bluuebunny/crossref_metadata_2025 huggingface dataset:
In situ high-temperature corrosion with the environmental SEM
Authors: Touryan L. A. , Hobbs L. W.
Published: June 2020

Electron microscopy has greatly aided in understanding the microstructure and morphological development of corrosion scales formed by high temperature oxidation and sulfidation of metals. However, this knowledge has been limited by the fact that the microstructure and morphological features could only be studied after corrosion had occurred. The recent development of the environmental scanning electron microscope (ESEM) permits actual in-situ observation of the evolution of high temperature corrosion scales at the scale-gas interface, allowing for a better understanding of the detailed mechanisms of scale growth. The objective of this study is to investigate the evolution of oxidation and sulfidation scales on various metals and alloys.

R.A. Rapp and associates adapted a conventional SEM for oxidation studies by developing a stage that could be heated in excess of 1000 C. Because of the vacuum restrictions of the SEM, a gas pipe directed at the surface of the samples was utilized in order to increase the local oxygen partial pressure, and this resulted in low (0.2 Torr) but sufficient pressures for oxidation.
Observation of corynebacterium species using Scanning Electron Microscopy
Authors: McWilliams Toya S. , Hammond Ernest C. , Luzarraga Marlene B.
Published: June 2020

Bacteria of the genus Corynebacterium are considered part of the bacterial flora of skin and mucosa. Even C. diphtheriae, a long recognized pathogen, may be isolated from the throat of healthy individuals. Recent evidence indicates that other Corynebacteria are associated with opportunistic conjunctival infections in aging laboratory mice.

Our goal of using scanning electron microscopy was to expand previous studies and to observe the association of the bacteria with the conjunctival surface of aged mice. To accomplish this, we needed a point of reference for identification of the corynebacteria which were frequently present in the company of other bacteria. We studied cultures of known corynebacteria of ocular origin during the exponential growth phase. These cultures contained pleomorphic cells that were round, ovoid and rod shaped, clustered together and surrounded by a biofilm. Several of the cylindrical rods appeared as V-shaped pairs, classic features of the genus Corynebacterium. The V-shape arrangement is accomplished by a snapping postfission movement.
Crystalline nanostructures in porous silicon and their relation to optical and electronic properties
Authors: Cullis Anthony G
Published: June 2020

Although Si normally emits only extremely weak infrared photoluminescence (PL) due to its relatively small and indirect band gap, light-emitting devices based upon Si would find many applications in both VLSI and display technologies. Therefore, there has been much interest in the recent demonstration of very efficient visible light emission from highly porous, electrochemically etched Si. Although it was originally proposed that the efficient PL was due to recombination of quantum-confined carriers in pore walls, evidence for this was only indirect and transmission electron microscopy (TEM) studies have been required to provide a detailed understanding of the light emission mechanism.

Porous Si samples are generally prepared by anodization in HF solution and porosities as high as ∼80% are required for efficient PL emission. Typical PL spectra from highly porous Si are shown in Fig. 1 where it is evident that emission is usually in the red and near infra-red regions of the spectrum.
TEM study of chemically converted SiC thin film on nanometer curved Si surface
Authors: Stepanova A. N. , Liu J. , Christensen K. N. , Son U. T. , Bachmann K. J. , Givargizov E. I. , Hren J. J.
Published: June 2020

Silicon whiskers with nanometer curvature have a variety of applications such as probes in STM and AFM, or field emission cathodes for vacuum microelectronic devices. For these and other applications it is essential to stabilize the sharply curved silicon surface during usage. Carburization of the silicon surface seems to be a very suitable solution to this problem, since SiC crystals have excellent physical properties and are chemically quite inert. There have been a number of reports of the carburization of flat surface silicon wafers by chemical reaction using both CVD and MBE methods. However, to carburize while maintaining a very sharp silicon tip is extremely difficult. It is also desirable to carburize only a very thin layer, so as to avoid excessive mechanical strain arising from the large difference (∼20%) in lattice parameters.

Our carburizations were carried out in a turbo-pumped ultra-high vacuum system. The silicon specimens were oxidation sharpened and cleaned in a buffered HF solution.
HREM of epitaxially grown Fe/TiO2 and Cu/TiO2 interfaces
Authors: Lu P. , Cosandey F.
Published: June 2020

High-resolution electron microscopy (HREM) has been used to provide information on atomic structures of metal/oxide interfaces, which are of both scientific and technological interest. In this report, we present results of a study on Fe/TiO2 and Cu/TiO2 interfaces by HREM. The Fe/TiO2 and Cu/TiO2 interfaces were formed by vapor deposition of Fe and Cu on TiO2 (110) surface, respectively, in a UHV chamber with a base pressure of ∽1x10−10 torr. Cross sectional HREM specimens were prepared using standard techniques involving mechanical polishing, dimpling and ion-milling. The samples were examined in an Topcon-002B high-resolution electron microscope. HREM simulations were performed using the EMS program.

Figs, 1a and 1b show a HREM micrograph and a select area diffraction pattern of Fe/TiO2 interface, respectively, taken along the TiO2 [001] direction. From Fig.la and Fig.1b, the following orientation relationship is obtained: [001]Fe//[001]TiO2 and (100)Fe//(110)TiO2. With this orientation, there is about 12.6% lattice misfitt along the TiO2 [10] direction.
Scanning-probe microscopy of polymers
Authors: Reneker Darrell H. , Patil Rajkumari , Kim Seog J. , Tsukruk Vladimir
Published: June 2020

Scanning probe microscopy techniques, particularly atomic force microscopy (AFM) and scanning tunneling microscopy (STM) are finding a rapidly growing number of applications to both synthetic and biological polymers. Segments of individual polymer molecules can often be observed with atom scale resolution. Observation of polymeric objects as large as 100 microns with nanometer resolution is possible with contemporary AFM, although features caused by the convolution of the shape of the sample and the shape of the tip must be recognized and properly interpreted. The vertical resolution of the atomic force microscope readily provides precise data about the heights of molecules, crystals, and other objects.

Lamellar crystals of polyethylene are well characterized objects with many features which can be observed with scanning probe microscopes. Figure 1 shows the fold surface near a fold domain boundary of a lamellar crystal of polyethylene, as observed with an AFM. The folded chain crystal is about 15 nm thick.
Morphological study of structured latex particles by Transmission Electron Microscopy
Authors: Segall Iris , Shaffer Olga L. , Dimonie Victoria L. , El-Aasser Mohamed S.
Published: June 2020

Transmission electron microscopy plays an important role in the study of the influence polymerization conditions have on the morphology of structured latex particles and thus in the understanding of the morphological effect of such particles on the structure-property relationships of polymeric end products.

Structured latex particles are prepared by seeded emulsion polymerization, where the first stage is a polymerization of ”the core” poly(n-butyl acrylate) (PBA), followed by a second stage polymerization of ”the shell” poly(benzyl methacrylate/styrene) (P(BM/St)) at various ratios. The changes in polymerization conditions include such variables as the polymerization mode (batch vs. semicontinuous), core/shell ratio, shell thickness, and shell composition. Morphology studies of the structured latex particles are performed by transmission electron microscopy on preferentially stained samples. In a small vial, a few drops of latex sample are combined with a few drops of uranyl acetate (UAc) 2% solution. The uranyl acetate serves as a negative staining to better delineate the particles edges.
Evaluation of matrix and interface properties in SiC/SiC composites
Authors: Surrett A.D. , More K.L. , Lowden R.A.
Published: June 2020

It has become increasingly important to characterize composite matrix materials in terms of processing-microstructure-property relationships. The characteristics of composite matrices can differ significantly from monolithic materials processed using more conventional techniques such as hot-pressing or sintering. Knowledge of the mechanical and thermophysical properties of the matrix as a function of processing parameters is necessary for the modeling and design of composite materials. In this study, the microstucture and mechanical properties of the matrix in the Nicalon/SiC composite system have been characterized as a function of processing temperature.

The composites were fabricated by stacking multiple layers of plain-weave Nicalon fabric rotated in a 30°-60°-90° sequence within the cavity of a graphite holder. The preforms were then coated with carbon at 1375 K and 3 kPa. The coated preforms were densified using a forced chemical vapor infiltration (FCVI) technique developed at ORNL. The SiC matrix was produced by the decomposition of methyltrichlorosilane carried in hydrogen at temperatures of 1000, 1100, 1200, 1300, and 1400°C in order to reveal the effect of temperature on the properties of the composite and matrix.
In situ crystallization of silicate glass films deposited on α-Al2O3
Authors: Mallamaci Michael P. , Bentley James , Barry Carter C.
Published: June 2020

Polycrystalline alumina compacts often contain amorphous films at grain boundaries and triple junctions as a result of the liquid-phase sintering process. An anorthite-based composition (CaAl2Si2O8) is typical of the glassy phases observed in these materials. With appropriate heat treatments the glass phase can be crystallized, which can influence the properties of the bulk material. Deposition of a thin film of glass on single-crystal α-Al2O3 is being used to study the influence of specific crystallographic orientations on the alumina-glass interface properties. Vapor-phase growth of glass on different orientations of α-Al2O3 has been accomplished previously and, through subsequent thermal treatments, the alumina was shown to facet preferentially when in contact with a glassy phase. In the present study, calcium-aluminosilicate glass films were grown on single-crystal α-Al2O3 at relatively low substrate temperatures (<950°C) by pulsed-laser deposition. These films were then heated in the electron microscope to determine the effect of α-Al2O3 crystallography on crystallization of calcium-aluminosilicate glasses.
Application of SEM to the study of multi-phase ceramic composites
Authors: Chan Helen M. , Harmer Martin P. , Miller Gary A.
Published: June 2020

Recent on-going research at Lehigh has focussed on the tailoring of multi-phase ceramic composite structures for enhanced mechanical behavior. Results have shown that by suitable control of the morphology and nature of the phases present, improvements may be obtained in properties such as microstructural stability, flaw tolerance, and strength. What follows is a brief discussion of examples illustrating applications of scanning electron microscopy (SEM) to this type of study for several specific systems.

Work by French et al. revealed that relative to single phase materials, duplex structures (which consist of ∼ 50:50 vol.% mixtures of mutually insoluble phases) show significantly enhanced resistance to grain coarsening. It was postulated that the slower grain growth rate in the duplex material resulted from the necessity for long-range diffusion. To test this hypothesis, the grain growth behavior of two duplex Al2O3:ZrO2 materials was compared, the difference being that a grain boundary glassy phase was deliberately incorporated into one of the structures.
Phase transformations in ceramics
Authors: Kriven W. M.
Published: June 2020

The study of phase transformations in ceramic has received limited coverage in ceramic text books, other than for example, ferroelectric transformations, (e.g., in barium titanate), zirconia and amorphous to crystalline transformations in glass. While Newnham has comprehensively reviewed the crystal chemistry of “ferroic” (ferroelectric, ferroelastic or ferromagnetic) ceramics, the success of “transformation toughening” as a mechanism for reducing the brittleness of ceramics has stimulated the search for other potential transformation tougheners alternative to zirconia.

While phase transformations have been widely studied in metals over the past 50 years, caution needs to be exercized in transplanting conventional wisdom from metals to ceramics. The differences in bonding in ceramics ((mixed covalent and ionic ), can lead to profound differences in crystal structures and transformation mechanisms. An alternative approach which has been particularly helpful in our work is that of Hyde et al., which empasizes cation arrangements, into the interstices of which, the anions are inserted, rather than the inverse perspective of putting cations into a packed anion array.
Spherical aberration-free observation of reconstructed Au(011)2 × 1 surface by HRTEM using defocus-modulation image processing
Authors: Takai Yoshizo , Taniguchi Yoshifumi , Ikuta Takashi , Shimizu Ryuichi
Published: June 2020

The surface profile imaging technique by HRTEM has a good potential for observing surface reconstructions. It also has possibilities for measuring with high accuracy the displacement of atoms in the direction perpendicular to the surface. However, surface profile images have been strongly influenced by imaging parameters such as defocus and spherical aberration. Therefore atom images generally appear to be appreciably displaced from their actual positions in crystal. In order to correct the spherical aberration in the image, the authors have recently developed a novel approach based on defocus-modulation image processing and experimentally confirmed that spherical aberration can be corrected very well by this method, as shown in a symmetric Thon diagram reproduced from amorphous carbon images,

In the present paper, a reconstructed (011) gold surface has been observed by HRTEM (HF-2000) with a field emission gun at an accelerating voltage of 200kV. processing system, which records through focus images by changing the objective lens current while controlling image shift coils to compensate image drift.
The effect of beam and crystal tilt on quantitative HREM measurememts of grain boundary volume expansion
Authors: Buckett M. I. , Merkle Karl L.
Published: June 2020

The effects of both beam and crystal tilt on quantitative high resolution electron microscopy (HREM) measurements of grain boundary volume expansion have been investigated. As volume expansion - or rigid body translation normal to a given boundary - has been found to directly vary with the grain boun-dary energy, it is important that accurate measurements of this quantity can be made. The type of measurement we consider is a technique first outlined by Stobbs and co-workers and modified by Merkle. The technique utilizes a linear least squares fit to the centers of gravity of either peak or valley positions in the HREM image. The interplanar distances on both sides of the boundary outside the strain fields of the core are first determined, and the measured width of the boundary region is extrapolated. The volume expansion is then determined as the difference between this measured width and the effective unrelaxed width of an ideal boundary.
Towards 1-Ångstrom-resolution STEM
Authors: von Harrach H.S. , Jesson D.E. , Pennycook S.J.
Published: June 2020

Phase contrast TEM has been the leading technique for high resolution imaging of materials for many years, whilst STEM has been the principal method for high-resolution microanalysis. However, it was demonstrated many years ago that low angle dark-field STEM imaging is a priori capable of almost 50% higher point resolution than coherent bright-field imaging (i.e. phase contrast TEM or STEM). This advantage was not exploited until Pennycook developed the high-angle annular dark-field (ADF) technique which can provide an incoherent image showing both high image resolution and atomic number contrast.

This paper describes the design and first results of a 300kV field-emission STEM (VG Microscopes HB603U) which has improved ADF STEM image resolution towards the 1 angstrom target. The instrument uses a cold field-emission gun, generating a 300 kV beam of up to 1 μA from an 11-stage accelerator. The beam is focussed on to the specimen by two condensers and a condenser-objective lens with a spherical aberration coefficient of 1.0 mm.
In situ studies of heterogeneous reactions using surface electron microscopies LEEM, MEM, and PEEM
Authors: Engel W. , Rausenberger B. , Swiech W. , Rastomjee C. S. , Bradshaw A. M. , Zeitler E.
Published: June 2020

The preferred imaging techniques for the observation of physical and chemical processes at solid surfaces with high temporal and spatial resolution are low-energy electron microscopy (LEEM), mirror electron microscopy (MEM) and photoemission electron microscopy (PEEM). In these techniques the energy transfer to the surface during the imaging process itself is small so that surface processes such as adsorption, diffusion, chemical reactions etc. remain largely undisturbed.

LEEM, MEM and PEEM, which all can be performed in an ultra-high-vacuum surface microscope of the Bauer/Telieps type, have been applied to the study of CO/O reaction-diffusion fronts on a Pt(100) surface saturated with CO. These fronts develop after admission of oxygen to the surface (10-6 mbar) at surface defects which provide adsorption sites for oxygen and thus initiate the autocatalytic oxidation process. The formed CO2 is instantaneously desorbed, freeing adsorption sites which are then occupied by oxygen from the gas phase. The front propagates over the whole surface, leaving behind an oxygen-covered region.
Materials science aspects in designing giant magnetoresistance in heterogeneous Cu1-xCox thin films
Authors: Hütten Andreas , Thomas Gareth
Published: June 2020

The recent discovery of giant magnetoresistance (GMR) in heterogeneous Cu1-xCox thin films has brought new insights in the phenomenon of GMR, which was previously believed to be restricted to multilayered structures only. Subsequent theoretical analyses of GMR in this new materials class have shown that GMR is mainly controlled by the mean radius and the volume fraction of single domain ferromagnetic particles. In addition to these parameters, the mean free path for electron in the non-magnetic matrix as well as coherency between particles and matrix are influencing the amplitude of GMR. Clearly, the key to increase the amplitude of GMR is to determine the decomposition kinetics and from which to optimize the single domain ferromagnetic Co particle size distribution in heterogeneous Cu1-xCox thin films.

Cu81Col9 films, 50 nm in thickness, have been deposited by dc magnetron sputtering from separate Cu and Co targets onto 30 nm thick silicon nitride electron transparent grids.
Microstructural analysis of cobalt alloy single and multilayer longitudinal recording media
Authors: Kuwabara M. , Visokay M.R.
Published: June 2020

Co-based alloys have been successfully used as sputtered thin film media for hard disk drives. Media with higher recording density and lower media noise are required for the future hard disk drives. The magnetic properties can be controlled by processing and alloy composition. However, the origin of the magnetic properties, such as film coercivity and transition noise, are not fully understood yet. In this paper the analysis of the magnetic properties versus microstructure of Co-based alloy single and multilayer media is reported.

Co-alloy media were prepared by DC magnetron sputtering of Cr, Co-alloy (CoCrNi and CoCrPt) and overcoat materials(C and Zr) on Ultra Densified Amorphous Carbon (UDAC) substrates. The sputtering pressure and deposition temperature were 3-5 mTorr and between 30°C and 300°C, respectively.

The coercivity of CoCrNi and CoCrPt media increases with the deposition temperature in the range between room temperature and a few hundred degree Celsius. Figure 1 shows cross-section TEM(XTEM) images of CoCrPt media.
Magnetic-domain imaging techniques
Authors: McFadyen Ian R.
Published: June 2020

The concept of domains in ferromagnets was introduced by Weiss in 1906. However, they were not observed until 1931 when Bitter showed that domain boundaries could be observed by decorating them with fine magnetic particles. Since then the field of magnetic domain imaging has expanded enormously.

The original Bitter technique involved the decoration of a magnetic sample with a colloidal suspension of fine magnetic particles (usually magnetite) and observation by dark field optical microscopy. This is still a commonly used method and has been extended to finer particles, which include clusters directly deposited on the magnetic sample from a chemical vapor and observation of the clusters in the SEM or TEM at magnifications in excess of 20,000x.

Another very popular means of observing magnetic domains employs the magneto-optic Kerr effect. Both polar and longitudinal Kerr techniques has been utilized. In the polar Kerr technique a magnetic sample is illuminated by a beam of plane polarized light normal to the sample surface.
STEM of order and dynamics in novel magnetic materials
Authors: Mankos Marian , Cowley J.M. , Chamberlin R.V. , Scheinfein M. , Ayers J.D.
Published: June 2020

The new detection system of the HB5 STEM enables the operation of the microscope in a variety of modes. If the specimen is placed inside the objective lens, high resolution bright and dark field images revealing the microstructure can be obtained. Since the specimen is located in a high magnetic field, magnetic ordering phenomena are disturbed and no magnetic structure contrast is observed. In the out-of-field position, magnetic structure may be revealed in the Fresnel and Differential Phase Contrast modes of Lorentz Microscopy. Fresnel images are obtained with a static beam, i.e. the scanning coils are not excited. In the Fresnel mode the objective lens focus is changed slightly and domain walls appear in the shadow image as dark and bright lines, switching contrast when the objective lens is changed between overfocussing and underfocussing. Electrons, passing through the sample, are deflected by the Lorentz force and appear to converge towards or diverge from the domain walls.
Application of electron holography to material science studies on magnetic domain states of small particles
Authors: Hirayama T. , Ru Q. , Tanji T. , Tonomura A.
Published: June 2020

The observation of small magnetic materials is one of the most important applications of electron holography to material science, because interferometry by means of electron holography can directly visualize magnetic flux lines in a very small area. To observe magnetic structures by transmission electron microscopy it is important to control the magnetic field applied to the specimen in order to prevent it from changing its magnetic state. The easiest method is tuming off the objective lens current and focusing with the first intermediate lens. The other method is using a low magnetic-field lens, where the specimen is set above the lens gap.

Figure 1 shows an interference micrograph of an isolated particle of barium ferrite on a thin carbon film observed from approximately [111]. A hologram of this particle was recorded by the transmission electron microscope, Hitachi HF-2000, equipped with an electron biprism. The phase distribution of the object electron wave was reconstructed digitally by the Fourier transform method and converted to the interference micrograph Fig 1.
Microstructure and magneto-optic properties of unannealed and annealed Fe/Pt and Co/Pt multilayers
Authors: Visokay Mark R.
Published: June 2020

Two requirements for magneto-optical storage media are remanent perpendicular magnetization and large magneto-optic Kerr rotations. Several film structures and material systems have been proposed for this purpose, including amorphous rare earth-transition metal alloys, Co/Pt multilayer films and Co/Pt alloys. Another structure that has potential for magneto-optic applications are thin films of ordered alloys based on the Llo structure, with two possible materials systems being Fe/Pt and Co/Pt. Ordered CoPt and FePt both adopt the Llo crystal structure, are ferromagnetic, and are magnetically easy along the unique axis. Thin films oriented such that the c axis is out of the film plane are expected to have large perpendicular anisotropy, and both FePt and CoPt are known to have large Ken-rotations, so both of the requirements mentioned above can be met with these materials.

In order to produce the ordered structures oriented with the c axis out of the plane epitaxial multilayers of the two constituents were produced by magnetron sputtering onto epitaxial Pt [001] seed layers deposited onto MgO [001], resulting in multilayers stacked along Pt [001].
Experimental low-voltage-point projection microscopy
Authors: Spence J.C.H. , Qian W. , Liu J. , Lo W.
Published: June 2020

The remarkable achievement of atomic resolution by low voltage point projection microscopy has revived interest in this instrument, and, since resolution is approximately equal to virtual source size, demonstrates field-emission from tip regions of atomic dimensions. Ray-tracing calculations show the aberration coefficients and size of the virtual source to be subnanometer. The brightness of such a nanotip has been measured to be 7.7 × 1010 A cm -2 sr -1 (at 100 kV), somewhat greater than conventional cold field emitters or synchrotrons. The images require the theory of transmission LEED for interpretation and are always out of focus by the tip to sample distance zl. Their relationship to HREM images and coherent CBED is discussed elsewhere The instruments hold promise for imaging small organic molecules (across holey carbon grids), LB and other thin organic films where radiation damage is dominated by inner-shell processes.
Direct structure information using the focus-variation method
Authors: Van Dyck D. , Op de Beeck M.
Published: June 2020

1. Introduction
In, a new method was proposed to reconstruct the exit wavefunction of an object from a combination of images at closely spaced focus values. Recently, in the framework of a Brite-Euram project, the method has been implemented on a Philips CM20 ST electron microscope equipment with Field emission source and CCD camera. The first experimental results for the high TC superconductor YBa2Cu4O8 are presented in. In this case, the object is very thin so that the phase of the wavefunction directly reveals the projected potential of the atom columns. The oxygen columns could be observed with a resolution of 0.13 nm. However, when the object is thicker, the one-to-one correspondence between the wavefunction and the projected structure is not so straightforward due to the dynamical diffraction. This is shown in Figure 1 for Ba2NaNb5O15 where the heavy columns are revealed in the amplitude and the bright columns in the phase.
High-resolution imaging with the schottky emitter FEG TEM
Authors: Otten Max T.
Published: June 2020

The Philips CM-series Field Emission TEMs, equipped with the Schottky field emitter and operating at 200 kV (CM20 FEG and the newer CM200 FEG) and 300 kV (CM30 FEG) have a dramatically improved performance in HRTEM imaging relative to their LaB6 equivalents (Table 1). The spatial and temporal coherence of these microscopes far exceeds that of similar microscopes equipped with LaB6 filaments. As a result, the information in the HRTEM images proceeds well beyond the point resolution (the information limit for the 200 kV microscopes typically lies around 0.6× their point resolution) (Fig. 1).

The information limit is determined by brightness (controlling the illumination semi-angle α and thus the spatial coherence) and the energy spread (controlling the temporal coherence). These two factors are inversely related — if one goes up, the other goes down. The energy spread under HRTEM conditions is ∼0.8 eV, a value that is not inherent to the Schottky emitter but is due to the total system including the emitter and high-tension tank and accelerator.
Performance and applications of the holography electron microscope
Authors: Tonomura Akira
Published: June 2020

Electron holography is a two-step imaging method. However, the ultimate performance of holographic imaging is mainly determined by the brightness of the electron beam used in the hologram-formation process. In our 350kV holography electron microscope (see Fig. 1), the decrease in the inherently high brightness of field-emitted electrons is minimized by superposing a magnetic lens in the gun, for a resulting value of 2 × 109 A/cm2 sr. This high brightness has lead to the following distinguished features. The minimum spacing (d) of carrier fringes is d = 0.09 Å, thus allowing a reconstructed image with a resolution, at least in principle, as high as 3d=0.3 Å. The precision in phase measurement can be as high as 2π/100, since the position of fringes can be known precisely from a high-contrast hologram formed under highly collimated illumination. Dynamic observation becomes possible because the current density is high.
Quantitative electron holography applied to crystal wedges and interfaces
Authors: Gajdardziska-Josifovska M.
Published: June 2020

Electron holography is unique among transmission electron microscopy techniques in that it allows retrieval of phase of the electron wave, information which is lost with other imaging techniques. With access to the phase, interactions of the incident electron wave with the electrostatic and magnetic potentials of the specimen can be studied directly with high spatial resolution. Besides resolution enhancement, the original goal for electron holography, applications to wide range of materials problems are currently under investigation. This work will address applications to measurements of mean inner potential of crystals and to epitaxial crystal interfaces.

In non-magnetic materials, in the absence of external electrical fields and/or charge layers, the electrostatic potential which alters the phase of the exit surface wave results from the atomic potentials. For amorphous and polycrystalline samples of known thickness, the phase change depends on the volume average of the atomic potentials, i.e. the mean inner potential V0.
Application of electron holography to ferroelectric study
Authors: Zhang X. , Joy D. C. , Allard L. F. , Nolan T. A.
Published: June 2020

With the development of FE TEM, electron holography becomes a reality to materials scientists, which opens a new window for materials study. Weak phase objects, such as a thin transparent specimen or an electric or a magnetic field, which have little or no effect on the intensity of the transmitted wave, can readily be observed via holography because of the phase shift that they produce. Application of the electron holographic method has been extended to the study of ferroelectric domain wall structures. This work presents the most recent results in this area.

Polarization gradients within domain walls are extremely important for the understanding of the extrinsic elastio-dielectric properties of ferroelectrics. Electron holographic studies of the local domain wall profiles provide essential input parameters for phenomenological theories of domain structure and of the macroscopic properties derived from the theories. Figure 1(a) is an electron hologram of the ferroelectric (BaTiO3) 90° domain wall area.
Electron-diffraction studies of amorphous carbon thin films
Authors: Muller David A.
Published: June 2020

The sp2 rich amorphous carbons have a wide variety of microstructures ranging from flat sheetlike structures such as glassy carbon to highly curved materials having similar local ordering to the fullerenes. These differences are most apparent in the region of the graphite (0002) reflection of the energy filtered diffracted intensity obtained from these materials (Fig. 1). All these materials consist mainly of threefold coordinated atoms. This accounts for their similar appearance above 0.8 Å-1. The fullerene curves (b,c) show a string of peaks at distance scales corresponding to the packing of the large spherical and oblate molecules. The beam damaged C60 (c) shows an evolution to the sp2 amorphous carbons as the spherical structure is destroyed although the (220) reflection in fee fcc at 0.2 Å-1 does not disappear completely. This 0.2 Å-1 peak is present in the 1960 data of Kakinoki et. al. who grew films in a carbon arc under conditions similar to those needed to form fullerene rich soots.
Dry-Etch-induced damage in GaAs investigated via TEM
Authors: Cole M.W. , McLane G.F.
Published: June 2020

Plasma-assisted etching is an important III-V semiconductor fabrication technique for patterning device structures on the nanometer scale with high accuracy. The quality of the processed surface is of primary importance for most electronic applications. It is well documented that reactive ion etching (RIE), with its high self-biases, usually incurs material damage via ion bombardment which ultimately limits device performance. Magnetron ion etching (MIE) is an attractive alternative to RIE. Specifically, MIE has a lower sheath voltage than RIE and the discharge contains low to moderate energy ions, both of which allow wafer processing with less ion-induced damage. This study investigated the nature and extent of near surface disorder resultant from MIE with freon-12 (CCl2F2) via cross-sectional transmission electron microscopy (TEM). The effect of residual damage on device performance was evaluated via Schottky diode measurements. The GaAs wafers were etched under the following conditions:
Direct observation of Fe-Al-Zn ternary intermetallic compound and its transformation during the early stage of hot-dip galvanizing
Authors: Lin C. S. , Chiou W. A. , Meshii M.
Published: June 2020

The galvannealed steel sheets have received ever increased attention because of their excellent post-painting corrosion resistance and good weldability. However, its powdering and flaking tendency during press forming processes strongly impairs its performance. In order to optimize the properties of galvanneal coatings, it is critical to control the reaction rate between solid iron and molten zinc.

In commercial galvannealing line, aluminum is added to zinc bath to retard the diffusion rate between iron and zinc by the formation of a thin layer of Al intermetallic compound on the surface of steel at initial hot-dip galvanizing. However, the form of this compound and its transformation are still speculated. In this paper, we report the direct observations of this compound and its transformation.

The specimens were prepared in a hot-dip simulator in which the steel was galvanized in the zinc bath containing 0.14 wt% of Al at a temperature of 480 °C for 5 seconds and was quenched by liquid nitrogen.
TEM sample preparation of wear-tested room-temperature pulsed-laser-deposited thin films of MoS2 by ultramicrotomy
Authors: Lloyd Pamela F. , Walck Scott D.
Published: June 2020

Pulsed laser deposition (PLD) is a novel technique for the deposition of tribological thin films. MoS2 is the archetypical solid lubricant material for aerospace applications. It provides a low coefficient of friction from cryogenic temperatures to about 350°C and can be used in ultra high vacuum environments. The TEM is ideally suited for studying the microstructural and tribo-chemical changes that occur during wear. The normal cross sectional TEM sample preparation method does not work well because the material’s lubricity causes the sandwich to separate. Walck et al. deposited MoS2 through a mesh mask which gave suitable results for as-deposited films, but the discontinuous nature of the film is unsuitable for wear-testing. To investigate wear-tested, room temperature (RT) PLD MoS2 films, the sample preparation technique of Heuer and Howitt was adapted.

Two 300 run thick films were deposited on single crystal NaCl substrates. One was wear-tested on a ball-on-disk tribometer using a 30 gm load at 150 rpm for one minute, and subsequently coated with a heavy layer of evaporated gold.
Interfacial study of nanophase Pt or Pd particles on the surface of nanophase WO3 or TiO2 particles
Authors: Hsu Chi-Ming , Lin Hong-Ming , Tung Chiun-Yen , Hsu Teh-Yu , Yang Chao-Cheng
Published: June 2020

Nanocrystalline (NC) metals are a subdivision of the family of nanostructural materials. Nanostructural materials are single phase or multi-phase polycrystals, the crystal size of which is of the order of a few (typically 1-100) nanometers in at least one dimension. Nanocrystalline materials have many interesting physical and chemical properties which attract researchers. Particularly in catalyst’s utility, it can provide a large specific surface area and active sites. Its size efficiency (Kubo efficiency) may create different electron energy gap which permits us to do other functional designs. Some phenomenons contribute to attractiveness of nanocrystalline material as catalysts or sensors. The interfacial study between NC metal and oxides became an important issue to evaluate the performance of the these applications.

Gas-condensation technique is used to produce the nanophase WO3 or TiO2 by evaporating the tungsten in 10 mbar O2 atmosphere or pure titanium in (10 mbar O2/90 mbar He) atmosphere, respectively.
Electons' eyeview of buckytubes and friends
Authors: Lin Xiwei , Wang Yun-Yu , Wang X.K. , Yee A. , Dravid Vinayak P. , Chang R.P.H. , Ketterson J.B.
Published: June 2020

Synthesis, characterization and properties of various all-carbon molecules, the fullerene family (buckyballs), have been on the research forefront since the large scale production scheme developed by Krätschmer et al. Recently, Iijima and coworkers have reported TEM observations of hollow graphitic tubules of nanometer scale (buckytubes). In particular, the large scale buckytube synthesis method of Ebbesen and Ajayan has stirred considerable interest similar to that after the Krätschmer et al. discovery of large scale buckyball synthesis.

We have synthesized gram-scale quantities of buckytubes and their derivatives based on an arc method similar to that of Ebbesen and Ajayan. The arc was formed between a 1” and a 1/2 “ diameter graphite rods under 100 torr atmosphere of helium at a current of 180-200 Amps and a voltage of 20-30 V. The cross section of the resulting build-up rod consists of a gray core, followed by a black ring and another gray shell.
Location of adatoms on Si(100) surface using the electron channeling effect on Auger electron emission
Authors: Qian W. , Spence J.C.H. , Hembree G.G.
Published: June 2020

Atomic-site location by channeling enhanced microanalysis (ALCHEMI) is a powerful technique for identifying both the atomic number and the location of impurity atoms in crystals. The principle of the technique is simple: electron intensities on particular crystallographic sites within unit cell oscillate with variation of the incident beam direction. The corresponding characteristic emission spectra from atoms at those atomic sites follow these oscillations if the inelastic scattering events are localized. By careful analyzing the spectra of the impurity species and those of the reference atoms on known sites at various tilting angles, the location of the impurity atoms can be obtained. However, most applications of this technique have used the channeling effect on characteristic x-ray emission or energy loss spectra for location of impurity atoms in bulk crystals Here we study the possibility of applying this technique for locating adatom positions on a crystal surface, using the channeling effect on characteristic Auger emissions.
Structural defects induced by heavy-ion irradiation in superconducting oxides
Authors: Zhu Yimei , Zhang H. , Cai Z.X. , Budhani R.C. , Welch D.O. , Suenaga M.
Published: June 2020

We studied the the structure and properties of high Tc superconductors using heavy ions. While irradiation of YBa2Cu3O7-δ (hereafter denoted as 123) with 300 MeV Au+24 and 276 MeV Ag+21 ions produces columns of amorphous tracks along the ion trajectories, such defects are only created occasionally during irradiation with 236 MeV Cu+18, and are not induced with 182 MeV Si+13. A comprehensive electron microscopy study of defect formation in Bi2Sr2Ca2Cu3Ox, and in oxygen-reduced and ozone-treated 123, shows that the degree of radiation damage (the size and the shape of the defect) by the heavy ions depends on: (a) the rate at which ions lose their energy in the target; (b) crystallographic orientations with respect to the incident ion-beam (Fig.1); (c) thermal conductivity and chemical state (eg. oxygen concentration of 123) of the sample, and (d) the extent of pre-existing defects in the crystal. Calculation and simulation of the strain contrast surrounding the amorphous column using two-beam dynamical theory agree well with the observations and suggest that the reduced hole density observed in the crystal near the amorphous region is mainly due to lattice distortion.
Microstructural characterization of a cast RENi5-based alloy
Authors: Micha G. M. , Zhang L.
Published: June 2020

RENi5 (RE: rare earth) based alloys have been extensively evaluated for use as an electrode material for nickel-metal hydride batteries. A variety of alloys have been developed from the prototype intermetallic compound LaNi5. The use of mischmetal as a source of rare earth combined with transition metal and Al substitutions for Ni has caused the evolution of the alloy from a binary compound to one containing eight or more elements. This study evaluated the microstructural features of a complex commercial RENi5 based alloy using scanning and transmission electron microscopy.

The alloy was evaluated in the as-cast condition. Its chemistry in at. pct. determined by bulk techniques was 12.1 La, 3.2 Ce, 1.5 Pr, 4.9 Nd, 50.2 Ni, 10.4 Co, 5.3 Mn and 2.0 Al. The as-cast material was of low strength, very brittle and contained a multitude of internal cracks. TEM foils could only be prepared by first embedding pieces of the alloy in epoxy.
Characterization of laser-irradiated C60 solution and cell damage by SEM,TEM and atomic-force microscopy
Authors: Brandelik Donna M. , Sutherland Richard L. , Jiang Hao , Lloyd Pamela , Wade Adams W.
Published: June 2020

Investigation of laser irradiated purple C60/toluene solutions revealed a photochemical change of the solution at high incident laser fluences. The initial purple solution turned pink and a black precipitate formed which was insoluble in toluene. Interaction at the cell surface was indicated as cell damage occurred before the solution changes were seen. Subsequent chemical analysis by Mass Spectroscopy showed that the pink solution contained C60 and adducts. The black precipitate was found to contain no C60, but instead contained only adducts and lower fuller-enes NMR on the pink solution revealed a SiCHx peak as evidence of glass etching.

Scanning electron microscopy revealed needle crystals from a pure C60 sample, in figure 1. Figure 2 shows the crystals from the pink solution. The black precipitate appears to have a porous,very grainy texture and lacks the crystalline structure of the other samples (figure 3). All three samples were deposited on carbon coated grids. The pyrex glass cell was damaged by the laser and showed an etching pattern (figure 4).
Structure determination of inorganic structures by HREM, Cip, and electron diffraction
Authors: Zou Xiaodong , Zubkov V.G. , Svensson Gunnar , Hovmöller Sven
Published: June 2020

High resolution electron microscopy (HREM) combined with crystallographic image processing (CIP) is becoming a powerful technique for solving inorganic structures. With the image processing systems CRISP and ELD, running on a personal computer, this technique can be easily established in other laboratories. HREM images and electron diffraction patterns are digitized by a CCD camera and transferred into a PC. Phases and amplitudes are extracted from the Fourier transform of the HREM images. For thin crystals of metal oxides, the phases obtained by HREM and CIP inside the Scherzer resolution of the microscope are identical to the x-ray structure factor phases.

Electron diffraction extends to much higher resolution than EM images (beyond 1 Å). The quality of the amplitudes is also higher than that from images, since ED data is not affected by the contract transfer function (CTF). Amplitudes extracted by ELD are close to x-ray diffraction amplitudes (within 30%).
Is electron holography at atomic dimensions going to meet the expectations of Dennis Gabor?
Authors: Lichte Hannes
Published: June 2020

Electron microscopy faces the following basic situation: The electron wave transmitted through the object is modulated both in amplitude a and phase φ. In order to display the object structure, the object wave a exp(i φ) is transferred by the electron lenses into an image wave A exp(i φ) at sufficiently high magnification, modulated in amplitude and phase as well. However, due to the lens aberrations in the high resolution domain, image and object wave generally do not agree. One has to distinguish between coherent and incoherent aberrations. Coherent aberrations (e.g. spherical) are independent of electron energy andangle of illumination; preferably, their effect is taken into account in Fourier space by means of the wave transfer function WTF(u) = exp(i х (u)) depending on the spatial frequency u; х (u) means the wave aberration of the objective lens.
Scanning Tunneling Microscopy (STM) and Transmission Electron Microscopy (TEM) of biological structures
Authors: Engel A. , Stemmer A. , Aebi U.
Published: June 2020

STM and TEM have both demonstrated their capability to achieve atomic resolution. They provide complementary information of accute interest in structural biology: STM topographs are expected to give high resolution information on the surface structure of biomacromolecules whereas their three-dimensional mass distribution can be obtained from projections recorded by TEM. However, two kinds of limitations appear to be common to STM and TEM. Firstly, the interaction between image forming probe and sample can introduce significant structural rearrangements. In the STM this could be a disruption of the sample by the tip scanning too closely to the surface as well as a damage due to the high current density (1 nA at 1 V bias deposits 0.13* 106 W/cm2 on the sample via a 1 nm tunneling probe; this corresponds to a dose of 8*106 electrons/nm2 if one pixel of 1 nm diameter is recorded within 1 ms). In the TEM the high energy electrons (100 keV) generate beam damage at a dose of 102 to 103 electrons/nm2.