bluuebunny/crossref_metadata_2025 huggingface dataset:
Possible artifacts due to sampling procedures in biological electron microscopy
Authors: Jakstys B. P.
Published: June 2020

Artifacts in biological electron microscopy may originate from numerous sources, not the least of which may be the result of inadequate or inappropriate specimen sampling. Concern for adequate sampling most often arises when quantitative analyses such as morphometry or stereology, which require statistical evaluations, are to be performed. To obtain the most accurate and representative results, appropriate sampling should be done even if statistical analyses are not to be used. This applies to scanning and transmission electron microscopy.

Depending on the specimen source, its nature, complexity of the study and preparation, random sampling should be carried out at various levels. In some instances, however, random sampling at the recommended levels is not feasible, as in the case of clinical specimens. In this situation the sampling should be done as is practicable. Ideally sampling should be performed on entire populations, as well as at the following levels: organ, tissue, block, section, grid, grid square, and different magnifications.
Fixation artifacts in transmission electron microscopy
Authors: Bowers Blair
Published: June 2020

Cell and tissue preparations for transmission EM contain artifacts introduced at each step of the preparative method. Fixation, as a first and crucial step, is subject to both gross and subtle artifact. For familiar tissues, gross artifacts are easily recognized. Artifacts in unfamiliar cells and subtle distortions or alterations of structure or localizations of molecules of interest are more difficult to assess.

Three general approaches are useful for identification of fixation artifacts. Especially in the case of single cells, it is possible to make direct comparison of living and fixed specimens. Advanced light microscopic methods allow very high-resolution imaging of cells and comparison of structure before and after fixation. Light microscopic observation during fixation has documented examples both of creation of structure and disappearance of structure. A more widely applicable approach is the comparison of structure in the same tissue after fixation by different procedures.
Artifacts from dehydration and drying in biological specimen preparation for scanning electron microscopy
Authors: Crang R. F. E.
Published: June 2020

Experienced electron microscopists recognize that common problems can exist if care is not taken with biological sample preparation, but such situations may not often be recognized by students or technicians with limited experience. The problems encountered in biological SEM specimen preparation may involve all steps in obtaining the tissue, fixing and/or washing it, dehydration, drying, mounting or coating. Specifically, attention in this presentation is directed at problems and techniques in dehydration and drying. Although some of the remedies require specialized equipment, most suggested ways of coping with problems are based on procedures which involve only commonly available supplies and facilities.
Characterization of the low accelerating voltage performance of a microchannel plate based detector system for scanning microscopy
Authors: Cochran Raymond F.
Published: June 2020

The Galileo SEM2000 microchannel plate (MCP) detector collects onaxis symmetrical secondary electron images at accelerating voltages as low as 200 eV and beam currents less than 5 picoamps. Symmetrical images are particularly useful in metrology and for viewing features that are shielded by topology from an off-axis detector. Backscatter images from the same on-axis orientation can be obtained at accelerating voltages below 500 eV and beam currents less than 10 picoamps.

The ability to image secondary and backscattered electrons in the same orientation, together with extremely high detection efficiency for low energy electrons make it a valuable tool for direct analysis of beam-sensitive or dielectric samples. Additional topographic enhancement can be obtained by A-B signal processing at accelerating voltages as low as 200 eV.
Cryo-Scanning tunneling microscopy of DNA
Authors: Harris John , Partridge Aaron , Partridge Joshua , Nielsen Randy
Published: June 2020

Scanning tunneling microscopy has found increasing interest in biological sciences. Several problems face the investigator imaging samples of biological origin. These include low conductivity, poor attachment of the sample to substrate and thermal/mechanical drift of the sample while scanning. Several approaches have tried to overcome these problems. These include coating with metal, freeze drying and/or freeze fracturing and tunneling in water. Another useful method is to freeze the sample on the STM holder and image frozen. The biological structure should stay rigid under the scanning tip, should not be swept away from the substrate and should provide highly reproducible images.

Calf thymus DNA (Sigma #D-1501) was mixed in deionized water-tween 20 (0.1%). DNA concentrations varied between 10 μg/ml and 1 μg/ml. The sample was heated slightly, a small drop placed on highly oriented pyrolytic graphite (HOPG) and air dried. The sample holder was immediatel) placed in an Atomis variable temperature cryo-STM with a 6 micron scan range head (Surface Interface, Inc., Mountain View, CA), frozen and scanned.
Design of a new objective lens for an HB-501A STEM
Authors: Kirkland Earl J. , Keyse Robert J.
Published: June 2020

An ultra-high resolution pole piece with a coefficient of spherical aberration Cs=0.7mm. was previously designed for a Vacuum Generators HB-501A Scanning Transmission Electron Microscope (STEM). This lens was used to produce bright field (BF) and annular dark field (ADF) images of (111) silicon with a lattice spacing of 1.92 Å. In this microscope the specimen must be loaded into the lens through the top bore (or exit bore, electrons traveling from the bottom to the top). Thus the top bore must be rather large to accommodate the specimen holder. Unfortunately, a large bore is not ideal for producing low aberrations. The old lens was thus highly asymmetrical, with an upper bore of 8.0mm. Even with this large upper bore it has not been possible to produce a tilting stage, which hampers high resolution microscopy.
Electron cryo-microscopy of macromolecular assembly at 400 kV
Authors: Chiu Wah , Schmid Michael F. , Jakana Joanita , Matsudaira Paul
Published: June 2020

Electron cryo-microscopy has proven to be a valuable technique for determining 3-dimensional structures of biological macromolecules. The cryo technique is capable of preserving biological specimens in their native conformation and of reducing radiation damage during the microscopic observation. Computer processing is used to combine data from different angular views for 3-dimensional reconstruction. The structural detail revealed in this type of analysis can be limited by the quality of the electron microscopic images and the computational procedures used to retrieve the low contrast signals. So far, the highest resolution study of electron cryo-microscopy is bacteriorhodopsin where the polypeptide chain can be traced and some of the amino acid side chains can be identified. Though high resolution structure can be obtained by electron crystallographic analysis, further improvement can be made in several areas. These include specimen flatness, specimen movement induced by the electrons, and achievement of better signal to noise ratios in the images.
X-ray spatial resolution in electron microbeam analysis
Authors: Armstrong John T. , Carpenter Paul K.
Published: June 2020

The spatial resolution of characteristic x-ray production from electron bombardment in thick specimens is dependent upon the rate of energy loss of the primary electrons, the degree of electron scattering, the degree of x-ray absorption by the matrix, and the extent of secondary fluorescence of the x-rays by higher energy characteristic and continuum x-rays. The x-ray spatial resolution in thick specimens is much coarser than the secondary or backscattered electron resolution, typically being of the order of a fraction of a μm to several μm when secondary fluorescence is not significant, or as much as 100 to 200 μm when it is. The size of the excited volume of x-ray production is dependent upon the accelerating potential of the electron beam, the critical excitation potential, and the sample density. The size of the excited volumes of different elements’ x-ray lines can be considerably different in the same matrix, due to differences in critical excitation potential; the emitting volumes can vary even more, due to differences in mass absorption.
Role of HVEM for in situ studies in materials science: The microlaboratory
Authors: Allen Charles W. , Westmacotp Kenneth H.
Published: June 2020

With the development of the Atomic Resolution Microscope (JEOL ARM-1000) about a decade ago and the current availability of new ultra high resolution HVEMs, the important role of HVEM in high resolution imaging has been well achieved. Higher spatial resolution imaging is attainable with higher energy electrons without sacrificing sample tilting capability by virtue of a smaller CSλ value. When commercial HVEMs first became available in the mid 1960's, however, it was not the prospect of high resolution imaging which seemed most important but rather the fact that, for a given material, significantly thicker specimens could be examined.

The microstructures (ultrastructures) and physical behavior of these foils (up to 15 μm thick) would be more representative of those for the bulk material. And especially for materials science applications two other factors were also of paramount importance: (1) the controlled generation of vacancy-interstitial (Frenkel) pairs in crystalline pure elements and alloys by high energy electron irradiation became possible and (2) the increased working space in the objective lens region allowed some miniaturized experimental apparatus to be incorporated.
The spatial resolution of x-ray microanalysis in thin foils
Authors: Williams D. B. , Michael J. R. , Goldstein J. I. , Romig A. D.
Published: June 2020

The spatial resolution of x-ray microanalysis in a thin foil is determined by the size of the beam-specimen interaction volume. This volume is a combination of the incident electron beam diameter (d) and the beam broadening (b) due to elastic scatter within the specimen. Definitions of spatial resolution have already been proposed on this basis but all present a worst case value for the resolution based on the dimensions of the beam emerging from the exit face of the foil.
Resolution limitations in the Electron microscopy of surfaces
Authors: Cowley J.M.
Published: June 2020

Atoms on surfaces scatter high voltage electrons in much the same way as isolated atoms and, in principle, could be imaged with the same resolution. The practical limits on resolution of surface structure arise from the complications imposed by the presence of the bulk sample. In high resolution transmission imaging of crystals in principle orientations, the contrast of the atomic rows is highly non-linear with thickness so that the addition of atoms on surfaces or the subtraction of atoms at vacancies gives very little contrast. Surface structure and internal point defects are best seen when the resolution is degraded by an objective aperture which excludes the inner Bragg reflections from the bulk lattice. The profile imaging technique remains as the only method for applying the full resolution of transmission electron microscopes to the imaging of surface atoms.
Resolution in the scanning tunneling microscope
Authors: Wilson R. J. , Chambliss D. D. , Chiang S. , Hallmark V. M.
Published: June 2020

Scanning tunneling microscopy (STM) has been used for many atomic scale observations of metal and semiconductor surfaces. The fundamental principle of the microscope involves the tunneling of evanescent electrons through a 10Å gap between a sharp tip and a reasonably conductive sample at energies in the eV range. Lateral and vertical resolution are used to define the minimum detectable width and height of observed features. Theoretical analyses first discussed lateral resolution in idealized cases, and recent work includes more general considerations. In all cases it is concluded that lateral resolution in STM depends upon the spatial profile of electronic states of both the sample and tip at energies near the Fermi level. Vertical resolution is typically limited by mechanical and electronic noise.
Studies of supported catalysts by high-resolution SEM in an UHV STEM
Authors: Liu J. , Spinnler G. E.
Published: June 2020

In the studies of the materials used in practical heterogeneous catalysis scanning transmission electron microscopy (STEM) is particularly suited for the characterization of particle size, shape, structure and composition of inhomogeneous catalyst systems by the combined use of a variety of techniques. Recently a high resolution surface imaging technique has been realized in STEM by collecting secondary electrons (SE) emitted at the exit surface of the sample. The application of this imaging mode to the study of supported metal catalysts has proven very useful in the characterization of the support topography with subnanometer resolution. However these studies are confined to extremely thin areas due to the fact that the incident beam will be scattered before encountering the exit surfaces of the sample. This will affect the resolution of SE images, especially for the study of high surface area support materials such as γ-Al2O3 carriers. Furthermore it has been frequently found diat metal particles are not usually seen in the SE images even when the particles are situated on the exit surfaces of the supporting materials.1 As part of an on-going project for characterizing supported catalysts we report here some preliminary results on high resolution SE imaging of supported catalysts in a UHV STEM.
The effect of specimen tilt on back-scattered electron image contrast in scanning electron microscopy
Authors: Meng-Burany X. , Curzon A.E.
Published: June 2020

The present work concerns the back-scattered electron image contrast of a thin film of Cu64Mo36 on a silicon substrate. The contrast is defined by the ratio

(1)

where If and Ib are the backscattered electron signals from the film and from an adjacent bulk reference specimen. In previous work on thin sputtered films of Cu-Mo, Cu-W and Cu-Al both the film and the bulk reference specimen were perpendicular to the incident electron beam. It was found that the dependence of r on the accelerating voltage of the electron beam could be used to obtain both the thickness and the composition of the films. It is the purpose of the present work to determine whether the simple method previously used to extract the required information can be extended to include tilted specimens. As will be seen the method can be adapted to films tilted by less than 50°.
Analysis of electroless nickel thin films
Authors: Price C. W. , Lindsey E. F.
Published: June 2020

Thickness measurements of thin films are performed by both energy-dispersive x-ray spectroscopy (EDS) and x-ray fluorescence (XRF). XRF can measure thicker films than EDS, and XRF measurements also have somewhat greater precision than EDS measurements. However, small components with curved or irregular shapes that are used for various applications in the the Inertial Confinement Fusion program at LLNL present geometrical problems that are not conducive to XRF analyses but may have only a minimal effect on EDS analyses. This work describes the development of an EDS technique to measure the thickness of electroless nickel deposits on gold substrates. Although elaborate correction techniques have been developed for thin-film measurements by x-ray analysis, the thickness of electroless nickel films can be dependent on the plating bath used. Therefore, standard calibration curves were established by correlating EDS data with thickness measurements that were obtained by contact profilometry.
Optimized images of immunogold markers with backscattered electrons
Authors: de Harven Etienne , Ackerley Cameron , Leung Richard , Christensen Hilary
Published: June 2020

The use of colloidal gold markers of small diameter (≤5nm) may permit direct quantification of the numbers of labeled molecules expressed on cell surfaces. To achieve this goal direct immunolabelina must be used and an imaging mode chosen which will revealALLthe present gold markers, i.e. baokscattered electron imaging mode (BEI). Baokscattered electron detectors resolving one nm gold particles have recently been described and immunoconjugate prepared with Fab fragments of TgG molecules will further increase labeling efficiency for more accurate quantitative studies.

Meanwhile, it is desirable to optimize imaging of 5nm gold markers in the BEI mode, using conventional scanning electron microscopes. To that effect, we have been labeling cells with gold particles of two distinct sizes. 5 and 10 nm. The presence of 15nm particles facilitated fine tuning of the SEM in the BET mode for subsequent Imaging of the 5nm markers. We have compared two types of SEMs.
Imaging of drug compounds using Electron Microscopy, x-ray microanalysis, and electron diffraction
Authors: Neilly J. P. , Miller M. F.
Published: June 2020

Solid drug delivery systems are becoming increasingly more complex and their development requires the precise control of materials used in their assembly and manufacture. Characteristics such as particle size distribution of powders, distribution of various components in tableted mixtures, thickness and continuity of particle or tablet coatings and drug crystallinity all affect the final performance of a drug in vivo. In this paper we describe the use of secondary and backscatter SEM, X-ray mapping with an SEM based energy dispersed X-ray spectrometer (EDXS) and electron diffraction to image and help understand the successfulness of a variety of formulation efforts.
HREM imaging of single unit cell carbide precipitates in Pt-C alloys
Authors: Witcomb M.J. , Dahmen U. , O'Keefe M.A. , Westmacott K.H.
Published: June 2020

Dilute Pt-C alloys are prototypical for studying oversize carbide phase precipitation from interstitial solid solution. Earlier studies showed the essential function of quenched-in vacancies in the precipitation process. Vacancies play a dual, volume accommodation and structural, role in the transformation by modifying both the habit plane spacing and stacking sequence. It was also shown how the precipitation sequence in interstitial Pt-C alloys is analogous to that in substitutional Al-Cu alloys. Initially a “GP zone” consisting of a monolayer plate of carbon atoms and vacancies forms. Atomic resolution images of the socalled a precipitates have confirmed their structure. During subsequent coarsening of the precipitates, α’ platelets form. Schematic diagrams illustrating the α and α’ structures in <100> projection are given in Fig. 1. The single-layer a structure, or GP zone is identical to a ﹛100﹜ stacking fault stabilized by an intercalation of carbon. The two-layer α’ structure is the first true precipitate phase and has a crystal structure anti-isomorphous with calcium fluoride.
Heterogeneous nucleation of Ti2AlC precipitates at γ-TiAl grain boundaries in a Ti-52A1-3C alloy
Authors: Xiao S. Q. , Foitzik A. H. , Pirouz P. , Heuer A. H.
Published: June 2020

Defects like dislocations and grain boundaries usually serve as preferred sites for nucleation of both coherent and incoherent precipitates. The catalytical effect of these defects are different for different kinds of precipitates. The purpose of this paper is to present a TEM observation of heterogeneous nucleation of Ti2AlC (α) precipitates at some special grain boundaries in γ-TiAl.

A Ti-52A1-3C alloy fabricated at the University of California, Santa Barbara was annealed for 100 h at 1528 K and then creep tested for about 20 h at 1255 K. Thin foils were cut from the crept sample using a diamond saw and 3 mm discs were cut using an ultrasonic cutting machine. The discs were ground to 200 μm thickness from both sides. Final thinning was done by jetpolishing in a 10% HC104 and 90% CH3OH solution at 250 K and 40 V. The specimens were examined with a Philips EM400T microscope operating at 120 kV.
Structure of second phases in TiAl alloys containing Cr and B
Authors: Hall Ernest L. , Huang Shyh-Chin
Published: June 2020

Addition of interstitial elements to γ-TiAl alloys is currently being explored as a method for improving the properties of these alloys. Previous work in which a number of interstitial elements were studied showed that boron was particularly effective in refining the grain size in castings, and led to enhanced strength while maintaining reasonable ductility. Other investigators have shown that B in γ-TiAl alloys tends to promote the formation of TiB2 as a second phase. In this study, the microstructure of Bcontaining TiAl alloys was examined in detail in order to describe the mechanism by which B alters the structure and properties of these alloys.
Electron Microscope studies of the microstructures in as-quenched and aged HSLA-100 production steels and correlation with mechanical properties
Authors: Fox A.G. , Mattes V.R. , Mikalac S. , Vassilaros M.G.
Published: June 2020

Because of their excellent weldability, high strength low alloy (HSLA) ultra low carbon bainitic (ULCB) steels are finding increasing applications in ship and submarine construction. In order to achieve the required strength and toughness in ULCB HSLA steels it is necessary to control chemical composition and thermo-mechanical processing very carefully so that the desired microstructure and mechanical properties can be achieved. For instance HSLA 100 ULCB steel (nominal yield strength 100 ksi) used by the U.S. Navy in shipbuilding applications can derive its strength and toughness from the following sources:- (1) solid solution strengthening (2) small prior austenite grain size derived from niobium carbonitride precipitation at austenite grain boundaries (3) dislocation substructure and (4) from copper precipitates (in aged alloys). The object of the present work is to correlate the microstructure and mechanical properties of production batches of HSLA 100 in the quenched and aged conditions. Because many of the salient features of these microstructures are submicron in size it was found necessary to use SEM and TEM.
Strain-induced martensite effects on transgranular carbide precipitation in type 304 stainless steels
Authors: Advani A.H. , Murr L.E. , Matlock D.
Published: June 2020

Thermomechanically induced strain is a key variable producing accelerated carbide precipitation, sensitization and stress corrosion cracking in austenitic stainless steels (SS). Recent work has indicated that higher levels of strain (above 20%) also produce transgranular (TG) carbide precipitation and corrosion simultaneous with the grain boundary phenomenon in 316 SS. Transgranular precipitates were noted to form primarily on deformation twin-fault planes and their intersections in 316 SS.

Briant has indicated that TG precipitation in 316 SS is significantly different from 304 SS due to the formation of strain-induced martensite on 304 SS, though an understanding of the role of martensite on the process has not been developed. This study is concerned with evaluating the effects of strain and strain-induced martensite on TG carbide precipitation in 304 SS. The study was performed on samples of a 0.051%C-304 SS deformed to 33% followed by heat treatment at 670°C for 1 h.
On the disappearance of fine, disc-like features from thin foils of steel
Authors: Thompson S. W.
Published: June 2020

Fine carbide particles form in quenched-and-aged specimens of iron containing a small amount of carbon. Similar precipitation occurs in ferrite grains within dual-phase steels. The particles have been described as discs or loops, typically about 20 run in diameter and 2 nm thick, which lie on ﹛100﹜ planes within ferrite grains. The precipitates are believed to form in association with vacancies and produce increases in hardness and yield strength. Two studies showed that these features disappeared after heating specimens in the transmission electron microscope (TEM), and this note reports further on this phenomenon.

Continuously annealed and cold-rolled sheet steel (provided by Inland Steel Company) contained (in wt pet) 0.087 C, 0.97 Mn, 0.27 Si, 0.034 Al, 0.008 S, and 0.005 N. Specimens were intercritically annealed at 770°C for five minutes and quenched in iced water. Tensile testing was conducted within one day of heat treatment, and then specimens were stored at room temperature for about six months. Thin foils were produced by conventional thinning methods and jet polished at 75 V and 80 mA in an electrolyte containing 95% acetic acid and 5% perchloric acid. Specimens were examined in a Philips EM400 operated at 120 kV.
A Transmission Electron Microscopy examination of the effect of post-weld heat treatment on spot welded Ti-14Al-21Nb
Authors: Acoff V.L. , Griffin R.D. , Janowski G.M. , Radhakrishnan B. , Thompson R. G.
Published: June 2020

Titanium aluminides have great potential in structural, aerospace, and high temperature engineering applications. In the majority of these uses, it is expected fusion welding will be used as the primary method of joining. However, control of the as-welded microstructure (and mechanical properties) is difficult to obtain since cooling rates and, therefore, the microstructures can vary considerably.

Samples of 14.2 Al, 21.3 Nb, 0.018 C, 0.05 Fe, 0.012 N, 0.013 H, and 0.10 O (in wt.%), commonly known as Ti-24Al-11Nb (in at.%), were placed on a copper block and spot welded inside of a Iucite box using a gas tungsten arc welder (GTAW). The specimens were then sealed in argon backfilled fused quartz tubes and heat treated in the α2, + B2 field of the phase diagram. The conditions of this post-weld heat treatment (PWHT) were 982°C for 0.5, 1, 2, or 4 hours. Transmission electron microscopy and microhardness tests were used to characterize the alloy.
The role of the electron microscope in the cold fusion controversy
Authors: Murr L.E.
Published: June 2020

More than two years ago, thousands of scientists around the world raced to confirm the claims of electrochemically induced fusions especially in the palladium/deuterium system. Interestingly enough, it was also claimed during the 1920's that ordinary hydrogen absorbed in palladium fuses to form helium.

The author has recently argued that a significant feature of the controversy involving palladium electrodes in electrochemical systems where either hydrogen or deuterium absorption is crucial, probably depends strongly on the palladium microstructure. indeed there is no compelling evidence that has involved a systematic evaluation of the palladium metallurgy or specific microstructural alterations which may have been correlated with heat generation or other fusion-related phenomena.
High-spatial-resolution elemental analysis of annealed MgO surfaces by reflection reflection electron energy-loss spectroscopy
Authors: Crozier P.A. , Gajdardziska-Josifovska M. , Cowley J.M.
Published: June 2020

The technique of reflection electron energy-loss spectroscopy (REELS) can be used to perform elemental analysis of surfaces in an electron microscope. The information obtained from this technique can be combined with topographic information from reflection imaging and with crystallographic information from the RHEED pattern. We have applied these techniques to study the (100) surface of MgO subject to high temperature annealing. By utilizing small probes available in modern analytical electron microscopes we have been able to measure differences in the surface compositions of small topographic features and we show for the first time that the Ca distribution on the surface is not uniform.
Atomic force microscopy of mica surface after ion replacement
Authors: Dixon Northern B. L. , Chen Y. L. , Israelachvili J.N. , Zasadzinski J.A.N.
Published: June 2020

Atomic Force Microscope (AFM), is the newest, and potentially most powerful of the scanning probe microscopes. The (AFM) is capable of resolutions approaching atomic dimensions on ideal surfaces. One of the favorite such surfaces is that of mica. Muscovite mica has a platelike structure consisting of an octahedral alumina sheet sandwiched by two tetrahedral silicate sheets. As a result of this structure, mica cleaves readily along a plane leaving a molecularly smooth surface. Because of the isomorphous substitution of the tetravalent silicon by trivalent aluminium, mica has an excess negative surface charge.

This negative surface charge of 2.1-1014 charges per cm2 is neutralized by an equal number of positive monovalent ions, mainly potassium ions. The ion-exchangable surface ions of mica, in aqueous solution, can be readily replaced by other monovalent or multivalent ions. This ion exchange alters the surface of the mica. We then follow these changes by imaging with the AFM in air.
REM observations of oxygen-annealed rutile (001) surfaces
Authors: Liu J. , Wang L. , Cowley J. M.
Published: June 2020

Rutile (single crystal TiO2) is widely used in electrochemistry, photochemical energy conversion and photocatalytic reactions of gases as a catalytic material. It is important to characterize the surface properties of rutile in order to understand its catalytic behavior. The rutile (001) surface is extremely unstable, forming facets on annealing as revealed by the LEED results. In this paper we report some preliminary results on the investigation of oxygen annealed rutile (001) surface, obtained by reflection high energy electron diffraction (RHEED) and reflection electron microscopy (REM) techniques.

The crystal was cut into strips, finely polished, cleaned and chemically etched in NaOH and H2SO4 before annealing. The samples were annealed in pure oxygen at 1473 K for 36 h. The purposes of annealing the samples in pure oxygen are to preserve surface stoichiometry and to prevent surface reactions with elements other than oxygen during the annealing process. The RHEED and REM observations were performed in a Philips 400T microscope operated at 120 kV.
In situ heating studies at high resolution
Authors: Sinclair Robert
Published: June 2020

It is well-known that interfaces in solids have a crucial influence on the properties of materials. The structures of such interfaces are a direct consequence of their means of formation, be it by deposition, reaction, interdiffusion or epitaxial growth. Even subtle changes during processing or service can alter the anticipated behavior. High resolution electron microscopy (HREM) has become an invaluable, and virtually routine, characterization tool in understanding the influence of structure on properties. Its strength lies in the ability to derive direct structural information at the atomic level, not only about topography but also about interfacial defects such as dislocations or ledges, contamination residue, intermediate phases etc. It complements well the broad-beam spectroscopic characterization methods such as Auger, ECSA, SIMS and RBS, which do not provide structural information and can be ambiguous to interpret.
Effect of strain on ADF-STEM high-resolution images
Authors: Kelly M. , Bird D.M.
Published: June 2020

It is well known that strain fields can have a strong influence on the details of HREM images. This, for example, can cause problems in the analysis of edge-on interfaces between lattice mismatched materials. An interesting alternative to conventional HREM imaging has recently been advanced by Pennycook and co-workers where the intensity variation in the annular dark field (ADF) detector is monitored as a STEM probe is scanned across the specimen. It is believed that the observed atomic-resolution contrast is correlated with the intensity of the STEM probe at the atomic sites and the way in which this varies as the probe moves from cell to cell. As well as providing a directly interpretable high-resolution image, there are reasons for believing that ADF-STEM images may be less suseptible to strain than conventional HREM. This is because HREM images arise from the interference of several diffracted beams, each of which is governed by all the excited Bloch waves in the crystal.
On effects of non-systematic reflections on weak-beam images of partial dislocations
Authors: Botros K. Z. , Sheinin S. S.
Published: June 2020

The main features of weak beam images of dislocations were first described by Cockayne et al. using calculations of intensity profiles based on the kinematical and two beam dynamical theories. The feature of weak beam images which is of particular interest in this investigation is that intensity profiles exhibit a sharp peak located at a position very close to the position of the dislocation in the crystal. This property of weak beam images of dislocations has an important application in the determination of stacking fault energy of crystals. This can easily be done since the separation of the partial dislocations bounding a stacking fault ribbon can be measured with high precision, assuming of course that the weak beam relationship between the positions of the image and the dislocation is valid. In order to carry out measurements such as these in practice the specimen must be tilted to "good" weak beam diffraction conditions, which implies utilizing high values of the deviation parameter Sg.
Advances in ALCHEMI
Authors: Turner P. S. , White T. J. , O'Connor A. J. , Rossouw C. J.
Published: June 2020

ALCHEMI - atom location by channeling enhanced microanalysis - is an important technique of analytical electron microscopy, introduced nearly 10 years ago by Spence and Taftø which utilises the phenomenon of electron channeling to determine the partitioning of impurity species on atomic sites in crystals from ratios of normalised x-ray counts for channeling and non-channeling orientations. The original “ratio” method has been used with success in a number of cases (see reviews by Krishnan and Smyth and McCormick) but is limited in its range of applicability by several factors. We have described an alternative approach to the collection and analysis of electron channeling data for ALCHEMI, which is less sensitive to these factors, and can provide greater precision and reliability. In this paper, a general form of our analysis is described, and the two methods are compared and contrasted.
Electron-energy-loss spectra of silicon carbide of 4H and 6H structures
Authors: Liu D. R. , Shinozaki S. S. , Hangas J. U. , Maeda K.
Published: June 2020

The properties of silicon carbide can be tailored with addition of various sintering aides. It is desirable to understand the microstructure of these materials as related to their properties. For example, there is a debate whether there is some Be at all in the 4H structure of SiC doped with BeO. It is very difficult to use the conventional EELS quantification procedure to investigate the Be presence of minute amount in SiC. In any spectrum collected from SiC doped with BeO, the huge Si-L23 edge at 100 eV would extend well above 200 eV and make it impossible to identify a small Be-K edge at 111 eV. However, progress has been made in solving this problem as reported in the present paper. A spectrum from SiC with the BeO additive is compared with a spectrum from SiC without BeO, and the difference of the two spectra starting at 111 eV, if present, should be the Be-K edge signal. Thus, one does not have to fit the background before the Be-K edge with the usual power law A.E-r, and the background subtraction error is greatly reduced.
Compositional analysis of mercury zinc telluride by EDS and WDS
Authors: Price M. W. , Zuo H. , Janowsk G. M. , Andrews R. N.
Published: June 2020

Semiconducting alloys of II-VI compounds have become the materials of choice for numerous infrared detection applications. However, compositional inhomogeneities in II-VI materials can adversely affect device performance. Extensive work has been conducted to evaluate the influence of growth parameters on the compositional redistribution in directionally solidified bulk alloys. Energy Dispersive Spectroscopy (EDS) has proven to be a valuable tool both in evaluating the compositional homogeneity of II-VI alloys and gaining information about the influence of growth parameters on compositional redistribution.

In the work reported here, samples of directionally solidified mercury zinc telluride (MZT) were analyzed by SEM/EDS. The specimens were prepared by longitudinal sectioning, polishing to a 0.25 am finish, chemical polishing with a 2 vol% bromine/methanol solution, and rinsing with distilled water, acetone, and ethanol. Standards of Zn, Te, ZnTe, and HgTe were prepared in a similar manner for the quantitative analysis.
Microstructural dependence of magnetic properties of Pt/Co multilayers for magneto-optical recording devices
Authors: Li Z.G. , Carcia P.F.
Published: June 2020

Pt/Co ultrathin multilayer films are a new candidate for magneto-optical (MO) recording devices. We have previously shown that their magnetic properties are improved by sputtering them with either Kr or Xe instead of Ar. Specifically, Arsputtered films have too small coercivity for recording. In this study we demonstrate that high resolution electron microscopy (HREM) is a powerful technique to study the relationship of the multilayer microstructure and magnetic properties. We used a Philips CM30 and a JEM 2000FX microscope to study multilayers with a typical total thickness in the 10 nm range, consisting of only 1-2 atomic layers of Co and 4-6 atomic layers of Pt.

Figure 1 compares the cross sectional microstructure of nearly identical Pt/Co multilayers (~10x[4Å Co+13Å Pt]) sputtered in (A) 7 mTorr of Ar, (B) 7 mTorr of Kr, and (C) 5 mTorr of Xe. The layers sputtered in Ar are extremely flat and continuous. Sputtering with a larger mass gas (Kr or Xe) progressively increased the layer roughness, and the lateral continuity of layers was more frequently interrupted by grain boundaries, which were very distinct in Kr- and Xe-sputtered films compared to Ar-sputtered films.
Effects of surface oxide on low-temperature epitaxial growth of Si
Authors: Bretz K. C. , Kuan T. S. , Agnello P. D. , Sedgwick T. O.
Published: June 2020

The Si epitaxial growth temperature using Chemical Vapor Deposition (CVD) has been steadily reduced in the last few years to temperatures as low as 600°C. Blanket and selective Si epitaxy at atmospheric pressure is now achieved at low temperature through purification processes which exclude O2 and H2O impurities from the deposition zone. In addition to maintaining the deposition system ultra-clean, the initial Si growth surface must be free of surface oxide to achieve low defect density in the epitaxial layer. Previous experiments have shown that a slight presence of surface oxide leads to generation of extended defects. Therefore, an effective surface cleaning process is as important as an oxygen-free environment for achieving perfect epitaxy at low temperatures. In this work we use electron microscopy to study the structure of defects nucleated from surface oxide and the mechanism of defect formation under different growth conditions. High-resolution observations are made to establish quantitative linkage between surface cleanliness and defect population.
Transmission electron microscopy applications in integrated circuit processing
Authors: Kim Ki-Bum , Ritz Ken , Raaijmakers Ivo
Published: June 2020

The present demand for higher integration density in IC processing with submicron design rules and the development of new materials require a routine application of highly sophisticated characterization techniques as regards both failure analysis and materials development. One such an example is the utilization of conventional and high resolution transmission electron microscopy (TEM) in an IC processing environment. In this paper, we summarize several examples of how TEM can support various IC development programs.

Trends in modern IC processing require the formation of thin, high quality, epitaxial layers with abrupt, well-controlled dopant transition profiles. One of the key factors in achieving such an epitaxial layer is the maintenance of a clean surface during the deposition. Surface residues such as oxygen and carbon form SiO2 and SiC particles during layer deposition and, thereby, lead to the formation of a poor quality epitaxial layer.
Hexagonal phase in tensile low-pressure CVD poly-Si film
Authors: Nguyen Tai D.
Published: June 2020

Polycrystalline silicon (poly-Si) films have found many applications in integrated circuits, and in actuators and sensors. Important considerations in the processing of these devices are structural stability and repeatable mechanical properties of the films. The texture and stress state of the films depend strongly on the microstructures and morphology of the films. Tensile films, which are preferred to compressive films in devices whose lateral dimensions of clamped structures are not to be restricted by compressive buckling, are characterized by equiaxial grain morphology, while compressive films are characterized by columnar grain growth during deposition.

A diamond hexagonal (d.h.) Si structure with lattice parameters of a = 3.8Å and c = 6.28Å was first reported in 1963. More recently, transformation from the diamond cubic (d.c.) Si to the hexagonal phase has been observed in Si under hydrostatic pressure at temperatures between 350 C and 700 C, in heavily ion-implanted silicon, and in as-grown, implanted, and annealed CVD Si thin films, in addition to the known high pressure Si phases.
Dislocations Induced by Heavy Boron Doping of Silicon
Authors: Ning X. J. , Pirouz P.
Published: June 2020

Diffusion-induced dislocations in silicon have long been of interest in semiconducting devices. Several investigations concerning the dislocations induced by doping of Si were carried out during the early sixties. However, there are still a number of unresolved questions concerning this problem. Because the boron doped chemical etch-stop technique is widely used in the fabrication of microsensors, new interest has arisen in the role of dislocations induced by boron diffusion and the behavior of these dislocations on the mechanical properties of microsensors. The doping of Si in this technique is heavy (>5x1019cm-3) and, consequently, the density of induced dislocations in the wafer is large. The dislocations will probably then play a critical role on the mechanical properties of thin Si wafers used in the etch-stop technique.
In situ studies of silicide-mediated crystallization of amorphous Si
Authors: Hayzelden C. , Batstonc J.L.
Published: June 2020

Metal silicides in thin films play an essential role in the increasingly fine-scale fabrication of integrated circuits. Although commonly produced by interfacial reaction between metal films and silicon, buried metal silicides have recently been produced in crystalline Si by ion-implantation. Cammarata et al., have reported the use of ion-implantation to form buried nickel silicide precipitates in amorphous Si thin films, in which the first (and only) phase to form was NiSi2. The kinetics of the nucleation and growth of NiSi2 precipitates were investigated and an enhancement of the crystallization kinetics of the amorphous Si, apparently due to the migration of silicide precipitates, was found. In this paper, we describe the results of an in-situ transmission electron microscopy (TEM) and high resolution electron microscopy (HREM) investigation of the silicide-mediated crystallization of amorphous Si.
Electron beam testing of multilevel metal integrated circuits
Authors: Russell P. E. , Radzimski Z. J. , Ricks D. A. , Vitarelli J. P.
Published: June 2020

Fundamentally, voltage contrast is a well established technique for determination of voltages on metal surface which can be directly probed with an electron beam. However, actual integrated circuits (IC) consist of two or more conducting layers (metal and doped polysilicon) separated by dielectrics and covered by a dielectric passivation layer. Our work has addressed: i) the removal of dielectric layers (depassivation) by reactive ion etching (RIE) or selectively by focused ion beam etching to allow access to exposed metal lines; ii) modelling effort to understand how the materials and geometric parameters of multilevel IC's affect voltage contrast measurements, and iii) improvements in retarding field spectrometer based measurement techniques.
Cathodoluminescence of semiconductors at 200 eV?
Authors: Myhajlenko S.
Published: June 2020

Brillson and Vitturo have recently reviewed the application of low energy (300 - 3000 eV) cathodoluminescence (CL) to surface studies of various semiconductors. In principle, the resulting electron penetration (40 - 1500 Å) at these energies should make it possible to differentiate near surface from bulk phenomena. The above authors demonstrated that deep level spectral features could be correlated with changes in the electronic structure of the surface as a result of metallization, laser annealing and thermal desorption. However, the experimental configuration used in the above studies was a room temperature, UHV-based, glancing incidence electron beam apparatus, i.e., no imaging capabilities. A future development in this area would be measurements performed in a regular SEM at cryogenic temperatures. The luminescence efficiency of GaAs greatly increases at low temperatures, and therefore, this would be beneficial to CL signal detection. We also require a better understanding of the factors which may limit progress in this matter. For example, the role of surface recombination velocity, the properties of luminescence dead layers and cross-over voltage phenomena are important to such an investigation. We report on progress in addressing some of these questions.
The study of compound semiconductor heterostructures by High-resolution transmission electron microscopy
Authors: Cullis A.G.
Published: June 2020

Heteroepitaxial compound semiconductor systems have increasing importance for the fabrication of advanced electronic devices. Microstructural characterisation of the finest features of these materials can be carried out using transmission electron microscopy (TEM) and this paper demonstrates the use of high resolution work for heterointerface and related investigations in two different areas.

The epitaxial growth of wide band gap II-VI compounds offers potential for a number of optoelectronic device applications. Indeed, in some cases, such as for CdS, it is possible to prepare very high quality Wurtzite-structure layers on Sphalerite substrates, despite the presence of substantial misfit. When hexagonal close-packed CdS is grown by metal-organic chemical vapour deposition on (111)A GaAs, the layer is oriented with (0001)cds //(111)GaAs and [110]cds//[10]GaAs. A cross-sectional, high resolution micrograph of the interface is shown in Fig. 1a where the different atomic stacking in the CdS (ABAB....) and GaAs (ABCABC....) regions is evident.
Structural aspects of silicon diffusion in quaternary III-V thin-film semiconductors
Authors: Ponce F. A. , Thornton R. L. , Anderson G. B.
Published: June 2020

The InGaAlP quaternary system allows the production of semiconductor lasers emitting light in the visible range of the spectrum. Recent advances in the visible semiconductor diode laser art have established the viability of diode structures with emission wavelengths comparable to the He-Ne gas laser. There has been much interest in the growth of wide bandgap quaternary thin films on GaAs, a substrate most commonly used in optoelectronic applications. There is particular interest in compositions which are lattice matched to GaAs, thus avoiding misfit dislocations which can be detrimental to the lifetime of these materials. As observed in Figure 1, the (AlxGa1-x)0.5In0.5P system has a very close lattice match to GaAs and is favored for these applications.

In this work, we have studied the effect of silicon diffusion in GaAs/InGaAlP structures. Silicon diffusion in III-V semiconductor alloys has been found to have an disordering effect which is associated with removal of fine structures introduced during growth. Due to the variety of species available for interdiffusion, the disordering effect of silicon can have severe consequences on the lattice match at GaAs/InGaAlP interfaces.