电子束对物质的作用

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Originally published in 2005, this book covers the closely related techniques of electron microprobe analysis (EMPA) and scanning electron microscopy (SEM) specifically from a geological viewpoint. Topics discussed include: principles of electron-target interactions, electron beam instrumentation, X-ray spectrometry, general principles of SEM image formation, production of X-ray 'maps' showing elemental distributions, procedures for qualitative and quantitative X-ray analysis (both energy-dispersive and wavelength-dispersive), the use of both 'true' electron microprobes and SEMs fitted with X-ray spectrometers, and practical matters such as sample preparation and treatment of results. Throughout, there is an emphasis on geological aspects not mentioned in similar books aimed at a more general readership. The book avoids unnecessary technical detail in order to be easily accessible, and forms a comprehensive text on EMPA and SEM for geological postgraduate and postdoctoral researchers, as well as those working in industrial laboratories.

The generation and evolution of modulated particle beams and their interactions with resonant radiofrequency (RF) structures are of fundamental interest for both particle accelerator and vacuum electronic systems. When the constraint of propagation in a vacuum is removed, the evolution of such beams can be greatly affected by interactions with matter including scattering, absorption, generation of atmospheric plasma, and the production of multiple generations of secondary particles. Here, we study the propagation of 21 MeV and 25 MeV electron beams produced in S-band and L-band linear accelerators, and their interaction with resonant RF structures, under a number of combinations of geometry, including transmission through both air and metal. Both resonant and nonresonant interactions were observed, with the resonant interactions indicating that the RF modulation on the electron beam is at least partially preserved as the beam propagates through air and metal. When significant thicknesses of metal are placed upstream of a resonant structure, preventing any primary beam electrons from reaching the structure, RF signals could still be induced in the structures. This indicated that the RF modulation present on the electron beam was also impressed onto the x-rays generated when the primary electrons were stopped in the metal, and that this RF modulation was also present on the secondary electrons generated when the x-rays struck the resonant structures. The nature of these interactions and their sensitivities to changes in system configurations will be discussed.

Homeland security and military defense technology considerations have stimulated intense interest in mobile, high power sources of millimeter-wave (mmw) to terahertz (THz) regime electromagnetic radiation, from 0.1 to 10THz. While vacuum electronic sources are a natural choice for high power, the challenges have yet to be completely met for applications including noninvasive sensing of concealed weapons and dangerous agents, high-data-rate communications, high resolution radar, next generation acceleration drivers, and analysis of fluids and condensed matter. The compact size requirements for many of these high frequency sources require miniscule, microfabricated slow wave circuits. This necessitates electron beams with tiny transverse dimensions and potentially very high current densities for adequate gain. Thus, an emerging family of microfabricated, vacuum electronic devices share many of the same plasma physics challenges that are currently confronting “classic” high power microwave (HPM) generators including long-life bright electron beam sources, intense beam transport, parasitic mode excitation, energetic electron interaction with surfaces, and rf air breakdown at output windows. The contemporary plasma physics and other related issues of compact, high power mmw-to-THz sources are compared and contrasted to those of HPM generation, and future research challenges and opportunities are discussed.

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Interaction of Fast Charged Particles with Matter, A. Mozumder Ionization and Secondary Electron Production by Fast Charged Particles, L. H. Toburen Modelling of Physicochemical and Chemical Processes in the Interactions of Fast Charged Particles with Matter, S.M. Pimblott and A. Mozumber Interaction of Photons with Molecules - Photoabsorption, Photoionozation and Photodissociation Cross Sections, N. Kouchi and Y. Hatano Reactions of Low Energy Electrons, Ions, Excited Atoms and Molecules and Free Radicals in the Gas Phase as Studied by Pulse Radiolysis Methods, M. Ukai and Y. Hatano Electron and Anion Solvation, C.D. Jonah Electrons in Nonpolar Liquids, R.A. Halroyd Low-Energy Electron Interactions with Atomic and Molecular Solids, A.D. Bass and L. Sanche The Radiation Chemistry of Liquid Water, G.V. Buxton Radiation Chemistry of Liquid Alkanes, L. Wojnarovits LET-Effects in Radiation Chemistry, J.A. LaVerne Reactions Initiated by Ionizing Radiation in Biological Systems - The Critical Target is DNA, W.A. Bernhard and D.M. Close Photon Induced Biological Consquences, K. Kobayashi and K. Hieda Track Structure - Studies of Biological Systems, H. Nikjoo Microdosimetry and Its Medical Applications, M. Zaider and J. F. Dicello Charged Particle and Photon Interactions in Nanocolloids and Photographic Systems Studies, J. Belloni and M. Mostafavi Applications of Radiation-Chemical Reactions to the Construction of Functional Organic Materials, T. Ichikawa Applications to Reaction Mechanism Studies of Organic Systems, T. Majima Applications of Radiation Chemistry to Nuclear Technology, Y. Katsumura Electron-Beam Application to Flue Gas Treatment, H. Namba Ion-Beam Therapy. A. Wambersie, J. Gueulett and D.T.L. Jones Food Irradiation, J. Farkas New Applications of Ion Beams to Material, Space and Biological Science and Engineering, M. Saidoh, H. Itoh, A. Tanaka and M. Fukuda

The theoretical description of a quantitative electron probe model, IntriX, is presented. It consists of a numerical reconstruction of the in-depth ionization distribution Φ(ρz) through the use of basic physical macroscopic parameters describing the electron beam–matter interaction. With the aim of characterizing nanometer features in samples, specific attention is paid to the treatment of analysis performed on in-depth non-homogeneous samples (films on substrates) and also at low beam energies E0 (E0<5 keV) and near the ionization threshold Ec (E0/Ec<2). © 1998 John Wiley & Sons, Ltd.

Electron microscopy allows the extraction of multidimensional spatiotemporally correlated structural information of diverse materials down to atomic resolution, which is essential for figuring out their structure-property relationships. Unfortunately, the high-energy electrons that carry this important information can cause damage by modulating the structures of the materials. This has become a significant problem concerning the recent boost in materials science applications of a wide range of beam-sensitive materials, including metal-organic frameworks, covalent-organic frameworks, organic-inorganic hybrid materials, 2D materials, and zeolites. To this end, developing electron microscopy techniques that minimize the electron beam damage for the extraction of intrinsic structural information turns out to be a compelling but challenging need. This article provides a comprehensive review on the revolutionary strategies toward the electron microscopic imaging of beam-sensitive materials and associated materials science discoveries, based on the principles of electron-matter interaction and mechanisms of electron beam damage. Finally, perspectives and future trends in this field are put forward.

An artificial intelligence system called MENNDL, which used 25,200 NVIDIA Volta GPUs on Oak Ridge National Laboratory's Summit machine, automatically designed an optimal deep learning network in order to extract structural information from raw atomic-resolution microscopy data. In a few hours, MENNDL creates and evaluates millions of networks using a scalable, parallel, asynchronous genetic algorithm augmented with a support vector machine to automatically find a superior deep learning network topology and hyper-parameter set than a human expert can find in months. For the application of electron microscopy, the system furthers the goal of improving our understanding of the electron-beam-matter interactions and real-time image-based feedback, which enables a huge step beyond human capacity towards nanofabricating materials automatically. MENNDL has been scaled to the 4,200 available nodes of Summit achieving a measured 152.5 PFlops, with an estimated sustained performance of 167 PFlops when the entire machine is available.

Abstract Structural degradation in calcium-A zeolites (Ca-A) subjected to electron beam irradiation was studied in a Transmission Electron Microscope. Several structural changes observed are reported and their possible nature, under the light of the electron beam-matter interaction, is discussed as well. Key Words: ZeolitesTEMelectron beam

RF-modulated electron beams, such as those produced by an RF linear accelerator, propagating through vacuum, air, and solid matter are well known to drive signals in microwave cavities and waveguides via interactions with these structures. Past experiments with a microwave waveguide in a radiation-shielded vault indicated the presence of a multipath propagation phenomenon, hypothesized to be a result of reflections of RF-modulated x rays. In this work, we study the signals induced in a microwave coaxial cable from nearby beam interactions with materials commonly found in accelerator facilities in order to better understand RF production and propagation in these environments. Our results show that (1) when an RF-modulated electron beam is incident on a block of aluminum, lead, or concrete, the frequency content of the induced microwave signals is strongly dependent on the orientation of the block and the relative position of the detector, (2) at least some of the detected signals are consistent with reflections off of the blocks, and (3) beam interactions with the blocks can induce appreciable microwave signals in detectors located tens of cm from the block.

Semiconductor nanowires of high purity and crystallinity hold promise as building blocks for miniaturized optoelectrical devices. Using scanning-excitation single-wire emission spectroscopy, with either a laser or an electron beam as a spatially resolved excitation source, we observe standing-wave exciton polaritons in ZnO nanowires at room temperature. The Rabi splitting between the polariton branches is more than 100 meV. The dispersion curve of the modes in the nanowire is substantially modified due to light-matter interaction. This finding forms a key aspect in understanding subwavelength guiding in these nanowires.

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The past decade has seen great advances in developing color centers in diamond for sensing, quantum information processing, and tests of quantum foundations.Increasingly, the success of these applications as well as fundamental investigations of light-matter interaction depend on improved control of optical interactions with color centers -from better fluorescence collection to efficient and precise coupling with confined single optical modes.Wide ranging research efforts have been undertaken to address these demands through advanced nanofabrication of diamond.This review will cover recent advances in diamond nano-and microphotonic structures for efficient light collection, color center to nanocavity coupling, hybrid integration of diamond devices with other material systems, and the wide range of fabrication methods that have enabled these complex photonic diamond systems. CONTENTSI. Introduction 1 II.Diamond for Quantum Photonics 2 A. Material Properties 2 B. Defect Centers in Diamond 2 III.Fabrication of Diamond Photonic Devices 3 A. Synthetic Creation of Diamond 3 B. Diamond Thin Film Fabrication 3 C. Focused Ion Beam Milling 4 D. Direct Electron Beam Lithography 4 E. Transferrable

PART I: OVERVIEW AND MATERIALS 1. An Introduction to Microelectronic Fabrication 1.1 Microelectronic Technologies -- A Simple Example 1.2 Unit Processes and Technologies 1.3 A Roadmap for the Course 1.4 Summary 2. Semiconductor Substrates 2.1 Phase Diagrams and Solid Solubility 2.2 Crystallography and Crystal Structure 2.3 Crystal Defects 2.4 Czochralski Growth 2.5 Bridgman Growth of GaAs 2.6 Float Zone Growth 2.7 Water Preparation and Specifications 2.8 Summary and Future Trends Problems References PART II: UNIT PROCESSING I: HOT PROCESSING AND ION IMPLANTATION 3. Diffusion 3.1 Fick's Diffusion Equation in One Dimension 3.2 Atomistic Models of Diffusion 3.3 Analytic Solutions of Fick's Law 3.4 Corrections to Simple Theory 3.5 Diffusion Coefficients for Common Dopants 3.6 Analysis of Diffused Profiles 3.7 Diffusion in SiO2 3.8 Diffusion Systems 3.9 SUPREM Simulations of Diffusion Profiles 3.10 Summary Problems References 4. Thermal Oxidation 4.1 The Deal-Grove Model of Oxidation 4.2 The Linear and Parabolic Rate Coeffients 4.3 The Initial Oxidation Regime 4.4 The Structure of SiO2 4.5 Oxide Characterization 4.6 The Effects of Dopants During Oxidation and Polysilicon Oxidation 4.7 Oxidation Induced Stacking Faults 4.8 Alternative Gate Insulations 4.9 Oxidation Sytems 4.10 SUPREM Oxidations 4.11 Summary Problems References 5. Ion Implantation 5.1 Idealized Ion Implantation Systems 5.2 Coulomb Scattering 5.3 Vertical Projected Range 5.4 Channeling and Lateral Projected Range 5.5 Implantation Damage 5.6 Shallow Junction Formation 5.7 Buried Dielectrics 5.8 Ion Implantation Systems -- Problems and Concerns 5.9 Implanted Profiles Using SUPREM+ 5.10 Summary Problems References 6. Rapid Thermal Processing 6.1 Gray Body Radiation, Heat Exchange, and Optical Absorption 6.2 High Density Optical Sources and Chamber Design 6.3 Temperature Measurement 6.4 Temperature Measurement 6.4 Thermoplastic Stress 6.5 Rapid Thermal Activation of Impurities 6.6 Rapid Thermal Processing of Dielectrics 6.7 Silicidation and Contact Formation 6.8 Alternative Rapid Thermal Processing Systems 6.9 Summary Problems References PART III: UNIT PROCESSES 2: PATTERN TRANSFER 7. Optical Lithography 7.1 Lithography Overview 7.2 Diffraction 7.3 The Modulation Transfer Function and Optical Exposures 7.4 Source Systems and Spatial Coherence 7.5 Contact/Proximity Printers 7.6 Projection Printers 7.7 Advanced Mask Concepts 7.8 Surface Reflections and Standing Waves 7.9 Alignment 7.10 Summary Problems References 8. Photoresists 8.1 Photoresist Types 8.2 Organic Materials and Polymers 8.3 Typical Reactions of DQN Positive Photoresist 8.4 Contrast Curves 8.5 The Critical Modulation Transfer Function 8.6 Applying and Developing Photoresist 8.7 Second Order Exposure Effects 8.8 Advanced Photoresists and Photoresist Processes 8.9 Summary Problems References 9. Nonoptical Lithographic Techniques 9.1 Interactions of High Energy Beams with Matter 9.2 Direct Write Electron Beam Lithography Systems 9.3 Direct Write Electron Beam Lithography Summary and Outlook 9.4 X-Ray Sources 9.5 Proximity X-Ray Exposure Systems 9.6 Membrane Masks 9.7 Projection X-Ray Lithography 9.8 Projection Electron Beam Lithography (SCALPEL) 9.9 E-bean and X-Ray Resists 9.10 Radiation Damage in MOS Devices 9.11 Summary Problems References PART IV: UNIT PROCESSES 3: THIN FILMS 10. Vacuum Science and Plasmas 10.1 The Kinetic Theory of Gasses 10.2 Gas Flow and Conductance 10.3 Pressure Ranges and Vacuum Pumps 10.4 Vacuum Seals and Pressure Measurement 10.5 The DC Glow Discharge 10.6 RF Discharges 10.7 High Density Plasmas 10.8 Summary Problems References 11. Etching 11.1 Wet Etching 11.2 Chemical Mechanical Publishing 11.3 Basic Regimes of Plasma Etching 11.4 High Pressure Plasma Etching 11.5 Ion Milling 11.6 Reactive Ion Etching 11.7 Damage in Reative Ion Etching 11.8 High Density Plasma (HDP) Etching 11.9 Liftoff 11.10 Summary Problems References 12. Physical Deposition: Evaporation and Sputtering 12.1 Phase Diagrams: Sublimation and Evaporation 12.2 Deposition Rates 12.3 Step Coverage 12.4 Evaporator Systems: Crucible Heating Techniques 12.5 Multicomponent Films 12.6 An Introduction to Sputtering 12.7 Physics of Sputtering 12.8 Deposition Rate: Sputter Yield 12.9 High Density Plasma Sputtering 12.10 Morphology and Step Coverage 12.11 Sputtering Methods 12.12 Sputtering of Specific Materials 12.13 Stress in Deposited Layers 12.14 Summary Problems References 13. Chemcial Vapor Deposition 13.1 A Simple CVD System for the Deposition of Silicon 13.2 Chemical Equilibrium and the Law of Mass Action 13.3 Gas Flow and Boundary Layers 13.4 Evaluation of the Simple CVD System 13.5 Atmospheric CVD of Dielectrics 13.6 Low Pressure CVD of Dielectrics and Semiconductors in Hot Wall Systems 13.7 Plasma Enhanced CVD of Dielectrics 13.8 Metal CVD + 13.9 Summary Problems References 14. Exiptaxial Growth 14.1 Water Cleaning and Native Oxide Removal 14.2 The Thermodynamics of Vapor Phase Growth 14.3 Surface Reactions 14.4 Dopant Incorporation 14.5 Defects in Epitaxial Growth 14.6 Slective Growth 14.7 Halide Transport GaAs Vapor Phase Epitaxy 14.8 Incommensurate and Strained Layer Heterooepitaxy 14.9 Metal Organic Chemical Vapor Deposition (MOCVD) 14.10 Advanced Silicon Vapor Phase Epitaxial Growth Techniques 14.11 Molecular Beam Epitaxy Technology 14.12 BCF Theory 14.13 Gas Source MBE and Chemical Beam Epitaxy 14.14 Summary Problems References PART V: PROCESS INTEGRATION 15. Device Isolation, Contacts, and Metallization 15.1 Junction and Oxide Isolation 15.2 LOCOAS Methods 15.3 Trench Isolation 15.4 Silicon on Insulator Isolation Techniques 15.5 Semi-insulating Substrates 15.6 Schottky Contacts 15.7 Implanted Ohmic Contacts 15.8 Alloyed Contacts 15.9 Multilevel Metallization 15.10 Planarization and Advanced Interconnect 15.11 Summary Problems References 16. CMOS Techniques 16.1 Basic Long Channel Device Behavior 16.2 Early MOS Technologies 16.3 The Basic 3 um Technology 16.4 Device Scaling 16.5 Hot Carrier Effects and Drain Engineering 16.6 Processing for Robust Oxides 16.7 Latchup 16.8 Shallow Source/Drains and Tailored Channel Doping 16.9 Summary Problems References 17. GaAs Technologies 17.1 Basic MESFET Operation 17.2 Basic MESFET Technology 17.3 Digital Technologies 17.4 MMC Technologies 17.5 MODFETs 17.6 Optoelectronic Devices 17.7 Summary Problems References 18. Silicon Bipolar Techniques 18.1 Review of Bipolar Devices -- Ideal and Quasi-ideal Behavior 18.2 Second Order Effects 18.3 Performance of BJTs 18.4 Early Bipolar Processes 18.5 Advaned Bipolar Processes 18.6 Hot Electron Effects in Bipolar Transitions 18.7 BiCMOS 18.8 Analog Bipolar Technolgies 18.9 Summary Problems References 19. MEMS (co-authored with G. Cibuzar, University of Minnesota) 19.1 Fundamentals of Mechanics 19.2 Stress in Thin Films 19.3 Mechanical to Electrical Transduction 19.4 Mechanics of Common MEMS Devices 19.5 Bulk Micromachining Etching Techniques 19.6 Bulk Micromachining Process Flow 19.7 Surface Micromachining Basics 19.8 Surface Micromachining Process Flow 19.9 MEMS Actuators 19.10 High Aspect Ratio Microsystems Technology (HARMST) 19.11 Summary Problems References 20. Integrated Circuit Manufacturing 20.1 Yield Prediction and Yield Tracking 20.2 Particle Control 20.3 Statistical Process Control 20.4 Full Factorial Experiments and ANOVA 20.5 Design of Experiments 20.6 Computer Integrated Manufacturing 20.7 Summary Problems References APPENDICES I. Acronyms and Common Symbols II. Properties of Selected Semiconductor Materials III. Physical Constants IV. Conversion Factors V. The Complimentary Error Function VI. F Values VII. SUPREM Commands Index

The main objective of this Account is to assess the challenges of transmission electron microscopy (TEM) of molecules, based on over 15 years of our work in this field, and to outline the opportunities in studying chemical reactions under the electron beam (e-beam). During TEM imaging of an individual molecule adsorbed on an atomically thin substrate, such as graphene or a carbon nanotube, the e-beam transfers kinetic energy to atoms of the molecule, displacing them from equilibrium positions. Impact of the e-beam triggers bond dissociation and various chemical reactions which can be imaged concurrently with their activation by the e-beam and can be presented as stop-frame movies. This experimental approach, which we term ChemTEM, harnesses energy transferred from the e-beam to the molecule via direct interactions with the atomic nuclei, enabling accurate predictions of bond dissociation events and control of the type and rate of chemical reactions. Elemental composition and structure of the reactant molecules as well as the operating conditions of TEM (particularly the energy of the e-beam) determine the product formed in ChemTEM processes, while the e-beam dose rate controls the reaction rate. Because the e-beam of TEM acts simultaneously as a source of energy for the reaction and as an imaging tool monitoring the same reaction, ChemTEM reveals atomic-level chemical information, such as pathways of reactions imaged for individual molecules, step-by-step and in real time; structures of illusive reaction intermediates; and direct comparison of catalytic activity of different transition metals filmed with atomic resolution. Chemical transformations in ChemTEM often lead to previously unforeseen products, demonstrating the potential of this method to become not only an analytical tool for studying reactions, but also a powerful instrument for discovery of materials that can be synthesized on preparative scale.

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Understanding and controlling cell adhesion on engineered scaffolds is important in biomaterials and tissue engineering. In this report we used an electron-beam (e-beam) lithography technique to fabricate patterns of a cell adhesive integrin ligand combined with a growth factor. Specifically, micron-sized poly(ethylene glycol) (PEG) hydrogels with aminooxy- and styrene sulfonate-functional groups were fabricated. Cell adhesion moieties were introduced using a ketone-functionalized arginine-glycine-aspartic acid (RGD) peptide to modify the O-hydroxylamines by oxime bond formation. Basic fibroblast growth factor (bFGF) was immobilized by electrostatic interaction with the sulfonate groups. Human umbilical vein endothelial cells (HUVECs) formed focal adhesion complexes on RGD- and RGD and bFGF-immobilized patterns as shown by immunostaining of vinculin and actin. In the presence of both bFGF and RGD, cell areas were larger. The data demonstrate confinement of cellular focal adhesions to chemically and physically well-controlled microenvironments created by a combination of e-beam lithography and "click" chemistry techniques. The results also suggest positive implications for addition of growth factors into adhesive patterns for cell-material interactions.

Structural characterisation of individual molecules by high-resolution transmission electron microscopy (HRTEM) is fundamentally limited by the element and electron energy-specific interactions of the material with the high energy electron beam. Here, the key mechanisms controlling the interactions between the e-beam and C-H bonds, present in all organic molecules, are examined, and the low atomic weight of hydrogen-resulting in its facile atomic displacement by the e-beam-is identified as the principal cause of the instability of individual organic molecules. It is demonstrated theoretically and proven experimentally that exchanging all hydrogen atoms within molecules with the deuterium isotope, and therefore doubling the atomic weight of the lightest atoms in the structure, leads to a more than two-fold increase in the stability of organic molecules in the e-beam. Substitution of H for D significantly reduces the amount of kinetic energy transferred from the e-beam to the atom (main factor contributing to stability) and also increases the barrier for bond dissociation, primarily due to the changes in the zero-point energy of the C-D vibration (minor factor). The extended lifetime of coronene-d12 , used as a model molecule, enables more precise analysis of the inter-molecular spacing and more accurate measurement of the molecular orientations.

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Compact laser-driven accelerators are pursued heavily worldwide because they make novel methods and tools invented at national laboratories widely accessible in science, health, security, and technology [V. Malka et al., Principles and applications of compact laser-plasma accelerators, Nat. Phys. 4, 447 (2008)]. Current leading laser-based accelerator technologies [S. P. D. Mangles et al., Monoenergetic beams of relativistic electrons from intense laser-plasma interactions, Nature (London) 431, 535 (2004); T. Toncian et al., Ultrafast laser-driven microlens to focus and energy-select mega-electron volt protons, Science 312, 410 (2006); S. Tokita et al. Single-shot ultrafast electron diffraction with a laser-accelerated sub-MeV electron pulse, Appl. Phys. Lett. 95, 111911 (2009)] rely on a medium to assist the light to particle energy transfer. The medium imposes material limitations or may introduce inhomogeneous fields [J. R. Dwyer et al., Femtosecond electron diffraction: ``Making the molecular movie,'', Phil. Trans. R. Soc. A 364, 741 (2006)]. The advent of few cycle ultraintense radially polarized lasers [S. Carbajo et al., Efficient generation of ultraintense few-cycle radially polarized laser pulses, Opt. Lett. 39, 2487 (2014)] has ushered in a novel accelerator concept [L. J. Wong and F. X. K\"artner, Direct acceleration of an electron in infinite vacuum by a pulsed radially polarized laser beam, Opt. Express 18, 25035 (2010); F. Pierre-Louis et al. Direct-field electron acceleration with ultrafast radially polarized laser beams: Scaling laws and optimization, J. Phys. B 43, 025401 (2010); Y. I. Salamin, Electron acceleration from rest in vacuum by an axicon Gaussian laser beam, Phys. Rev. A 73, 043402 (2006); C. Varin and M. Pich\'e, Relativistic attosecond electron pulses from a free-space laser-acceleration scheme, Phys. Rev. E 74, 045602 (2006); A. Sell and F. X. K\"artner, Attosecond electron bunches accelerated and compressed by radially polarized laser pulses and soft-x-ray pulses from optical undulators, J. Phys. B 47, 015601 (2014)] avoiding the need of a medium or guiding structure entirely to achieve strong longitudinal energy transfer. Here we present the first observation of direct longitudinal laser acceleration of nonrelativistic electrons that undergo highly directional multi-$\mathrm{GeV}/\mathrm{m}$ accelerating gradients. This demonstration opens a new frontier for direct laser-driven particle acceleration capable of creating well collimated and relativistic attosecond electron bunches [C. Varin and M. Pich\'e, Relativistic attosecond electron pulses from a free-space laser-acceleration scheme, Phys. Rev. E 74, 045602 (2006)] and x-ray pulses [A. Sell and F. X. K\"artner, Attosecond electron bunches accelerated and compressed by radially polarized laser pulses and soft-x-ray pulses from optical undulators, J. Phys. B 47, 015601 (2014)].

Both Fe2O3 thin films and nanorod arrays are deposited using electron beam evaporation through normal thin film deposition and oblique angle deposition (OAD) and are characterized structurally, optically, and photocatalytically. The morphologies of the thin films are found to be arrays of very thin and closely packed columnar structures, while the OAD films are well-aligned nanorod arrays. All films were determined to be in the hematite phase (α-Fe2O3), as confirmed by both structural and optical characterization. Texture measurements indicate that films have similar growth modes where the [110] direction aligns with the direction of material growth. Under visible light illumination, the thin film samples were more efficient at photocatalytically degrading methylene blue, while the nanorod arrays were more efficient at inactivating E. coli O157:H7. The size of the targeted agent and the different film morphologies result in different reactant/surface interactions, which is the main factor that determines photoactivity. Furthermore, an analytic mathematical model of bacterial inactivation based on chemotactic bacterial diffusion and surface deactivation is developed to quantify and compare the inactivation rate of the samples. These results indicate that α-Fe2O3 nanorods are promising candidates for antimicrobial applications and are expected to provide insight into the development of better visible-light antimicrobial materials for food products and processing environments, as well as other related applications.

This paper reviews and discusses recent experimental, theoretical, and numerical studies of plasma-wall interaction in a weakly collisional magnetized plasma bounded with channel walls made from different materials. A low-pressure <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> × <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> plasma discharge of the Hall thruster was used to characterize the electron current across the magnetic field and its dependence on the applied voltage and the electron-induced secondary electron emission (SEE) from the channel wall. The presence of a depleted anisotropic electron energy distribution function with beams of secondary electrons was predicted to explain the enhancement of the electron cross-field current observed in experiments. Without the SEE, the electron cross-field transport can be reduced from anomalously high to nearly classical collisional level. The suppression of the SEE was achieved using an engineered carbon-velvet material for the channel walls. Both theoretically and experimentally, it is shown that the electron emission from the walls can limit the maximum achievable electric field in the magnetized plasma. With nonemitting walls, the maximum electric field in the thruster can approach a fundamental limit for a quasi-neutral plasma.

A study has been made to determine the resolution limitations of electron beams interacting with thin films, due to scattering in the film and substrate. For a typical film thickness of 3000 Å, and an incoming Gaussian electron distribution with half-amplitude at 1500 Å radius, forward-scattering becomes significant for solids with atomic number Z≳20. Back-scattering from a substrate produces negligible resolution loss, and in fact heavy substrates may be used to advantage to increase electron densities in the thin film. Computer programs have been written that are capable of determining scattering data for a large range of materials and incident electron conditions.

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1. An Introduction to Electron Energy-Loss Spectroscopy.- 1.1 Interaction of Fast Electrons with a Solid.- 1.2. The Electron Energy-Loss Spectrum.- 1.3. The Development of Experimental Techniques.- 1.4. Comparison of Analytical Methods.- 1.4.1. Ion-Beam Methods.- 1.4.2. Incident Photons.- 1.4.3. Electron-Beam Techniques.- 1.5. Further Reading.- 2. Instrumentation for Energy-Loss Spectroscopy.- 2.1. Energy-Analyzing and Energy-Selecting Systems.- 2.1.1. The Magnetic-Prism Spectrometer.- 2.1.2. Energy-Selecting Magnetic-Prism Devices.- 2.1.3. The Wien Filter.- 2.1.4. Cylindrical-Lens Analyzers.- 2.1.5. Retarding-Field Analyzers.- 2.1.6. Electron Monochromators.- 2.2. The Magnetic-Prism Spectrometer.- 2.2.1. First-Order Properties.- 2.2.2. Higher-Order Focusing.- 2.2.3. Design of an Aberration-Corrected Spectrometer.- 2.2.4. Practical Considerations.- 2.2.5. Alignment and Adjustment of the Spectrometer.- 2.3. The Use of Prespectrometer Lenses.- 2.3.1. Basic Principles.- 2.3.2. CTEM with Projector Lens On.- 2.3.3. CTEM with Projector Lens Off.- 2.3.4. Spectrometer-Specimen Coupling in a High-Resolution STEM.- 2.4. Recording the Energy-Loss Spectrum.- 2.4.1. Serial Acquisition.- 2.4.2. Electron Detectors for Serial Recording.- 2.4.3. Scanning the Energy-Loss Spectrum.- 2.4.4. Signal Processing and Storage.- 2.4.5. Noise Performance of a Serial Detector.- 2.4.6. Parallel-Recording Detectors.- 2.4.7. Direct Exposure of a Diode-Array Detector.- 2.4.8. Indirect Exposure of a Diode Array.- 2.4.9. Removal of Diode-Array Artifacts.- 2.5. Energy-Filtered Imaging.- 2.5.1. Elemental Mapping.- 2.5.2. Z-Contrast Imaging.- 3. Electron Scattering Theory.- 3.1. Elastic Scattering.- 3.1.1. General Formulas.- 3.1.2. Atomic Models.- 3.1.3. Diffraction Effects.- 3.1.4. Electron Channeling.- 3.1.5. Phonon Scattering.- 3.2. Inelastic Scattering.- 3.2.1. Atomic Models.- 3.2.2. Bethe Theory.- 3.2.3. Dielectric Formulation.- 3.2.4. Solid-State Effects.- 3.3. Excitation of Outer-Shell Electrons.- 3.3.1. Volume Plasmons.- 3.3.2. Single-Electron Excitation.- 3.3.3. Excitons.- 3.3.4. Radiation Losses.- 3.3.5. Surface Plasmons.- 3.3.6. Single, Plural, and Multiple Scattering.- 3.4. Inner-Shell Excitation.- 3.4.1. Generalized Oscillator Strength.- 3.4.2. Kinematics of Scattering.- 3.4.3. Ionization Cross Sections.- 3.5. The Spectral Background to Inner-Shell Edges.- 3.6. The Structure of Inner-Shell Edges.- 3.6.1. Basic Edge Shapes.- 3.6.2. Chemical Shifts in Threshold Energy.- 3.6.3. Near-Edge Fine Structure (ELNES).- 3.6.4. Extended Energy-Loss Fine Structure (EXELFS).- 4. Quantitative Analysis of the Energy-Loss Spectrum.- 4.1. Removal of Plural Scattering from the Low-Loss Region.- 4.1.1. Fourier-Log Deconvolution.- 4.1.2. Approximate Methods.- 4.1.3. Angular-Dependent Deconvolution.- 4.2. Kramers-Kronig Analysis.- 4.3. Removal of Plural Scattering from Inner-Shell Edges.- 4.3.1. Fourier-Log Deconvolution.- 4.3.2. Fourier-Ratio Method.- 4.3.3. Van Cittert'1. An Introduction to Electron Energy-Loss Spectroscopy.- 1.1 Interaction of Fast Electrons with a Solid.- 1.2. The Electron Energy-Loss Spectrum.- 1.3. The Development of Experimental Techniques.- 1.4. Comparison of Analytical Methods.- 1.4.1. Ion-Beam Methods.- 1.4.2. Incident Photons.- 1.4.3. Electron-Beam Techniques.- 1.5. Further Reading.- 2. Instrumentation for Energy-Loss Spectroscopy.- 2.1. Energy-Analyzing and Energy-Selecting Systems.- 2.1.1. The Magnetic-Prism Spectrometer.- 2.1.2. Energy-Selecting Magnetic-Prism Devices.- 2.1.3. The Wien Filter.- 2.1.4. Cylindrical-Lens Analyzers.- 2.1.5. Retarding-Field Analyzers.- 2.1.6. Electron Monochromators.- 2.2. The Magnetic-Prism Spectrometer.- 2.2.1. First-Order Properties.- 2.2.2. Higher-Order Focusing.- 2.2.3. Design of an Aberration-Corrected Spectrometer.- 2.2.4. Practical Considerations.- 2.2.5. Alignment and Adjustment of the Spectrometer.- 2.3. The Use of Prespectrometer Lenses.- 2.3.1. Basic Principles.- 2.3.2. CTEM with Projector Lens On.- 2.3.3. CTEM with Projector Lens Off.- 2.3.4. Spectrometer-Specimen Coupling in a High-Resolution STEM.- 2.4. Recording the Energy-Loss Spectrum.- 2.4.1. Serial Acquisition.- 2.4.2. Electron Detectors for Serial Recording.- 2.4.3. Scanning the Energy-Loss Spectrum.- 2.4.4. Signal Processing and Storage.- 2.4.5. Noise Performance of a Serial Detector.- 2.4.6. Parallel-Recording Detectors.- 2.4.7. Direct Exposure of a Diode-Array Detector.- 2.4.8. Indirect Exposure of a Diode Array.- 2.4.9. Removal of Diode-Array Artifacts.- 2.5. Energy-Filtered Imaging.- 2.5.1. Elemental Mapping.- 2.5.2. Z-Contrast Imaging.- 3. Electron Scattering Theory.- 3.1. Elastic Scattering.- 3.1.1. General Formulas.- 3.1.2. Atomic Models.- 3.1.3. Diffraction Effects.- 3.1.4. Electron Channeling.- 3.1.5. Phonon Scattering.- 3.2. Inelastic Scattering.- 3.2.1. Atomic Models.- 3.2.2. Bethe Theory.- 3.2.3. Dielectric Formulation.- 3.2.4. Solid-State Effects.- 3.3. Excitation of Outer-Shell Electrons.- 3.3.1. Volume Plasmons.- 3.3.2. Single-Electron Excitation.- 3.3.3. Excitons.- 3.3.4. Radiation Losses.- 3.3.5. Surface Plasmons.- 3.3.6. Single, Plural, and Multiple Scattering.- 3.4. Inner-Shell Excitation.- 3.4.1. Generalized Oscillator Strength.- 3.4.2. Kinematics of Scattering.- 3.4.3. Ionization Cross Sections.- 3.5. The Spectral Background to Inner-Shell Edges.- 3.6. The Structure of Inner-Shell Edges.- 3.6.1. Basic Edge Shapes.- 3.6.2. Chemical Shifts in Threshold Energy.- 3.6.3. Near-Edge Fine Structure (ELNES).- 3.6.4. Extended Energy-Loss Fine Structure (EXELFS).- 4. Quantitative Analysis of the Energy-Loss Spectrum.- 4.1. Removal of Plural Scattering from the Low-Loss Region.- 4.1.1. Fourier-Log Deconvolution.- 4.1.2. Approximate Methods.- 4.1.3. Angular-Dependent Deconvolution.- 4.2. Kramers-Kronig Analysis.- 4.3. Removal of Plural Scattering from Inner-Shell Edges.- 4.3.1. Fourier-Log Deconvolution.- 4.3.2. Fourier-Ratio Method.- 4.3.3. Van Cittert's Method.- 4.3.4. Effect of a Collection Aperture.- 4.4. Background Fitting to Ionization Edges.- 4.4.1. Energy Dependence of the Background.- 4.4.2. Background-Fitting Procedures.- 4.4.3. Background-Subtraction Errors.- 4.5. Elemental Analysis Using Inner-Shell Edges.- 4.5.1. Basic Formulas.- 4.5.2. Correction for Incident-Beam Convergence.- 4.5.3. Effect of Sample Orientation.- 4.5.4. Effect of Specimen Thickness.- 4.5.5. Choice of Collection Angle.- 4.5.6. Choice of Integration and Fitting Regions.- 4.5.7. Microanalysis Software.- 4.5.8. Calculation of Partial Cross Sections.- 4.6. Analysis of Extended Energy-Loss Fine Structure.- 4.6.1. Spectrum Acquisition.- 4.6.2. Fourier-Transform Method of Data Analysis.- 4.6.3. Curve-Fitting Procedure.- 5. Applications of Energy-Loss Spectroscopy.- 5.1. Measurement of Specimen Thickness.- 5.1.1. Measurement of Absolute Thickness.- 5.1.2. Sum-Rule Methods.- 5.2. Low-Loss Spectroscopy.- 5.2.1. Phase Identification.- 5.2.2. Measurement of Alloy Composition.- 5.2.3. Detection of Hydrogen and Helium.- 5.2.4. Zero-Loss Images.- 5.2.5. Z-contrast Images.- 5.2.6. Plasmon-Loss Images.- 5.3. Core-Loss Microanalysis.- 5.3.1. Choice of Specimen Thickness and Incident Energy.- 5.3.2. Specimen Preparation.- 5.3.3. Elemental Detection and Mapping.- 5.3.4. Quantitative Microanalysis.- 5.3.5. Measurement and Control of Radiation Damage.- 5.4. Spatial Resolution and Elemental Detection Limits.- 5.4.1. Electron-Optical Considerations.- 5.4.2. Loss of Resolution due to Electron Scattering.- 5.4.3. Statistical Limitations.- 5.4.4. Localization of Inelastic Scattering.- 5.5. Structural Information from EELS.- 5.5.1. Low-Loss Fine Structure.- 5.5.2. Orientation Dependence of Core-Loss Edges.- 5.5.3. Core-Loss Diffraction Patterns.- 5.5.4. Near-Edge Fine Structure.- 5.5.5. Extended Fine Structure.- 5.5.6. Electron-Compton Measurements.- Appendix A. Relativistic Bethe Theory.- Appendix B. FORTRAN Programs.- B.3. Incident-Convergence Correction.- B.4. Fourier-Log Deconvolution.- B.5. Kramers-Kronig Transformation.- Appendix C. Plasmon Energies of Some Elements and Compounds.- Appendix D. Inner-Shell Binding Energies and Edge Shapes.- Appendix E. Electron Wavelengths and Relativistic Factors Fundamental Constants.- References.

We discuss the effect of the surrounding matrix on the resonant scattering of an electron from a molecule imbedded in a solid. Under the conditions outlined, coupling between the resonantly trapped electrons and acoustical phonons leads to a suppression of the elastic component of the scattered beam. When this happens, a multiphonon loss structure occurs, whose shape and temperature dependence is given for the model explored in the present paper. We discuss the recent experimental studies of slow-electron scattering from solid ${\mathrm{N}}_{2}$ films reported by Sanche and collaborators, with these results in hand.

No abstract

Abstract This paper is a guide to the ANSI standard C code of CASINO program which is a single scattering Monte CArlo SImulation of electroN trajectory in sOlid specially designed for low‐beam interaction in a bulk and thin foil. CASINO can be used either on a DOS‐based PC or on a UNIX‐based workstation. This program uses tabulated Mott elastic cross sections and experimentally determined stopping powers. Function pointers are used for the most essential routine so that different physical models can easily be implemented. CASINO can be used to generate all of the recorded signals (x‐rays, secondary, and backscattered) in a scanning electron microscope either as a point analysis, as a linescan, or as an image format, for all the accelerated voltages (0.1–30 kV). As an example of application, it was found that a 20 nm Guinier‐Preston Mg 2 Si in a light aluminum matrix can, theoretically, be imaged with a microchannel backscattered detector at 5 keV with a beam spot size of 5 nm.

The possibility of extracting absolute inelastic electron scattering cross sections K(T) (differential in energy loss T and path length) for solids from experimental electron spectra is studied. Assuming homogeneous scattering properties for the solid, a formula is found, which allows a direct determination of [\ensuremath{\lambda}L/(\ensuremath{\lambda}+L)]K(T) from a measured reflected electron-energy-loss spectrum (REELS) resulting from a monoenergetic beam of electrons incident on the surface of the solid. Here \ensuremath{\lambda} is the inelastic electron mean free path and L\ensuremath{\simeq}2${\ensuremath{\lambda}}_{1}$ where ${\ensuremath{\lambda}}_{1}$ is the transport mean free path for elastic electron scattering. The formula is applied to experimental REELS spectra of aluminum. The resulting cross sections are discussed in relation to a theoretical calculation based on dielectric-response theory. The determined cross sections are applied to remove the inelastic background signal from Mg--K\ensuremath{\alpha}(h\ensuremath{\nu}\ensuremath{\simeq}1254 eV) and synchrotron-radiation-excited (h\ensuremath{\nu}\ensuremath{\simeq}250 eV) photoelectron spectra of aluminum. The resulting primary excitation spectra are discussed in relation to the results of existing procedures.

A highly accurate method for measuring beam properties in a variable-shaped electron beam (VSB) system has been developed. This method is based on a knife-edge method with a solid-state detector (SSD) and scattering apertures. In VSB system, it is necessary to measure both beam profile and beam position for a long time. To meet this requirement, many aperture marks on a silicon membrane were prepared in a measurement unit. Using this unit, the accuracy and stability of beam-size and beam position measurements were evaluated in VBS system (HL-7000D, Hitachi-HITEC). As a result, the repeatability error for beam size was obtained to be smaller than 2 nm (3σ) and the repeatability error for beam position was obtained to be 0.82 nm (3σ). Moreover, a multitude of repeat experiments showed that this measurement unit can be used for more than ten years. Consequently, it was confirmed that this measurement method is useful for the high accuracy of a VSB system.

Abstract The influence of electron transport on the signal generation process in electron beam techniques is reviewed. A survey of the fundamental physical quantities for the electron–solid interaction is presented and sources for these quantities in the literature as well as semi‐empirical formulae are given. The theoretical approaches used to describe multiple scattering in solids are outlined. These include the partial intensity approach and the continuous slowing down approximation to describe multiple energy losses and the transport approximation to tackle multiple deflections. A detailed description of the Monte Carlo technique is presented because this constitutes an effective means to study transport processes. The different theoretical approaches are illustrated in a survey of applications. These include: quantitative description of the surface sensitivity in Auger and photoelectron spectroscopy; line shape analysis of electron spectra; extracting information on the compositional depth profile from the combined energy/angular distribution in an electron spectrum; quasi‐elastic electron reflection; inelastic electron backscattering; depth distribution of production of x‐rays caused by electron bombardment; and the surface sensitivity in total electron yield electron spectroscopy. These applications demonstrate that the outlined approaches have a broad field of application, not only for electrons with energies ranging from thermal to the relativistic energy range, but also for other microbeam analysis techniques. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Ionizing radiation has become the most effective way to modify natural and synthetic polymers through crosslinking, degradation, and graft polymerization. This review will include an in-depth analysis of radiation chemistry mechanisms and the kinetics of the radiation-induced C-centered free radical, anion, and cation polymerization, and grafting. It also presents sections on radiation modifications of synthetic and natural polymers. For decades, low linear energy transfer (LLET) ionizing radiation, such as gamma rays, X-rays, and up to 10 MeV electron beams, has been the primary tool to produce many products through polymerization reactions. Photons and electrons interaction with polymers display various mechanisms. While the interactions of gamma ray and X-ray photons are mainly through the photoelectric effect, Compton scattering, and pair-production, the interactions of the high-energy electrons take place through coulombic interactions. Despite the type of radiation used on materials, photons or high energy electrons, in both cases ions and electrons are produced. The interactions between electrons and monomers takes place within less than a nanosecond. Depending on the dose rate (dose is defined as the absorbed radiation energy per unit mass), the kinetic chain length of the propagation can be controlled, hence allowing for some control over the degree of polymerization. When polymers are submitted to high-energy radiation in the bulk, contrasting behaviors are observed with a dominant effect of cross-linking or chain scission, depending on the chemical nature and physical characteristics of the material. Polymers in solution are subject to indirect effects resulting from the radiolysis of the medium. Likewise, for radiation-induced polymerization, depending on the dose rate, the free radicals generated on polymer chains can undergo various reactions, such as inter/intramolecular combination or inter/intramolecular disproportionation, b-scission. These reactions lead to structural or functional polymer modifications. In the presence of oxygen, playing on irradiation dose-rates, one can favor crosslinking reactions or promotes degradations through oxidations. The competition between the crosslinking reactions of C-centered free radicals and their reactions with oxygen is described through fundamental mechanism formalisms. The fundamentals of polymerization reactions are herein presented to meet industrial needs for various polymer materials produced or degraded by irradiation. Notably, the medical and industrial applications of polymers are endless and thus it is vital to investigate the effects of sterilization dose and dose rate on various polymers and copolymers with different molecular structures and morphologies. The presence or absence of various functional groups, degree of crystallinity, irradiation temperature, etc. all greatly affect the radiation chemistry of the irradiated polymers. Over the past decade, grafting new chemical functionalities on solid polymers by radiation-induced polymerization (also called RIG for Radiation-Induced Grafting) has been widely exploited to develop innovative materials in coherence with actual societal expectations. These novel materials respond not only to health emergencies but also to carbon-free energy needs (e.g., hydrogen fuel cells, piezoelectricity, etc.) and environmental concerns with the development of numerous specific adsorbents of chemical hazards and pollutants. The modification of polymers through RIG is durable as it covalently bonds the functional monomers. As radiation penetration depths can be varied, this technique can be used to modify polymer surface or bulk. The many parameters influencing RIG that control the yield of the grafting process are discussed in this review. These include monomer reactivity, irradiation dose, solvent, presence of inhibitor of homopolymerization, grafting temperature, etc. Today, the general knowledge of RIG can be applied to any solid polymer and may predict, to some extent, the grafting location. A special focus is on how ionizing radiation sources (ion and electron beams, UVs) may be chosen or mixed to combine both solid polymer nanostructuration and RIG. LLET ionizing radiation has also been extensively used to synthesize hydrogel and nanogel for drug delivery systems and other advanced applications. In particular, nanogels can either be produced by radiation-induced polymerization and simultaneous crosslinking of hydrophilic monomers in "nanocompartments", i.e., within the aqueous phase of inverse micelles, or by intramolecular crosslinking of suitable water-soluble polymers. The radiolytically produced oxidizing species from water, •OH radicals, can easily abstract H-atoms from the backbone of the dissolved polymers (or can add to the unsaturated bonds) leading to the formation of C-centered radicals. These C-centered free radicals can undergo two main competitive reactions; intramolecular and intermolecular crosslinking. When produced by electron beam irradiation, higher temperatures, dose rates within the pulse, and pulse repetition rates favour intramolecular crosslinking over intermolecular crosslinking, thus enabling a better control of particle size and size distribution. For other water-soluble biopolymers such as polysaccharides, proteins, DNA and RNA, the abstraction of H atoms or the addition to the unsaturation by •OH can lead to the direct scission of the backbone, double, or single strand breaks of these polymers.

No abstract

Electron diffraction and microscopy are among the most important techniques for studying the structures of solids. This review aims to give a comprehensive introduction to the basic principles of the scattering of fast electrons and to highlight selected applications of importance. It begins by discussing electron scattering by single atoms and describes how single atoms may be imaged. The geometry of diffraction from perfect single crystals is then considered and a simple kinematical theory which yields approximate values for diffracted intensities is given. It is shown how simple principles have been used to image monatomic steps on the surface of crystals. More accurate methods of calculating diffracted intensities are given and particular attention is paid to describing concepts often found to be difficult, for example the dispersion surface. Principles of various recent electron scattering techniques are outlined including high-voltage electron microscopy, scanning electron microscopy, convergent-beam electron diffraction and the critical voltage effect. Applications described range from measuring bonding electron charge densities to the imaging of dislocations. Finally some recent theoretical developments on the problem of imaging imperfect crystals at atomic resolution are discussed.

Solid silicon monoxide is an amorphous material which has been commercialized for many functional applications. However, the amorphous structure of silicon monoxide is a long-standing question because of the uncommon valence state of silicon in the oxide. It has been deduced that amorphous silicon monoxide undergoes an unusual disproportionation by forming silicon- and silicon-dioxide-like regions. Nevertheless, the direct experimental observation is still missing. Here we report the amorphous structure characterized by angstrom-beam electron diffraction, supplemented by synchrotron X-ray scattering and computer simulations. In addition to the theoretically predicted amorphous silicon and silicon-dioxide clusters, suboxide-type tetrahedral coordinates are detected by angstrom-beam electron diffraction at silicon/silicon-dioxide interfaces, which provides compelling experimental evidence on the atomic-scale disproportionation of amorphous silicon monoxide. Eventually we develop a heterostructure model of the disproportionated silicon monoxide which well explains the distinctive structure and properties of the amorphous material.

No abstract

Measurements have been made of the fraction of an electron beam backscattered from thin films of copper and gold at incident energies from 5 to 25 kev. The results from very thin films indicate that approximately 50% of backscattering from a solid target must be due to single scattering. A comparison with existing theories shows that the results can be fitted by a combination of the single scattering treatment of Everhart and the albedo theory of Bothe, if recent experimental values of the electron range are inserted. A degree of agreement also obtains with the comprehensive theory of backscattering due to Dashen.

No abstract

The interaction of an electron beam with a solid can be modeled by the so-called Monte Carlo method. This technique produces a stepwise simulation of the electron trajectory by using random numbers to predict scattering angles on the basis of theoretical probability distributions or empirical models. The physical basis of electron scattering in a solid is described and two generic types of Monte Carlo model are then developed together with suggested examples of their application. An IBM PC compatible disc containing these programs is available from the author.

A new, compact (approximately fist sized), efficient electron-spin analyzer is described. It is based on low-energy (150 eV) diffuse scattering from a high-Z target, for example, an evaporated polycrystalline Au film opaque to the incident electron beam. By collecting a large solid angle of scattered electrons, a figure of merit S2I/I0=10−4 is achieved with an analyzing power S=0.11. The figure of merit degrades only marginally (&amp;lt;10%) for beams with an energy width of 40 eV or after one month of operation at 10−8 Torr. The electron optical acceptance is of order 100 mm2 sr eV. The details of the design and construction are discussed and its performance is compared to six other spin analyzers. Illustrative results are presented from an application to scanning electron microscopy with polarization analysis (SEMPA) to image magnetic microstructure.

Electron-beam-induced deposition (EBID) is a versatile micro- and nanofabrication technique based on electron-induced dissociation of metal-carrying gas molecules adsorbed on a target. EBID has the advantage of direct deposition of three-dimensional structures on almost any target geometry. This technique has occasionally been used in focused electron-beam instruments, such as scanning electron microscopes, scanning transmission electron microscopes (STEM), or lithography machines. Experiments showed that the EBID spatial resolution, defined as the lateral size of a singular deposited dot or line, always exceeds the diameter of the electron beam. Until recently, no one has been able to fabricate EBID features smaller than 15–20nm diameter, even if a 2-nm-diam electron-beam writer was used. Because of this, the prediction of EBID resolution is an intriguing problem. In this article, a procedure to theoretically estimate the EBID resolution for a given energetic electron beam, target, and gaseous precursor is described. This procedure offers the most complete approach to the EBID spatial resolution problem. An EBID model was developed based on electron interactions with the solid target and with the gaseous precursor. The spatial resolution of EBID can be influenced by many factors, of which two are quantified: the secondary electrons, suspected by almost all authors working in this field, and the delocalization of inelastic electron scattering, a poorly known effect. The results confirm the major influence played by the secondary electrons on the EBID resolution and show that the role of the delocalization of inelastic electron scattering is negligible. The model predicts that a 0.2-nm electron beam can deposit structures with minimum sizes between 0.2 and 2nm, instead of the formerly assumed limit of 15–20nm. The modeling results are compared with recent experimental results in which 1-nmW dots from a W(CO)6 precursor were written in a 200-kV STEM on a 30-nm SiN membrane.

Systematic measurements and simulations are reported for the transition from growth by nucleation and accretion of two-dimensional islands to step advancement on misoriented GaAs(001) surfaces during epitaxial growth. The growth conditions have been chosen in order to satisfy as much as possible the underlying assumptions of a solid-on-solid model of epitaxial growth, namely, that the adatom mobility is isotropic (by using a surface misoriented toward the [010] direction), the effect of the As is not rate determining (by using a As/Ga ratio of 2.5), and that the presence of any surface reconstruction can be subsumed in effective migration parameters, i.e., that no explicit account of surface reconstruction is required if the reconstruction does not change (by maintaining the 2\ifmmode\times\else\texttimes\fi{}4 reconstruction). The diffraction conditions for reflection high-energy electron-diffraction (RHEED) measurements were chosen to eliminate as much as possible the contribution of well-known incoherent features to the specular intensity on GaAs(001). Using these growth and diffraction conditions, the parameters of a solid-on-solid model have been optimized by performing extensive simulations to quantitatively reproduce the measured misorientation-angle dependence and the Ga flux dependence of the growth-mode transition temperature. Since at the chosen diffraction conditions, the kinematic diffraction is insensitive to surface morphologies, we have modeled the growth-induced loss of intensity from the specular beam as being due to the steps on the surface, with each step acting as an individual source of scattering. Direct comparisons between the time-dependent density of surface steps of the simulated surfaces and the RHEED specular intensity profiles measured during growth reveal several qualitative and quantitative similarities. The most striking of these is that the two quantities show the same relative change of magnitude with time and temperature for a given misorientation and Ga flux. The implications of these comparisons are discussed for the growth dynamics of GaAs(001), for the scattering processes in RHEED, and the morphological sensitivity of RHEED for these diffraction conditions.

The product of two empirical relations, for the practical range and the transmission probability of normally incident electrons through plane sheets of matter, may be differentiated to yield a simple formulation of the energy deposition by electron beams, in agreement with more complex formulations and with experimental data. When combined with the $\ensuremath{\delta}$-ray distribution formula, these results provide a theory of the spatial distribution of ionization energy about the path of a rapidly moving ion, which is basic to theories of radiation damage and detection.

Focused electron beam induced deposition (FEBID) is a single-step, direct-write nanofabrication technique capable of writing three-dimensional metal-containing nanoscale structures on surfaces using electron-induced reactions of organometallic precursors. Currently FEBID is, however, limited in resolution due to deposition outside the area of the primary electron beam and in metal purity due to incomplete precursor decomposition. Both limitations are likely in part caused by reactions of precursor molecules with low-energy (<100 eV) secondary electrons generated by interactions of the primary beam with the substrate. These low-energy electrons are abundant both inside and outside the area of the primary electron beam and are associated with reactions causing incomplete ligand dissociation from FEBID precursors. As it is not possible to directly study the effects of secondary electrons in situ in FEBID, other means must be used to elucidate their role. In this context, gas phase studies can obtain well-resolved information on low-energy electron-induced reactions with FEBID precursors by studying isolated molecules interacting with single electrons of well-defined energy. In contrast, ultra-high vacuum surface studies on adsorbed precursor molecules can provide information on surface speciation and identify species desorbing from a substrate during electron irradiation under conditions more representative of FEBID. Comparing gas phase and surface science studies allows for insight into the primary deposition mechanisms for individual precursors; ideally, this information can be used to design future FEBID precursors and optimize deposition conditions. In this review, we give a summary of different low-energy electron-induced fragmentation processes that can be initiated by the secondary electrons generated in FEBID, specifically, dissociative electron attachment, dissociative ionization, neutral dissociation, and dipolar dissociation, emphasizing the different nature and energy dependence of each process. We then explore the value of studying these processes through comparative gas phase and surface studies for four commonly-used FEBID precursors: MeCpPtMe3, Pt(PF3)4, Co(CO)3NO, and W(CO)6. Through these case studies, it is evident that this combination of studies can provide valuable insight into potential mechanisms governing deposit formation in FEBID. Although further experiments and new approaches are needed, these studies are an important stepping-stone toward better understanding the fundamental physics behind the deposition process and establishing design criteria for optimized FEBID precursors.

The deposition profiles for the pulsed electron beams in solid radiation sensitive plastics have been measured and indicate a pronounced range shortening at charge fluences greater than 0.5 microcoulombs/cm2. This range shortening, due to charge trapping and the attendant internal field, reaches a constant value in the absence of apparent breakdown which is independent of charge fluence at current densities greater than about 33 amps/cm2 for mean electron energies of 1.35 MeV. The dose depth profiles at charge fluences greater than 0.5 microcoulomb/ cm2 exhibit a linearly decreasing back edge which extrapolates to approximately 35% of the low fluence range and a low intensity tail extending to greater than 55% of this range. As the charge fluence increases, the tail of the dose profile decreased in relation to the forward portion. These phenomena are interpreted in terms of a charge deposition model including radiation induced conductivity.

Electron-beam-induced deposition was performed to fabricate nanostructures using a subnanometer-sized probe of high-energy electrons emitted by a 200 kV transmission electron microscope equipped with a field emission gun. We fabricated nanometer-sized dots with a diameter of less than 5 nm, controlling their position and size by the introduction of a organometallic precursor gas near the substrate surface. The relation between the size of the deposit and the deposition time was studied, and, in addition, the effect of the substrate thickness was examined.

Electron-energy deposition in thin Au foils irradiated by a tightly pinched electron beam has been studied on the Proto I accelerator (1.1 MV, 300 kA, 25 nsec). X-ray diode measurements indicate front surface temperatures of 15-20 eV, in agreement with calculations assuming deposition rates of \ensuremath{\gtrsim}5x${10}^{13}$ W/g. These results are consistent with magnetically enhanced deposition due to self-beam fields (enhancement \ensuremath{\sim}3-5).

Electron beam melting (EBM) is a metal powder bed fusion additive manufacturing (AM) technology that facilitates the production of metal parts by selectively melting areas in layers of metal powder. The electron beam melting process is conducted in a vacuum chamber environment regulated with helium (He) at a pressure on the scale of 10−3 mbar. One of the disadvantages of vacuum environments is the effect of vapor pressure on volatile materials: indeed, elements in the pre-alloyed powder with high vapor pressure are at risk of evaporation. Increasing the He pressure in the process can improve the thermodynamic stability of the pre-alloyed components and decrease the composition volatility of the solid. However, increasing the pressure can also attenuate the electrons and consequently reduce the energy deposition efficiency. While it is generally assumed that the efficiency of the process is 90%, to date no studies have verified this. In this study, Monte Carlo simulations and detailed thermal experiments were conducted utilizing EGS5 and an Arcam Q20+ machine. The results reveal that increasing the gas pressure in the vacuum chamber by one order of magnitude (from 10−3 mbar to 10−2 mbar) did not significantly reduce the energy deposition efficiency (less than 1.5%). The increase in gas pressure will enable the melting of alloys with high vapor pressure elements in the future.

The enhancement by a magnetic field of the deposition of energy by a relativistic electron beam is formulated via the diffusion approximation to the relativistic Fokker-Planck equation, valid when mean free path and/or gyration radius are much less than other characteristic lengths. Analytic solutions are given for a beam normally incident on a slab with $\stackrel{\ensuremath{\rightarrow}}{\mathrm{B}}$ parallel to the face. These indicate that the effect can be important.

An analytical electron-resist interaction (ERI) model is developed based on detailed investigation of secondary electron production and binding energy related exposure events. Analysis shows that 80% of the exposure events are directly caused by secondary electrons for 100 keV primary electron energy. The number of secondary electrons and further cascade electrons is 1/20 and 1/300, respectively, of the incoming electrons. An algebraic expression is derived to describe the spatial distribution of the exposure events. The ERI model can be extended to chemically amplified resists.

We have studied focused electron beam induced deposition from W(CO)6 at beam primary energies between 20 and 0.06 keV. Submicrometer resolution with 4 nA beam current was maintained at very low primary energies using a retarding field configuration. Decomposition cross sections of W(CO)6 for primary energies below about 1 keV were found to be about a factor of 4 larger than those at 20 keV. Depending on the scan conditions, the resistivity of the deposits formed using low primary energies was found to be up to about a factor of 4 lower than at 20 keV implying a higher metallic content. These results form the basis of an improved method for repairing clear defects on x-ray masks and for making conducting tracks on semiconducting materials.

No abstract

The feasibility is demonstrated of a numerical method to calculate dose deposition by broad high-energy electron beams in homogeneous matter or in heterogeneous matter in which the heterogeneities are arranged in slabs perpendicular to the beam axis. The method is based only on the basic physical interaction processes of high-energy electrons and matter. The method is an extended version of the phase space time evolution method as described by Cordaro and Zucker (1971). The calculated depth-dose curves, energy spectra and angular distributions agree very well with results of the extensive class II Monte Carlo calculations of Andreo and Brahme (1984) and Andreo (1985), but require much less computer time: typically 3 minutes on a VAX 785 with floating point accelerator. This demonstrates the power of a numerical method in comparison with Monte Carlo methods.

The electron deposition in an Ar–Kr–F2 mixture, based on a solution of the electron Boltzmann equation, is presented. The model is relevant to an electron-beam generated KrF* laser amplifier at atmospheric pressure. Sets of cross sections for Ar, Kr, and F2 have been compiled. Calculations have been performed to determine the electron energy distribution function, energy per electron–ion pair and the ionization and excitation rates. It is found that the inclusion of inner shell ionization and the subsequent Auger emission are essential for matching known results on both the energy per electron–ion pair Wei and the stopping power in pure Ar or Kr target gases. For the chosen Ar–Kr–F2 mixture, Wei is calculated to be 24.6 eV. The excitation-to-ionization ratio is calculated to be 0.38 for Ar and 0.54 for Kr at low input power density Pbeam (1 kW/cm3). Both ratios increase with Pbeam, particularly for Kr which attains 0.8 at 1 MW/cm3. The dependency on Pbeam and the excitation efficiency for Kr is significantly higher than previously assumed in KrF* kinetic models. Results are also compared with the continuous slowing down approximation to demonstrate that this approach is limited to the regime of low power deposition.

Abstract : Electron impact excitation and ionization cross sections for N, N, +, O, and O+ are provided. Electron kinetic energies range from threshold to or = 5 MeV. Available experimental and theoretical are summarized and compared. Keywords: Ionization cross sections; High energy electron; Excitation cross sections; Nitrogen; Oxygen.

Electron-beam-induced deposition of platinum from methylcyclopentadienyl-platinum-trimethyl was performed with a focused electron beam at low landing energies, down to 10eV. The deposition growth rate is maximal at 140eV, with the process being over ten times more efficient than at 20kV. No significant dependence of composition with landing energy was found in the deposits performed at energies between 40 and 1000eV. This study provides further evidence for the dissociation process being primarily driven by the sub-20-eV secondary electrons.

A quantitative knowledge of the energy deposited by low-energy electron beams is often necessary for microelectronic applications. Three calculations of energy deposition in a metal-oxide-semiconductor (MOS) structure irradiated by a beam of 20- keV electrons are compared in this note. The error resulting from equating electron penetration to path length is illustrated.

We have investigated the use of low-energy electron beams to nucleate and stimulate the deposition and growth of thin films of metals. Selective area growth of Fe from Fe(CO)5 using low-energy focused electron beams (&amp;lt;5 keV) has been deomnstrated. Low-energy electron-beam irradiation (0.5–3.0 keV) can be used to nucleate growth of Fe on a Si surface. Subsequent thermal decomposition of Fe(CO)5 on Fe is ∼900 times faster than on Si at 125 °C resulting in thick, polycrystalline Fe films deposited only in areas irradiated by the electron beam. We have demonstrated nucleation and growth of 150 nm Fe features using 3 keV, 100-nm-diam electron beam. Fluxes and energies of low-energy electrons passing through the surface (primaries, secondaries, backscatters) are calculated by a Monte Carlo technique using an accurate scattering cross section for low-energy electrons. Spatial distributions of backscatters and secondaries at primary energies &amp;lt;3000 eV are seen to be confined primarily to a radius of &amp;lt;10 nm from the point of impact, and it appears that scattering contributes little to the spatial distribution of deposited film. Minimal electron scattering at low-energy makes this regime attractive for direct write, selective area processing.

Electron beam propagation in a dense gas medium is numerically investigated. All the main phenomena that determine electron beam behavior in a gas (scattering and energy losses of the electrons on the gas atom molecules, ionization and excitation, electron thermalization, beam pinching, and influence of a magnetic guide field) are taken into account. The initial beam energy and the gas chamber dimensions are varied in a wide range: typical gas mixtures for the excimer lasers are considered. Graphs are given that allow the choice of the optimal electron beam energy that provides the maximum efficiency of the beam energy deposition into the gas, depending on the gas chamber dimensions.

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We have investigated the low energy electron beam irradiation (LEEBI) annealing kinetics of Mg-doped GaN films grown by metalorganic chemical vapor deposition. Our results show that LEEBI annealing at room temperature, monitored by cathodoluminescence spectroscopy as a function of irradiation time, occurs rapidly initially and then proceeds gradually until saturation. We have also demonstrated that LEEBI annealing is effective even at liquid helium temperature, indicating its athermal mechanism. Our observations support the dynamic model involving electronically stimulated dissociation of Mg–H bonds and the escaping and retrapping of atomic hydrogens.

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The electron distribution function is calculated for a plasma created when a high-current, high-energy (∼MeV) electron beam enters nitrogen gas. No spatial dependence is considered for the distribution function and the velocity is expanded in the two-term approximation. Time dependence is retained. Benchmark calculations are presented that compare code output with experimental results of electron deposition studies and swarm studies in nitrogen. Production efficiencies are given. The effect of inner-shell processes is discussed. An example illustrates the importance of the beam-induced electric field on the plasma generation and behavior. It shows that considerable ohmic energy deposition can be involved and that, consequently, production of certain species can be greatly enhanced.

A discrete, time-dependent energy deposition model is used to study high-energy electron-beam (100 eV–10 MeV) deposition in N and N+. Both time-dependent and steady-state secondary electron distributions are computed. The loss function, mean energies per electron-ion pair production (W), production efficiencies, and distribution functions are presented for a wide range of energies. The latest experimental and theoretical cross sections are used in the model which predicts that W is approximately 31 eV for N and 72 eV for N+ over a wide range of beam energies. The sensitivity of these results to assumed background ionization fractions is also investigated.

Relative cross sections for dissociative electron attachment (DEA) and dissociative ionization (DI) of the FEBID precursor, trimethyl (methylcyclopentadienyl) platinum(iv), MeCpPtMe(3), are presented. The most pronounced DEA process is the loss of one methyl radical, while the loss of two or three methyl groups along with hydrogen is the main pathway in DI. Further fragments are formed in DEA and through DI by more complex rearrangement reactions but complete dissociation to bare Pt(-) in DEA or Pt(+) in DI is minor. The transient negative ion (TNI) formation in DEA is discussed and fragmentation mechanisms are proposed for individual processes. From the thermodynamics of the DEA processes we derive a lower limit for the electron affinity of the MeCpPtMe(2) radical (1.7 eV). Appearance energies (AE) of MeCpPtMe(3)(+) (7.7 eV) and Pt(+) (18.6 eV) formation through electron impact ionisation (EI) and through DI, respectively, are determined. Finally, the current DEA and DI results are compared and brought into context with earlier surface science studies on electron-induced decomposition of adsorbed MeCpPtMe(3) as well as gas phase and surface science studies on the FEBID precursors [Co(CO)(3)NO] and [Pt(PF(3))(4)]. These comparisons strongly indicate that DEA is an important process in the electron-induced decomposition of these molecules in FEBID.

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Calculations for electron deposition in electron beam generated KrF laser at atmospheric pressure have been performed. The impact of the Ar/Kr/F2 gas mixture on the electron energy distribution function, electron density, and mean energy, energy per electron–ion pair, attachment, dissociation, excitation, and ionization rates have been investigated. The F2 abundance controls the low energy (≲9 eV) component of the distribution function, while both the fluorine and krypton mole fraction affect the distribution in the midenergy domain (9 to ∼25 eV). Consequently, the F2 attachment rate coefficient varies with the F2 mole fraction (xF2) such that the electron density scales as 1/xF20.7. The rate coefficient for direct dissociation of F2 is smaller than for attachment but the former contributes more to the total power dissipation (∼8% at xF2=0.01). The excitation-to-ionization ratio for Kr is not constant, as generally assumed, but increases by a factor of two with a decrease in either the Kr or F2 abundance. Combining the former and present investigations leads to a set of fitting formulas to be used in beam kinetics codes for various collision rates as a function of both the electron beam power density and the composition.

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In electron lithography, resist heating is a serious practical problem that requires proper modeling. To decrease complexity of the problem, simplified representations of a single electron heat source were examined. This was shown that simplified descriptions can lead to significant errors in temperature simulation. These simple models can only be used for temperature simulation at a long time/long distance from the current electron flash. An analytic mode of electron scattering and Monte Carlo modeling have shown comparably good accuracy when used for thermal simulations. They both were embedded in TEMPTATION software tool.

Wire-fed electron beam directed energy deposition (EB-DED) is gaining increasing attention owing to its significant advantage of producing high-quality, large-scale metallic components. In this study, EB-DED of a near-α titanium alloy (Ti–6Al–2Zr–1Mo–1V) was conducted, and the effect of post-deposition single annealing treatment on the microstructure, texture, and anisotropy of the tensile properties was investigated. Optical microscopy, scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy were employed to study the microstructure and texture characteristics. The tensile properties along the vertical (Z axis) and horizontal (Y axis) directions were evaluated at both room temperature and 500 °C. The results indicated that the prior β grains had a strong < 001 >β texture along the grain growth direction. Although the α variant selection occurred in some micro-regions, the overall α phase texture was weak. In terms of tensile properties, the vertical specimens exhibited lower strength but higher ductility than the horizontal specimens at both room and elevated temperatures. The anisotropic elongation results from the directional columnar prior β grains and continuous grain boundary α phase, which facilitated the intergranular cracking. The tensile strength and ductility were simultaneously enhanced by annealing at 950 °C for 2 h to meet the standard requirements for wrought counterparts. Moreover, the anisotropy of the tensile properties was decreased significantly. The enhanced and isotropic mechanical properties can be attributed to the combined effect of the bi-lamellar microstructure, discontinuous grain boundary α phase, and the weak α texture.

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The phase space time evolution model of Huizenga and Storchi and Morawska-Kaczyńska and Huizenga has been modified to accommodate calculations of energy deposition by arbitrary electron beams in three-dimensional heterogeneous media. This is a further development aimed at the use of the phase space evolution model in radiotherapy treatment planning. The model presented uses an improved method to control the evolution of the phase space state. This new method results in a faster algorithm, and requires less computer memory. An extra advantage of this method is that it allows the pre-calculation of information, further reducing calculation times. Typical results obtainable with this model are illustrated with the cases of (i) a 20 MeV pencil beam in a water phantom, (ii) a 20 MeV 5 x 5 cm2 beam in a water phantom containing two air cavities, and (iii) a 20 MeV 5 x 5 cm2 beam in a water phantom containing an aluminium region. The results of the dose distribution calculations are in good agreement with and require significantly less computation time than results obtained with Monte Carlo methods.

Relativistic electron beam (REB) energy deposition in thin gold and aluminum targets has been investigated experimentally using radiation temperature measurements in the soft x-ray, vacuum ultraviolet (XUV) and optical spectral regions on two different particle accelerators. Energy deposition measurements were compared with numerical calculations utilizing particle-in-cell (PIC) diode codes, condensed history Monte-Carlo codes, and coupled radiation-hydrodynamic codes. The specific power deposited (i.e., power deposited/unit mass) was observed to be greater than that due to an average electron making a single pass through a thin target (6.4 ..mu..m thick gold foil on the Hydra accelerator and 38 and 6 ..mu..m thick aluminum foils on the Proto I accelerator). Self-magnetic field effects were primarily responsible for deposition enhancement in 6.4 ..mu..m gold foils on the Hydra accelerator (..nu../..gamma.. approx. = 2.5). Reduction of electron scattering with aluminum foils on Proto I where ..nu../..gamma.. approx. = 1 led to deposition enhancement due to both self electric and magnetic fields.

For pt.I, see ibid., vol.34, p.1371-96 (1989). The phase space time evolution model of Huizenga and Storchi has been modified to handle dose deposition calculations by broad high-energy electron beams in homogeneous non-water media and in a multi-layered geometry. This is a further development aimed at the use of a phase space time evolution model in radiotherapy treatment planning. In the model presented a different approach to the step-size choice and photon energy deposition has been chosen. The results of the numerical depth-dose calculations are in very good agreement with Monte Carlo calculations with the ITS and EGS codes and for lighter materials like water aluminium. For high-Z materials like gold or lead agreement between numerical and Monte Carlo results is also moderately good.

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In this article the energy deposition function in the case of e-beam lithography is calculated analytically. The distribution of electrons as a function of depth and energy is calculated first using a method based on the Boltzmann transport equation which is easily applicable in the case of multilayer substrates. Next the lateral distribution of the electrons is calculated and each contribution (primary, secondary, and backscattered electrons) is considered separately. Energy dissipation results are used as input to a cell removal model for the resist development simulation.

The electron beam assisted etch rates for SiO2 by using XeF2 and CF4 gases were measured as a function of primary electron energy. The deposition rate of Fe on SiO2 substrate with Fe(CO)5 as a source gas was also measured. It is seen that both the etch rate and the deposition rate are higher at lower primary electron energies in the region of 1 keV to 15 keV.

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SUMMARY Images in the scanning electron microscope (SEM) are formed from both low‐energy secondary, and high‐energy backscattered, electrons. The quantitative interpretation of SEM images therefore requires a model which can predict the magnitude of both of these signal components for a specimen whose geometry and chemistry is known. It is shown that the combination of a simple electron diffusion model with a Monte Carlo trajectory simulation allows both yields to be calculated, simultaneously, with good accuracy. Data, such as the magnitude and energy of the maximum secondary yield, the secondary variation with tilt, and the contribution of backscattered electrons to the secondary yield coefficient, computed from this model are in excellent agreement with experimental data.

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The quality of an image generated by a scanning electron microscope is dependent on secondary emission, which is a strong function of surface condition. Thus, empirical formulae and available databases are unable to take into account actual metrology conditions. This paper introduces a simple and reliable measurement technique to measure secondary electron yield (delta) and backscattered electron yield (eta) that is suitable for in-situ measurements on a specimen immediately prior to imaging. The reliability of this technique is validated on a number of homogenous surfaces. The measured electron yields are shown to be within the range of published data and the calculated signal-to-noise ratio compares favourably with that estimated from the image.

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On the basis of the characteristic of secondary electron emission, the number of secondary electrons ( δ PEθ ) released per primary electron entering metals in the incident energy ( W p0 ) range 10-102 keV and the incident angle ( θ ) range 0-89° was deduced. In addition, the number of secondary electrons released per primary electron entering metals at θ= 0 ( δ PE0 ) was obtained. Based on the deduced δ PEθ , the characteristic of the emission angle distribution of the backscattered electrons and the definition of β θ , the relationships among β θ , cos θ and the parameter x were given, where β θ is the ratio of the average number of secondary electrons generated by a single backscattered electron to that generated by a single primary electron entering the emitter at θ . Considering the relationship between δ PEθ and δ PE0 and the relationship between the secondary electron yields at W p0 =10-102 keV and θ= 0-89° ( δ θ ) and the secondary electron yields at θ= 0( δ 0 ), a universal formula for expressing δ θ through δ 0 , the backscattered coefficient at θ ( η θ ), the backscattered coefficient at θ= 0( η 0 ), cos θ and the parameter x were deduced. Further, the parameters x related to beryllium, uranium, aluminium and copper were computed with the deduced formula and experimental results; then, the formulae for expressing δ θ from the four metals through δ 0 , η θ , η 0 and cos θ were obtained; and the relationships between β θ of the four metals and cos θ were found. The δ θ calculated with the formulae and the yields measured experimentally were compared. Finally, it is concluded that the formulae for δ θ and β θ from the four metals at W p0 =10-102 keV and θ= 0-89° have been established, respectively.

Based on a simple atomic model giving the potential between electrons and atoms as V(r)=Ze2as −1/srs, the range of electrons penetrating solid targets is derived. Starting from the generalized power law involving the energy loss, the Lenard-type absorption law, and the assumption that the distribution of the secondary electrons due to both incident and backscattered electrons within the target is isotropic, a theoretical universal reduced yield curve of secondary electrons and the resulting maximum yield, which are found to be in good accordance with results obtained experimentally, are deduced as a function of three parameters such as atomic number, resonance potential and backscattering coefficient.

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The discharge parameters in Hall thrusters depend strongly on the yield of secondary electron emission from channel walls. Comparative measurements of the yield of secondary electron emission at low energies of primary electrons were performed for several dielectric materials used in Hall thrusters with segmented electrodes. The measurements showed that at low energies of primary electrons the actual energetic dependencies of the total yield of secondary electron emission could differ from fits, which are usually used in theoretical models. The observed differences might be caused by electron backscattering, which is dominant at lower energies and depends strongly on surface properties. Fits based on power or linear laws are relevant at higher energies of primary electrons, where the bulk material properties play a decisive role.

The so-called “total yield” approach often fails to explain the measured sign of the surface potential, VS, and the shift of the nominal critical energy EC2∘ (where δ°+η°=1) of electron irradiated insulators. Here, a simple modification of this approach consists in including some extra interactions of the secondary and backscattered electrons with the electron traps generated previously by the irradiation itself. The trends in the evolution of the total yield, δ+η, and of VS as a function of the irradiation time (from their initial values up to their steady values) are then deduced for a wide primary beam energy range (1–50 keV) and for different external collector (or specimen holder) bias. New mechanisms are suggested for the contrasts observed in insulators investigated in scanning electron microscopy (SEM). The present analysis applies for a wide variety of electron beam techniques (SEM, Auger electron spectroscopy, and electron probe microanalysis) operated on a wide variety of insulating specimens and this analysis can be easily extended to any device based on the electron emission from insulators.

Abstract Monte Carlo modeling of electron‐solid interactions requires a detailed and accurate supply of experimental data on which to base its physics and against which to test its predictions. To meet this need, a collection of data—comprising measurements of secondary and backscattered electron yields, electron stopping powers, and x‐ray ionization cross sections, as a function of energy—has been assembled from published sources. The quality and quantity of the compilation varies widely, with little or no data being available for the majority of elements in the periodic table, while results for complex materials of current technologic interest are also almost nonexistent. To meet the needs of Monte Carlo simulation in areas such as dimensional metrology or microanalysis, a program of systematic measurements is required.

In this paper, we show the influence of the chemical structure of four different conformers on the secondary electron emission and backscattering of an electron beam from a gel of methacrylic acid. The conformers have different permanent dipole moments, which determines the cross sections for elastic collisions with electrons. The cross sections are used in Monte Carlo simulations of an electron beam, which enters the gel of methacrylic acid. The secondary electron yield and the backscattering coefficient are computed as a function of the beam energy.

The transmission (ηT) and backscattering (ηR) of electrons with energies between 0.5 and 4 keV in thin films of Be, Al, Ge, Cu, and Ag, together with their secondary yields (δT, δR), were measured with a three-collector system. The SE efficiencies of backscattered electrons were 3 to 15 times greater than those of incident PE. The energy distributions of the transmitted electrons were measured with a spherical retarding field analyser. Average and most probable energies were obtained. Transmission characteristics could be normalized by the maximal penetration range R and in this way generality is achieved for initial energies up to 1 MeV. Die Transmission (ηT) und Rückstreuung (ηR) von Elektronen mit Energien zwischen 0,5 und 4keV in dünnen Be-, Al-, Ge-, Cu- und Ag-Schichten, zusammen mit ihren Sekundärausbeuten (δT, δR), wurden in einem Drei-Kollektorsystem gemessen. Die SE-Effektivitäten rückgestreuter Elektronen lagen 3 bis 15mal höher als die einfallender PE. Die Energieverteilungen transmittierter Elektronen wurden mit einem sphärischen Gegenfeldanalysator auǐgenommen. Mittlere und wahrscheinlichste Energien wurden ermittelt. Die Transmissionscharakteristiken konnten mit Hilfe der maximalen Eindringtiefe R normalisiert werden. Auf diesen Wege wird eine Verallgemeinerung für Anfangsenergien bis zu 1 MeV erzielt.

Measurements of the secondary electron yields delta and delta T on the incident and the opposite surfaces respectively of transparent Al and Au films are reported for the normal incidence of 10-100 keV electrons, using an apparatus with accurate separation of secondary, backscattered and transmitted electrons. Results are discussed for the ratios beta and beta T of the mean secondary electron yield of respectively backscattered and transmitted electrons for one incident primary electron. The results are compared with calculated values using the energy and angular distributions of the backscattered and transmitted electrons. They can be explained by the assumption that the mean secondary electron yield of one primary, backscattered or transmitted electron is proportional to the Bethe energy loss inside the exit depth of the secondaries. There is no experimental evidence the conservation of momentum causes an additional factor r to be used for the secondary electron emission of electrons with a momentum directed outside the surface.

It is shown experimentally that backscattered electrons emitted from solids under electron bombardment contribute significantly to the observed secondary yield, even for the case of low backscattering coefficients. Thus, it was found that in Al with a backscattering coefficient of only 0.14, about 40% of all secondaries are produced by backscattered electrons for initial energies from several kev to several tens of kev. The large contribution of backscattered electrons to secondary formation even for materials of low atomic number agrees approximately with what one would expect from the larger rate of energy loss and the greater path lengths of the backscattered electrons in the secondary electron escape region compared to that of the incoming primaries.

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While several studies have suggested that secondary electrons dominate electron beam induced deposition (EBID), we demonstrate that primary electrons (PE’s) contribute significantly to the deposition for nanoscale EBID over the electron beam energy range (500–20keV). High-aspect ratio pillar growth is a signature of EBID; W nanopillar growth on SiO2 substrate yielded a growth rate of 6nms−1 and a nanopillar aspect ratio of ∼50. A simple integration of the primary, secondary, and backscattered electron distributions versus a dissociation cross section for WF6 suggests that all three electron species should contribute to the total volume of the deposited nanopillar, contrary to reports that suggest that secondary electrons dominate the process. A three-dimensional, Monte Carlo simulation including time correlated gas dynamics and species specific deposition was developed to help elucidate which of the relevant electron species, primary (PE’s), secondary (SE’s), and/or backscattered electrons (BSE’s), induce the dissociation of precursor gas and lead to nanopillar growth. PE’s and secondary electrons produced from the incident beam (SEI’s) were found to induce the vertical nanopillar growth component relative to secondary electrons induced from backscattered electrons (SEII’s) and BSE’s.

The Monte Carlo technique was applied to the fundamentals of the Electron Probe Microanalyzer (EPMA) and the Scanning Electron Microscope (SEM). A model based on the multiple scattering formula of Lewis was applied to simulate the scattering processes of the primary electrons in the specimen and was exemplified by comparison with the experimental results on the escape electrons, the backscattered electrons, and the secondary-electron yield, and good agreements were obtained. As simple approaches to further study, the lateral distributions of the backscattered electrons and the secondary electrons on the specimen surface were calculated from the Monte Carlo procedure which has brought about very useful knowledge on the resolving power of both the scanning image of the backscattered electrons in EPMA and SEM.

Within the framework of a project sponsored by the European Space Agency (ESA), we have developed a software tool to predict the occurrence of multipactor discharge in a simple radio frequency (RF) device modeled as parallel plates. The tool uses a micro-level explicit representation of the electrons (i.e., each electron in the system is modeled separately), and includes a detailed Monte Carlo model of the secondary electron emission process in the plates. Materials secondary emission yield (SEY) is described using either the usual parameter set (E/sub 1/, E/sub 2/, and /spl sigma//sub max/), or a more detailed model, where the contributions due to true secondary, backscattered or elastically reflected electrons are given their own sets of parameters, together with additional parameters for the angle dependence. The simulator has been validated using experimental data gathered at ESA and the Universidad Auto/spl acute/noma de Madrid, Madrid, Spain. The simulator helped in the selection of material coatings for the mitigation of Multipactor effect in RF transmission lines on-board satellite payloads.

The influence of work-function reduction and variation of the incident-beam angle on the secondary-electron yield and secondary-electron energy distribution from the (111) face of Ge have been studied. Reduction of the work function from 4.79 to 2.3 eV by deposition of Na increased the maximum yield from 1.2 to a value near 3.6, while the primary energy at which the maximum yield occurred increased from 700 to 2000 eV. The energy width of the slow secondary-electron energy distribution function decreased strongly both with increasing primary energy and decreasing work function. An investigation of the energy of secondary electrons involved in the yield variation with incident beam angle suggests that this variation in yield is a direct result of variation in the primary-electron backscattering coefficient. A bulk plasma loss of 16.7 eV is manifested in the total secondary-electron energy distribution function by a series of peaks lying at multiples of 16.7 eV below the elastic peak. In addition, a shoulder on the first 16.7 eV loss peak indicates the existence of an 11 eV surface plasma loss. An overlayer of Na does not seriously affect the bulk plasma loss spectrum, but shifts the 11-eV surface loss to about 13 eV and causes the appearance of a second 3.5-eV surface loss peak.

When an electron beam is used to initiate Auger electron spectra, the secondary electrons backscattered from the solid can also cause ionization and Auger emission. This leads to an enhancement of the Auger yield, allowed for by defining a backscattering factor. This paper presents a simple model which enables the backscattering factor and energy dependence of the ionization cross section to be measured. Results are reported of measurements made on silver and silicon specimens.

Abstract Measurements of the electron range R, and the backscattering coefficient η and the secondary electron yield δ at normal and tilted incidence for different elements show characteristic differences for electron energies in the range of 0.5 to 5 keV, compared with energies larger than 5 keV. The backscattering coefficient does not increase monotonically with increasing atomic number; for example, the secondary electron yield shows a lesser increase with increasing tilt angle. This can be confirmed in back‐scattered electron (BSE) and secondary electron (SE) micrographs of test specimens. The results are in rather good agreement with Monte Carlo simulations using elastic Mott cross‐sections and a continuous‐slowing‐down model with a Rao Sahib‐Wittry approach for the stopping power at low electron energies. Therefore, this method can be used to calculate quantities of BSE and SE emission, which need a larger experimental effort. Calculations of the angular distribution of BSEs show an increasing intensity with increasing atomic number at high takeoff angles than expected from a cosine law that describes the angular characteristics at high electron energies. When simulating the energy distribution of BSEs, the continuous‐slowing‐down model should be substituted by using an electron energy‐loss spectrum (EELS) that considers plasmon losses and inner‐shell ionizations individually (single‐scattering‐function model). The EELS can be approached via the theory for aluminium or from EELS spectra recorded in a transmission electron microscope for other elements. Measurements of electron range Rα E n of 1 to 10 keV electrons are obtained from transmission experiments with thin films of known mass thickness. In agreement with other authors the exponent n is lower than at higher electron energies.

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Experimental evidence is presented for the proportionality between secondary electron yield and the energy dissipated by electrons near the surface of a solid. Using measurements of the energy carried away by electrons transmitted and reflected from thin foils of aluminum and carbon, the energy dissipated in an incremental layer at the exit surface was obtained. Simultaneous measurements of the secondary electron yield showed a close proportionality between the number of secondaries produced and the energy dissipation density near the surface independent of the incident electron energy between 1 and 10 kev. By subtracting the contribution of the backscattered electrons to the yield at the front surface of a thick aluminum target, the yield of secondaries was found to be proportional to the rate of energy loss calculated from the Bohr-Bethe theory over the energy range investigated.

In addition to improvements in lateral resolution in scanning electron microscopy, recent developments of interest here concern extension of the incident beam energy, E(0), over two decades, from approximately 20 keV to approximately 0.1-0.5 keV and the possibility of changing the take-off emission, alpha, of detected secondary electrons. These two degrees of freedom for image acquisition permit a series of images of the same field of view of a specimen to be obtained, each image of the series differing from the others in some aspect. The origins of these differences are explored in detail and they are tentatively interpreted in terms of the change in the secondary electron emission yield delta vs. E(0), delta = f(E(0)), and also of the change in delta vs. alpha, partial differentialdelta/ partial differentialalpha. Various origins for the chemical contrast and topographic contrast have been identified. Illustrated by correlating a secondary electron image and a backscattered electron image, use of the scatter diagram technique facilitates image comparison. The difference between the lateral resolution and the size of the minimum detectable detail is outlined to avoid possible errors in nanometrology. Some aspects related to charging are also considered and possible causes of contrast reversal are suggested. Finally, the suggested strategy consists of the acquisition of various images of a given specimen by changing one parameter: primary beam energy and take-off angle for conductive specimens; working distance or beam intensity for high-resolution experiments; scanning frequency for insulating specimens.

A full spherical retarding-field energy analyser with three grids was made to measure the total secondary electron yield σ, the backscattering coefficient η, and the secondary electron spectrum N(E) as a function of angle of incidence and primary energy in UHV. The instrumental effects of the grid meshes in the measurement of N(E) were minimized by using the sample-bias-modulation technique. The values of σ and η for polycrystalline copper were found to be rather higher than previously published values. The N(E) curves are almost independent of the angle of incidence (θ) between θ=0° and 40°. The halfwidth of N(E) increases as the primary energy is reduced. These suggest that in metals the electron-electron interaction is dominant. Also, the dependence of N(E) on primary energy is believed to be caused by variations in both the excitation depth and the initial energy distribution of internal secondaries.

Spacecraft charging has commonly been attributed to electrons with several kilovolts of energy impinging upon spacecraft surfaces. Recent experimental evidence from the SCATHA satellite has shown that charging correlates well with electrons of energies greater than 30 keV. In this paper it is shown that the SCATHA observations are consistent with the model of charging in which a satellite is immersed in a Maxwellian plasma, particle collection is orbit limited, and dominant surface effects are the emission of secondary and backscattered electrons. The energy dependence of the secondary yield for multikilovolt incident electrons determines the charging threshold. In the past, inadequate representations of the secondary yield have led experimenters to question the validity of the charging model. The accuracy of the secondary electron yield formulation based on electron stopping power, such as the one in NASA Charging Analyzer Program (NASCAP), gives good agreement with the SCATHA results. A Maxwellian representation of the magnetospheric plasma is justified by choosing effective temperatures and densities that minimize the error in calculating charging current densities.

Spatial distributions of 811-nm emission from the 2${p}_{9}$ and 2${p}_{7}$ (Paschen notation) levels of Ar have been measured for electrical discharges in Ar at very high ratios of electric field to gas density (E/n) and low nd, where d is the electrode separation. Normalization of the lowest-E/n data to published electron excitation coefficients yields absolute excitation coefficients for 270E/n43 000 Td (1 Td=${10}^{\mathrm{\ensuremath{-}}21}$ V ${\mathrm{m}}^{2}$) and for 6.4\ifmmode\times\else\texttimes\fi{}${10}^{19}$nd3.5\ifmmode\times\else\texttimes\fi{}${10}^{21}$ ${\mathrm{m}}^{\mathrm{\ensuremath{-}}2}$. Direct and cascade excitation of 811-nm emisison by electrons calculated using a ``single-beam'' nonequilibrium electron model is an order of magnitude too small to account for the observed emission at the higher E/n.A model which includes Ar excitation and ionization by ${\mathrm{Ar}}^{+}$ and by fast Ar (10--200 eV) is developed to explain the observations. The fast atoms are produced by charge-transfer collisions of ${\mathrm{Ar}}^{+}$ with Ar. The estimated excitation by ions is negligible and has the wrong spatial dependence. Using the very limited published cross-section data for 811-nm excitation by fast Ar, the model yields spatial dependencies of emission which agree with experiment, but which are too small by factors ranging from 2.5 at 43 kTd to 10 at 6.3 kTd. This variation in the 811-nm emission with E/n is used to obtain energy-dependent excitation cross sections for fast atoms. The good fit of theory to the experimental spatial dependence near the cathode at the higher E/n shows the importance of ionization of Ar by fast Ar atoms. Excitation by backscattered secondary electrons is an important source of 811-nm emission near the anode. Electrical-breakdown and discharge-maintanance voltages from various experiments, including ours, are compared with the predictions of the model. These analyses show that ionization by ions and fast atoms dominates that by electrons from E/n&gt;15 kTd. The estimated ionization by electrons backscattered from the anode provides sufficient feedback to explain much of the electrical-breakdown data and our discharge-maintenance data. Other breakdown data require either a large yield of ionization by backscattered electrons or a very large ion-induced electron yield at the cathode.

A Monte Carlo tool is presented for the simulation of secondary electron (SE) emission in a scanning electron microscope (SEM). The tool is based on the Geant4 platform of CERN. The modularity of this platform makes it comparatively easy to add and test individual physical models. Our aim has been to develop a flexible and generally applicable tool, while at the same time including a good description of low-energy (<50 eV) interactions of electrons with matter. To this end we have combined Mott cross-sections with phonon-scattering based cross-sections for the elastic scattering of electrons, and we have adopted a dielectric function theory approach for inelastic scattering and generation of SEs. A detailed model of the electromagnetic fields from an actual SEM column has been included in the tool for ray tracing of secondary and backscattered electrons. Our models have been validated against experimental results through comparison of the simulation results with experimental yields, SE spectra and SEM images. It is demonstrated that the resulting simulation package is capable of quantitatively predicting experimental SEM images and is an important tool in building a deeper understanding of SEM imaging.

A new Monte Carlo calculation model is presented to simulate not only the primary electron behavior but also the secondary electron cascade in a specimen bombarded with an electron beam. Electrons having energy greater than 0.1 keV are treated as ‘‘fast electrons’’ and the previous single scattering Monte Carlo model is adopted. Electrons having energy smaller than 0.1 keV are treated as ‘‘slow electrons’’ and the electron cascade Monte Carlo model is used. The calculated results for the energy distribution of secondary electrons, and primary electron energy dependence of the total secondary yield and the backscattering yield are in good agreement with experimental results.

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A novel method to measure net secondary electron emission yield due to primary electron irradiation from a tokamak scrape-off layer plasma is described. High emission coefficients close to unity are obtained independent of the electron temperature. Enhanced elastic backscattering of low-energy primary electrons, already identified as an important phenomenon in many other fields of research, is likely to explain the high yields.

This article concerns the foundations of a new technology for surface modification of metallic materials based on the use of original sources of low-energy, high-current electron beams. The sources contain an electron gun with an explosive-emission cathode and a plasma anode, placed in a guide magnetic field. The acceleration gap and the transportation channel are prefilled with plasma with the use of spark plasma sources or a low-pressure reflected discharge. The electron-beam sources produce electron beams with the parameters as follows: electron energy 10–40 keV; pulse duration 0.5–5 μs; energy density 0.5–40 J/cm2, and beam cross-section area 10–50 cm2. They are simple and reliable in operation. Investigations performed with a variety of constructional and tool materials (steels, aluminum and titanium alloys, hard alloys) have shown that the most pronounced changes of the structure-phase state occur in the near-surface layers quenched from the liquid state, where the crystallization front velocity reaches its maximum. In these layers partial or complete dissolving of second phases and formation of oversaturated solid solutions and ordered nanosized structures may take place. This makes it possible to improve substantially the electrochemical and strength properties of the surface layers. It has been established that the deformation processes occurring in the near-surface layers have the result that the thickness of the modified layer with improved strength properties is significantly greater than that of the heat-affected zone. Some examples of the use of low-energy, high-current electron beams for improving the performance of materials and articles are given.

The surface chemistry of polystyrene, used as tissue culture ware, subjected to electron beam irradiation was studied. Core-level and valence-band (VB) X-ray photoelectron spectroscopy (XPS) showed that electron beam (EB) treatment resulted in surface oxidation plus sterilization of the polymer material. The extent of oxidation by EB is linear with the dose and, as such, is analogous to gamma-radiation-induced oxidation. The data indicate that EB-radiation treatment alone provides a polystyrene surface analogous to that obtained by corona discharge or plasma plus low gamma sterilization.

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In this work we present a study of the thermal processes taking place during surface modification of steels performed by a scanning electron beam. The model is based on solving the heat transfer equation by means of Green functions. The thermal field was calculated, together with the size of the zone of structural changes in tool steel samples. The comparison of the zones of thermal treatment as experimentally obtained and theoretically calculated and the corresponding structural changes show a very good agreement.

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The aim of the study was to assess the suitability of different Ti-6Al-4V surfaces produced by the electron beam melting (EBM) process as matrices for attachment, proliferation, and differentiation of human fetal osteoblasts (hFOB 1.19). Human osteoblasts were cultured in vitro on smooth and rough-textured Ti-6Al-4V alloy disks. By means of cell number and vitality and SEM micrographs cell attachment and proliferation were observed. The differentiation rate was examined by using quantitative real-time PCR analysis for the gene expression of alkaline phosphatase (ALP), type I collagen (Coll-I), bone sialoprotein (BSP) and osteocalcin (OC). After 3 days of incubation there was a significant higher vitality (p < 0.02) and proliferation (p < 0.02) of hFOB cells on smooth surfaces (R(a) = 0.077 microm) and compact surfaces with adherent partly molten titanium particles on the surface (R(a) </= 24.9 microm). On these samples cells spread over almost the whole surface. On porous surfaces with higher R(a) values, cell proliferation was reduced significantly. Quantitative real-time PCR analysis showed that the expression of osteogenic differentiation markers was not influenced by surface characteristics. Gene expression did not differ more than twofold for the different samples. Compact titanium samples with adherent partly molten titanium particles on the surface (R(a) </= 24.9 microm) fabricated by the EBM process turned out to be best suited for cell proliferation, while highly rough surfaces (R(a) >/= 56.9 microm) reduced proliferation of hFOB cells. Surface characteristics of titanium can easily be changed by EBM in order to further improve proliferation.

In this study we present a method to produce nanostructured surfaces containing bio-adhesive features inside a non bio-adhesive matrix. The strategy is based on the combination of low pressure plasma polymerization and electron beam lithography processes and allows the\nfabrication of the structured materials in just two steps without using any solvents. In a first step, a thin protein-and-cell-repelling coating (~10 nm) is obtained by plasma polymerization of Di-glyme. Then, in a second step, the bio-adhesive properties of the layer are tuned by\nmonitoring the concentration of ether bonds of the film by irradiating it locally by different irradiation doses with an electron beam. Time-of-flight secondary ion mass spectroscopy and atomic force microscopy analysis have been used to characterize the produced surfaces.\nExperiments with a model protein (bovine serum albumin) on the patterned surfaces show preferential adhesion to the irradiated regions, indicating the potential of this simple technique for the development of highly compacted sensitive bio-sensing devices.

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Electron-beam-induced grafting of hydrophilic polymers was applied to modify PVDF membranes for biomedical applications. Grafting was performed by immersing the membrane in an aqueous solution of different hydrophilic polymers followed by electron-beam irradiation. The two polymer types are able to cross-link by recombination of adjacent radicals formed via the irradiation. Although the untreated membrane was already quite hydrophilic, the modification resulted in even lower water contact angles at the membrane surface indicating improved water wettability. The presence of different functional groups originating from the hydrophilic polymers was detected on the membrane surface by electrokinetic measurements. SEM investigations as well as porosimetry experiments showed that the grafted hydrophilic polymer layer is very thin; therefore, the membrane pore structure is not negatively affected. Soxhlet extraction revealed the stability of the modification for selected polymers: surface contact angles were comparable after extraction, and total organic carbon investigation of the extraction water revealed no significant loss of organic material. Investigated mechanical properties confirmed an increased stability due to cross-linking of the polymers. Undesired hemolysis was not detected with hemocompatibility tests, and coagulation was decreased with selected hydrophilic polymers. Because of the absence of any toxic material during surface modification and the high stability of the product, this method is believed to be suitable for the modification of membranes for medical applications, e.g. for improving the hemo- or biocompatibility.

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A new approach to fabricate TiNi surfaces combining the advantages of both monolithic and porous materials for implants is used in this work. New materials were obtained by depositing a porous TiNi powder onto monolithic TiNi plates followed by sintering at 1200°C. Then, further modification of the material surface with a high-current-pulsed electron beam (HCPEB) was carried out. Three materials obtained (one after sintering and two after subsequent beam treatment by 20 and 30 pulses, respectively) were studied by XRD, SEM, EDX, EIS methods, profilometry and OCP measurements. Structural and compositional changes caused by HCPEB treatment were investigated. Surface properties of the samples during their storage in saline for 10 days were studied and a model experiment with cell growth (MCF-7) was carried out for the sample unmodified with electron beam to detect cell appearance on different surface locations.

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The microstructure and corrosion resistance of arc sprayed FeCrAl coatings treated by high current pulsed electron beam (HCPEB) have been investigated. It was found that after treated by HCPEB, the pores in the surface of as-sprayed coating is remarkably reduced, and a big amount of discrete bulged nodules, which mainly contains Fe-Cr column grains, have been produced on surface due to rapid solidification after HCPEB; Corrosion resistance results show that the corrosion potential has increased, and the corrosion currency and rate have decreased by one order of magnitude after treated by HCPEB with pulse duration of 50μs.

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In this study, the possibilities for modification and improvement of the surface structure and properties of titanium substrates by a formation of composite Ti/TiC layers are presented. The layers were fabricated by a two-step electron-beam surface modification technique. The first step consists of injection of C powder within the pure Ti substrates by electron-beam alloying technology. The second step is the refinement and homogenization of the microstructure by the electron-beam remelting procedure. During the remelting, the speed of the motion of the samples was varied, and two (most representative) velocities were chosen: 5 and 15 mm/s. Considering both speeds of the motion of the specimens, a composite structure in the form of fine TiC particles distributed within the base titanium matrix was formed. The remelting speed of 5 mm/s led to the formation of a much thicker composite layer, where the TiC particles were significantly more homogeneously distributed. The results obtained for the Vickers microhardness exhibit a significant increase in the value in the mentioned mechanical characteristic in comparison with the base Ti substrate. In the case of the lower speed of the motion of the specimen during the remelting procedure, the microhardness is 510 HV, or about 2.5 times higher than that of the titanium substrate. The application of a higher speed of the specimen motion leads to a decrease in the microhardness in comparison with the case of lower velocity. However, it is still much higher than that of the base Ti material. The mean microhardness of the sample obtained by the remelting speed of motion of 15 mm/s is 360 HV, or it is 1.8 times higher than that of the base material.

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In the present work, we present results on the influence of electron beam surface modification on the resistance to plastic deformation and plasticity of Inconel alloy 625. During the treatment procedure, the electron beam currents were 10 and 20 mA, corresponding to beam powers of 600 W and 1200 W. The structures of the modified specimens were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The nanohardness and Young’s modulus were studied through nanoindentation experiments. The plasticity of the treated materials as well as of the untreated ones was studied through an evaluation of H3/E2, which points to resistance to plastic deformation. The results obtained show that the electron beam surface modification procedure leads to a reorientation of microvolumes and the formation of a preferred crystallographic orientation. The surface treatment of the samples using an electron beam with a power of 600 W did not lead to major changes in the structures of the samples. However, the use of a beam with a power of 1200 W led to the formation of a clearly separated modified zone with a thickness in the range of 13 to 15 μm. The Young’s modulus increased from about 100 to 153 GPa in the case of electron beam surface modification using the lower-power electron beam. The application of the higher-power electron beam did not lead to a significant change in the modulus of elasticity as compared to the untreated specimen. Also, it was found that the treatment procedure pointed to a decrease in nanohardness when the maximum power of the electron beam was applied. The resistance to plastic deformation, i.e., the H3/E2 ratio, showed that the ratio decreased significantly in both cases of electron beam surface modification, pointing to an improvement in the plasticity of the surface of the Inconel alloy 625.

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This paper is focused on the basic properties of ceramic composite materials used as thermal barrier coatings in the aerospace industry like SiC, ZrC, ZrB₂ etc., and summarizes some principal properties for thermal barrier coatings. Although the aerospace industry is mainly based on metallic materials, a more attractive approach is represented by ceramic materials that are often more resistant to corrosion, oxidation and wear having at the same time suitable thermal properties. It is known that the space environment presents extreme conditions that challenge aerospace scientists, but simultaneously, presents opportunities to produce materials that behave almost ideally in this environment. Used even today, metal-matrix composites (MMCs) have been developed since the beginning of the space era due to their high specific stiffness and low thermal expansion coefficient [1]. These types of composites possess properties such as high-temperature resistance and high strength, and those potential benefits led to the use of MMCs for supreme space system requirements in the late 1980s. Electron beam physical vapor deposition (EB-PVD) is the technology that helps to obtain the composite materials that ultimately have optimal properties for the space environment, and ceramics that broadly meet the requirements for the space industry can be silicon carbide that has been developed as a standard material very quickly, possessing many advantages. One of the most promising ceramics for ultrahigh temperature applications could be zirconium carbide (ZrC) because of its remarkable properties and the competence to form unwilling oxide scales at high temperatures, but at the same time it is known that no material can have all the ideal properties [²]. Another promising material in coating for components used for ultra-high temperature applications as thermal protection systems is zirconium diboride (ZrB₂), due to its high melting point, high thermal conductivities, and relatively low density [3]. Some composite ceramic materials like carbon-carbon fiber reinforced SiC, SiC-SiC, ZrC-SiC, ZrB₂-SiC, etc., possessing low thermal conductivities have been used as thermal barrier coating (TBC) materials to increase turbine inlet temperatures since the 1960s. With increasing engine efficiency, they can reduce metal surface temperatures and prolong the lifetime of the hot sections of aero-engines and land-based turbines.

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The microstructures of ZrO 2 –20 wt% Y 2 O 3 thermal barrier coatings formed by electron beam‐physical vapor deposition on a Nibase superalloy have been studied by transmission electron microscopy. The coating systems consist of several layers, including a superalloy substrate, a bond coat, an Al 2 O 3 scale, and the PVD coating. The overall ceramic thermal barrier coatings were characterized, with special emphasis being given to the α‐Al 2 O 3 scale which forms between the bond coat and the ZrO 2− Y 2 O 3 coating. The oxide scale exhibited various morphologies in different coating systems; the majority of the porosity formed in this region for all coatings.

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As part of a study on the deposition of superconducting films of YBa2Cu3O7−δ, a three-dimensional electron beam physical vapor deposition process of yttrium in a vacuum chamber is investigated both computationally and experimentally. The numerical analysis employs the direct simulation Monte Carlo (DSMC) method. The experimental studies consist of atomic absorption spectra taken in the evaporated yttrium plume and deposited film thickness profiles. Some important modeling issues such as atomic collision cross sections for metal vapors and hyperfine electronic structure of the atomic absorption spectra are addressed. Film deposition thicknesses on the substrate and atomic absorption spectra given by the DSMC method and experiment are in excellent agreement. Collisions between the atoms are found to have a significant effect on the film growth rate and area of uniform deposition as the evaporation rate of yttrium increases.

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Abstract The paper addresses the effect of processing parameters on microstructure and lifetime of electron beam physical vapor deposition, partially yttria-stabilized zirconia (EB-PVD PYSZ) coatings deposited onto NiCoCrAlY-coated Ni-base superalloys. In particular, the formation of a thermally grown oxide layer, an equi-axed zone, and various columnar arrangements of the highly textured PYSZ layers are discussed with respect to processing conditions. Three different microstructures were cyclically tested at 1100°C. The intermediate columnar structure was superior with respect to cyclic life times to a fine and to a coarse columnar structure which was mainly attributed to differences in the elastic properties. The effect of PYSZ microstructure on hot corrosion behavior of the thermal barrier coating (TBC) system at 950°C is briefly discussed.

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We have grown thin film libraries of the Mg-Al system using a high-throughput synthesis methodology that combines the sequential deposition of pure elements (Mg and Al) by an electron-beam (e-beam) evaporation technique and the use of a special set of moving shadow masks. This novel mask has been designed to simultaneously prepare four identical arrays of different compositions that will permit the characterization of the same library after several treatments. Wavelength dispersive spectroscopy (WDS) and micro-X-ray diffraction have been used as high-throughput screening techniques for the determination of the composition and structure of every member of the library in the as-deposited state and after hydrogenation at 1 atm of H2 during 24 h at three different temperatures: 60, 80, and 110 degrees C. We have analyzed the influence of the Mg-Al ratio on the hydrogenation of magnesium, as well as on the appearance of complex hydride phases. We have also found that aluminum can act as a catalyzer for the hydrogenation reaction of magnesium.

Abstract Thermal barrier coatings (TBCs) are widely used in aerospace and aviation industries for materials required to withstand severe environments such as oxidation, hot-corrosion failure and CMAS (calcia–magnesia–alumina–silica) attack or vermiculite corrosion. This is particularly apparent in vermiculite, which can penetrate sand, volcanic ash and is the most destructive damage mechanism in the TBC system. Impurities from the desert environment such as calcia–magnesia–alumina–silica (CMAS) cause degradation of TBCs. In this research, CoNiCrAlY metallic bond coatings were deposited on Inconel 718 nickel based superalloy substrates with a thickness of around 100 μm using a Cold Gas Dynamic Spray (CGDS) technique. Production of TBCs were carried out with deposition of YSZ ceramic top coating material using Electron Beam Physical Vapor Deposition (EB-PVD), with a thickness of around 200 μm. The effect of CMAS with spreading naturally-occurring mineral (vermiculite) on TBC samples were investigated using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) analysis and X-ray diffraction (XRD). The microstructure evolution of YSZ and failure mechanism of TBC were evaluated.

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SUMMARY Frozen hydrated specimens of various latex spheres were used as well‐defined systems for the study of electron beam radiation damage to organic inclusions in vitreous, cubic and hexagonal ice. We found that radiolysis of organic material is modified by the presence of ice and that radiolysis in vitreous ice is different from that in crystalline ice. The pattern of damage depends also on the nature of the irradiated polymer, e.g., damage to poly(vinylchloride) is quite different from damage to polyacrylates, although in both polymers the main radiolytic process is chain scission. Some polymers such as polyacrylates were found to be much more stable in vitreous ice than in crystalline ice. The experimental results indicate that free radicals formed at the ice–organic matter interface play an important role in the radiolysis process which affects both the ice and embedded organic particles. Ice may play also a physical role in the process by limiting the diffusion of free radicals away from the interface. Although net mass loss is not much affected by ice, massive structural changes including repolymerization take place in its presence.

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Abstract A method is proposed to enhance contrast between microdomains of two‐component polymer systems using electron beam radiation damage. The technique is based on the different damage patterns to crosslinking‐type and scission‐type polymer particles embedded in ice. Whereas the former lose little mass and cavities form in the ice around them, the latter lose much more mass, become cellular in appearance, and occasionally swell. Applications of the technique are demonstrated by revealing the microstructure of two‐stage poly(butylacrylate)/polystyrene latices, their size distributions, and the presence of single‐component particles in the two‐component system.

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Of interest to the paper industry is how cellulose fibers shrink, swell, and break during wetting and drying of paper. The Environmental Scanning Electron Microscope (ESEM) is a new tool for examining wetting and drying. However, surfaces of cellulose fibers appeared smoothed in an unexpected way while examined in the ESEM (made by Electroscan, Wilmington, MA, USA) during wetting and drying. Closer examination revealed that the smoothed appearance was due to electron beam radiation damage that occurs while the fibers are wet. Shown below is evidence that damage to wet cellulose fibers is due to attack from free radicals that are products of radiolysis of ice.

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Abstract The superlattice and domain structures exhibited by the ordered compound V6C5 are disrupted by electron microscope beam bombardment. The effect is attributed to the disordering of the carbon sublattice that results from displacement of the carbon atoms by the impinging electrons. Studies have been made of the disordering rate under electron bombardment at energies from 33 kev to 100 kev, using a Faraday cup to measure superlattice spot intensities. The results are compared with the predictions of a simple theory for the damage process, from which it is concluded that the displacement energy of carbon atoms in V6C5 has the surprisingly low value of 5·4 ev.

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Laser-generated electron beams are distinguished from conventional accelerated particles by ultrashort beam pulses in the femtoseconds to picoseconds duration range, and their application may elucidate primary radiobiological effects. The aim of the present study was to determine the dose-rate effect of laser-generated ultrashort pulses of 4 MeV electron beam radiation on DNA damage and repair in human cells. The dose rate was increased via changing the pulse repetition frequency, without increasing the electron energy. The human chronic myeloid leukemia K-562 cell line was used to estimate the DNA damage and repair after irradiation, via the comet assay. A distribution analysis of the DNA damage was performed. The same mean level of initial DNA damages was observed at low (3.6 Gy/min) and high (36 Gy/min) dose-rate irradiation. In the case of low-dose-rate irradiation, the detected DNA damages were completely repairable, whereas the high-dose-rate irradiation demonstrated a lower level of reparability. The distribution analysis of initial DNA damages after high-dose-rate irradiation revealed a shift towards higher amounts of damage and a broadening in distribution. Thus, increasing the dose rate via changing the pulse frequency of ultrafast electrons leads to an increase in the complexity of DNA damages, with a consequent decrease in their reparability. Since the application of an ultrashort pulsed electron beam permits us to describe the primary radiobiological effects, it can be assumed that the observed dose-rate effect on DNA damage/repair is mainly caused by primary lesions appearing at the moment of irradiation.

Radiation damage induced by high-energy (200 keV) electron irradiation in zircon has been studied thoroughly using imaging, diffraction, and electron energy-loss spectroscopy techniques in transmission electron microscopy. Both structural and compositional changes during the damage were measured using the above techniques in real time. It was found that the damage was mainly caused by the preferential sputtering of O. The loss of O occurred initially within small sporadic regions with dimension of several nanometers, resulting in the direct transformation of zircon into ZrxSiy. These isolated patches gradually connect each other and eventually cover the whole area of the electron beam. These differ from the previous observations either in the self-irradiated natural and synthetic zircon or in ion-beam irradiated thin zircon specimen.

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A new method to estimate the trajectories of particle motion and the amount of cumulative beam damage in electron cryo-microscopy (cryo-EM) single-particle analysis is presented. The motion within the sample is modelled through the use of Gaussian process regression. This allows a prior likelihood that favours spatially and temporally smooth motion to be associated with each hypothetical set of particle trajectories without imposing hard constraints. This formulation enables the <i>a posteriori</i> likelihood of a set of particle trajectories to be expressed as a product of that prior likelihood and an observation likelihood given by the data, and this <i>a posteriori</i> likelihood to then be maximized. Since the smoothness prior requires three parameters that describe the statistics of the observed motion, an efficient stochastic method to estimate these parameters is also proposed. Finally, a practical algorithm is proposed that estimates the average amount of cumulative radiation damage as a function of radiation dose and spatial frequency, and then fits relative <i>B</i> factors to that damage in a robust way. The method is evaluated on three publicly available data sets, and its usefulness is illustrated by comparison with state-of-the-art methods and previously published results. The new method has been implemented as Bayesian polishing in <i>RELION</i>-3, where it replaces the existing particle-polishing method, as it outperforms the latter in all tests conducted.

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The soft-electron beam (low-energy electrons) and gamma-radiation sensitivities of phosphine-resistant (PHR) and -susceptible (PHS) strains of adults lesser grain borer Rhyzopertha dominica (F.) were studied, with particular reference to DNA damage assessed using single-cell electrophoresis (comet assay). Results showed that mortality in adult R. dominica varied significantly between both PHR and PHS strains. Adults of the PHR strain were found to be more tolerant toward soft-electron and gamma radiation than adults of the PHS strain. Studies on the longevity of strains showed that mean survival time and dose rate were highly correlated with both strains and treatments. Results also showed that adults of the PHR strain lived longer than adults of PHS strain for both treatments. Radiation sensitivity indices, however, decreased as radiation dose increased in both strains. Analysis of DNA damage, after 40- and 160-Gy gamma radiation, was carried out using cells obtained from both strains. Gamma-irradiated adults of both strains showed typical DNA fragmentation, compared with cells from nonirradiated adults, which showed more intact DNA. Investigations using the comet assay showed that tail length, moment, olive-tail moment, percentage of tail DNA, and percentage of DNA damage were all greater in the PHS strain compared with the PHR strain and the control insects. Results also showed that DNA damage remained at a constant level for up to 24 h after irradiation. The results have been discussed in relation to the observed strain differences in radiation sensitivity and resistance to phosphine.

We present an accurate measurement and a quantitative analysis of electron-beam-induced displacements of carbon atoms in single-layer graphene. We directly measure the atomic displacement ("knock-on") cross section by counting the lost atoms as a function of the electron-beam energy and applied dose. Further, we separate knock-on damage (originating from the collision of the beam electrons with the nucleus of the target atom) from other radiation damage mechanisms (e.g., ionization damage or chemical etching) by the comparison of ordinary (12C) and heavy (13C) graphene. Our analysis shows that a static lattice approximation is not sufficient to describe knock-on damage in this material, while a very good agreement between calculated and experimental cross sections is obtained if lattice vibrations are taken into account.

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The authors report micro-Raman investigation of changes in the single and bilayer graphene crystal lattice induced by the low and medium energy electron-beam irradiation (5–20 keV). It was found that the radiation exposures result in the appearance of the strong disorder D band around 1345 cm−1, indicating damage to the lattice. The D and G peak evolution with increasing radiation dose follows the amorphization trajectory, which suggests graphene’s transformation to the nanocrystalline and then to amorphous form. The results have important implications for graphene characterization and device fabrication, which rely on the electron microscopy and focused ion beam processing.

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Many experimental and theoretical advances have recently allowed the study of direct and indirect effects of low-energy electrons (LEEs) on DNA damage. In an effort to explain how LEEs damage the human genome, researchers have focused efforts on LEE interactions with bacterial plasmids, DNA bases, sugar analogs, phosphate groups, and longer DNA moieties. Here, we summarize the current understanding of the fundamental mechanisms involved in LEE-induced damage of DNA and complex biomolecule films. Results obtained by several laboratories on films prepared and analyzed by different methods and irradiated with different electron-beam current densities and fluencies are presented. Despite varied conditions (e.g., film thicknesses and morphologies, intrinsic water content, substrate interactions, and extrinsic atmospheric compositions), comparisons show a striking resemblance in the types of damage produced and their yield functions. The potential of controlling this damage using molecular and nanoparticle targets with high LEE yields in targeted radiation-based cancer therapies is also discussed.

A minimally perturbing plastic scintillation detector has been developed for the dosimetry of high-energy beams in radiotherapy. The detector system consists of two identical parallel sets of radiation-resistant optical fibre bundles, each connected to independent photomultiplier tubes (PMTs). One fibre bundle is connected to a miniature water equivalent plastic scintillator and so scintillation as well as Cerenkov light generated in the fibres is detected at its PMT. The other 'background' bundle is not connected to the scintillator and so only Cerenkov light is detected by its PMT. The background signal is subtracted to yield only the signal from the scintillator. The water-equivalence of plastic scintillation detectors is studied for photon and electron beams in the radiotherapy range. Application of Burlin cavity theory shows that the energy dependence of such detectors is expected to be better than the commonly used systems (ionization chambers, LiF thermoluminescent dosimeters, film and Si diodes). It is also shown that they are not affected by temperature variations and exhibit much less radiation damage than either photon or electron diode detectors.

In situ structural evolution from Cu(OH)2 nanobelts to copper nanowires has been studied by transmission electron microscopy in a vacuum of 3 × 10-8 Torr. The decomposition follows the sequence of Cu(OH)2 → CuO → Cu2O → Cu. The decomposition from Cu(OH)2 to CuO is attributed to electron beam radiation damage. The reduction from CuO to Cu2O is attributed to heat-induced decomposition between 50 and 200 °C. For the Cu(OH)2 nanobelts synthesized using the copper grid with and without a carbon coating, the decomposition from Cu2O to Cu takes place between 200 and 300 °C and 300 and 600 °C, and the final Cu takes the forms of polycrystalline nanowires sheathed with graphitic carbon and nanoparticles, respectively. Therefore, because of the nanostructured nature of the nanowires and large surface area, introducing carbon into the sample synthesis can reduce the decomposition temperature by almost half. This study demonstrates a possible approach for creating metallic copper nanowires by heat-induced decomposition under vacuum at 300 °C or even lower.

Electron microscopy is an essential tool for the evaluation of microstructure and properties of the catalyst layer (CL) of proton exchange membrane fuel cells (PEMFCs). However, electron microscopy has one unavoidable drawback, which is radiation damage. Samples suffer temporary or permanent change of the surface or bulk structure under radiation damage, which can cause ambiguity in the characterization of the sample. To better understand the mechanism of radiation damage of CL samples and to be able to separate the morphological features intrinsic to the material from the consequences of electron radiation damage, a series of experiments based on high-angle annular dark-field-scanning transmission scanning microscope (HAADF-STEM), energy filtering transmission scanning microscope (EFTEM), and electron energy loss spectrum (EELS) are conducted. It is observed that for thin samples (0.3-1 times λ), increasing the incident beam energy can mitigate the radiation damage. Platinum nanoparticles in the CL sample facilitate the radiation damage. The radiation damage of the catalyst sample starts from the interface of Pt/C or defective thin edge and primarily occurs in the form of mass loss accompanied by atomic displacement and edge curl. These results provide important insights on the mechanism of CL radiation damage. Possible strategies of mitigating the radiation damage are provided.

Radiation damage due to electron beam annealing has been investigated in MOS devices underlying an electron beam annealed Silicon-on-Insulator structure. A high degree of residual damage (surface state and positive charge) is found to exist in MOS devices. The damage can be easily annealed out by low temperature (500–550°C) furnace annealing, when underlying MOS devices exist outside the electron beam range. However, high temperature furnace annealing at about 1000°C is necessary to eliminate the damage, when the electron beam penetrate through the gate oxides in MOS devices. Use of a low energy electron beam is recommended, based on these results, for the Silicon-on-Insulator formation for three-dimensional ICs.