH obtained via the activation of plentiful Co2+ effectively improved the MOR. Density functional theory calculations confirmed that the selective exposed (311) facet has the lowest Eads for CH3OH molecules. This work puts forward acid etching as the facet modification and defect engineer for nanostructured non-noble catalysts, which is expected to result in superior electrochemical performance required for advanced alkaline direct methanol fuel cells.

The application of nanocrystals as heterogeneous catalysts and plasmonic nanoparticles requires fine control of their shape and chemical composition. A promising idea to achieve synergistic effects is to combine two distinct chemical and/or physical functionalities in bimetallic core@shell nanocrystals. Although techniques for the synthesis of single-component nanocrystals with spherical or anisotropic shape are well-established, new methods are sought to tailor multicomponent nanocrystals. Here, we probe etching in a controlled redox environment as a synthesis technique for multicomponent nanocrystals. Our Monte Carlo computer simulations demonstrate the appearance of characteristic non-equilibrium intermediate microstructures that are further thermodynamically tested and analyzed with molecular dynamics. Convex platelet, concave polyhedron, pod, cage, and strutted-cage shapes are obtained at room temperature with fully coherent structure exposing crystallographic facets and chemical elements along distinct particle crystallographic directions. We observe that structural and dynamic properties are markedly modified compared to the untreated compact nanocrystal.

In situ liquid phase transmission electron microscopy (TEM) and three-dimensional electron tomography are powerful tools for investigating the growth mechanism of MOFs and understanding the factors that influence their particle morphology. However, their combined application to the study of MOF etching dynamics is limited due to the challenges of the technique such as sample preparation, limited field of view, low electron density, and data analysis complexity. In this research, we present a study employing in situ liquid phase TEM to investigate the etching mechanism of colloidal zeolitic imidazolate framework (ZIF) nanoparticles. The etching process involves two distinct stages, resulting in the development of porous structures as well as partially and fully hollow morphologies. The etching process is induced by exposure to an acid solution, and both in situ and ex situ experiments demonstrate that the outer layer etches faster leading to overall volume shrinking (stage I) while the inner layer etches faster giving a hollow morphology (stage II), although both the outer layer and inner layer have been etched in the whole process. 3D electron tomography was used to quantify the properties of the hollow structures which show that the ZIF-67 crystal etching rate is larger than that of the ZIF-8 crystal at the same pH value. This study provides valuable insights into MOF particle morphology control and can lead to the development of novel MOF-based materials with tailored properties for various applications.

Rapid, mild, and scalable routes to superhydrophobic corrosion-resistant surfaces are highly desired for light alloys. Here, we report a two-step process that combines etching-assisted phosphating with Al(H2PO4)3 and a subsequent low-surface-energy modification. The treatment builds a micro/nano hierarchical texture together with a phosphate/hydroxide conversion layer within <1 h, yielding a superhydrophobic interface with a static water contact angle of ∼166.9°. Electrochemical impedance spectroscopy (3.5 wt. % NaCl) evidences a pronounced barrier effect, with the low-frequency |Z| at 0.01 Hz reaching ∼108 Ω cm2, and remaining high over 1 h/24 h/7 d immersion. Equivalent-circuit analysis (two time constants) together with postexposure SEM supports a dual-protection mechanism in which the superhydrophobic top layer blocks electrolyte access while the conversion layer passivates the substrate. Mechanical and chemical stability tests further confirm robust performance under abrasion and saline/alkaline exposures. Overall, this mild and time-efficient strategy balances anticorrosion efficacy with wettability control and manufacturability, offering a practical route for protecting light-alloy surfaces.

Thermoelastic stress generated within SiC crystals during the cooling process can induce various types of dislocation defects. In this study, a newly designed cooling protocol was proposed to investigate the correlation between cooldown rate and defect formation in 4H-SiC single crystals. Three distinct cooldown rates, 10~30 °C/min, 1~5 °C/min, and less than 1 °C/min, were applied to assess their impact on the development of thermoelastic stress and resulting crystal quality. Notable variations in ingot color and surface morphology were observed depending on the applied cooldown rate. Dislocation types, including basal plane dislocations (BPDs), threading edge dislocations (TEDs), and threading screw dislocations (TSDs), were quantified through etch pit density (EPD) measurements after molten KOH etching at 600 °C for 14 minutes. The results indicate that higher cooldown rates led to an increase in BPD density due to enhanced plastic deformation, while lower cooldown rates resulted in higher TED and TSD densities, likely due to increased thermal stress. These findings demonstrate that precise control of the cooldown rate is critical for suppressing thermoelastic stress and minimizing defect densities in SiC crystal growth.

Despite the widespread adoption of Zn anodes for aqueous energy storage, the presence of an inherent passivation layer and the polycrystalline interface of commercial Zn foil consistently lead to non‐uniform electrodeposition, undermining stability and practicality. Herein, the study introduces a chemically polished Zn metal anode (CP‐Zn) fabricated via a simple immersion method. This “chemically polishing” process can effectively remove the interfacial passivation layer (de‐passivation), providing ample active sites for plating/stripping and ensuring the uniformly distributed electric field and Zn2+ ion flux. Additionally, selective etching during chemical polishing exposes more (002) crystal planes, promoting homogeneous and smooth zinc deposition while suppressing related side reactions. Demonstrated by CP‐Zn anode, the symmetric cell exhibits stable cycling over 4600 h at 1 mA cm−2 and 240 h at 50% depth of discharge (DOD), with a CP‐Zn||VO2 full cell maintaining ≈75.3% capacity retention over 1000 cycles at 3 A g−1. This chemically polishing strategy presents a promising avenue for advancing the commercialization of aqueous zinc‐ion batteries.

Aqueous Zn metal batteries (ZMBs) are largely hampered by the poor stability of zinc (Zn) anode in aqueous electrolyte due to uncontrollable deposition behavior and parasitic reactions. Hence, a stable Glu@Zn anode via acid etching is developed that simultaneously exposes (002) plane and modifies exposed grain boundaries. The surface‐preferred (002) plane is achieved by minimizing its surface energy. And the exposed grain boundaries are also modified by decomposition products of acid etching, which can greatly reduce the adverse effects caused by highly active grain boundaries. These features favor Glu@Zn anode by accrediting a long‐term cycle lifespan exceeding 4400 h with a high average coulombic efficiency (CE) of 98.9%. Surprisingly, Glu@Zn anode can run for more than 250 h with 50% Zn utilization. The assembled Glu@Zn//NH4V4O10 full batteries deliver a specific capacity of 291.6 mAh g−1 after 400 cycles even at a low current density of 0.5 A g−1. It can also obtain a stable cycling performance up to 2000 cycles. To further verify its stability, a pouch cell is constructed that can preserve stable 400 cycles with 5 mAh. This study sheds light on surface energy regulation exposing preferred crystal plane to develop highly stable and reversible cycling aqueous ZMBs.

Transition Metal Dichalcogenides (TMDs), which are increasingly recognized as promising materials for next-generation electronics, exhibit excellent carrier transport properties due to their low surface defect density, superior crystallinity, and unique electronic structures. WSe 2 has a hexagonal crystal structure, and its carrier transport ability varies depending on the crystal orientation. Characterizing the in-plane electrical conductance of WSe 2 is essential for optimizing the performance of electronic devices. This study aims to precisely identify the crystal orientation of WSe 2 , thereby optimizing the performance of WSe 2 -based electronic devices. The electrical properties of WSe 2 with respect to crystal orientation were characterized through anisotropic wet etching using an SC-1 solution (NH 4 OH, H 2 O 2 , H 2 O). Circular holes were first created on the WSe 2 surface using reactive ion etching (RIE), followed by anisotropic etching with the SC-1 solution, which resulted in hexagonal-shaped holes due to the inherent hexagonal nature of the WSe 2 crystal structure. When the H 2 O 2 concentration is low, the surface with fewer dangling bonds etches slowly, while the sidewalls of holes, with a higher density of dangling bonds, etch more rapidly. This method effectively differentiates the etching rates for each crystal direction, providing essential information for device fabrication. Subsequently, Pt was deposited on the WSe 2 , and rapid thermal annealing was performed at 650°C to form a Pt-WSe 2 alloy. The formation of this alloy between Pt and WSe 2 facilitates the achievement of ohmic contacts and allows for the exclusion of vertical carrier transport, thus enabling the evaluation of lateral electrical characteristics. This approach clearly revealed the differences in carrier transport performance depending on the crystal orientation of WSe 2 . This study provides critical foundational data for improving the performance of WSe 2 -based devices and is expected to contribute to the development of high-performance 2D electronic materials. In particular, the method for optimizing carrier transport based on crystal orientation will serve as a key foundation for the design and fabrication of next-generation electronic devices. This work was supported by the Korea Research Institute for Defense Technology Planning and Advancement (KRIT) grant funded by Defense Acquisition Program Administration (DAPA) (KRIT-CT-21-034).

Metal Zn anode encounters uncontrolled dendrite growth, resulting in poor cycling stability and low coulombic efficiency (CE). Herein, a novel approach for oriented‐electrochemical etching of Zn (ECE‐Zn) in deep eutectic solvent (DES) is presented to adjust the interface concentration and electric fields, effectively mitigating intractable issues. The oriented etches off the crystal edges between the (002), (100), and (101) principal crystal planes of commercial Zn foil, subsequently etches the (100) and (101) crystal planes, resulting in the formation well‐organized Zn columns. Comprehensive experimental investigations and theoretical analyses reveal that Zn ions directionally nucleate and grow between Zn columns, enabling epitaxial growth at the (002) crystal plane. The ECE‐Zn‐2 anodes demonstrate remarkable stability, along with low nucleation and polarization voltages. Specifically, the symmetric ECE‐Zn‐2 cells show sustained operation for 5400 h, and long‐term 10 000 cycles at 40 mA cm−2. More significantly, the asymmetric cells exhibit an average CE as high as 99.92% over 6000 cycles at 5.0 mA cm−2. When assembled with a V2O5 cathode, a high retention of 81.5% can be maintained even under severe condition (N/P ratio of 7.35). This strategy of oriented‐electrochemical etching for commercial Zn opens up a new pathway for dendrite‐free Zn metal anode.

The etching process can be a useful method for the morphology control of nanostructures. Using precise experiments and theoretical calculations, we report a new ZnO etching process triggered by the reaction of ZnO with transition metal cations and demonstrate that the etching rate and direction could be controlled by varying the kind of transition metal cation. In addition, the developed etching process was introduced to form a thin and uniform ZnO layer, which was utilized for the fabrication of an improved propylene-selective ZIF-8 membrane via conversion seeding and secondary growth.

This study utilizes the Hubbard interpolation method to partition the etching directions of quartz crystal into 96 triangular regions based on 13 crystal planes. The etching rates in various directions on each crystal plane of quartz can be obtained through mask design and rate measurement experiment. By measuring the etching rates of multiple types of crystal-cut wafers and considering the symmetry of quartz, the etching rates in various directions on the 13 crystal planes can be determined. At the boundaries of the triangular regions, a series of sampling points are selected to further subdivide the triangular regions into smaller triangles. Utilizing the Hubbard interpolation method, the etching rates of crystal orientations within each small region can be computed. Finally, employing Hubbard interpolation on each triangular region yields the complete quartz crystal etching rate database covering all directions.

The unsatisfactory electrochemical performance of Zn metal batteries (ZMBs) caused by uncontrollable Zn dendrite growth and detrimental parasitic reactions has significantly hindered their large‐scale applications. Herein, periodic hemispherical structures with a preferential exposure of Cu (100) crystal plane are designed and obtained using facile photolithography, which is followed by wet etching treatment. An exposed zincophilic Cu (100) crystal plane with low nucleation barriers acts as the preferred deposition site to induce homogeneous Zn deposition. Additionally, the periodic hemispherical structure with an enlarged surface area not only suppresses the Zn dendrite growth by reducing the local current density, but also synergistically buffers the volume expansion during the cycling process. As a result, the as‐prepared faceted Cu hemispherical electrodes achieve ultra‐stable Coulombic efficiency of over 99.9% for 1500 cycles at a current density of 5 mA cm−2. This work has significant potential for the rational design of dendrite‐free Zn anodes to boost their potential for practical applications.

No abstract available

Zn‐ion battery (ZIB) has drawn huge attentions as a prospective energy storage system for the next generation, but dendrite and side reaction issues related to Zn have limited their potential applications. Here, a combined approach involving the modification of surface texture and the implementation of a passivation layer is proposed to tackle the problem. A zinc‐silane composite layer is coated on (002)‐preferred Zn (ZSi@Zn) by selective acid etching, concomitant with the hydrolysis of Mercaptosilane. The preferred (002) crystal plane, in conjunction with the zinc‐silane composite layer, leads in integrated interfacial transport and deposition control. As a result, the ZSi@Zn electrode has dramatically increased stability and uniform Zn deposition behavior. Remarkably, it exhibits a Coulombic efficiency of approximately 99.4%, a long lifespan of around 3000 hours at the current density of 1 mA cm−2 with a capacity of 0.5 mAh cm−2. The excellent reversibility of zinc persists with current densities of 2, 5, and 10 mA cm−2. Furthermore, Zn‐MnO2 battery constructed with ZSi@Zn also delivers excellent performance, manifesting a capacity retention of 88.4% after 4000 cycles.

Zinc metal has a severe dendrite issue caused by the uneven Zn plating/stripping during continual cycles, which hinders the practical application of ZIBs. The surficial atomic structure of zinc anode plays a decisive role in solving dendrites and improving the electrochemical performance. According to the density functional theory results, Zn (100) plane possesses a much stronger adsorption energy of zinc atom compared with the (002), thus zinc atom preferentially nucleates on the (100) surface. It subsequently continues to grow vertically on (100). Herein, the zinc anode is designed with hexagonal-hole patterns (h-Zn) through a phosphoric acid etching reaction. An abundance of Zn (100) crystal planes are exposed perpendicularly to the anode surface, while the (002) surfaces are at the bottom of these hexagonal holes. Zinc prefers to deposit in hexagonal holes at the (100) surfaces, favoring the restraining of the surficial dendrite growth and accelerating the Zn deposition kinetics. Thus, the symmetric cell using h-Zn exhibits a long cycling lifespan for over 1200 h and extremely low polarization voltage of ≈80 mV at 5 mA cm-2 and 1 mAh cm-2 . This work provides an insight into the surficial structure design and crystal plane regulation to fabricate brilliant zinc metal anodes.

A comparative analysis of methods for estimating the density of dislocation etching pits (EPD) on single-crystal GaAs plates has been carried out: classical counting from nine fields and using the automated «Колибри» («Colibry») system. It is shown that the manual method is labor-intensive, subjective, and underestimates EPD values due to missing defects, while automation of the process provides objective calculation, obtaining statistically significant information, and mapping EPD across the entire plate. To speed up the process, a hybrid approach was proposed: automated analysis using two basic diameters, which reduces time by 70-80% while maintaining accuracy and reproducibility comparable to a full scan. The results confirm the advantage of automated techniques and their suitability for production quality control of GaAs wafers.

No abstract available

With the advent of the first silicon-based transistor in 1954, integrated circuit technology has advanced substantially. Nonetheless, the progression of high-power devices has been hindered by the inherent limitations of silicon's narrow bandgap (1.1 eV) and its relatively low breakdown voltage (~0.3 MV/cm), necessitating the exploration of alternative high-power semiconductor materials. Leading candidates for next-generation high-power semiconductors include wide bandgap materials such as gallium nitride (GaN) and silicon carbide (SiC), as well as ultra-wide bandgap materials like gallium oxide (Ga2O3, with a bandgap of 4.8-5.3 eV and breakdown field of ~10 MV/cm). Ga2O3 is known for its five different phases (α, β, γ, κ, ε) and exhibits high thermal, chemical, and radiation hardness, along with physical stability, making it suitable for high-power semiconductor devices in extreme and aerospace environments. Among five phases, the β-Ga2O3 is garnering significant research interest for its stability, monoclinic structure, and the capability of being grown over large areas with high crystallinity via melt growth methods. The physical and chemical stability of Ga2O3 has rendered conventional etching techniques ineffective, prompting the exploration of alternative methods such as inductively coupled plasma reactive ion etching (ICP-RIE) and metal-assisted chemical (MAC) etching. In contrast to ICP-RIE, which may induce defects via ion bombardment in the dry etching process, MAC etching passivates defects through wet etching process. The characteristics of MAC etching enable selective etching of β-Ga2O3 planes through patterning of the metal catalyst which locally amplifies the etching reactions. The highly asymmetric monoclinic crystal structure (C2/m) of β-Ga2O3 contributes to the anisotropic electrical properties observed in β-Ga2O3. Forming Ohmic contacts with low on resistance is crucial in many electronic devices, and research has been conducted to identify crystal orientations that demonstrate low contact resistance. Previous studies focused on the comparison of contact resistances in surface contacts on substrates with different surface orientations. Comparing across distinct substrates failed to account for the variations in contact resistance caused by doping and defects. In this study, MAC etching was performed to form trench contacts on an undoped β-Ga2O3 (Nd-Na ~1017) bulk substrate with a (010) plane as the surface orientation. The trenches had orientations of (001), (100), (101), (102), (201), and (-201) planes, and TLM patterns with channel lengths of 5, 10, 15, 20, 25, and 30 μm were fabricated for each plane. This approach eliminated the effects of doping and defects, allowing for the precise examination of contact resistance in each plane orientations. Analyzing the contact resistance of β-Ga2O3 based on plane orientations will contribute to understanding the anisotropic electrical properties of β-Ga2O3 and advance the industrialization of β-Ga2O3 in the field of high-power electronic devices. Figure 1

The paper considers a method for optimizing the process of selective etching of GaAs plates to increase the accuracy of automated calculation of the density of dislocation etching pits (EPD). The problem of a high density of defects leads to the imposition of pits and a decrease in the accuracy of their recognition on micrographs. An additional stage of polishing etching with a composition based on sulfuric acid and hydrogen peroxide is proposed, which removes the minimum surface layer and forms clear pit boundaries. It is shown that this technique improves the segmentation of objects by means of computer vision and increases the accuracy of the EPD method. The results can be used to implement more reliable quality control procedures for single crystal GaAs.

Dendritic growth and parasitic reactions at the zinc (Zn) anode surface critically limit the performance and durability of aqueous zinc metal batteries (AZMBs). Therefore, a surface etching strategy using leucine was proposed to in-situ regulate the Zn anode interface. During etching, the Zn (101) crystal plane is selectively preserved, and its fast reaction kinetics promote uniform Zn plating. Meanwhile, a stable leucine-zinc interfacial layer is formed on the Zn surface, which increases the contact angle with water and significantly suppresses parasitic reactions, leading to 67.8 % reduction in corrosion. In addition, the leucine-zinc interface provides abundant adsorption-active sites that accelerate the desolvation of Zn(H2O)62+, thereby effectively inhibiting dendritic growth, with dendrite height reduced over 50 % compared with Bare Zn. Theoretical calculations reveal that the Zn (101) crystal plane exhibits the strongest affinity and electronic interaction with leucine, which promoted the formation of a stable leucine‑zinc interface layer, effectively protecting the surface from the attack of H+ in the etchant. As a result, the modified Zn anode (denoted as Leu@Zn) enables stable cycling for up to 2900 h at 25 mA cm-2 in symmetric cells and the full cells assembled with MnO2 cathode delivers a prolonged cycle life of 50,000 cycles at 5 A g-1.

GaN-based laser diodes have been developed rapidly in recent years, but the hexagonal crystal system is not involved in the design of a ridge waveguide structure for an edge-emitting laser diode. In this study, m-plane was set to be the facet of the ridge sidewall of the GaN-based laser diode, which was etched by tetramethylammonium hydroxide (TMAH) solution to remove dry-etching damage and improve the device performance, with the threshold current decreasing from 194 mA to 183 mA, and the slope efficiency increasing from 0.49 W/A to 0.59 W/A. This work shows that the tilt and rough sidewall morphology after dry etching can be restructured by TMAH corrosion, accompanied by carrier injection efficiency improvement and internal loss reduction.

Artificial photosynthesis is a promising approach to produce clean fuels via renewable solar energy. However, it is practically constrained by two issues of slow photogenerated carrier migration and rapid electron/hole recombination. It is also a challenge to achieve a 2:1 ratio of H2 and O2 for overall water splitting. Here we report a rational design of spatially differentiated two-dimensional Bi4Ti3O12 nanosheets to enhance overall water splitting. Such a spatially differentiated structure overcomes the limitation of charge transfer across different crystal planes in a single crystal semiconductor. The experimental results show a redistribution of charge within a crystal plane. The resulting photocatalyst produces 40.3 μmol h–1 of hydrogen and 20.1 μmol h–1 of oxygen at a near stoichiometric ratio of 2:1 and a solar-to-hydrogen efficiency of 0.1% under simulated solar light. Via specific acid etching, the authors report the production of spatially differentiated Bi4Ti3O12 nanosheets to accelerate photogenerated charge transfer and separation for effective water splitting in a one-step excitation system with a solar-to-hydrogen efficiency of 0.1%.

No abstract available

No abstract available

This paper proposes a method for classifying crystal planes based on the bond angle characteristics of quartz unit cells and constructs an etch rate model for quartz crystal planes at both macro and micro scales. By omitting oxygen atoms from the quartz cell structure, a method based on bond angle characteristics was established to partition the atomic arrangement of the crystal surface. This approach was used to analyze the etching processes of typical quartz crystal planes (R, r, m, and (0001)), approximating the etching process of crystals as a cyclic removal of certain bond angle characteristics on the crystal planes. This led to the development of an etch rate model based on micro-geometric parameters of crystal planes. Additionally, using the proposed bond angle classification method, the common characteristics of atomic configurations on the crystal plane surfaces within the X_cut type were extracted and classified into seven regions, further expanding and applying the etch rate model. The computational results of this model showed good agreement with experimental data, indicating the rationality and feasibility of the proposed method. These also provide a theoretical basis for understanding the microstructural changes during quartz-based MEMS etching processes.

No abstract available

No abstract available

Aqueous zinc-ion batteries (AZIBs) are regarded as promising candidates for next-generation energy storage systems due to their high safety, low cost, and environmental benignity. However, the practical application of AZIBs is severely hindered by uncontrollable zinc dendrite growth and parasitic reactions on the zinc metal anode during cycling. Herein, we proposed a structural engineering strategy via in situ etching of zinc metal surface using hydroxyethylidene diphosphonic acid (HEDP) to address these issues. By tuning the etching time, the proportion of (002) crystal plane on the zinc surface is significantly increased, facilitating ordered Zn2+ deposition. The zinc anode etched in HEDP for 30 min (30HE-Zn) exhibits the optimal electrochemical performance. Specifically, the 30HE-Zn symmetric cell achieves a stable cycle life of 5400 h at 1 mA cm-2, and the Cu//30HE-Zn half-cell maintains stable cycling for 3600 cycles at 2 mA cm-2 with a high coulombic efficiency of nearly 100%. When assembled with an α-MnO2 cathode, the full-cell retains a high specific capacity of 110 mAh g-1 after 1500 cycles at 1.5 A g-1. In situ dendrite microscopy and ex situ characterizations confirmed that 30HE-Zn enables uniform and dense Zn2+ deposition/stripping, effectively suppressing dendrite formation and hydrogen evolution reaction. This work provides a facile and effective interface modification approach of zinc anodes, offering valuable insights for advancing high-performance ZIBs in the energy storage field.

No abstract available

No abstract available

The performance of GaN-based Light Emitting Diode (LED) devices may be significantly improved by optimizing the use of maskless growth of GaN layers directly on the sidewalls of Patterned Sapphire Substrates (PSSs). In order to control the structure, arrangement, and inclination angles of the sidewalls, the use of anisotropic wet etching of sapphire needs to be clarified. To this end, this paper presents a Level Set approach to simulate the wet etching process on sapphire for the first time, thus enabling the optimization of the mask pattern for the preparation of suitable PSSs. By using the complete etch rate distribution obtained from an etched sapphire hemisphere for different concentrations and temperatures, the proposed method is expected to provide a flexible tool to determine the etched profiles of complex MEMS structures on different cuts of sapphire. In fact, the simulation results show good agreement with experiment for both transient and stable sidewalls of the trench profiles. By considering various arrays as examples, the level set algorithm is demonstrated to be applicable for simulating the fabrication of PSSs by wet etching.

No abstract available

No abstract available

InGaN-based red micro-light-emitting diodes (µLEDs) of different sizes were prepared in this work. The red GaN epilayers were grown on 4-inch sapphire substrates through metal-organic chemical vapor deposition (MOCVD). Etching, sidewall treatment, and p- and n-contact deposition were involved in the fabrication process. Initially, the etching process would cause undesirable damage to the GaN sidewalls, which leads to an increase in leakage current. Hence, we employed KOH wet treatment to rectify the defects on the sidewalls and conducted a comparative and systematic analysis of electrical as well as optical properties. We observed that the µLEDs with a size of 5 µm exhibited a substantial leakage current, which was effectively mitigated by the application of KOH wet treatment. In terms of optical performance, the arrays with KOH demonstrated improved light output power (LOP). Additionally, while photoelectric performance exhibited a decline with increased current density, the devices treated with KOH consistently outperformed their counterparts in terms of optoelectronic efficiency. It is noteworthy that the optimized devices displayed enhanced photoelectric characteristics without significantly altering their original peak wavelength and FWHM. Our findings point to the elimination of surface non-radiative recombination by KOH wet treatment, thereby enhancing the performance of small-sized red µLEDs, which has significant potential in realizing full-color micro-displays in near-eye projection applications.

The efficiency of AlGaInP micro light-emitting diodes (micro-LEDs) was far weaker than that of GaN-based micro-LEDs in structure and performance. Consequently, there was an urgent demand to enhance their efficiency. In this study, a citric acid treatment strategy is proposed to improve the efficiency of red micro-LEDs, and the etching uniformity of different concentrations was first confirmed. We optimized the concentration of citric acid to 1:1 and modulated the wet etching time at 0, 30, 60, 90, and 120 s to treat the sidewalls of devices. Under an injection current density of 68 nA/cm2, the forward voltage (Vf) of micro-LEDs after soaking in citric acid ranged from 1.40 to 1.45 V. Compared with the sample operated at the forward voltage without citric acid sidewall treatment, AlGaInP micro-LEDs displayed significantly enhanced forward voltage. This indicates that citric acid effectively removed N-GaAs without damaging the electrical properties of the devices. Among all citric acid-treated micro-LEDs, the sample with a 60 s wet etching process showed the best improvement, with the light output power and external quantum efficiency (EQE) increased by 31.08% and 5.4%, respectively. Our proposed method to treat AlGaInP micro-LEDs presents promising opportunities for the future development of high-performance optoelectronics.

Quasivertical gallium nitride trench‐gate metal–oxide–semiconductor field‐effect transistors with different etch radio frequency power and the impact of the order of annealing process in tetramethylammonium hydroxide wet treatment have been fabricated and studied. The high‐power device has a threshold voltage of 5.3 V and a maximum saturation current density of 552 A cm−2, whereas the low‐power device has a threshold voltage of 4.5 V and a maximum saturation current density of 650 A cm−2. However, the low‐power device has more severe off‐state leakage due to more fixed charges and defects on the device surface. Furthermore, the annealing process serves as an additional step before wet treatment. Scanning electron mircoscope image indicates that annealing at high temperatures prior to etching can eliminate surface oxide and redistribute surface imperfections, resulting in a smoother sidewall morphology. The relationship between temperature and mobility confirms the impact of the crystal surface feature on device performance.

In this Letter, we report on a novel two-step epitaxial growth technique that enables a significant improvement of the crystal quality of nitrogen-polar GaN. The starting material is grown on 4° vicinal sapphire substrates by metal-organic vapor-phase epitaxy, with an initial high-temperature sapphire nitridation to control polarity. The material is then converted to a regular array of hexagonal pyramids by wet-etching in a KOH solution and subsequently regrown to coalesce the pyramids back into a smooth layer of improved crystal quality. The key points that enable this technique are the control of the array geometry, obtained by exploiting the anisotropic behavior of the wet-etch step, and the use of regrowth conditions that preserve the orientation of the pyramids’ sidewalls. In contrast, growth conditions that cause an excessive expansion of the residual (0001̅) facets on the pyramids’ tops cause the onset of a very rough surface morphology upon full coalescence. An X-ray diffraction study confirms the reduction of the threading dislocation density as the regrowth step develops. The analysis of the relative position of the 0002̅ GaN peak, with respect to the 0006 sapphire peak, reveals a macroscopic tilt of the pyramids, probably induced by the large off-axis substrate orientation. This tilt correlates very well with an anomalous broadening of the 0002̅ diffraction peaks at the beginning of the regrowth step.

GaN mesas were fabricated by sequential dry and wet etching of a +c-oriented GaN layer onto a lattice-matched AlInN layer for future applications of positive beveled edge termination, which is desirable for preventing premature breakdown of power devices. The dry etching produced hexagonal AlInN/GaN mesas surrounded by m-plane sidewalls with six protrusions at the vertices. The subsequent hot phosphoric acid etching selectively etched the AlInN layer to expose and etch the chemically unstable −c surface of the GaN layer, which formed reverse-tapered { 101¯2¯ } facets. The protrusions were sacrificed during the wet etching to prevent undesirable positive tapering at the vertices.

Nanowires fabricated using the top-down method can offer high uniformity and precise morphology. However, achieving well-controlled dry and wet etching processes is essential to produce large-area uniform nanowires. It is also interesting to have control on their shape, since tapered structures can have favorable light extraction properties, whereas cylindrical shapes are preference for electronics or photodetection. This paper presents a comprehensive study on the fabrication of GaN nanowires using a top-down approach facilitated by nanosphere lithography. We focus on optimizing both dry and wet etching processes to achieve high-aspect-ratio nanowires with controlled shapes. The final wet etching step, critical for shaping the nanowires, was performed with a crystallography-selective method, resulting in nanowires with vertical m-plane facets or tapered structures, depending on the initial diameter of the spheres. This demonstrates the process's adaptability to control nanowire geometry.

In this Letter, a high-performance quasi-vertical GaN Schottky barrier diode (SBD) with low leakage current and high on/off ratio based on a unique lateral polarity structure (LPS) is presented. The SBD features with the III-polar domain as the active region and the partially wet etched N-polar domain as the current-spreading region, completely eliminating plasma damages. Compared to the SBD fabricated by the conventional plasma etching technique, the leakage current of the LPS-based SBD is two orders of magnitude lower. A high Ion/Ioff of 107, an ideality factor of 1.04, a breakdown voltage of 290 V, and a critical electric field of 2.1 MV/cm were demonstrated for the proposed structure.

Photoelectrochemical (PEC) water splitting has been considered as of the future technology to store solar-energy in the chemical-bonds. However, due to the search of ideal heterostructured materials for photoanode/cathode, the full potential of this technology has not been realized yet. Herein we present, nanotextured hexagonal micro-well of p-GaN [p-GaN(Et)] synthesized via wet chemical etching route as a photocathode (PC) for PEC water splitting. The p-GaN(Et) was further modified by interconnected nanowall network of two dimensional (2D) transition metal dichalcogenide (MoS2) [2D-MoS2/p-GaN(Et)]. Both PCs were characterized for their morphology, structures, optical and electronic properties. The overall PEC performance was validated through photocurrent values followed by the amount of hydrogen and oxygen evolution. This combination of 2D-MoS2/p-GaN(Et) outplayed pristine p-GaN(Et) by several order of magnitude in overall PEC performance. The extraordinary stability under a continuous operating condition with 1 sun illumination (100 mW/cm2) provides the much-needed flavour of an efficient photocathode. The optimized photocathode [2D-MoS2/p-GaN(Et)] shows the highest applied bias photon-to-current conversion efficiency (ABPE) of ~3.18 % with hydrogen evolution rate of 89.56 µmol/h at -0.3 V vs RHE. This wafer-level cost-effective synthesis of 2D-MoS2/GaN heterostructure based PCs, opens a new way for large-scale solar-fuel conversion.

Micro-scale patterned arrays and nano-scale rough morphology are promising for improving the light-extraction performance of GaN-based thin film light-emitting diodes (TFLEDs), while the light-extraction mechanisms of the multiscale architectures combining these two structures have not been investigated yet. In this report, we have adopted a pattern transfer and wet etching combined method to fabricate multiscale patterned arrays with rough morphology (msPARM) on n-GaN layers for TFLEDs and investigated their light-extraction mechanisms by the finite-difference time domain and ray-tracing combined method. The results show that the TFLEDs achieve the maximum radiant efficacy using the msPARM with an etching time of 8 min, which is increased by 16.3% and 1.7% compared with that achieved using only the patterned arrays or only the rough morphology, respectively. Most importantly, optical simulation reveals that the msPARM can provide a high transmittance for light with large emission angles from the active region using the inclined surface of micro-scale concave cones, while effectively suppressing the reflection loss for light with small emission angles using the scattering effect of nano-scale rough morphology, resulting in enhancing the light-extraction of the TFLEDs. Consequently, this study can provide a better understanding to design the multiscale structures for achieving high efficiency LEDs.

Surface-engineered nanostructured nonpolar (112̅0) gallium nitride (GaN)-based high-performance ultraviolet (UV) photodetectors (PDs) have been fabricated. The surface morphology of a nonpolar GaN film was modified from pyramidal shape to flat and trigonal nanorods displaying facets along different crystallographic planes. We report the ease of enhancing the photocurrent (5.5-fold) and responsivity (6-fold) of the PDs using a simple and convenient wet chemical-etching-induced surface engineering. The fabricated metal–semiconductor–metal structure-based surface-engineered UV PD exhibited a significant increment in detectivity, that is, from 0.43 to 2.83 (×108) Jones, and showed a very low noise-equivalent power (∼10–10 W Hz–1/2). The reliability of the nanostructured PD was ensured via fast switching with a response and decay time of 332 and 995 ms, which were more than five times faster with respect to the unetched pyramidal structure-based UV PD. The improvement in device performance was attributed to increased light absorption, efficient transport of photogenerated carriers, and enhancement in conduction cross section via elimination of recombination/trap centers related to defect states. Thus, the proposed method could be a promising approach to enhance the performance of GaN-based PD technology.

The external quantum efficiency of a high-Al content (>0.6) AlGaN deep-ultraviolet (DUV) light-emitting diode is typically below 1% in the sub-250 nm wavelength range. One of the main reasons for this low efficiency is the fundamental properties of high-Al content AlGaN comprising the transverse-magnetic (TM)-dominant emission and low light extraction due to the total internal reflection (TIR). This work demonstrates a truncated pyramid nanostructure with fine-tuned multiple facets in an (AlN)8/(GaN)2 digital alloy to achieve highly efficient DUV emission at 234 nm. By applying nanoimprint lithography, dry and wet etching, a hexagonal truncated pyramid nanohole structure is fabricated featuring multiple crystal facets of (0001), (10-13), and (20-21) planes. These fine-tuned multiple facets act as reflecting mirrors that can effectively modulate the light propagation and extraction patterns to overcome the TIR via multiple reflections and enhanced scattering. Consequently, significant light extraction enhancements of 5.6 times and 1.1 times for TM and transverse-electric emissions are achieved in the truncated pyramid nanohole structure, respectively. The total luminous intensity of this unique nanostructure is greatly increased by 191% compared to that of a conventional planar structure. The truncated pyramid AlN/GaN nanostructure with fine-tuned multiple facets used in this work provides a promising approach for realizing highly efficient sub-250 nm DUV light-emitting devices.

No abstract available

The controlled fabrication of vertical, tapered, and high-aspect ratio GaN nanowires via a two-step top-down process consisting of an inductively coupled plasma reactive ion etch followed by a hot, 85% H3PO4 crystallographic wet etch is explored. The vertical nanowires are oriented in the [0001] direction and are bound by sidewalls comprising of {336¯2} semipolar planes which are at a 12° angle from the [0001] axis. High temperature H3PO4 etching between 60 °C and 95 °C result in smooth semipolar faceting with no visible micro-faceting, whereas a 50 °C etch reveals a micro-faceted etch evolution. High-angle annular dark-field scanning transmission electron microscopy imaging confirms nanowire tip dimensions down to 8–12 nanometers. The activation energy associated with the etch process is 0.90 ± 0.09 eV, which is consistent with a reaction-rate limited dissolution process. The exposure of the {336¯2} type planes is consistent with etching barrier index calculations. The field emission properties of the nanowires were investigated via a nanoprobe in a scanning electron microscope as well as by a vacuum field emission electron microscope. The measurements show a gap size dependent turn-on voltage, with a maximum current of 33 nA and turn-on field of 1.92 V nm−1 for a 50 nm gap, and uniform emission across the array.

The effect of air-gap/GaN DBR structure, fabricated by selective lateral wet-etching, on InGaN light-emitting diodes (LEDs) is investigated. The air-gap/GaN DBR structures in LED acts as a light reflector, and thereby improve the light output power due to the redirection of light into escape cones on both front and back sides of the LED. At an injection current of 20 mA, the enhancement in the radiometric power as high as 1.91 times as compared to a conventional LED having no DBR structure and a far-field angle as low as 128.2° are realized with air-gap/GaN DBR structures.

Vertically aligned InGaN/GaN nanorod light emitting diode (LED) arrays were created from planar LED structures using a new top-down fabrication technique consisting of a plasma etch followed by an anisotropic wet etch. The wet etch results in straight, smooth, well-faceted nanorods with controllable diameters and removes the plasma etch damage. 94% of the nanorod LEDs are dislocation-free and a reduced quantum confined Stark effect is observed due to reduced piezoelectric fields. Despite these advantages, the IQE of the nanorod LEDs measured by photoluminescence is comparable to the planar LED, perhaps due to inefficient thermal transport and enhanced nonradiative surface recombination.

No abstract available

Coupling heterogeneous photocatalysis with free chlorine (HOCl/ClO-) emerges as an effective strategy to enhance the yield of reactive species, while the chlorine activation mechanism is yet to be clear. In this study, facet- and morphology-engineered BiVO4 was synthesized and employed to activate HOCl/ClO- under visible light irradiation, termed as Vis/BiVO4/chlorine process. The HOCl/ClO- activation mechanisms in the Vis/BiVO4/chlorine process was investigated through use of of oxalate (hole (hVB+) quencher) or Cu2+ (electron (eCB-) shuttle). eCB- and superoxide radicals (O2•-) activates HOCl to form hydroxyl radicals (HO•) (one-electron transfer pathways) while only reduces ClO- to Cl- (two-electron transfer pathways). O2 not only promotes HO• production, but also enables more HO• to reach target compound without being scavenged. The reactions between hVB+ and chlorine are both chlorine species- and valance band (VB) potential-dependent. hVB+ activates both HOCl and ClO- to form ClO•. While at pH 5.0, the more positive VB potential of BiVO4 than the E°(Cl+/HOCl) enables hVB+ to oxidize HOCl to HO• and Cl+, which reacts rapidly with H2O to regenerate HOCl. Using truncated bipyramid-like BiVO4 at larger exposed area of {110} facet (hVB+-dominated) and plate-like BiVO4 at larger exposed area of {010} facet (eCB-/O2•--dominated) favors the hVB+- and eCB-/O2•--induced HOCl/ClO- activation pathway, respectively. These findings provide novel insights into the chlorine activation mechanism and the modulation of reaction pathways that HOCl and ClO- undergo and the corresponding radicals/ions.

BiVO4 has garnered significant attention as a photocatalyst for water splitting and environmental remediation. The photocatalysis over BiVO4 could be adjusted by the exposed facet but has not been explored over the NO abatement in ambient air. In this work, four distinct morphologies of monoclinic BiVO4 crystals were hydrothermally synthesized by modulating the pH of the precursor solution. Among these, the sample with the preferentially exposed {040} facet exhibited a platelike fragmented morphology and demonstrated superior NO photocatalytic oxidation (79% removal rate) under visible light (>420 nm) over the one with the preferentially exposed {110} facet. Compared to the {110} facet, the {040} facet of BiVO4 was more stable against oxygen vacancy formation and V5+ reduction to V4+ that could create a shallow midgap state. This higher stability, along with its higher flat-band energy, promotes the creation of superoxide radicals that are crucial for the thorough oxidation of NO. Singlet oxygen was found to be quite important in the oxidation of NO because NO2 was produced even if water is absent in the air. This study highlights the considerable potential of BiVO4-based catalysts for efficient atmospheric pollutant degradation.

Zinc metal powder (ZnMP) anodes present significant advantages over conventional zinc foil anodes in aqueous zinc‐ion batteries (AZIBs), offering higher electrochemically active surface area and improved mass utilization. However, the 3D morphology of ZnMP particles poses challenges for crystallographic control, as their random orientations and large surface areas intensify hydrogen evolution reactions (HER), corrosion, and dendritic growth. Here, a dual‐functional etching strategy using trifluoroacetic acid (TFA) is reported to selectively modify ZnMP surfaces and enrich thermodynamically stable (002) crystal planes. Upon dissociation, TFA releases H+ ions that preferentially etch high‐energy facets, while CF3COO− anions selectively adsorb onto (002) planes, forming protective layers that stabilize the etching process. This treatment produces a distinctive stepped hexagonal morphology enriched in (002) planes that mitigates parasitic reactions and promotes uniform zinc deposition. The TFA‐modified ZnMP (TFA@ZnMP) electrodes exhibit remarkable stability, operating for over 1000 h in symmetric cells. In practical 4 × 3 cm2 pouch cells paired with V2O5 cathodes, the electrodes retain 79.8% of their capacity after 1000 cycles at 10 A g−1. Density functional theory calculations and phase‐field modeling confirm the preferential ion adsorption mechanism and its contribution to enhanced electrochemical performance. These findings establish this surface‐engineering strategy as a scalable pathway for high‐performance AZIBs.

Electrocatalysts play a crucial role in hydrogen production via water splitting, yet their effectiveness is hampered by the bubble effect, particularly under high‐current‐density conditions. Herein, nickel foam with mountain‐shaped nanostripes (NFMN) is developed as a universal substrate for electrocatalysts to remove gas bubbles efficiently, ensuring high‐performance high‐current‐density water splitting. The NFMN is fabricated through facet engineering of nickel foam (NF) via thiocyanate‐guided acid etching. Specifically, when immersed into an acidic thiocyanate solution, the (220) plane of NF is preferentially adsorbed by SCN−, protecting it, while the (111) and (200) facets remain exposed and are selectively etched by the acid. As the etching proceeds parallelly to the (220) direction, mountain‐shaped nanostripes are obtained. The nanostripes confer the benefits of superaerophobicity and local circulation, allowing the NFMN to efficiently release gas bubbles. As a proof‐of‐concept application, the NFMN is employed as a novel substrate to support the FeOOH anode and Ni2P cathode for a prototype electrolyzer, which exhibits a low cell voltage of 1.847 V at a large current density of 500 mA cm−2 with high stability. This work opens up new opportunities to construct efficient substrates for high‐current‐density water splitting and beyond.

Removal of bromate (BrO3-) has gained increasing attention in drinking water treatment process. Photocatalysis technology is an effective strategy for bromate removal. During the photocatalytic reduction of bromate process, the photo-generated electrons are reductive species toward bromate reduction and photo-generated holes responsible for water oxidation. In this study, the monoclinic bismuth vanadate (BiVO4) single crystal was developed as a visible photocatalyst for the effective removal of bromate. The as-synthesized BiVO4 photocatalyst with optimized {010} and {110} facets ratio could achieve almost 100% removal efficiency of BrO3- driven by visible light with a first-order kinetic constant of 0.0368 min-1. As demonstrated by the electron scavenger experiment and density functional theory (DFT) calculations, the exposed facets of BiVO4 should account for the high photocatalytic reduction efficiency. Under visible light illumination, the photo-generated electron and holes were spatially transferred to {010} facets and {110} facets, respectively. The BiVO4 single crystal photocatalyst may serve as an attractive photocatalyst by virtue of its response to the visible light, spatially charge transfer and separation as well as high photocatalytic activity, which will make the removal of BrO3- in water much easier, more economical and more sustainable.

Designing composite photocatalytic systems with nanoscale precision is crucial. While conventional facet-selective photo-deposition successfully utilizes spherical co-catalysts, the directed deposition of pre-synthesized two-dimensional (2D) materials onto specific facets remains extremely challenging. This work demonstrates an electrostatic assembly strategy for the precise deposition of 2D transition metal carbides (MXenes) onto anisotropic single-crystal semiconducting metal oxides. By precisely controlling the solution pH, we modulated the surface charge of the MXenes and the distinct crystallographic facets of the metal oxides, enabling selective deposition driven by electrostatic attraction. Negatively charged Mo4/3C MXenes were selectively deposited on the electron-rich (101) surface of TiO2 at pH 3, the (100) surface of Cu2O exposed at pH 11, and the (010) surface of BiVO4 at pH 1.5. The high facet selectivity was confirmed through a combination of advanced techniques, including electron microscopy, electron spectroscopy, and synchrotron-based spectromicroscopy. This selective interfacial engineering promotes spatially separated charge carrier migration toward distinct facets, while Schottky barriers form at the MXenes/oxides interfaces. The MXenes act as efficient reduction co-catalysts, facilitating the rapid consumption of electrons, thereby enhancing photocatalytic hydrogen evolution. This work establishes a generalizable, non-photolytic method for integrating challenging 2D co-catalysts with facet-engineered semiconductors for designing composite photocatalysts.

Crystal facet and defect engineering are crucial for designing heterogeneous catalysts. In this study, different solvents were utilized to generate NiO with distinct shapes (hexagonal layers, rods, and spheres) using nickel-based metal-organic frameworks (MOFs) as precursors. It was shown that the exposed crystal facets of NiO with different morphologies differed from each other. Various characterization techniques and density functional theory (DFT) calculations revealed that hexagonal-layered NiO (NiO-L) possessed excellent low-temperature reducibility and oxygen migration ability. The (111) crystal plane of NiO-L contained more lattice defects and oxygen vacancies, resulting in enhanced propane oxidation due to its highest O2 adsorption energy. Furthermore, the higher the surface active oxygen species and surface oxygen vacancy concentrations, the lower the C-H activation energy of the NiO catalyst and hence the better the catalytic activity for the oxidation of propane. Consequently, NiO-L exhibited remarkable catalytic activity and good stability for propane oxidation. This study provided a simple strategy for controlling NiO crystal facets, and demonstrated that the oxygen defects could be more easily formed on NiO(111) facets, thus would be beneficial for the activation of C-H bonds in propane. In addition, the results of this work can be extended to the other fields, such as propane oxidation to propene, fuel cells, and photocatalysis.

Cuprous oxide (Cu2O) has received enormous interest for photocatalysis owing to its narrow band gap of 2.17 eV, which is beneficial for visible-light absorption. In this work, we succeeded in synthesizing Cu2O nanocrystals with two morphologies, cube and sphere, at room temperature via a simple wet-chemistry strategy. The morphologies of Cu2O change from cube to sphere when adding PVP from 0 g to 4 g and the mainly exposed crystal faces of cubic and spherical Cu2O are (100) and (111), respectively. The photocatalytic properties of the as-prepared Cu2O were evaluated by the photocatalytic degradation of methyl orange (MO). Cubic Cu2O(100) showed excellent photocatalytic activity. After the optical and photoelectric properties were investigated, we found that cubic Cu2O(100) has better photoelectric separation efficiency than spherical Cu2O(111). Finally, the possible mechanism was proposed for cubic Cu2O(100) degrading MO under visible light.

Achieving spatial charge separation between different facets on a single crystal is one of the most efficient approaches to improve the charge separation efficiency of semiconductor-based photocatalysts. However, how the...

Cu2O semiconductors are highly regarded in photocatalysis for their outstanding photogenerated carrier dynamics. However, the mechanisms underlying carrier separation and recombination in Cu2O remain elusive, largely due to the intricate interplay between defects and facet engineering. Herein, we elucidate the critical synergy between internal defects and facets in Cu2O for carrier dynamics. Specifically, split Cu vacancy and H interstitial defects preferentially capture holes and electrons, respectively, leading to effective separation of photogenerated carriers in the different Cu2O facets. Moreover, H interstitials can also convert split Cu vacancies into H-filled Cu vacancies, eliminating midgap states and extending the photogenerated carrier lifetime of Cu2O. The efficient separation and extended lifetime of carrier enhances the photocatalytic efficiency of Cu2O. Our findings reveal the defect-dependent mechanism for photogenerated carrier dynamics in photocatalysts with different facets, offering valuable insights for facet regulation in high-performance photocatalysis.

Electrolysis of seawater is considered a green route for hydrogen generation; however, its practical application is limited by strong electrode corrosion and slow OER kinetics in chloride-rich media. Herein, we report a crystal-facet engineering strategy to construct nickel hydroxide with a parallel array structure on nickel foil (denoted as Ni(OH)2/NFPA, where NFPA represents nickel foil with parallel array) via a facile two-step etching-hydrothermal method. Structural characterization confirms the formation of high-index Ni(220) surfaces and well-aligned hydroxide nanostripes, which promote more favorable bubble–electrode interactions and contribute to improved interfacial stability. Owing to its characteristic parallel array configuration, Ni(OH)2/NFPA exhibits outstanding OER performance in alkaline electrolyte, delivering a low overpotential of 256 mV at 10 mA·cm−2 together with a Tafel slope as small as 74.9 mV·dec−1, surpassing commercial RuO2 and disordered Ni(OH)2 nanosheets. The optimized electrode also delivers remarkable durability, maintaining stable operation for 48 h at 100 mA·cm−2 even under harsh alkaline seawater conditions at 80 °C. Bubble dynamics analysis reveals that the ordered array morphology produces a superaerophobic surface, enabling rapid detachment of oxygen bubbles and ensuring efficient mass transport. This study highlights facet-controlled construction of parallel nanoarrays as a promising approach to improve catalytic efficiency, corrosion resistance, and bubble management in seawater electrolysis, offering useful implications for the rational design of high-performance electrodes for practical hydrogen production.

Titania (TiO2) nanosheets are crystals with controlled, highly ordered structures that improve the functionality of conventional TiO2 nanoparticles. Various surface modification methods have been studied to enhance the effectiveness of these materials as photocatalysts. Surface modifications using electrical polarization have attracted considerable attention in recent years because they can improve the function of titania without changing its composition. However, the combination of facet engineering and electrical polarization has not been shown to improve the functionality of TiO2 nanosheets. In the present study, the dye-degradation performance of polarized TiO2 nanosheets was evaluated. TiO2 nanosheets with a F/Ti ratio of 0.3 were synthesized via a hydrothermal method. The crystal morphology and structure were evaluated using transmission electron microscopy and X-ray diffraction. Then, electrical polarization was performed under a DC electric field of 300 V at 300 °C. The polarized material was evaluated using thermally stimulated current measurements. A dye-degradation assay was performed using a methylene blue solution under ultraviolet irradiation. The polarized TiO2 nanosheets exhibited a dense surface charge and accelerated decolorization. These results indicate that electrical polarization can be used to enhance the photocatalytic activity of TiO2.

Encapsulating guests in metal–organic frameworks (MOFs) can widely expand their functionality, but usually reduces porosity, hindering reactant and product diffusion. Herein, a simple and rapid room temperature directional etching technique is developed to engineer MOFs with tailored hierarchical structures. With H3PMo12O40 (PMo12) as an etchant, classical cubic morphology of WNi@Z8, a ZIF‐8 MOF encapsulating SiW11NiO39 (WNi), can be transformed into various defect‐engineered hollow structures, and a comprehensive phase diagram is established by systematically adjusting etching parameters. Mechanistic studies reveal that PMo12 infiltrates ZIF‐8 preferentially through {111} facet, followed by controlled etching along {110} and {100} facets, enabling precise spatial control over cavity formation. The etched WNi@Z8 achieves an exceptional H2 evolution rate of 12,667 µmol g−1 h−1, nearly threefold enhancement over the non‐etched counterpart due to the enhanced exposure of encapsulated WNi clusters in the hollow structure. This work provides a generalizable strategy for engineering guest@MOFs to achieve high‐efficiency catalysis.

Defect engineering is recognized as an effective route to obtaining highly active photocatalytic materials. However, the current understanding of the role of defects in photocatalysts mainly comes from their independent functional analysis, ignoring the synergy between defects and the chemical environment, especially with crystal facets. Herein, oxygen vacancy (VO)-rich TiO2 nanostructures with different dominant exposed facets were prepared, and the microstructural changes induced by the synergy between the VO and facet effect and the performance difference of photocatalytic O2 activation were explored. The results showed that the combination of high concentration VO and the {101} facet is more conducive to improving the photocatalytic performance of TiO2, which is significantly superior to the combination of low concentration VO and the {101} facet as well as the combination of high concentration VO and the {001} facet. The experimental and theoretical results clarified the dependence of each stage of photocatalysis on two factors. Specifically, VO plays a more significant role in energy band regulation, improving the dynamic behavior of photogenerated charges and enhancing the adsorption and activation of O2, while the facet effect made more contributions to reducing the thermodynamic energy barrier of ROS formation and conversion. The excellent ability of O2 activation enables T101-VO to show potential application characteristics in the removal of RhB and bacterial disinfection. This work established a link between defect and facet effects, providing new insights into understanding defect function in photocatalysts.

This study provides a rigorous mathematical proof of the equivalence between the convex hull method and the classical Wulff-Jaccodine (WJ) method in crystal etching morphology prediction. By establishing the correspondence between the convex hull of the reciprocal rate function and the intersection of half-spaces, we demonstrate that the morphological boundaries constructed by the two methods are completely identical. This result not only confirms the mathematical rigor of the convex hull method but also highlights its significant engineering value: by automatically selecting key directions and eliminating redundant constraints, the convex hull method substantially reduces computational complexity compared with traditional approaches. In modeling problems involving three-dimensional complex structures or high-dimensional rate functions, the convex hull method can markedly improve computational efficiency while preserving predictive accuracy. This feature renders it directly applicable to MEMS device design, crystal etching process optimization, and large-scale numerical simulations. Looking ahead, the method shows strong potential for extension to multi-faceted three-dimensional modeling and multi-physics coupled etching problems, thereby providing more reliable and efficient modeling tools for micro-nano fabrication.

Selective oxidative etching is one of the most effective ways to prepare hollow nanostructures and nanocrystals with specific exposed facets. The mechanism of selective etching in noble metal nanostructures mainly relies on the different reactivity of metal components and the distinct surface energy of multimetallic nanostructures. Recently, phase engineering of nanomaterials (PEN) offers new opportunities for the preparation of unique heterostructures, including heterophase nanostructures. However, the synthesis of hollow multimetallic nanostructures based on crystal‐phase‐selective etching has been rarely studied. Here, a crystal‐phase‐selective etching method is reported to selectively etch the unconventional 4H and 2H phases in the heterophase Au nanostructures. Due to the coating of Pt‐based alloy and the crystal‐phase‐selective etching of 4H‐Au in 4H/face‐centered cubic (fcc) Au nanowires, the well‐defined ladder‐like Au@PtAg nanoframes are prepared. In addition, the 2H‐Au in the fcc‐2H‐fcc Au nanorods and 2H/fcc Au nanosheets can also be selectively etched using the same method. As a proof‐of‐concept application, the ladder‐like Au@PtAg nanoframes are used for the electrocatalytic hydrogen evolution reaction (HER) in acidic media, showing excellent performance that is comparable to the commercial Pt/C catalyst.

AgCl microcrystals are used in visible light photocatalysis. However, their properties depend strongly on the morphology of the crystals and the degree of exposure of the crystal planes. Despite extensive research conducted on the synthesis of AgCl microcrystals, the majority of existing studies have focused on the stable growth of crystals. The role of Cl− ions concentration as a key factor controlling the microcrystals morphology has not been fully explored, which limits the precise tuning of the morphology of AgCl microcrystals. In this study, AgCl microcrystals with controllable morphology are successfully synthesized by a facile solvothermal method. During the preparation process, ethylene glycol (EG) is utilized as a solvent, while polyvinylpyrrolidone (PVP) is employed as a surfactant. We systematically investigate the etching mechanism of AgCl microcrystals by analyzing the effect of sodium chloride (NaCl) concentration on their morphology. This investigation involves the integration of diverse characterization methods, including scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and geometrical struc-ture analysis. The results demonstrate that Cl− functions as both a surfactant, thereby promoting the nucleation of cubic microcrystals, and as an etchant, selectively etching the crystal surface. The order of selective etching on the crystal surface follows (100) planes > (110) planes > (111) planes. Based on this new mechanism, AgCl microcrystals with various morphologies, such as cube, octopod and dendrite, are successfully prepared, which provides a new idea for the precise design of noble metal halide microcrystals.

Interface engineering has been regarded as a promising strategy for enhancing the catalytic activities of heterojunction photocatalysts. Herein, we have adopted an in situ etching sulfurization method to construct a Zn2GeO4-x/ZnS intimate heterojunction, which exhibited excellent photocatalytic H2 production in the absence of a Pt co-catalyst. Distinctively, TEM and HRTEM measurements showed that the interface of the Zn2GeO4-x/ZnS heterojunction became rough (topologically) due to in situ etching sulfurization, and etching was found to be strongly dependent on the crystal orientation. Moreover, the surface of the Zn2GeO4 nanorods from flat (100) planes evolved into an irregular coastline-like structure topologized with (110) and (113) high-index planes. ICP and elemental distribution measurements indicated that during the precipitation of ZnS via in situ etching sulfurization, the migration and dissolution of Zn and Ge ions on the Zn2GeO4(100) plane led to the roughening of the interface and the evolution of crystal planes. XPS and EPR analyses showed that Zn2GeO4-x/ZnS contained more oxygen vacancies with structural evolution. The theoretical calculations demonstrated that oxygen defects were prone to be generated on the Zn2GeO4(113) plane and formed the Ge3c3+-VO complexes. Compared to the inactive (100) plane, etching caused the Zn2GeO4(110) planes to have a higher number of threefold coordinated germanium (Ge3c4+) and (113) high-index planes that possessed abundant active sites (Ge3c3+-VO complexes), which dramatically decreased the barrier and reaction energy of H2O dissociation. This work not only provides fundamental insights into the topological interface evolution and facet-dependent defect distribution but also offers a strategy for the design of efficient photocatalysts for H2 production without the use of Pt as a co-catalyst based on a multifunctional interface.

Femtosecond laser micromachining technology has revolutionized the traditional single-process manufacturing paradigm, offering high-precision and high efficiency processing of hard and brittle material. This study investigates the role of pulse overlap rates in femtosecond laser ablation of sapphire crystals and develops a hybrid laser-etching technique for surface quality enhancement. Through experimentation with varying longitudinal (δa) and transverse (δp) overlap rates, three significant findings were demonstrated: firstly, quantitative determination of the ablation threshold (6.74 J cm−2 at 1030 nm/250 fs) accompanied by observed fluence-dependent groove morphology transitions; secondly, identification of δa as the dominant factor controlling subsurface depth while δp governs microgroove formation; thirdly, discovery of a phase-selective etching mechanism where laser-induced alumina phase transformation enables preferential material removal in KOH solution. The hybrid laser-etching strategy combining optimized laser parameters (δa = 74%, δp = 83%) with subsequent chemical etching achieved a 57.5% reduction in surface roughness (374 nm versus the original 650 nm), demonstrating a strong synergistic effect between pulse overlap control and phase-selective etching. These results provide fundamental insights into overlap parameter effects in ultrafast laser processing and establish a practical methodology for precision surface engineering of transparent crystalline materials, with direct applications in optical component manufacturing and semiconductor substrate processing.

Aqueous zinc-ion batteries (AZIB) are significantly constrained by the poor stability of Zn anodes in aqueous electrolytes, which is caused by uncontrollable deposition behavior and parasitic reactions. The construction of specific crystalline surfaces represents an effective method for stabilizing Zn anodes. Therefore, a stable Malic acid@Zn (MA@Zn) anode with a highly (101) texture configuration is developed through acid etching. The mechanism of MA selective etching is investigated through theoretical calculations, where Zn atoms detach from the (002) crystal surface due to the strong interaction of MA with the (002) surface, leading to the preferential corrosion of the (002) surface and the formation of a unique (101) texture configuration morphology. This texture is conducive to the MA@Zn anode, as it enhances the affinity of MA@Zn for Zn2+ and optimizes the electric field distribution on the surface, thereby facilitating a more stable Zn deposition. Consequently, the MA@Zn symmetric battery is subjected to stable cycling for a period exceeding 2400 h at a current density of 5 mA cm-2. In comparison, the cycle life of the Zn//V2O5 full battery is significantly improved by >6000 cycles, pouch battery also shows better performance.

No abstract available

Surface and nanoscale morphology of thin poly(3-hexylthiophene) (P3HT) films are effectively controlled by blending the polymer with a soluble derivative of fullerene, and then selectively dissolving out the fullerene from the blend films. A combination of the polymer blending with fullerene and a use of diiodooctane (DIO) as a processing additive enhances the molecular ordering of P3HT through nanoscale phase separation, compared to the pristine P3HT. In organic thin-film transistors, such morphological changes in the blend induce a positive effect on the field-effect mobility, as the mobility is ~5–7 times higher than in the pristine P3HT. Simple dipping of the blend films in butyl acetate (BA) causes a selective dissolution of the small molecular component, resulting in a rough surface with nanoscale features of P3HT films. Chemical sensors utilizing these morphological features show an enhanced sensitivity in detection of gas-phase ammonia, water, and ethanol.

Solid oxide cells (SOCs) are promising energy‐conversion devices due to their high efficiency under flexible operational modes. Yet, the sluggish kinetics of fuel electrodes remain a major obstacle to their practical applications. Since the electrochemically active region only extends a few micrometers, manipulating surface architecture is vital to endow highly efficient and stable fuel electrodes for SOCs. Herein, a simple selective etching method of nanosurface reconstruction is reported to achieve catalytically optimized hierarchical morphology for boosting the SOCs under different operational modes simultaneously. The selective etching can create many corrosion pits and exposure of more B‐site active atoms in Sr2Co0.4Fe1.2Mo0.4O6‐δ fuel electrode, as well as promote the exsolution of CoFe alloy nanoparticles. An outstanding electrochemical performance of the fabricated cell with the power density increased by 1.47 times to 1.31 W cm−2 at fuel cell mode is demonstrated, while the current density reaches 1.85 A cm−2 under 1.6 V at CO2 electrolysis mode (800 °C). This novel selective etching method in perovskite oxides provides an appealing strategy to fabricate hierarchical electrocatalysts for highly efficient and stable SOCs with broad implications for clean energy systems and CO2 utilization.

Low-temperature post oxidation annealing of 4H-SiC at 900 °C for 90 min after photoelectric chemical (PEC) etching in alkaline solution can eliminate the porous structures that form during the etching process, reduce the porosity, and optimize the surface morphology, which has minimal effect on unetched surfaces, allowing for selective treatment between etched and unetched surfaces. Additionally, it can improve the etching depth and enable effective repetition of the etching process. These benefits make PEC etching a valuable technique for microstructure fabrication and surface treatment.

The article examines the morphology of porous silicon doped with phosphorus and boron obtained by metal-stimulated etching using Cr. Selective Sirtles etchant with the composition of HF - 100 cm3, CrO3 - 50 g, H2O - 120 cm3 was chosen. The application of the Cr film was carried out by thermal sputtering in a vacuum. The thickness of the film was 10–40 nm. After the etching process, a macroporous structure with pyramid-shaped pores was revealed on the surface of the plates. It was established that with an increase in the thickness of the metal catalyst film and with an increase in the duration of etching, the size of the pores and etching pits increases. A uniform macroporous structure can be obtained by etching silicon with a chromium film 10–15 nm thick. When using a film with a thickness of 20–30 nm, the size of etching pits increases sharply. When using a chromium film with a thickness of more than 30 nm, uneven etching of the film is possible, which leads to uneven pore formation. The size of the pores on the surface of silicon doped with boron is much smaller than on the surface of silicon doped with phosphorus, which is caused by a decrease in the concentration of the doping impurity.

In this paper, we reported on wafer-scale nanoporous (NP) AlGaN-based deep ultraviolet (DUV) distributed Bragg reflectors (DBRs) with 95% reflectivity at 280 nm, using epitaxial periodically stacked n-Al 0.62 Ga 0.38 N/u-Al 0.62 Ga 0.38 N structures grown on AlN/sapphire templates via metal–organic chemical vapor deposition (MOCVD). The DBRs were fabricated by a simple one-step selective wet etching in heated KOH aqueous solution. To study the influence of the temperature of KOH electrolyte on the nanopores formation, the amount of charge consumed during etching process was counted, and the surface and cross-sectional morphology of DBRs were characterized by Scanning electron microscopy (SEM) and atomic force microscopy (AFM). As the electrolyte temperature increased, the nanopores became larger while the amount of charge reduced, which revealed that the etching process was a combination of electrochemical and chemical etching. The triangular nanopores and hexagonal pits further confirmed the chemical etching processes. Our work demonstrated a simple wet etching to fabricate high reflective DBRs, which would be useful for AlGaN based DUV devices with microcavity structures.

No abstract available

Ti3C2Tz MXenes are prepared under different etching conditions and tested as heterogeneous catalysts for the selective oxidation of styrene to benzaldehyde. A clear dependence is observed between the etching conditions (hydrofluoric acid concentration and etching time) and the surface chemistry, morphology and catalytic performance of the resulting MXenes. Under appropriate conditions, etching of the Ti3AlC2 MAX phase precursor with concentrated HF produces Ti3C2Tz MXenes with highly accessible accordion‐like structures and accessible Ti−O surface terminations that can act as active species for the catalytic process, keeping up with the best catalysts reported so far for this reaction. The present study represents one of the few existing reports on catalytic properties of MXenes under mild liquid‐phase conditions, paving the way for future developments of this new family of 2D materials for fine chemical applications.

No abstract available

Sapphire is an attractive material that stands to benefit from surface functionalization effects stemming from micro/nanostructures. Here we investigate the use of ultrafast lasers for fabricating sapphire nanostructures by exploring the relationship between irradiation parameters, morphology change, and selective etching. In this approach a femtosecond laser pulse is focused on the substrate to change the crystalline morphology to amorphous or polycrystalline, which is characterized by examining different vibrational modes using Raman spectroscopy. The irradiated regions are removed using a subsequent hydrofluoric acid etch. Laser confocal measurements quantify the degree of selective etching. The results indicate a threshold laser pulse intensity required for selective etching. This process was used to fabricate hierarchical sapphire nanostructures over large areas with enhanced hydrophobicity, with an apparent contact angle of 140 degrees, and a high roll-off angle, characteristic of the rose petal effect. Additionally, the structures have high broadband diffuse transmittance of up to 81.8% with low loss, with applications in optical diffusers. Our findings provide new insights into the interplay between the light-matter interactions, where Raman shifts associated with different vibrational modes can predict selective etching. These results advance sapphire nanostructure fabrication, with applications in infrared optics, protective windows, and consumer electronics.

In the present study, Ti3C2Tx type MXene was prepared by selective etching of Al from Ti3AlC2 with mesh size of 200. The powder form of raw material was used to fabricate Ti3C2Tx by in-situ HF etching method. The MXene is further coated on non-woven paper by simply dip coating method. The detailed structural, morphology and elemental content study of as prepared Ti3C2Tx MXene have demonstrated. The MXene (Ti3AlC2) powders show compact, layered morphology as expected for bulk layered ternary carbide. The detailed elemental analysis has carried out for Titanium carbide based MXene coated and uncoated woven paper. The lower conducting property obtained for paper coating due less amount of coating in the surface of paper instead of coating on glass substrate. The electrical property characterization of MXene coated non-woven paper and glass substrate have also been studied. Hence, the conductive coating of MXene-in water formulation achieved through simple dip coating methods is promising for low cost sensor, wearable shielding device fabrication towards renewable energy and healthcare applications.

Heterocrystals consisting of multiple species have received wide attention owing to the advantage of the cooperative effect contributed by different functional counterparts; therefore, a controlled growth strategy is highly desired. Herein, we report an effective method to synthesize dumbbell-like Au-PtCu solid and hollow nanorods, regulated by the unique surface capping and oxidation etching roles of copper ions. Dumbbell-like nanorods are prepared through site-selective co-deposition of platinum and copper on both tips of gold nanorods assisted by the capping effect of the CTAB-Cu+ complex to passivate the side surface. On the other hand, hollow dumbbell-like Au-PtCu nanorods are formed through triggering the etching effect of copper ions by increasing the reaction temperature to 80 °C. The manipulation of the morphology and extinction properties of the trimetallic Au-PtCu nanorods is demonstrated by adjusting the concentration of copper ions. Under excitation with a near-infrared 808 nm laser, the dumbbell-like Au-PtCu nanorods show excellent photothermal conversion, with a 3.1 times temperature increment (ΔT) compared to bare Au nanorods, while the hollow dumbbell-like Au-PtCu NRs demonstrate improved photocatalytic activity under xenon lamp irradiation.

Controlling the morphology of noble-metal nanoparticles is mandatory to tune specific properties such as catalytic and optical behavior. Heterodimers consisting of two noble metals have been synthesized, so far mostly in aqueous media using selective surfactants or chemical etching strategies. We report a facile synthesis for Au@Pd and Pd@Au heterodimer nanoparticles (NPs) with morphologies ranging from segregated domains (heteroparticles) to core-shell structures by applying a seed-mediated growth process with Au and Pd seed nanoparticles in 1-octadecene (ODE), which is a high-boiling organic solvent. The as-synthesized oleylamine (OAm) functionalized Au NPs led to the formation of OAm-Au@Pd heteroparticles with a "windmill" morphology, having an Au core and Pd "blades". The multiply twinned structure of the Au seed particles (⌀ ≈ 9-11 nm) is associated with a reduced barrier for heterogeneous nucleation. This leads to island growth of bimetallic Au@Pd heteroparticles with less-regular morphologies. The reaction process can be controlled by tuning the surface chemistry with organic ligands. Functionalization of Au NPs (Ø ≈ 9-11 nm) with 1-octadecanethiol (ODT) led to the formation of ODT-Au@Pd NPs with a closed Pd shell through a strong ligand-metal binding, which is accompanied by a redistribution of the electron density. Experiments with varied Pd content revealed surface epitaxial growth of Pd on Au. For OAm-Pd and ODT-Pd seed particles, faceted, Au-rich domain NPs and impeded core-shell NPs were obtained, respectively. This is related to the high surface energy of the small Pd seed particles (⌀ ≈ 5-7 nm). The metal distribution of all bimetallic NPs was analyzed by extended (aberration-corrected) transmission electron microscopy (HR-TEM, HAADF-STEM, EDX mapping, ED). The Au and Pd NPs, as well as the ODT-Au@Pd and OAm-Pd@Au heteroparticles, catalyze the reduction of 4-nitrophenol to 4-aminophenol with borohydride. The catalytic activity is dictated by the particle structure. OAm-Au@Pd heteroparticles with faceted Au domains had the highest activity because of a mixed Au-Pd surface structure, while ODT-Au@Pd NPs, where the active Au core is covered by a Pd shell, had the lowest activity.

No abstract available

A novel, yet simple and portable, sensing platform has been developed by using silver nanotriangles immobilized on a glass substrate and capped with an optical marker, which, just by dipping in an analyte solution in presence of iodide, can detect mercury (Hg2+) ions by both colorimetric and fluorometric detection modes. This method, which is highly selective for the Hg2+ ions, relies on the superior binding affinity of the Hg2+ with the thiolated ligand, whereby the ligands were extracted from the nanotriangle surfaces exposing them to etching by iodides present in solution. The resulting change in morphology of the surface-bound nanotriangles was manifested in terms of the optical responses by nanoparticles, leading to the colorimetric detection of the analyte in the nanomolar level. The ligands released in solution due to abstraction by Hg2+ allowed fluorometric detection due to the change in emission spectra of these free ligands, offering a unique bimodal sensing of the analyte. A comparison of the substrate-based sensing protocol with conventional solution-based study gave a better insight into the sensing event, helped in optimizing the sensing conditions and emphasized the diverse application potential of the current surface-immobilized sensing system. Our developed sensory platform not only offers easy portability and a bimodal sensing detection, it also the demonstrates an unprecedented wide-range of detection (0.1-10 μM) of Hg2+ ions while maintaining high sensitivity and selectivity for the analyte.

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With increasing industrialization in the modern era, the detection of hazardous gases like NH3 became a global issue due to its detrimental effect on mankind. MXene has emerged as an outstanding gas sensing candidate among two-dimensional materials due to its favorable characteristics like an abundance of interaction sites, metallic conductivity, tunable surface properties, band gap, and excellent mechanical strength. In the present work, a highly sensitive and selective NH3 gas sensor has been fabricated using MXene-based nanostructures. The morphological and structural characterizations of nanostructures have been performed using X-ray diffraction, field-emission scanning electron microscopy, and transmission electron microscopy. The successful etching of Al reveals the formation of MXene having exfoliated multilayered morphology with an average interlayer spacing of ~53 nm. The response kinetics of the sensor has been investigated by estimating their response and selectivity toward different oxidizing and reducing gases. The sensor exhibits high response transient curves toward 5–100 ppm of NH3 at room temperature (30 °C) with fast response and recovery time. Density functional theory has been used to elucidate the interaction mechanism between NH3 molecules and MXene surface.

Wet chemical etching serves as a critical fabrication process for gallium nitride (GaN)-based devices, while precisely measuring the overall etch rates of GaN is essential for both precise control and mechanism research of this process. In this study, the anisotropic etching behavior of Ga-face GaN in 5 wt % KOH/ethylene glycol (EG) solution (110-130 °C) is systematically investigated for the first time. By innovatively designing samples containing micrometer-level hemisphere and wagon-wheel structures, the overall etching rates of Ga-face GaN in the KOH/EG system are experimentally determined accurately. Subsequently, this research compares the etching rate distribution differences between the H3PO4 and KOH/EG systems for Ga-face GaN, and determines the activation energies of arbitrary crystal planes that can be calculated by the overall etching rate distribution in the KOH/EG system at different temperatures (110-130 °C). Furthermore, in this paper, the anisotropic mechanism of the etching rate is established under the assumption of step flow, the etching mechanism is given based on the calculated removal rate of atomic clusters, and the reasons for the etching rate distribution in different etchants are explained on the atomic scale. In addition, in GaN microstructure etching experiments, the evolution of the etching morphology of the hexagonal concave structure is accurately predicted based on the experimentally determined etching rate data of the overall crystal planes. The results of this paper provide critical experimental paths, overall etching rate distribution data, and theoretical support for the precision control of wet etching of GaN micro- and nanostructures.

Due to its high refraction index, silicon (Si) reflects a significant amount of solar light of more than 37% of the sun’s spectral range, particularly when it does not strike the surface perpendicularly. This effect consequentially reduces solar cell efficiency due to electrical and optical losses. Surface texturing is essential for increasing the cells' photon-trapping and absorbing capabilities to improve the efficiency of low-performance solar cells. In this study, pulsed Nd:YAG lasers are used to texturize surfaces of silicon wafers. This procedure is quicker and easier and does not produce waste or pollutants. However, there are some disadvantages to laser texturing; one is that it may lower solar cell efficiency if the damaged layer caused by the laser texturing is not removed. In this study, the laser damage layer is washed off with potassium hydroxide (20%), also known as KOH. This paper also compares the reflectance of laser texturing and wet chemical etching on surfaces of crystalline silicon wafers. The PerkinElmer Lambda 950 UV-VIS-NIR Spectrophotometer results indicate that laser texturing obtains a reflectance of 1% before and 9% after KOH treatment, in contrast to wet chemical etching, which has a reflectance of 16%. Laser texturing showed some efficiency, especially when texturing silicon wafer surfaces in parallel patterns, with a conversion efficiency of about 5% and grid patterns at 7.5%. This successful outcome demonstrates that laser texturing gives silicon solar cells a good alternative to traditional texturing techniques.

Molten-alkali etching has been widely used to reveal dislocations in 4H silicon carbide (4H-SiC), which has promoted the identification and statistics of dislocation density in 4H-SiC single crystals. However, the etching mechanism of 4H-SiC is limited misunderstood. In this letter, we reveal the anisotropic etching mechanism of the Si face and C face of 4H-SiC by combining molten-KOH etching, X-ray photoelectron spectroscopy (XPS) and first-principles investigations. The activation energies for the molten-KOH etching of the C face and Si face of 4H-SiC are calculated to be 25.09 and 35.75 kcal/mol, respectively. The molten-KOH etching rate of the C face is higher than the Si face. Combining XPS analysis and first-principles calculations, we find that the molten-KOH etching of 4H-SiC is proceeded by the cycling of the oxidation of 4H-SiC by the dissolved oxygen and the removal of oxides by molten KOH. The faster etching rate of the C face is caused by the fact that the oxides on the C face are unstable, and easier to be removed with molten alkali, rather than the C face being easier to be oxidized.

Anisotropic etching of silicon in potassium hydroxide (KOH) is an important technology in micromachining. The residue deposition from KOH etching of Si is typically regarded as a disadvantage of this technology. In this report, we make use of this residue as a second masking layer to fabricate two-layer complex structures. Square patterns with size in the range of 15–150 μm and gap distance of 5 μm have been designed and tested. The residue masking layer appears when the substrate is over-etched in hydrofluoric acid (HF) solution over a threshold. The two-layer structures of micropyramids surrounded by wall-like structures are obtained according to the two different masking layers of SiO2 and residue. The residue masking layer is stable and can survive over KOH etching for long time to achieve deep Si etching. The process parameters of etchant concentration, temperature, etching time and pattern size have been investigated. With well-controlled two-layer structures, useful structures could be designed for applications in plasmonic and microfluidic devices in the future.

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Combining dry and wet etching processes is a common technique to pattern III-N semiconductors integrated in optoelectronic devices with a controlled final shape and high-quality crystallographic facets. However, the wet mechanisms driving the final pattern morphology have never been deeply studied. In this work, we investigate the mechanisms involved during KOH wet etching applied on AlN and GaN pillars previously obtained by Cl2 plasma etching with a hexagonal hard mask, whose edges are oriented with an a or m nonpolar III-N crystallographic orientation. These pillars are intended to serve as the first building blocks for core-shell ultraviolet light-emitting diodes (UV LED), for which the quality of the patterning of the III-N core pillar plays a key role in the subsequent quantum well regrowth. We discuss the impact of the KOH concentration (5 wt % vs 44 wt %), the solution temperature (from room temperature to 80 °C), and the hard mask orientation on the etching kinetics, the etch propagation mechanisms, the crystallographic plane stability, and roughness formation. Our results show how the stability of the crystallographic c- and m-planes and the vulnerability of specific kink sites determine the progression of the KOH wet etching process and the formation of roughness depending on the wet etching conditions and the shape of the hard mask used. With this understanding, we developed a two-step process combining dry and wet etching capable of fabricating high-aspect ratio AlN and GaN nanopillars with the desired smooth and anisotropic m-oriented sidewalls.

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In Si substrate, anisotropic KOH etchants are mainly utilized to form pyramids like on the Si surface . However, this process is not well controlled way owing to the different and random etching pathway. In this work, we applied laser radiation during the anisotropic KOH wet etching process to modifies the topographical properties of Si substrate, as an efficient,simple and low cost texturing process for Si substrate. This approach employs different laser wavelength to modify the topographical features from a crater like structures to Si nanocrystallites in the form of pillars like structures on the Si surface. In order to investigate the formation of plasmonics species, gold nanoparticles was incorporated into Si surfaces by simple ion reduction process. The Si topographical features was studied with atomic scanning microscopy (AFM) images of Si before and after laser irradiation process. The irradiation with 405 laser wavelength, show the formation of thin and high density of Si nano pillars-like structures compared with more thick depther Si nano pillars like structures layer.

We report on the microfabrication of continuous aspherical optical surfaces with a single-mask process, using anisotropic etching of silicon in a KOH water solution. Precise arbitrary aspherical surfaces with lateral scales on the order of several millimeters and a profile depth on the order of several micrometers were fabricated using this process. We discuss the factors defining the precision of the formed component and the resulting surface quality. We demonstrate 1 mm and 5 mm replicated aspherical phase plates, reproducing defocus, tilt, astigmatism and high-order aberrations. The technology has a potential for serial production of reflective and refractive arbitrary aspherical micro-optical components.

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Potassium hydroxide (KOH)-based anisotropic wet etching is widely used in MEMS device fabrication due to its low cost, high etching rate, and minimal wafer damage. However, improper process parameters can lead to defects such as V-shaped notches and asymmetric sidewalls, especially in etching (110) Si wafers. These defects reduce pattern fidelity and bring dimensional errors in MEMS devices. This work presents wet etching experiments with COMSOL Multiphysics modeling to elucidate the influence of $\mathbf{K O H}$ concentration and solution temperature on (110) Si etch profile evolution. The findings demonstrate that etching with $\mathbf{1 0} \mathbf{~ w t \% ~} \mathbf{K O H}$ at $\mathbf{7 0}^{\circ} \mathrm{C}$ can yield optimal trench geometries with near-vertical sidewalls ($<89.5^{\circ}$) and negligible basal undercutting. These results provide practical guidelines for achieving submicron-scale dimension control in MEMS fabrication.

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Silicon anisotropic etching is the main process of bulk micromachining to fabricate microelectro-mechanical systems (MEMS) structures such as microcantilevers, diaphragms, mesa structures, etc. In this process, one of the most used anisotropic etchants is potassium hydroxide (KOH). Recently this etchant was modified by addition of NH2OH to alter the etching characteristics to obtain high etch rate and improved etch selectivity between silicon and thermal oxide (SiO2). In this work, we have studied the effect of surfactant Triton X-100 on bulk micromachining characteristics of NH2OH + KOH. Micromachining characteristics are investigated on Si{100} and Si{110} wafers. The addition of surfactant suppresses the undercutting at convex corners and the etch rate of Si{110}. The reduction of undercutting at convex corners is utilized to form mesa structures, while significantly low etch rate of Si{110} is exploited for the formation 45° slanted sidewalls (i.e., micromirror) by exposing {110} sidewalls at the mask edges aligned along <100> directions on Si{100} surface.

In wet anisotropic etching based silicon bulk micromachining, undercutting, which has both advantage and disadvantage, takes place at the convex corners of microstructures. In order to retain the desired shape of fabricated structure, corner compensation method is most commonly used to protect the convex corners. The design and shape of the compensation geometry depend on the type of etchant. In this work, various types of corner compensating structures to protect convex corners on Si{110} and Si{110} are studied in potassium hydroxide (KOH) modified by adding NH2OH solution. Silicon etch rate in NH2OH-added KOH is 3–4 times more than that in pure KOH solution, which is very useful for industrial application to improve productivity. Mesa shape structures are fabricated using different shapes corner compensating geometry to optimize the design to obtain best shape convex corner. Triangular shape and beam shape geometries are found most appropriate structures to obtain well-shaped convex corner on Si{100} and Si{110}, respectively.

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Diamond possesses excellent physical and electronic properties, and thus various applications that use diamond are under development. Additionally, the control of diamond geometry by etching technique is essential for such applications. However, conventional wet processes used for etching other materials are ineffective for diamond. Moreover, plasma processes currently employed for diamond etching are not selective, and plasma-induced damage to diamond deteriorates the device-performances. Here, we report a non-plasma etching process for single crystal diamond using thermochemical reaction between Ni and diamond in high-temperature water vapour. Diamond under Ni films was selectively etched, with no etching at other locations. A diamond-etching rate of approximately 8.7 μm/min (1000 °C) was successfully achieved. To the best of our knowledge, this rate is considerably greater than those reported so far for other diamond-etching processes, including plasma processes. The anisotropy observed for this diamond etching was considerably similar to that observed for Si etching using KOH.

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