原位液相电镜在催化方向和液相运动及自组装方向的研究工作

Metal oxides have attracted substantial attention over the years and are commonly used in the semiconductor industry because of their excellent physical and chemical properties. Among the various metal oxides, cuprous oxide (Cu2O) is regarded as a promising material. It is inexpensive, earthabundant, and nontoxic; therefore, it can be used in catalysis, sensors, solar cells and p-type semiconductors. However, the redox reaction of cuprous oxide is still uncertain. The size, morphology, and structure of Cu2O strongly influence its properties. In this work, we developed a new synthesis method of Cu2O that involves reducing the precursor by an electron beam without reducing agent. The growth process of Cu2O nanocubes were observed via in situ liquid cell transmission electron microscopy (in situ LCTEM). The nucleation kinetics, oscillating growth behavior, and redox reaction of the Cu2O nanocubes in the liquid phase were systematically studied. The electron beam decomposed the solution into radicals, which reduced the Cu2+ into Cu2O. The Cu2O exhibited a round shape at the beginning and transformed into a cubic shape afterward. Interestingly, the Cu2O nanocubes grew clearly under long-term observation; however, their diameters increased and fluctuated during the short-term observation. The electron beam not only stimulated the solution to reduce the nanocubes but also caused radiation damage to the nanocubes. During the Cu2O growth and dissolution, the cubic shape evolved with specific planes in the {100} family. Our direct observation sheds light on the preparation of Cu2O by a reduction method, extending the study of reaction kinetics and providing a new way to synthesize metal oxides.

The kinetics of mass transfer in a stagnant fluid layer next to an interface govern numerous dynamic reactions in diffusional micro/nanopores, such as catalysis, fuel cells, and chemical separation. However, the effect of the interplay between stagnant liquid and flowing fluid on the micro/nanoscopic mass transfer dynamics remains poorly understood. Here, by using liquid cell transmission electron microscopy (TEM), we directly tracked microfluid unit migration at the nanoscale. By tracking the trajectories, an unexpected mass transfer phenomenon in which fluid units in the stagnant liquid layer migrated two orders faster during gas-liquid interface updating was identified. Molecular dynamics (MD) simulations indicated that the chemical potential difference between nanoscale liquid layers led to convective flow, which greatly enhanced mass transfer on the surface. Our study opens up a pathway toward research on mass transfer in the surface liquid layers at high spatial and temporal resolutions.

Heterogeneous nanoparticles are widely used in catalysis, sensors and biology due to their versatile functions. Among the various heterogeneous nanoparticles, Au-Cu2O core-shell nanoparticles show high stability and short response times for use as sensors and catalysts and have thus attracted much attention. Previous studies show that the properties of Au-Cu2O are mainly related to the shape and size of the Au-Cu2O nanoparticles. However, the forming behavior of heterostructures and the mechanism have not been fully explored. In this work, liquid cell transmission electron microscopy (LCTEM) was used to investigate the formation of these interesting Au-Cu2O nanoparticles and their process of aggregation. The electron beam and dispersion of gold nanoparticles are both important parameters for the reduction reaction in in situ LCTEM. The Au-Cu2O core-shell nanoparticles can be synthesized to have two morphologies, multifaceted and cubic. The nanoparticles grew into these different morphologies due to the amount of remaining citrate ligands on the surface of the gold nanoparticles. For the multifaceted nanoparticles, the epitaxy of the two components is confirmed from high-resolution TEM images and electron diffraction patterns with an epitaxial relationship of Au (020)//Cu2O (020) and Au [101]//Cu2O [101]. The growth rate is approximately 210 nm2 s-1. On the other hand, the cubic nanoparticles nucleate and grow independently. The growth kinetics and elemental distributions have been systematically studied. In addition, the nanoclusters would float, rotate, and finally aggregate with the surrounding clusters. This in situ experiment sheds light on the growth mechanisms of nanostructures and will improve the applicability and controllability of heterostructure synthesis.

Free-standing ultra-thin (~2 nm) films of several oxides (Al2O3, TiO2, and others) have been developed, which are mechanically robust and transparent to electrons with Ekin ≥ 200 eV, and to photons. We demonstrate their applicability in environmental X-ray photoelectron and infrared spectroscopy for molecular level studies of solid-gas (≥1 bar) and solid-liquid interfaces. These films act both as membranes closing a reaction cell, and as substrates and electrodes for electrochemical reactions. The remarkable properties of such ultra-thin oxides membranes enable atomic/molecular level studies of interfacial phenomena, such as corrosion, catalysis, electrochemical reactions, energy storage, geochemistry, and biology, in a broad range of environmental conditions.

Self-assembled, porous coordination cages with a functional interior find application in controlled guest inclusion/release, drug delivery, separation processes, and catalysis. However, only few studies exist that describe their utilization for the development of self-assembled materials based on their 3-dimensional shape and external functionalization. Here, dodecyl chain-containing, acridone-based ligands (LA) and shape-complementary phenanthrene-derived ligands (LB) are shown to self-assemble to heteroleptic coordination cages cis-[Pd2(LA)2(LB)2]4+ acting as a gemini amphiphile (CGA-1; Cage-based Gemini Amphiphile-1). Owing to their anisotropic decoration with short polar and long nonpolar side chains, the cationic cages were found to assemble into vesicles with diameters larger than 100 nm in suitable polar solvents, visualized by cryo-TEM and Liquid-Cell Transmission Electron Microscopy (LC-TEM). LC-TEM reveals that these vesicles aggregate into chains and necklaces via long-range interactions. In addition, the cages show a rarely described ability to stabilize oil-in-oil emulsions.

Yolk–shell nanoparticles based on mesoporous SiO2 (mSiO2) coating of Au nanoparticles (Au NPs) hold great promise for many applications in e.g., catalysis, biomedicine, and sensing. Here, we present a single-step coating approach for synthesizing Au NP@mSiO2 yolk–shell particles with tunable size and tunable hollow space between yolk and shell. The Au NP–mSiO2 structure can be manipulated from core–shell to yolk–shell by varying the concentration of cetyltrimethylammonium chloride (CTAC), tetraethyl orthosilicate (TEOS), Au NPs, and NaOH. The growth mechanism of the yolk–shell particles was investigated in detail and consists of a concurrent process of growth, condensation, and internal etching through an outer shell. We also show by means of liquid-cell transmission electron microscopy (LC-TEM) that Au nanotriangle cores (Au NTs) in yolk–shell particles that are stuck on the mSiO2 shell, can be released by mild etching thereby making them mobile and tumbling in a liquid-filled volume. Due to the systematical investigation of the reaction parameters and understanding of the formation mechanism, the method can be scaled-up by at least an order of magnitude. This route can be generally used for the synthesis of yolk–shell structures with different Au nanoparticle shapes, e.g., nanoplatelets, nanorods, nanocubes, for yolk–shell structures with other metals at the core (Ag, Pd, and Pt), and additionally, using ligand exchange with other nanoparticles as cores and for synthesizing hollow mSiO2 spheres as well.

The nucleation and growth of nanoparticles are critical processes determining the size, shape, and properties of resulting nanoparticles. However, understanding the complex mechanisms guiding the formation and growth of colloidal multielement alloy nanoparticles remains incomplete due to the involvement of multiple elements with different properties. This study investigates in situ colloidal synthesis of multielement alloys using transmission electron microscopy (TEM) in a liquid cell. Two different pathways for nanoparticle formation in a solution containing Au, Pt, Ir, Cu, and Ni elements, resulting in two distinct sets of particles are observed. One set exhibits high Au and Cu content, ranging from 10 to 30 nm, while the other set is multi‐elemental, with Pt, Cu, Ir, and Ni, all less than 4 nm. The findings suggest that, besides element miscibility, metal ion characteristics, particularly reduction rates, and valence numbers, significantly impact particle composition during early formation stages. Density functional theory (DFT) simulations confirm differences in nanoparticle composition and surface properties collectively influence the unique growth behaviors in each nanoparticle set. This study illuminates mechanisms underlying the formation and growth of multielement nanoparticles by emphasizing factors responsible for chemical separation and effects of interplay between composition, surface energies, and element miscibility on final nanoparticles size and structure.

Electrochemical liquid-cell transmission electron microscopy (e-LCTEM) offers great potential for investigating the structural dynamics of nanomaterials during electrochemical reactions. However, challenges arise from the difficulty in achieving the optimal electrolyte thickness, leading to inconsistent electrochemical responses and limited spatial resolution. In this study, we present advanced e-LCTEM techniques tailored for tracking Pt/C degradation under electrochemical polarization at short intervals with high spatial resolution. Our innovative approach combines microfabrication-based sample preparation with in situ control of electrolyte thickness, ensuring reliable electrochemical signal acquisition and direct observation of sequential catalyst degradation. Quantitative imaging analyses conducted at both global areas and single-particle levels unveil a distinctive degradation mechanism primarily driven by nanoparticle migrations. Smaller nanoparticles exhibit a higher susceptibility to migration, leading to coalescence and final detachment in series. This migration-gated degradation mechanism provides a new perspective on the size-dependent durability of supported nanoparticles, complementing the prevailing explanation centered on the size-dependent dissolution kinetics of nanoparticles.

We present a novel in situ liquid-cell transmission electron microscopy (TEM) approach to study the behavior of metal nanoparticles under high-energy electron irradiation. By utilizing a radically-inert liquid environment, we aim to minimize radiolysis effects and explore the influence of charge-induced transformations. We observed complex dynamics in nanoparticle behavior, including morphological changes and transitions between amorphous and crystalline states. These transformations are attributed to the delicate interplay between charge accumulation on the nanoparticles and enhanced radiolysis, suggesting a significant role for charge-assisted processes in nanoparticle evolution. Our findings provide valuable insights into the fundamental mechanisms driving nanoparticle behavior at the nanoscale and demonstrate the potential of liquid-cell TEM for studying complex physicochemical processes in controlled environments.

Understanding the growth mechanisms of nanomaterials is crucial for effectively controlling their morphology which may affect their properties. Here, the growth process of indium nanoplates is studied using in situ liquid cell transmission electron microscopy. Quantitative analysis shows that the growth of indium nanoplate is limited by surface reaction. Besides, the growth process has two stages, which is different from that of other metal nanoplates reported previously. At the first stage, indium particles transform gradually from face-centered cubic to body-centered tetragonal (bct) structure as the seeds grow. At the second stage, the seeds grow faster than at the first stage and form indium triangular nanoplates. Indium triangular nanoplates have a bct structure with {011}-twin, which is found to form through kinetic reactions. In addition, the shape evolution of truncated triangle nanoplate with multiple twin planes is studied. The growth rate of truncated edge changes with the varied number of re-entrant grooves. The present work provides valuable insights into the growth mechanism of metal nanoplates with low-symmetric structure and the role of twin planes in the shape evolution of plate-like metal nanomaterials.

Summary In situ liquid-phase electrochemical transmission electron microscopy (ec-TEM) as a valuable technique has been widely used in studying metal deposition in battery materials. While real-time observations of metallic nucleation, growth, and dendrite formation using microscale ec-TEM liquid cells are investigated, existing cells exhibit nonuniform electric field distribution along electrodes, limiting measurement reliability and quantitative analysis. Here, we introduce an advanced electrode design for ec-TEM chips, ensuring a uniform electric field for precise characterization of early-stage metal deposition closer to practical battery conditions. Both simulation and experimental investigations demonstrate that these specially designed ec-TEM chips facilitate quantitative electrochemical characterization combined with the in situ TEM technique in comparison with commercially available chips. We thus provide a significant progression toward optimizing the performance and reliability of quantitative in situ liquid-phase TEM measurements, essential for understanding and improving electrochemical systems.

Unraveling nanoscale corrosion pathways is essential for understanding materials degradation mechanisms and designing corrosion-resistant metal alloys. Here, we directly visualize the corrosion of Pt-Ni nanododecahedra in 0.1 M HCl using liquid cell TEM. Each nanoparticle features a Ni-rich core and a Pt-rich frame. Our observation reveals that corrosion proceeds in two distinct stages: first the Ni-rich core dissolves without forming porosity, yielding small Pt nanocrystals and transient NiCl2·6H2O at the retreating interfaces; then the Pt-rich frame fragments into ∼5 nm Pt3Ni nanocrystals that subsequently dissolve uniformly, accompanied by fleeting Pt chlorides. A percolation-based theory explains the observed behaviors: The core's ∼8% Pt lies below the Pt connectivity threshold, preventing Pt scaffold formation, whereas the frame's 48% Ni exceeds the Ni percolation threshold and collapses. Ordered Pt3Ni suppresses Ni percolation, thereby enforcing uniform dissolution. These findings reveal how composition and structural ordering govern heterogeneous corrosion in Pt-Ni architectured nanoparticles.

Metastable phases—kinetically favoured structures—are ubiquitous in nature1,2. Rather than forming thermodynamically stable ground-state structures, crystals grown from high-energy precursors often initially adopt metastable structures depending on the initial conditions, such as temperature, pressure or crystal size1,3,4. As the crystals grow further, they typically undergo a series of transformations from metastable phases to lower-energy and ultimately energetically stable phases1,3,4. Metastable phases sometimes exhibit superior physicochemical properties and, hence, the discovery and synthesis of new metastable phases are promising avenues for innovations in materials science1,5. However, the search for metastable materials has mainly been heuristic, performed on the basis of experiences, intuition or even speculative predictions, namely ‘rules of thumb’. This limitation necessitates the advent of a new paradigm to discover new metastable phases based on rational design. Such a design rule is embodied in the discovery of a metastable hexagonal close-packed (hcp) palladium hydride (PdHx) synthesized in a liquid cell transmission electron microscope. The metastable hcp structure is stabilized through a unique interplay between the precursor concentrations in the solution: a sufficient supply of hydrogen (H) favours the hcp structure on the subnanometre scale, and an insufficient supply of Pd inhibits further growth and subsequent transition towards the thermodynamically stable face-centred cubic structure. These findings provide thermodynamic insights into metastability engineering strategies that can be deployed to discover new metastable phases. A metastable palladium hydride is synthesized where the unique environment in the liquid cell, namely the limited quantity of Pd precursors and the continuous supply of H, resulted in the formation of the hcp phase.

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Abstract In situ liquid cell transmission electron microscopy (TEM) is a very useful tool for investigating dynamic solid–liquid reactions. However, there are challenges to observe the early stages of spontaneous solid–liquid reactions using a closed-type liquid cell system, the most popular and simple liquid cell system. We propose a graphene encapsulation method to overcome this limitation of closed-type liquid cell TEM. The solid and liquid are separated using graphene to suspend the reaction until the graphene layer is destroyed. Graphene can be decomposed by the high-energy electron beam used in TEM, allowing the reaction to proceed. Fast dissolution of graphene-capped copper nanoparticles in an FeCl3 solution was demonstrated via in situ liquid cell TEM at 300 kV using a cell with closed-type SiNx windows.

We report two different formation mechanisms of a triangular Au nanoplate through the transformation of a truncated octahedron and the direct formation of a triangular seed using liquid-cell TEM. This work stresses the great significance of thermodynamics and kinetics in the formation and later shape transformation of a triangular nanoplate.

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In order to gain better control over the functionality of Pd nanostructures used in several CO2-mitigating electrochemical energy conversion systems, it is imperative to underpin different nanoscale phenomena influencing their structural durability. Hitherto, such analyses have been carried out before/after an electrochemical treatment, but not during the entire process. Here, we demonstrate monitoring of morphological evolution in Pd nanostructures over the entire course of electrochemical treatment using a liquid-cell transmission electron microscope (TEM) set-up. Our findings reveal new insights into nanoparticle growth, dissolution, detachment, and aggregation that are relevant for the development of functional Pd nanomaterials.

We studied silicon, carbon, and SiCx nanostructures fabricated using liquid-phase electron-beam-induced deposition technology in transmission electron microscopy systems. Nanodots obtained from fixed electron beam irradiation followed a universal size versus beam dose trend, with precursor concentrations from pure SiCl4 to 0 % SiCl4 in CH2Cl2, and electron beam intensity ranges of two orders of magnitude, showing good controllability of the deposition. Secondary electrons contributed to the determination of the lateral sizes of the nanostructures, while the primary beam appeared to have an effect in reducing the vertical growth rate. These results can be used to generate donut-shaped nanostructures. Using a scanning electron beam, line structures with both branched and unbranched morphologies were also obtained. The liquid-phase electron-beam-induced deposition technology is shown to be an effective tool for advanced nanostructured material generation.

Triton AX is the first liquid cell transmission electron microscopy (LCTEM) workflow solution to enable both liquid heating and cooling during nanoscale electrochemical analysis. With precise temperature control from -50°C to 300°C, it offers the broadest thermal range available in any LCTEM system. The integration of simultaneous electrochemistry and temperature control allows real-time observation of temperature-dependent processes such as battery degradation, electrocatalytic activity, and corrosion. By replicating realistic operating conditions in the TEM, Triton AX bridges the gap between nanoscale dynamics and macroscopic material performance, providing a versatile platform for advancing research in energy materials, nanotechnology, and materials science.

The study of ice nucleation and growth at the nanoscale is of utmost importance in geological and atmospheric sciences. However, existing transmission electron microscopy (TEM) approaches have been unsuccessful in imaging ice formation directly. Herein, we demonstrate how radical scavengers - such as TiO2 - encased with water in graphene liquid cells (GLCs) facilitate the observation of ice nucleation phenomena at low temperatures. Atomic-resolution imaging reveals the nucleation and growth of cubic ice-phase crystals at close proximity to TiO2-water nanointerfaces at low temperatures. Interestingly, both heterogeneously and homogeneously nucleated ice crystals exhibited this cubic phase. Ice crystal nuclei were observed to be more stable at the TiO2-water nanointerface, as compared with crystals in the bulk liquid (homogeneous nucleation), suggesting the radical scavenging efficacy of TiO2 nanoparticles mitigating the electron beam by-products. The present work demonstrates that the use of radical scavengers in GLC TEM shows great promise towards unveiling the nanoscale pathways for ice nucleation and growth dynamic events.

Nanocatalysts often experience structural changes during electrocatalytic reactions, such as carbon dioxide reduction, oxygen evolution reaction (OER), and so on. Tracking the dynamic structural evolution of catalysts, including their morphology, crystal structure, and valence states changes by real time imaging is challenging due to the complex reaction environment and limited experimental capabilities. My group has recently made breakthroughs in developing novel polymer electrochemical liquid cells for in-situ transmission electron microscopy (TEM) study of electrocatalysts during reactions. It has enabled direct observation of the atomic structure dynamics of Cu-nanowire catalysts during CO 2 electroreduction reactions [1]. Our real time imaging revealed a fluctuating liquid-like amorphous interphase on the Cu catalyst surface, and interphase dynamics mediates the catalyst surface restructuring. The combination of real-time observation and theoretical calculations unveils an amorphization-mediated restructuring mechanism. We have further studied Cu-based bimetallic nanocatalysts (e.g., CuAg, CuPd, etc.) and severe restructuring of the catalysts and unique intermediate states was revealed [2]. Lastly, we have also extended our study to Co-oxide and Co-hydroxide catalysts for OER [3]. Insights gained from these efforts assist the future control of the electrocatalytic reactions and novel design of catalysts. [1] Q. Zhang, Z. Song, X. Sun, Y. Liu, J. Wan, S. Betzler, Q. Zheng, J. Shangguan, K. Bustillo, P. Ercius, P. Narang, Y. Huang, H. Zheng. Nature 630, 643–647 (2024). [2] J. Wan, Q. Zhang, E. Liu, Y. Chen, J. Zheng, A. Ren, W. Drisdell, H. Zheng, “In-situ/operando study of Cu-based nanocrystals for CO2 electroreduction using electrochemical liquid cell TEM”, Frontiers in Chemistry 13, 1525245 (2025). [3] Y. Chen, H. Zheng et al. to be submitted (2025). [4] Acknowledgements: The above work was supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (BES), Materials Sciences and Engineering Division under Contract No. DE-AC02-05-CH11231 within the In-situ TEM (KC22ZH) program. Work at the Molecular Foundry (MF) LBNL, which was supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

Quantifying the role of experimental parameters on the growth of metal nanocrystals is crucial when designing synthesis protocols that yield specific structures. Here, the effect of temperature on the growth kinetics of radiolytically-formed branched palladium (Pd) nanocrystals is investigated by tracking their evolution using liquid cell transmission electron microscopy (TEM) and applying a temperature-dependent radiolysis model. At early times, kinetics consistent with growth limited is measured by the surface reaction rate, and it is found that the growth rate increases with temperature. After a transition time, kinetics consistent with growth limited by Pd atom supply is measured, which depends on the diffusion rate of Pd ions and atoms and the formation rate of Pd atoms by reduction of Pd ions by hydrated electrons. Growth in this regime is not strongly temperature-dependent, which is attributed to a balance between changes in the reducing agent concentration and the Pd ion diffusion rate. The observations suggest that branched rough surfaces, generally attributed to diffusion-limited growth, can form under surface reaction-limited kinetics. It is further shown that the combination of liquid cell TEM and radiolysis calculations can help identify the processes that determine crystal growth, with prospects for strategies for control during the synthesis of complex nanocrystals.

We developed a system to effectively trap nanoparticles suspended in solution, in dedicated suspended nanochannels for in-situ liquid phase transmission electron microscopy (LPTEM) measurements. The system was tested through single particle analysis using scanning TEM energy dispersive X-ray spectroscopy (STEM-EDX). Furthermore, electron diffraction characterization of metallic nanoparticles in solution was performed for the electron pair distribution function (ePDF). Finally, samples of biological origin were imaged in the liquid cell. The EDX data enabled elemental identification at the single particle level, facilitating the deduction of atomic scattering factors used in the ePDF analysis, which revealed bond lengths for Si-N, N-N from the chip, and Pt-Pt from the sample. We discuss the implications of these findings for in-situ studies of various applications of nanoparticles in liquids. The trap chip system will be useful for biological imaging, time-resolved studies, single particle statistics, and alternatives to x-ray experiments, offering new possibilities for probing dynamic processes with particles in liquids using TEM techniques.

The growth of silver shells on gold nanorods is investigated by in situ liquid cell transmission electron microscopy using an advanced liquid cell architecture. The design is based on microwells in which the liquid is confined between a thin Si3N4 membrane on one side and a few-layer graphene cap on the other side. A well-defined specimen thickness and an ultraflat cell top allow for the application of high-resolution TEM and the application of analytical TEM techniques on the same sample. The combination of high-resolution data with chemical information is validated by radically new insights into the growth of silver shells on cetrimonium bromide stabilized gold nanorods. It is shown that silver bromide particles already formed in the stock solution play an important role in the exchange of silver ions. The Ag shell growth can be directly correlated with the layer-by-layer dissolution of AgBr nanocrystals, which can be controlled by the electron flux density via distinctly generated chemical species in the solvent. The derived model framework is confirmed by in situ UV-vis absorption spectroscopy evaluating the blue shift in the longitudinal surface plasmon resonance of anisotropic NRs in a complementary batch experiment.

The study of in situ or operando electrochemistry entails observing electrochemical behavior of samples in environments as close to “real working conditions” as possible. Scanning/transmission electron microscopy (S/TEM) enables researchers to characterize physical behavior on the sub-nanometer scale, but conventional S/TEM techniques require sample imaging and analysis in a high-vacuum environment. Recent advances in sample holder technology for S/TEM – specifically, the introduction of closed-cell S/TEM holders and the development of MEMS-based sample supports – have overcome this limitation. Closed-cell holders allow researchers to study their electrochemical systems in liquid, including the option to flow or exchange electrolyte across the sample, by hermetically sealing the experiment from the high-vacuum environment of the S/TEM column. MEMS-based sample supports with integrated electrodes, thin membrane windows, and controlled flow of electrolyte allow researchers to apply electrical stimuli while imaging. Together, these technologies allow the direct observation of processes at the nanoscale that influence material performance, such as the formation of the solid electrolyte interphase (SEI) layer during lithium-ion battery cycling [1], the preferential corrosion of stainless steel at sulfite [2] and silicate [3] inclusions, and the dynamic evolution of shape-controlled nanocrystals for CO2 reduction [4-6]. Understanding the structure-function relationship of these materials at the nanoscale facilitates the efficient innovation of new materials that are more functional, cost-efficient, and environmentally friendly. In this presentation, we will share initial results from the next generation of in situ electrochemistry systems, pushing closer to “real working conditions” through advanced temperature control of the electrode-electrolyte interface. Many applications require increased temperatures, including research on fuel cell catalysts and corrosion. We will discuss the kinetics of well-known redox couples (Figure 1a) and of dendrite formation (Figure 1b) as a function of the temperature at the anode surface, the different spectroscopic techniques available when in situ electrochemistry is coupled with electron microscopy, and the implications of this new technology to research across numerous application fields including fuel cells, ionic liquids, batteries, corrosion, and electrocatalysis. [1] W. Dachraoui, et al. ACS Nano 2023 17(20), 20434-20444 [2] D. Kovalov, et al. Corros. Sci. 2022 199, 110184 [3] M. Tian, et al. Corros. Sci. 2022 208, 110659 [4] Y. Yang, et al. Nature 2023 614, 262-270 [5] Y. Yang, et al. J. Am. Chem. Soc. 2022 144(34), 15698-15708 [6] A.M. Abdellah, et al. Nat. Commun. 2024 15, 938 Figure 1

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In various domains spanning materials synthesis, chemical catalysis, life sciences, and energy materials, in situ transmission electron microscopy (TEM) methods exert a profound influence. These methodologies enable the real-time observation and manipulation of gas-phase and liquid-phase reactions at the nanoscale, facilitating the exploration of pivotal reaction mechanisms. Fundamental research areas like crystal nucleation, growth, etching, and self-assembly have greatly benefited from these techniques. Additionally, their applications extend across diverse fields such as catalysis, batteries, bioimaging, and drug delivery kinetics. However, the intricate nature of 'soft matter' presents a challenge due to the unique molecular properties and dynamic behavior of these substances that remain insufficiently understood. Investigating soft matter within in situ liquid-phase TEM settings demands further exploration and advancement compared to other research domains. This research harnesses the potential of in situ liquid-phase TEM technology while integrating deep learning methodologies to comprehensively analyze the quantitative aspects of soft matter dynamics. This study centers on diverse phenomena, encompassing surfactant molecule nucleation, block copolymer behavior, confinement-driven self-assembly, and drying processes. Furthermore, deep learning techniques are employed to precisely analyze Ostwald ripening and digestive ripening dynamics. The outcomes of this study not only deepen the understanding of soft matter at its fundamental level but also serve as a pivotal foundation for developing innovative functional materials and cutting-edge devices.

Liquid cell transmission electron microscopy has become a powerful and increasingly accessible technique for in situ studies of nanoscale processes in liquid and solution phase. Exploring reaction mechanisms in electrochemical or crystal growth processes requires precise control over experimental conditions, with temperature being one of the most critical factors. Here we carry out a series of crystal growth experiments and simulations at different temperatures in the well-studied system of Ag nanocrystal growth driven by the changes in redox environment caused by the electron beam. Liquid cell experiments show strong changes in both morphology and growth rate with temperature. We develop a kinetic model to predict the temperature-dependent solution composition, and we discuss how the combined effect of temperature-dependent chemistry, diffusion, and the balance between nucleation and growth rates affect the morphology. We discuss how this work may provide guidance in interpreting liquid cell TEM and potentially larger-scale synthesis experiments for systems controlled by temperature.

Metal ions are indispensable constituent elements of the human body, among which Cu2+ plays an important role in various biochemical reactions in the human body and is an essential element for maintaining human health. Studying the interaction between Cu2+ and DNA can be helpful to further understand the mechanism of Cu2+ behavior in organisms. In this paper, we investigated the DNA–Cu2+ complex by transmission electron microscopy (TEM) and used in situ liquid-cell TEM to observe the dynamic processes of interactions between DNA and Cu2+. Results show that the binding of Cu2+ to DNA leads to the bending of the DNA strand and provides an anchor site for activating Cu2+ for the nucleation and growth of copper crystals. Bound by the DNA strand, the copper crystals are arranged along the curved strand, showing the same arrangement pattern as guanine on the DNA sequence. It is believed that the study will further elaborate the interaction mechanism by directly observing the DNA–Cu2+ complex at the nanometer scale and benefit the related biomedical research studies.

Liquid phase (or liquid cell) transmission electron microscopy (TEM) has become a powerful platform for in situ investigation of various chemical processes at the nanometer or atomic level. The electron beam for imaging can also induce perturbation to the chemical processes. Thus, it has been a concern that the observed phenomena in a liquid cell could deviate from the real-world processes. Strategies have been developed to overcome the electron-beam-induced issues. This article provides an overview of the electron-beam effects, and discusses various strategies in liquid cell TEM study of nucleation, growth, and self-assembly of nanoscale materials, where an electron beam is often used to initiate the reactions, and highly electron-beam-sensitive electrochemical reactions.

Over the last several decades, colloidal nanoparticles have evolved into a prominent class of building blocks for materials design. Important advances include the synthesis of uniform nanoparticles with tailored compositions and properties, and the precision construction of intricate, higher-level structures from nanoparticles via self-assembly. Grasping the modern complexity of nanoparticles and their superstructures requires fundamental understandings of the processes of nanoparticle growth and self-assembly. In situ liquid phase transmission electron microscopy (TEM) has significantly advanced our understanding of these dynamic processes by allowing direct observation of how individual atoms and nanoparticles interact in real time, in their native phases. In this article, we highlight diverse nucleation and growth pathways of nanoparticles in solution that could be elucidated by the in situ liquid phase TEM. Furthermore, we showcase in situ liquid phase TEM studies of nanoparticle self-assembly pathways, highlighting the complex interplay among nanoparticles, ligands, and solvents. The mechanistic insights gained from in situ liquid phase TEM investigation could inform the design and synthesis of novel nanomaterials for various applications such as catalysis, energy conversion, and optoelectronic devices.

We have investigated the early stages of the formation of iron oxide nanoparticles from iron stearate precursors in the presence of sodium stearate in an organic solvent by in situ liquid phase transmission electron microscopy (IL-TEM). Before nucleation, we have evidenced the spontaneous formation of vesicular assemblies made of iron polycation-based precursors sandwiched between stearate layers. Nucleation of iron oxide nanoparticles occurs within the walls of the vesicles, which subsequently collapse upon the consumption of the iron precursors and the growth of the nanoparticles. We then evidenced that fine control of the electron dose, and therefore of the local concentration of reactive iron species in the vicinity of the nuclei, enables controlling crystal growth and selecting the morphology of the resulting iron oxide nanoparticles. Such a direct observation of the nucleation process templated by vesicular assemblies in a hydrophobic organic solvent sheds new light on the formation process of metal oxide nanoparticles and therefore opens ways for the synthesis of inorganic colloidal systems with tunable shape and size.

Liquid-phase transmission electron microscopy (LP-TEM) enables real-time imaging of nanoparticle self-assembly, formation, and etching with single nanometer resolution. Despite the importance of organic nanoparticle capping ligands in these processes, the effect of electron beam irradiation on surface-bound and soluble capping ligands during LP-TEM imaging has not been investigated. Here, we use correlative LP-TEM and fluorescence microscopy (FM) to demonstrate that polymeric nanoparticle ligands undergo competing crosslinking and chain scission reactions that nonmonotonically modify ligand coverage over time. Branched polyethylenimine (BPEI)-coated silver nanoparticles were imaged with dose-controlled LP-TEM followed by labeling their primary amine groups with fluorophores to visualize the local thickness of adsorbed capping ligands. FM images showed that free ligands crosslinked in the LP-TEM image area over imaging times of tens of seconds, enhancing local capping ligand coverage on nanoparticles and silicon nitride membranes. Nanoparticle surface ligands underwent chain scission over irradiation times of minutes to tens of minutes, which depleted surface ligands from the nanoparticle and silicon nitride surface. Conversely, solutions of only soluble capping ligand underwent successive crosslinking reactions with no chain scission, suggesting that nanoparticles enhanced the chain scission reactions by acting as radiolysis hotspots. The addition of a hydroxyl radical scavenger, tert-butanol, eliminated chain scission reactions and slowed the progression of crosslinking reactions. These experiments have important implications for performing controlled and reproducible LP-TEM nanoparticle imaging as they demonstrate that the electron beam can significantly alter ligand coverage on nanoparticles in a nonintuitive manner. They emphasize the need to understand and control the electron beam radiation chemistry of a given sample to avoid significant perturbations to the nanoparticle capping ligand chemistry, which are invisible in electron micrographs.

Nanoparticle motion and self-assembly have been regarded as a promising pathway for forming ordered nanostructures. However, the detailed dynamics processes induced by ligand involvement remained poorly understood. Here, we used in situ liquid-cell electron microscopy technology to image the formation of face-to-face Pt cube ordered structures: pairs, linear chains, and squares. The van der Waals interaction between the two neighboring cubes was quantified in real time. Interestingly, the two different formation processes of the square phase were achieved via a rotational and translational method. It is found that the space between two neighboring cubes was the same as the ex-TEM results. The density functional theory calculation demonstrated that it was attributed to the DMF ligand interactions of the cubes that promoted their face-to-face attachment.

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We use liquid-phase transmission electron microscopy (TEM) to study self-assembly dynamics of charged gold nanoarrows (GNAs), which reveal an unexpected "colloid-atom duality". On one hand, they assemble following the Derjaguin-Landau-Verwey-Overbeek theory for colloids when van der Waals attraction overruns slightly screened electrostatic repulsion. Due to concaveness in shape, GNAs adopt zipper motifs with lateral offset in their assembly matching with our modeling of inter-GNA interaction, which form into unconventional structures resembling degenerate crystal. On the other hand, more screening of electrostatic repulsion leads to merging of clusters assembled from GNAs, reminiscent of the coalescence growth mode in atomic crystals driven by minimization of surface energy, as we measure from the surface fluctuation of clusters. Liquid-phase TEM captures the initial formation of highly curved necks bridging the two clusters. Analysis of the real-time evolution of neck width illustrates the first-time observation of coalescence in colloidal assemblies facilitated by rapid surface diffusion of GNAs. We attribute the duality to the confluence of factors (e.g., nanoscale colloidal interaction, diffusional dynamics) that we access by liquid-phase TEM, taking turns to dominate at different conditions, which is potentially generic to nanoscale. The atom aspect, in particular, can inspire utilization of atomic crystal synthesis strategies to encode structure and dynamics in nanoscale assembly.

The ability to fabricate new materials using nanomaterials as building blocks, and with meta functionalities, is one of the most intriguing possibilities in the area of materials design and synthesis. Semiconducting quantum dots (QDs) and magnetic nanoparticles (MNPs) are co-dispersed in a liquid crystalline (LC) matrix and directed to form self-similar assemblies by leveraging the host’s thermotropic phase transition. These co-assemblies, comprising 6 nm CdSe/ZnS QDs and 5–20 nm Fe3O4 MNPs, bridge nano- to micron length scales, and can be modulated in situ by applied magnetic fields <250 mT, resulting in an enhancement of QD photoluminescence (PL). This effect is reversible in co-assemblies with 5 and 10 nm MNPs but demonstrates hysteresis in those with 20 nm MNPs. Transmission electron microscopy (TEM) and energy dispersive spectroscopy reveal that at the nanoscale, while the QDs are densely packed into the center of the co-assemblies, the MNPs are relatively uniformly dispersed through the cluster volume. Using Lorentz TEM, it is observed that MNPs suspended in LC rotate to align with the applied field, which is attributed to be the cause of the observed PL increase at the micro-scale. This study highlights the critical role of correlating multiscale spectroscopy and microscopy characterization in order to clarify how interactions at the nanoscale manifest in microscale functionality.

The structure and functionality of biomacromolecules are often regulated by chemical bonds, however, the regulation process and underlying mechanisms have not been well understood. Here, by using in situ liquid-phase transmission electron microscopy (LP-TEM), we explored the function of disulfide bonds during the self-assembly and structural evolution of sulfhydryl single-stranded DNA (SH-ssDNA). Sulfhydryl groups could induce self-assembly of SH-ssDNA into circular DNA containing disulfide bonds (SS-cirDNA). In addition, the disulfide bond interaction triggered the aggregation of two SS-cirDNA macromolecules along with significant structural changes. This visualization strategy provided structure information at nanometer resolution in real time and space, which could benefit future biomacromolecules research. The process and underlying mechanisms of sulfydryl biomacromolecules aggregation remains underexplored. Here, by using liquid-phase transmission electron microscopy, the authors report the self-assembly and aggregation of sulfydryl single-stranded DNA molecules and disulfide bond formation at nanometer resolution in real time.

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During nanoparticle coalescence in aqueous solution, dehydration and initial contact of particles are critically important but poorly understood processes. In this work, we used in situ liquid-cell transmission electron microscopy to directly visualize the coalescence process of Au nanocrystals. It is found that the Au atomic nanobridge forms between adjacent nanocrystals that are separated by a ∼0.5 nm hydration layer. The nanobridge structure first induces initial contact of Au nanocrystals over their hydration layers and then surface diffusion and grain boundary migration to rearrange into a single nanocrystal. Classical density functional theory calculations and ab initio molecular dynamics simulations suggest that the formation of the nanobridge can be attributed to the accumulation of auric ions and a higher local supersaturation in the gap, which can promote dehydration, contact, and fusion of Au nanocrystals. The discovery of this multistep process advances our understanding of the nanoparticle coalescence mechanism in aqueous solutions.

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Poly(N-isopropylacrylamide) (PNIPAM) microgels and PNIPAM colloidal shells attract continuous strong interest due to their thermoresponsive behavior, as their size and properties can be tuned by temperature. The direct single particle observation and characterization of pure, unlabeled PNIPAM microgels in their native aqueous environment relies on imaging techniques that operate either at interfaces or in cryogenic conditions, thus limiting the observation of their dynamic nature. Liquid Cell (Scanning) Transmission Electron Microscopy (LC-(S) TEM) imaging allows the characterization of materials and dynamic processes such as nanoparticle growth, etching, and diffusion, at nanometric resolution in liquids. Here we show that via a facile post-synthetic in situ polymer labelling step with high-contrast marker core-shell Au@SiO2 nanoparticles (NPs) it is possible to determine the full volume of PNIPAM microgels in water. The labelling allowed for the successful characterization of the thermoresponsive behavior of PNIPAM microgels and core shell silica@PNIPAM hybrid microgels, as well as the co-nonsolvency of PNIPAM in aqueous alcoholic solutions. The interplay between electron beam irradiation and PNIPAM systems in water resulted in irreversible shrinkage due to beam induced water radiolysis products, which in turn also affected the thermoresponsive behavior of PNIPAM. The addition of 2-propanol as radical scavenger improved PNIPAM stability in water under electron beam irradiation.

Thermal motion and interactions of sub–4-nm particles are directly observed by graphene liquid cell electron microscopy.

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Colloidal nanoparticles are synthesized in a complex reaction mixture that has an inhomogeneous chemical environment induced by local phase separation of the medium. Nanoparticle syntheses based on micelles, emulsions, flow of different fluids, injection of ionic precursors in organic solvents, and mixing the metal organic phase of precursors with an aqueous phase of reducing agents are well established. However, the formation mechanism of nanoparticles in the phase-separated medium is not well understood because of the complexity originating from the presence of phase boundaries as well as nonuniform chemical species, concentrations, and viscosity in different phases. Herein, we investigate the formation mechanism and diffusion of silver nanoparticles in a phase-separated medium by using liquid phase transmission electron microscopy and many-body dissipative particle dynamics simulations. A quantitative analysis of the individual growth trajectories reveals that a large portion of silver nanoparticles nucleate and grow rapidly at the phase boundaries, where metal ion precursors and reducing agents from the two separated phases react to form monomers. The results suggest that the motion of the silver nanoparticles at the interfaces is highly affected by the interaction with polymers and exhibits superdiffusive dynamics because of the polymer relaxation.

Cold welding of metals at the nanoscale has been demonstrated to play a significant role in bottom‐up manufacturing and self‐healing processes of nanostructures and nanodevices. However, the welding mechanism at the nanoscale is not well understood. In this study, a comprehensive demonstration of the cold welding process of gold nanorods with different modes is presented through in situ liquid cell transmission electron microscopy. The experimental results and molecular dynamics simulations reveal that the nanorods are welded through the facet‐dependent atomic surface diffusion and rearrangement along {100} facets. The density functional theory calculations indicate that the preferred coalescence of two {100} surfaces is thermodynamically favorable. Unlike the prevalent “oriented attachment” in the nanoparticle coalescence, the misalignment of nanorod orientations and local stresses can induce grain boundaries and stacking faults in the welded interface.

Liquid cell transmission electron microscopy is a powerful tool for visualizing nanoparticle (NP) assemblies in liquid environments with nanometer resolution. However, it remains a challenge to control the NP concentration in the high aspect ratio liquid enclosure where the diffusion of dispersed NPs is affected by the exposed surface of the liquid cell walls. Here, we introduce a semi-empirical model based on the 1D diffusion equation, to predict the NP loading time as they pass through the nanochannel into the imaging volume of the liquid cell. We show that loading of NPs into the imaging volume of the liquid cell may take several days if NPs are prone to attach to the surface of the mm-long nanochannel when using an industry-standard flat microchip. As a means to facilitate mass transport via diffusion, we tested a liquid cell incorporating a microchannel geometry resulting in a NP loading time in the order minutes that allowed us to observe the formation of a randomly oriented self-assembled monolayer in situ using scanning transmission electron microscopy.

Liquid-phase transmission electron microscopy (TEM) has been recently applied to materials chemistry to gain fundamental understanding of various reaction and phase transition dynamics at nanometer resolution. However, quantitative extraction of physical and chemical parameters from the liquid-phase TEM videos remains bottlenecked by the lack of automated analysis methods compatible with the videos’ high noisiness and spatial heterogeneity. Here, we integrate, for the first time, liquid-phase TEM imaging with our customized analysis framework based on a machine learning model called U-Net neural network. This combination is made possible by our workflow to generate simulated TEM images as the training data with well-defined ground truth. We apply this framework to three typical systems of colloidal nanoparticles, concerning their diffusion and interaction, reaction kinetics, and assembly dynamics, all resolved in real-time and real-space by liquid-phase TEM. A diversity of properties for differently shaped anisotropic nanoparticles are mapped, including the anisotropic interaction landscape of nanoprisms, curvature-dependent and staged etching profiles of nanorods, and an unexpected kinetic law of first-order chaining assembly of concave nanocubes. These systems representing properties at the nanoscale are otherwise experimentally inaccessible. Compared to the prevalent image segmentation methods, U-Net shows a superior capability to predict the position and shape boundary of nanoparticles from highly noisy and fluctuating background—a challenge common and sometimes inevitable in liquid-phase TEM videos. We expect our framework to push the potency of liquid-phase TEM to its full quantitative level and to shed insights, in high-throughput and statistically significant fashion, on the nanoscale dynamics of synthetic and biological nanomaterials.

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Liquid-cell transmission electron microscopy (LCTEM) is a powerful in situ videography technique that has the potential to allow us to observe solution-phase dynamic processes at the nanoscale, including imaging the diffusion and interaction of nanoparticles. Artefactual effects imposed by the irradiated and confined liquid-cell vessel alter the system from normal “bulk-like” behavior in multiple ways. These artefactual LCTEM effects will leave their fingerprints in the motion behavior of the diffusing objects, which can be revealed through careful analysis of the object-motion trajectories. Improper treatment of the motion data can lead to erroneous descriptions of the LCTEM system’s conditions. Here, we advance our anomalous diffusion object-motion analysis (ADOMA) method to extract a detailed description of the liquid-cell system conditions during any LCTEM experiment by applying a multistep analysis of the data and treating the x/y vectors of motion independently and in correlation with each other and with the object’s orientation/angle.

In situ liquid cell electron microscopy (LC‐EM) is a powerful platform for real time nanoscale imaging of liquid systems. In situ liquid cell scanning electron microscopy (LC‐SEM) as a relatively low cost and potentially more convenient characterization method, has not been as widely used as compared to in situ liquid cell transmission electron microscopy (LC‐TEM). This paper reports a real time high resolution and comprehensive characterization of Au nanoparticles (NPs) and nanoparticle clusters (NPCs), which are surface‐decorated with cetyltrimethylammonium bromide (CTAB), in an oleic acid (OA) emulsion system with LC‐SEM. Single NP resolution images are routinely collected with both secondary electron (SE) and backscattered electron (BSE) imaging modes, with different SEM systems. Energy dispersive spectroscopy (EDS) mapping data clearly demonstrates the single particle level chemical element distributions, particle stacking structure, as well as the preferred distribution of OA molecules on the Au particle surfaces. Moreover, both liquid droplet growth and particle motions are observed with LC‐SEM, among which, ways for faster tracking the single particle level dynamic motion behavior of Au NPs and NPCs are explored. We expect that our work will bring new insight of high resolution and fast analysis in a broad range of materials in liquid with LC‐SEM.

An understanding of nanoparticle growth is significant for controlled synthesis of nanomaterials with desired physical and chemical properties. Here we report the in situ study of platinum-nickel alloy nanoparticle growth using in situ liquid cell transmission electron microscopy (TEM). The observation revealed that Ni dendrites can form at the beginning and subsequently PtNi nanoparticles nucleate and grow by consumption of the Ni dendrites. The resulting PtNi alloy nanoparticles have a narrow size distribution with an average diameter of 3.7 nm, which are smaller than those obtained via classical solution growth. This work shed light on using such a unique growth pathway for the synthesis of novel nanoparticles.

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We demonstrate that silanization can control the adhesion of nanostructures to the SiN windows compatible with liquid-cell transmission electron microscopy (LC-TEM). Formation of an (3-aminopropyl)triethoxysilane (APTES) self-assembled monolayer on a SiN window, producing a surface decorated with amino groups, permits strong adhesion of Au nanoparticles to the window. Many of these nanoparticles remain static, undergoing minimal translation or rotation during LC-TEM up to high electron beam current densities due to the strong interaction between the APTES amino group and Au. We then use this technique to perform a direct comparative LC-TEM study on the behavior of ligand and nonligand-coated Au nanoparticles in a Au growth solution. While the ligand coated nanoparticles remain consistent even under high electron beam current densities, the naked nanoparticles acted as sites for secondary Au nucleation. These nucleated particles decorated the parent nanoparticle surface, forming consecutive monolayer assemblies of ∼2 nm diameter nanoparticles, which sinter into the parent particle when the electron beam was shut off. This method for facile immobilization of nanostructures for LC-TEM study will permit more sophisticated and controlled in situ experiments into the properties of solid-liquid interfaces in the future.

The origin of the viscoelastic behavior that many nanoparticles display during diffusive motion is unknown. Such dynamics are difficult to record without sophisticated methods that combine a suitable observation window of motion in time with high image resolution. Herein, we study and describe the diffusion of two types of particles in the form of emulsion droplets in situ via liquid phase TEM. For both, the observed particle motion in solution is anomalous (non-Brownian) and is either sub- or super-diffusive. Fractional Brownian motion (fBm) and random walks on fractals (RWF) are the two potential mechanisms. It can be challenging to differentiate these since they may have the same position or velocity autocorrelation function, but they diverge in the average number of sites visited, which is connected to the fractal dimension of the walk. We conclude that droplet-surface interactions and electron beam fluence create a fractal energy landscape yielding peculiar dynamics.

Significance Liquid cell transmission electron microscopy (LCTEM) is an emerging technique, which enables nanoscale visualization and tracking of single nanoparticles near interfaces with unprecedented spatial resolution. Here, we studied the diffusion of nanoparticles in LCTEM experiments using techniques powered by deep neural networks and statistical tests. We observed two underlying regimes of diffusive behavior which are governed by the interaction of the electron beam, the nanoparticle, the nearby substrate, and the liquid environment. This understanding forms the foundation to use LCTEM for single-nanoparticle tracking for a broad range of nanoparticles, interfaces, and liquids. The motion of nanoparticles near surfaces is of fundamental importance in physics, biology, and chemistry. Liquid cell transmission electron microscopy (LCTEM) is a promising technique for studying motion of nanoparticles with high spatial resolution. Yet, the lack of understanding of how the electron beam of the microscope affects the particle motion has held back advancement in using LCTEM for in situ single nanoparticle and macromolecule tracking at interfaces. Here, we experimentally studied the motion of a model system of gold nanoparticles dispersed in water and moving adjacent to the silicon nitride membrane of a commercial LC in a broad range of electron beam dose rates. We find that the nanoparticles exhibit anomalous diffusive behavior modulated by the electron beam dose rate. We characterized the anomalous diffusion of nanoparticles in LCTEM using a convolutional deep neural-network model and canonical statistical tests. The results demonstrate that the nanoparticle motion is governed by fractional Brownian motion at low dose rates, resembling diffusion in a viscoelastic medium, and continuous-time random walk at high dose rates, resembling diffusion on an energy landscape with pinning sites. Both behaviors can be explained by the presence of silanol molecular species on the surface of the silicon nitride membrane and the ionic species in solution formed by radiolysis of water in presence of the electron beam.

In the pursuit of more sustainable, lower cost and higher performance battery technology, alkaline metal-air batteries (AMABs) are considered promising candidates for future electrical energy storage due to their cost effectiveness, natural abundance of electrode materials, high specific capacity, and safety [1-2]. It is also believed that this battery technology has the potential to help decarbonize our energy grid. However, our knowledge of the phase and compositional changes that occur on the electrode in a working AMAB is limited, and the degradation mechanism of AMABs during repeated cycling have yet to be fully elucidated. To fill these knowledge gaps, advanced operando imaging techniques capable of nanoscale resolution are required to monitor interfacial electrochemical reactions during battery operation [3]. Operando imaging techniques, including magnetic resonance imaging, nuclear magnetic resonance, diffraction, and microscopy methods, have developed dramatically in recent years. They have yielded considerable insights into battery failure, as well as electrode and electrolyte degradation mechanisms, information that is critical to the design of batteries with improved lifetime and performance [3]. Among the operando imaging techniques, electrochemical liquid cell transmission electron microscopy (EC-TEM) holds significant advantages. It offers unique capability to directly image material transformations at the electrode-electrolyte interface in real-time at the nanoscale, while also acquiring quantitative electrochemical signals [4]. However, the use of EC-TEM in battery research has been limited to aqueous battery systems with neutral and mildly acidic electrolytes, leaving its application to alkaline environments unexplored. This is mainly due to chemical incompatibility concerns between alkaline electrolytes and the EC-TEM hardware (e.g. the holder and silicon-based chips). Given the practical significance of AMABs and the scientific opportunities presented by this battery system, it is imperative to advance the frontiers of EC-TEM to include application to alkaline systems. Here we describe EC-TEM investigation of metal electrode behaviors in alkaline environments under realistic battery conditions. Using Fe, Al, and Zn negative electrodes in an alkaline solution as model systems, we assess the feasibility and potential benefits of performing EC-TEM experiments with a pH of up to 14. We outline our approaches to obtaining reproducible cyclic voltammograms within the liquid cell, across a variety of counter electrode designs, and compare the results to those from traditional benchtop experiments. Furthermore, we highlight the challenges associated with electrolyte depletion and ion diffusion limitations within the liquid cell during battery discharge. Finally, we present observations of redox product changes at the electrode as captured by EC-TEM, and discuss the potential effects of electron beams on EC-TEM results. Our work is expected to provide new opportunities for investigating electrochemical processes in other key alkaline systems [5]. References: Y. Li and J. Lu, ACS Energy Letters, 2, 1370 (2017). W. H. Woodford, S. Burger, M. Ferrara and Y. M. Chiang, One Earth, 5, 212 (2022). C. P. Grey and J. M. Tarascon, Nature Materials, 16, 45 (2017). F. M. Ross, Science, 350 aaa9886 (2015). We acknowledge funding from the U.S. DOE Advanced Research Projects Agency-Energy under award DE-AR0000995. This work was carried out with the use of facilities and instrumentation supported by NSF through the Massachusetts Institute of Technology Materials Research Science and Engineering Center under Grant DMR-1419807, as well as facilities at MIT.nano.

Formation mechanisms of dendrite structures have been extensively explored theoretically, and many theoretical predictions have been validated for micro- or macroscale dendrites. However, it is challenging to determine whether classical dendrite growth theories are applicable at the nanoscale due to the lack of detailed information on the nanodendrite growth dynamics. Here, we study iron oxide nanodendrite formation using liquid cell transmission electron microscopy (TEM). We observe "seaweed"-like iron oxide nanodendrites growing predominantly in two dimensions on the membrane of a liquid cell. By tracking the trajectories of their morphology development with high spatial and temporal resolution, it is possible to explore the relationship between the tip curvature and growth rate, tip splitting mechanisms, and the effects of precursor diffusion and depletion on the morphology evolution. We show that the growth of iron oxide nanodendrites is remarkably consistent with the existing theoretical predictions on dendritic morphology evolution during growth, despite occurring at the nanoscale.

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We have designed and fabricated a TEM (transmission electron microscopy) liquid cell with hundreds of graphene nanocapsules arranged in a stack of two Si3N4-x membranes. These graphene nanocapsules are formed on arrays of nanoholes patterned on the Si3N4-x membrane by focused ion beam milling, allowing for better resolution than for the conventional graphene liquid cells, which enables the observation of light elements, such as atomic structures of silicon. We suggest that multiple nanocapsules provide opportunities for consecutive imaging under the same conditions in a single liquid cell. The use of single-crystal graphene windows offers an excellent signal-to-noise ratio and high spatial resolution. The motion of silicon nanoparticles (a low atomic number (Z) material) interacting with nanobubbles was observed, and analyzed, in detail. Our approach will help advance liquid-phase TEM observations by providing a straightforward method to encapsulate liquid between monolayers of various 2-dimensional materials.