Application Of High-resolution Electron Microscopy Research Articles

Chemical and topological disordering in M23C6 due to irradiation: An atomic-scale observation

To clarify the stability of M23C6 precipitate in steels under irradiation, the chemical and topological disordering behaviors in M23C6 subjected to ion irradiation at elevated temperatures were investigated with the combined application of high-resolution electron microscopy (HREM) and electron energy-loss spectroscopy (EELS). Results show that the duplex structured M23C6 which is the core-crystalline and shell-amorphous was observed in the specimen irradiated at 623 K, nevertheless, no amorphous phase was observed in the specimen irradiated at 673 K. HREM observation confirmed the occurrence of the chemical disordering in irradiated M23C6, and the disordering of W atoms in the M23C6 unit cell was clarified by the peak intensity profile of the atomic column from the HREM image. EELS analyses indicate that no obvious chemical shift was observed by the core-loss spectrum, however, the change in the electron mean free path (λ) due to irradiation was confirmed by the low-loss spectrum, which is related to the formation of both irradiation defects and amorphous phase. It is proposed that the decreased material density upon irradiation is ascribed to the formation of W-vacancy-dominated defect clusters. An obvious change in interatomic distance was not observed in the irradiated M23C6 based on the radical distribution function analysis by extended energy-loss fine structure spectrum. However, the peak intensity decreased by irradiation, confirming the occurrence of chemical and topological disordering, regardless of the carbide being crystalline or amorphous.

Machine-learning approach for quantified resolvability enhancement of low-dose STEM data

High-resolution electron microscopy is achievable only when a high electron dose is employed, a practice that may cause damage to the specimen and, in general, affects the observation. This drawback sets some limitations on the range of applications of high-resolution electron microscopy. Our work proposes a strategy, based on machine learning, which enables a significant improvement in the quality of Scanning Transmission Electron Microscope images generated at low electron dose, strongly affected by Poisson noise. In particular, we develop an autoencoder, trained on a large database of images, which is thoroughly tested on both synthetic and actual microscopy data. The algorithm is demonstrated to drastically reduce the noise level and approach ground-truth precision over a broad range of electron beam intensities. Importantly, it does not require human data pre-processing or the explicit knowledge of the dose level employed and can run at a speed compatible with live data acquisition. Furthermore, a quantitative unbiased benchmarking protocol is proposed to compare different denoising workflows.

Silica-protein composite layers of the giant basal spicules from Monorhaphis: Basis for their mechanical stability

The hexactinellid sponge Monorhaphis chuni possesses with its giant basal spicules the largest biosilica structure on Earth. The approximately 8.5-mm-thick spicules are composed of up to 800 lamellae. By application of high-resolution electron microscopy (HR-SEM), it is shown that within the siliceous lamellae a proteinaceous scaffold exists which is composed of one protein of a size of 27 kDa. Analyses with Fourier transform infrared (FT-IR) emission and energy-dispersive X-ray (EDX) spectroscopy support this localization of the protein. No evidence for the presence of protein on the surfaces of the lamellae could be obtained. Heating the giant basal spicule to 600 °C destroys and eliminates the protein scaffold. At a temperature of 1600 °C, the lamellae fuse to solid glass via a nonstructured, foamed-up molten transition state. Elevation of the temperature to 2700 °C results in the formation of silica drops (Euplectella aspergillum). After the elimination of the protein scaffold from the silica lamellae, the spicules lose their mechanical characteristics of the original hydrated silica/protein composite to be flexible and simultaneously stiff and tough. The data presented here are expected to contribute to technologies suited to fabricate novel organic/inorganic (silica) hybrid fibers.

Application of high-resolution electron microscopy for visualization and quantitative analysis of strain fields in heterostructures

The general principles, possibilities, and limitations of the classical geometric phase method have been considered. A new generalizing approach, implying analysis of all available spatial frequencies of a high-resolution electron microscopy image, is developed to expand the possibilities of the geometric phase method. Test models of strained Si-GeSi-Si heterostructures are developed and the effect of scattering by phonons and the surface amorphous layer on visualization of lattice distortions is studied within these models. A simple method is proposed for measuring elastic strains in multicomponent heterostructures with pseudomorphic layers.

Modern microscopy methods for the structural study of porous materials.

This article describes a number of important recent microscopy tools and their application in particular to the study of porous inorganic materials. The authors believe that these new techniques are on the threshold of delivering enormous new power in the chemist's arsenal for understanding new and complex behaviour in multi-component, hierarchical or composite materials. In particular we consider the contribution of electron crystallography, three-dimensional electron tomography, ultra-high resolution scanning electron microscopy as well as the combined application of high-resolution electron microscopy and atomic force microscopy to the study of surfaces and crystal growth. Much of this work has taken on a particular significance owing to the ground breaking work of scientists at Mobil and in Japan 10 years ago in the successful synthesis of materials with porosity on many length scales achieved through the cooperative self-assembly between inorganic and organic phases. This resulted in a series of materials known as M41S of which MCM-41 and MCM-48 were two of the first and most important structures to be synthesised. This has led to a wealth of new porous structures with order over many length scales and has presented new problems in characterisation. Microscopy methods properly executed are particularly important in the study of this new class of material.

Application of High-Resolution Electron Microscopy to the Study of Magnetic Thin Films and Multilayers

ABSTRACTThe performance of a wide range of modern magnetic thin-film materials for information storage is found to depend dramatically on grain nucleation and coherence at interfaces. Three such systems, Fe/Pt Multilayers, CO/Pt Multilayers, and CoCrTa/Cr bilayers are considered here. High-resolution electron Microscopy (HREM) shows that ordered CoPt and FePt L1o structures can be formed and oriented, using coherence with the substrate, with their magnetically easy c-axes perpendicular to the film plane. This orientation results in the perpendicular magnetization required for Magneto-optic recording Media. Different sputtering gases used in producing CO/Pt Multilayers result in varying degrees of interfacial intermixing, which is shown to strongly affect the perpendicular magnetic anisotropy energy. The required high in-plane coercivity of longitudinal recording media is also correlated with the observed interface coherence and the resulting oriented growth of CoCrTa with the magnetically hard <110> axis perpendicular to the film plane. Many features of the microstructure can be observed directly at the atomic level by HREM, and so the usefulness of this technique is emphasized in this paper.

Surface studies in UHV: Applications of High-resolution electron microscopy

The examination of surfaces requires not only that they be free of adsorbed layers but the environment of the sample must also be maintained at high vacuum so that the surfaces remain clean. The possibility of resolving surface structures with atomic resolution has provided the motivation for optimizing intermediate and high voltage electron microscopes for this particular application. Electron microscopy offers a variety of techniques which have the capability of achieving atomic level detail of surfaces including plan-view imaging, REM and profile imaging. Operation at higher voltages permits reasonable pole piece dimensions thereby providing space for in situ studies yet still compatible with high resolution. Moreover, video systems can be attached which permit observation and recording of dynamic phenomena without compromising microscope performance.

Characterization of thin films, interfaces and surfaces by high-resolution electron microscopy

Recent applications of high-resolution electron microscopy in our laboratory to the characterization of thin films, interfaces and surfaces are described. The information typically available using this technique about thin films is illustrated by studies of multiple quantum wells, metallic superlattices, magnetic films and X-ray optical elements. The problems associated with imaging interfaces are discussed by reference to silicon/silicide interfaces and grain boundaries in metals. Finally, recent observations of semiconductor surface reconstructions and beam-induced reactions at oxide surfaces are briefly summarized.

Applications of high-resolution Electron Microscopy to semiconductor interfaces

Practical applications of high-resolution electron microscopy (HREM) to semiconductor interfaces have been conducted in various areas. Among these are the use of the HREM as a diagnostic technique for interfacial quality, understanding of interfacial interactions, and analysis of misfit dislocations in heterostructures. These studies indicate that the HREM is a useful technique to provide in-depth understanding of interfaces for the process and defect controls.The quality of an interface often plays an important role in the film quality or the performance of a semiconductor device. Figure 1a shows one example illustrating the generation of threading dislocations from particles located at the lattice-mismatched In0.15Ga0.85As/GaAs interface. The HREM image shown in Fig. 1b indicates a particle to be located at a misfit dislocation. This observation suggests that a particle at the heterointerface can promote the nucleation of a dislocation and/or the formation of the misfit dislocation.

High resolution electron microscopy characterization of interfaces in group III–V semiconductors

The technique and application of high resolution electron microscopy (HREM) to the study of group III–V semiconductor multilayers is described. The theory of HREM contrast is briefly reviewed, emphasizing the need to bear in mind resolution and information limits to which the images may be interpreted. The role of image simulations in this interpretation is stressed. Examples are given of the application of HREM to the study of the morphology and chemical abruptness of GaInAs–AlInAs interfaces and the defect structure at GaSb–GaAs strained interfaces.

Production and characteristics of ultrafiltration membranes with uniform pores from two-dimensional arrays of proteins

Surface or S-layers, which represent the outermost cell wall component of many eubacteria archaebacteria, were used for the production of isoporous ultrafiltration membranes. S-layers are paracrystalline arrays of protein or glycoprotein subunits that are linked by non-covalent interactions and completely cover the cell surface. The porosity of S-layers ranges from 20 to 50%. So far, channels of 2–6 nm diameter have been identified in S-layer lattices, either by application of high-resolution electron microscopy or by permeability studies. For the production of S-layer ultrafiltration membranes (SUM), the isoporous S-layer material isolated from highly thermophilic eubacteria was deposited on commercially available microfiltration membranes by a pressure-dependent deposition procedure. The active ultrafiltration layer, which was responsible for the rejection characteristics, consisted of coherent S-layer material, whereas the only function of the microfiltration membrane was to provide the mechanical support. In order to improve the stability of the ultrafiltration membranes, the S-layer protein was crosslinked with glutaraldehyde. As expected for an isoporous structure, S-layer ultrafiltration membranes displayed very steep rejection curves, when proteins of progressively increasing molecular weight were taken as test molecules. SUM exhibited a remarkable resistance towards acid, alkali and organic solvents. Depending on the chemical modification procedures performed on the S-layer protein, SUM had different surface net charges. The amount of macromolecules adsorbed to SUM surfaces was strongly influenced by both the solution properties and the membrane surface characteristics.

High-resolution electron microscopic studies of some Y- and A-zeolites

Application of high-resolution electron microscopy to structural studies of Y- and A-type zeolites is described. The structure images of channels and some crystallographic imperfections in the samples, such as incoherent twinning boundaries, dislocations, metastable elastic distortion, and coin-like domains, were observed. The radiation damage processes were also recorded in situ.

High-resolution studies of order and disorder in alloys

A survey is given of the application of high-resolution electron microscopy (HREM) to the study of order-disorder phenomena in a number of alloy systems: Au-Mn, Pt-Ti and Al-Ti. It is shown that under the appropriate imaging conditions and for a suitable thickness the minority atom columns can be imaged as prominent bright dots in all of the alloys mentioned above. High-resolution images thus allow one to study long-period anti-phase boundary structures in detail. The application of HREM to the study of short-range order in alloys is illustrated and some of its limitations discussed. A number of image contrast phenomena occuring in ordered alloys is described briefly.

HREM of compound semiconductors

The application of high-resolution electron microscopy to the study of different structures and defects in compound semiconductors is illustrated. The study of epilayers and interfacial dislocations is illustrated for GaAs/Al xGa 1- x As and GaSb/InAs superlattices. A new method for preparing well defined grain boundaries in GaAs is reported together with new observations of defects produced by ion implantation and annealing of GaAs/Al xGa 1- x As superlattices is discussed. A brief comparison is made between simulated images for a conventional 125 kV machine and a 400 kV machine with 0.18 nm point-to-point resolution.

Placing the applications of high-resolution electron microscopy to chemical problems into wider perspective

After reviewing some of the structural problems that high-resolution electron microscopy (HREM), either alone or in concert with allied, electron-based techniques, is unlikely to be able to clarify, a summary of problems for which the technique is of unique value is presented with the aid of illustrative examples. These are drawn from the study of zeolites and other aluminosilicates, Fisher-Tropsch and other catalysts, carbon and graphite including various intercalates of the latter, defective diamonds, shape-selective sorbents and quasi-crystalline solids. Additional techniques with which HREM may be readily combined (electron-energy-loss and X-ray emission spectroscopy as well as Compton scattering of electrons) are also briefly discussed.

The application of high-resolution electron microscopy to problems in solid state chemistry: The exploits of a peeping TEM

High-resolution electron microscopy and using this technique to elucidate the structure of real crystalline solids and the mechanism of solid state reactions.

The application of electron microscopy and electron diffraction to solid state chemistry problems

The application of high-resolution electron microscopy and selected area electron diffraction to problems of solid state chemistry is illustrated by means of a number of case studies. Various stackings in mixed-layer compounds such as barium ferrites and lanthanum-thorium mixed oxides and in polytypic substances such as YSeF can be revealed by means of lattice and structure images. Detailed information on the domain structure of alloys such as Au 5Mn 2 and Au 4Mn can be obtained by the use of structure images which reveal columns of single atoms (in Au 4Mn) and (or) pairs of atoms (in Au 5Mn 2). Along inclined twin interfaces high-resolution electron microscopy allows the coincidence lattice on an atomic level to be revealed.