bluuebunny/crossref_metadata_2025 huggingface dataset:
Predation-induced E. coli filaments: Are they multicellular?
Authors: Gillott Marcelle A. , Holen Dale , Ekman Jonathan , Harry Michelle , Boraas Martin
Published: June 2020

Escherichia coli can have a filamentous growth form due to mutation or, in the current study, selection of predator-resistance when preyed on by a bactivorus protozoan. When used as food for the mixotrophic flagellate, Poterioochromonas malhamensis, filamentous E. coli appeared in continuous and batch cultures. The filamentous morphology of E. coli is persistent in plate and liquid culture in the absence of the flagellate. Typically, filament length is long in exponential growth and short in stationary phase.

A major question in the morphology of these filamentous E. coli (Fig. 1) is whether they are chains of cells that have failed to separate or whether they are a continuous filament without septa. Fluorescence light microscopy using DAPI, a DNA-specific stain, indicates that the filaments show both continuous fluorescence (Fig. 2a), indicating a continuous filament, and discrete units of fluorescence (Fig. 2b), indicating separate cells. Division patterns of living filaments observed with video microscopy show that cell division does occur, but it has been observed only at 10-20 μm from the ends of filaments.
Energy-dispersive x-ray mapping of grain boundaries in high-Tc superconductors
Authors: Barry J.C. , Auchterlonie G.J.
Published: June 2020

Superconductors are materials which carry electrical current without resistive loss below a certain critical temperature (Tc). There are many potential uses for materials that are superconducting, but until recently the Tc's of known materials were too low to be useful in large-scale applications such as power transmission. However, with the discovery of high Tc oxide superconductors, the feasibility of such projects are now being considered. The problem with the oxide superconductors is not that their critical temperature is too low (the Tc's of the oxides are almost an order of magnitude better than the metal superconductors), but rather that in bulk form their current carrying capacity (Jc) is too low. It is known that the bulk Jc is determined by intergranular conductivity. Low values for Jc may occur because of: (a) a change of stoichiometry at the grain boundaries, or (b) because of misorientation of adjacent grains. High Jc's can be achieved in thin films by texturing the material so that there are few grain boundaries across the direction of current flow but many grain boundaries perpendicular to the current flow.
Scanning electron microscopy of asbestos-containing material where the asbestos fibers are considered locked in a binder
Authors: Millette J. R. , Brown R. S.
Published: June 2020

The United States Environmental Protection Agency (EPA) has labeled as “friable” those building materials that are likely to readily release fibers. Friable materials when dry, can easily be crumbled, pulverized, or reduced to powder using hand pressure. Other asbestos containing building materials (ACBM) where the asbestos fibers are in a matrix of cement or bituminous or resinous binders are considered non-friable. However, when subjected to sanding, grinding, cutting or other forms of abrasion, these non-friable materials are to be treated as friable asbestos material. There has been a hypothesis that all raw asbestos fibers are encapsulated in solvents and binders and are not released as individual fibers if the material is cut or abraded. Examination of a number of different types of non-friable materials under the SEM show that after cutting or abrasion, tuffs or bundles of fibers are evident on the surfaces of the materials. When these tuffs or bundles are examined, they are shown to contain asbestos fibers which are free from binder material. These free fibers may be released into the air upon further cutting or abrasion.
The first decade of the disector
Authors: Gundersen H.J.G.
Published: June 2020

Nine years and eleven months ago the disector was described: a complete rule for uniform sampling of 3D structures strictly according to cardinality – and from sections, physical or just imaging planes.

Intuitively, the simplest situation is when particlenumber is wanted: with a uniform sample one just counts the number Q−in the sample and estimate numerical density NV or N directly (with the fractionator).

Along the way, it has been realized that under certain fortuitous circumstances one may also count other uniquebutnotisolated features of structure, like ’trees’ (ciliae, brush borders and other appendages on surfaces) and the complementary type, exemplied by glands and follicles. All these structures each have exactly one disk of connection to an easily recognizable surface, these disks may be counted in a disector.

The most basic mathematical definition of a 0-dimensional quantity or counting measure is that of the Euler number. The Euler number encompasses the number of isolated particles as a part of the definition, but is much more general.
Introduction to emission electron microscopy for the in situ study of surfaces
Authors: Kordesch Martin E.
Published: June 2020

The Photoelectron Emission Microscope (PEEM) and Low Energy Electron Microscope (LEEM) are parallel-imaging electron microscopes with highly surface-sensitive image contrast mechanisms. In PEEM, the electron yield at the illumination wavelength determines image contrast, in LEEM, the intensity of low energy (< 100 eV) electrons back-diffracted from the surface, as well as interference effects, are responsible for image contrast. Mirror Electron Microscopy is also possible with the LEEM apparatus. In MEM, no electron penetration into the solid occurs, and an image of surface electronic potentials is obtained.

While the emission microscope techniques named above are not high resolution methods, the unique contrast mechanisms, the ability to use thick single crystal samples, their compatibility with uhv surface science methods and new material-growth methods, coupled with real-time imaging capability, make them very useful.

These microscopes do not depend on scanning probes, and some are compatible with pressures up to 10-3Torr and specimen temperatures above 1300K.
In-situ measurements of scanned probe tip shape with etched nuclear tracks
Authors: Tentschert J. , Fraundorf P. , Armbruster B.
Published: June 2020

In air based Scanning Tunneling Microscopy (STM), tip geometry is often unknown so effects in images due to tip shape are difficult to quantify. While the importance of tip structure is often discussed, the methods for getting this information tend to be unsatisfactory in that they often involve ad hoc assumptions (seeing carbon atoms means a good tip) or they lack the ability to make measurements necessary to make quantitative assertions about unknowns. By exploiting the reproducibility of etched nuclear track pits, we have measured the tip interaction profile for an STM tip in air to a resolution of better than 4 nm in three dimensions.

As a source of nuclear track pits we coated Nuclepore filters to make them conductive for STM. We used holes in both the 50nm and 200nm range. As a height calibration we took an image of 30nm colloidal Au on HOPG. Our method was as follows: We took an image of an area containing several pits. Next, the image was flattened, several holes were cut and averaged, and a standard deviation image was calculated using the programming language Semper 6, see Figure 1.
Stereological ground rules
Authors: DeHoff R.T.
Published: June 2020

Microstructures have three primary attributes: chemistry; physics; and geometry. The chemical and physical attributes are routinely quantified. The geometry of microstructures is almost never quantified in spite of the existence of a sophisticated but easy to use measuring apparatus for the purpose called stereology.

Stereology is a mathematical apparatus that permits statistical inference of the geometric properties of three dimensional microstructures from information obtained from images of the structure that are essentially two dimensional. This tool is not widely used mostly because the ground rules have been presented vaguely, or with limited application, or perhaps because the basic relationships are too simple to be believable.

This presentation briefly reviews the geometric properties that may be accessed through the stereological apparatus, the kinds of measurements required, and the expected value theorems that connect the measurements to the three dimensional geometry.

Table 1 summarizes these three aspects of the content of stereology.
Image simulation in electron microscopy
Authors: Kilaas Roar
Published: June 2020

The theoretical calculation of High Resolution Transmission Electron Microscope (HRTEM) images has become a routine operation due largely to the existence of several commercially available computer programs. Associated with these “black box” calculations, exists a danger coming from the ease with which the programs can be used to produce images without any understanding of the underlying physical principles and approximations used in the calculations. While hopefully the majority of users of image simulation take the care to understand the limitations of the technique, there are several basic principles that must be understood in order to use the technique within the limits of its applicability. An example of this is shown in figure 1.

Although image simulation is fairly straightforward, and the technique has been applied successfully to many problems in HRTEM, figure 2, it is not an optimum tool for solving unknown structures. Each image depends on many adjustable parameters, the structure itself being the most important, and the task of computing hundreds of images and comparing them visually is a tedious task to say the least.
Image reconstruction using a focus series on thick biological specimens: TEM CTF correction
Authors: Han Karen F. , Sedat John W. , Agard David A.
Published: June 2020

The primary project of our laboratory is the investigation of chromatin structure by three dimensional electron microscope tomography. Three dimensional tomography involves the reconstruction of an object by combining multiple projection views of the object at different tilt angles. There are two complications that give rise to an inaccurate representation in the image of the projected object mass density: 1) electron-specimen interactions, and 2) electron microscope lens aberrations. In our abstract, “Analysis of Electron-specimen Interactions of Thick Biological Specimens in Transmission Electron Microscopy at 200 keV” elsewhere in these proceedings, we investigated image formation at the level of electron-specimen interactions at 200 keV. We extrapolated that at 300 keV, there is still a significant amount of elastic scattering for thick (up to 0.7 microns) biological specimens . Here, we demonstrate that this allows the correction of the microscope aberration function through multiple focus observations can enhance contrast.

For high resolution electron microscopy of crystalline materials, some authors have demonstrated that the focus variation method to reconstruct the specimen exit-surface electron wave can lead to an improvement in resolution.
Automated 3-D cell population analysis in thick tissue sections using laser-scanning confocal-microscopy data
Authors: Ancin Hakan
Published: June 2020

This paper presents methods for performing detailed quantitative automated three dimensional (3-D) analysis of cell populations in thick tissue sections while preserving the relative 3-D locations of cells. Specifically, the method disambiguates overlapping clusters of cells, and accurately measures the volume, 3-D location, and shape parameters for each cell. Finally, the entire population of cells is analyzed to detect patterns and groupings with respect to various combinations of cell properties. All of the above is accomplished with zero subjective bias.

In this method, a laser-scanning confocal light microscope (LSCM) is used to collect optical sections through the entire thickness (100 - 500μm) of fluorescently-labelled tissue slices. The acquired stack of optical slices is first subjected to axial deblurring using the expectation maximization (EM) algorithm. The resulting isotropic 3-D image is segmented using a spatially-adaptive Poisson based image segmentation algorithm with region-dependent smoothing parameters. Extracting the voxels that were labelled as "foreground" into an active voxel data structure results in a large data reduction.
A new method for determining sample thickness: A comparison to experimental results
Authors: Blackson John , Luo Suichu , Joy David C
Published: June 2020

Sample thickness is an important parameter in quantitative electron microscopy,. Several methods for determining sample thickness have been described previously. A theoretical method presented here utilizes the low loss region of the electron energy loss spectrum to calculate sample thickness. The method avoids many of the limitations of other methods and is applicable to a wide variety of samples. The method is compared to film thicknesses determined experimentally as described below.

Chromium films were deposited simultaneously onto collodion supported TEM grids and cured epoxy blanks using a Denton Hi Res 100 coater equipped with a Syton quartz crystal monitor. The cured epoxy blanks were covered with a layer of unpolymerized epoxy that was then cured. The chromium sandwich was cross sectioned using ultramicrotomy techniques employing a diamond knife. Sections were produced which were as thin as possible (<50 nm) to minimize measurement errors. Chromium film thickness was determined directly using transmission electron microscopy (Fig. 1).
Microanalysis of boundaries by AEM at different voltages
Authors: Garratt-Reed Anthony J.
Published: June 2020

It is well known that theory predicts a number of benefits for high-resolution analytical electron microscopy (AEM) in raising the electron energy. These benefits arise from three principal effects, namely, an anticipated linear decrease in the beam broadening in the foil with increasing energy, and an increase in the electron gun brightness with increasing energy, and an increase in the X-ray peak-tobackground ratio as the electron energy is raised. In addition, the decrease in the electron wavelength with increasing energy can also lead to improvement in the image resolution, although generally not in the microanalytical resolution. To set off against these benefits is the disadvantage that the ionization cross-section decreases with increasing beam voltage. However, although for the case of nonrelativistic electrons this can be a significant effect, in most cases, for relativistic electrons (those used for intermediate-voltage AEM, for example) this decrease is not severe. For example, fig. 1 plots the ionization cross-section for iron for electrons in the range 20-500kV, according to the relativistic equation of Chapman et. al. A further area of interest is the effect of radiation damage in the sample, which may increase or decrease at higher voltages.
Quantitative single-cell fluorescence imaging of indicator dyes
Authors: Gross David J. , Mahoney M礨 G. , Slakey Linda L.
Published: June 2020

The use of fluorescent molecular probes in combination with quantitative optical microscopy has burgeoned in the past few years due to dramatic advances in both fluorophore design and imaging instrumentation. A number of probes that exhibit fluorescence spectral shifts with ligand binding have been synthesized. Among them is fura-2, which has a high binding affinity for calcium ion and which shows an excitation spectral shift between the calcium-bound and calcium-unbound states. This talk will focus on fura-2-loaded arterial smooth muscle cells (SMC) stimulated to produce temporally and spatially dynamic changes in free cytosolic calcium ion concentration ([Ca2+]i) as measured by a charge-coupled device imaging system.

Intracellular Ca2+ is known to play a critical role in the regulation of the contractile state of vascular SMCs. A variety of extracellular agonists have been shown to stimulate transient [Ca2+]i elevation in vascular SMCs; among them are nucleotides that activate specific cell surface receptors.
The NSLS X-1AL scanning x-ray microscope
Authors: Jacobsen Chris , Kirz Janos , Lindaas Steve , Wirick Sue , Zhang Xiaodong , Williams Shawn , Anderson Erik , Kern Dieter , Ade Harald
Published: June 2020

Soft x rays are well suited to the study of low-Z elements in 0.1-10 μm thick specimens. A variety of soft x-ray microscopes are now under operation, several of which achieve image resolutions of 0.03-0.1 μm. Scanning x-ray microscopes offer some desirable charactistics: they are able to operate in a variety of imaging modes, including transmission, luminescence, dark field, and photoemission, and they enable minimum dose imaging by utilizing highly efficient photon counting detectors and placing moderate efficiency optics between the source and specimen rather than between specimen and detector.

The NSLS X-1AL scanning x-ray microscope uses an undulator at the National Synchrotron Light Source at Brookhaven National Laboratory as a tunable, high-brightness soft x-ray source. Monochromatized, spatially coherent illumination is focussed by a Fresnel zone plate fabricated using electron beam lithography. The sample is scanned through the 0.055 μm Rayleigh resolution focal spot using stepping motors (for large scans) and linearized piezos.
Cone-beam 3D image reconstruction in x-ray microtomography
Authors: Wang G. , Cheng P. C. , Lin T. H. , Shinozaki D. M. , Kim H.
Published: June 2020

An X-ray shadow projection microscope system using a scannable point source of X-rays is under development at AMIL-ARTS, SUNY at Buffalo, USA. The point source is generated by a focussed electron beam, which can be steered electromagnetically in a plane perpendicular to the optical axis of the microscope. A specimen is mounted on a rotatable mechanical stage for microtomography. Considering the hardware characteristics of this system and the limitations of current cone-beam reconstruction algorithms, a generalized Feldkamp’s cone-beam image reconstruction algorithm has been developed at our laboratories. In our cone-beam reconstruction, there are mainly two kinds of scanning scanning modes: planar and helix-like. A planar scanning locus is used to handle spherical or plate-like specimens. A typical case of planar scanning loci is a circle, which is used in Feldkamp’s cone-beam reconstruction. A helix-like scanning locus is used to deal with rod-shaped specimens. Without loss of generality, a locus turn of the X-ray source can be defined in cylindrical coordinates by the following equation:
Electron diffraction of copper phthalocyanine on the HVEM
Authors: Tivol W. F. , Turner J. N. , McCourt M. P. , Dorset D. L.
Published: June 2020

The use of high-energy (1200 kV) electrons has been shown to be advantageous in the ab initio structure analysis from electron diffraction of organic compounds. Previous studies showed that ab initio analysis of copper perchlorophthalocyanine could be accomplished ; accelerating voltages at or above 1000 kV, but net at 400 kV for crystals which are about 10 nm thick. Copper perbromophthalocyanine could also be analyzed ab initio at 1200 kV, but the presence of severe dynamical scattering precluded such analysis at lower voltages.

A study of copper perchlorophthalocyanine at accelerating voltages from 200 kV to 1200 kV showed that dynamical scattering accounted for the differences among the diffraction patterns which lead the failure of ab initio analysis at the lower voltages. The series of phthalocyanines offers a good model for the study of dynamical scatterin and direct phasing methods, since it consists of relatively radiation-resistant compounds for which high-resolution diffraction patterns can be obtained.
High-resolution electron diffraction analysis of structural changes associated with the photocycle of bacteriorhodopsin
Authors: Han Bong-Gyoon
Published: June 2020

Bacteriorhodopsin (bR) is a membrane protein fromHalobacterium halobiumwhich acts as a light-driven proton pump. This protein is a single polypeptide and contains a single prosthetic group, retinal. When light illuminates bR, protons are pumped from inside to outside to generate an electrochemical potential gradient. The light activated retinal drives a sequential photocycle. Intermediates of the photocycle can be distinguished by visible absorption spectroscopy. The intermediates are named bR, J, K, L, M, N and O. In the L to M step, a proton is released from bR to the outside of the cell, to generate a proton concentration gradient. This proton gradient can be used later by ATP synthase for ATP synthesis. Recently, two M substates linked by one irreversible step have been detected and named M1 and M2 . FTIR data has shown that these two M1 and M2 substates can be trapped by illuminating with green light at -33 °C and -13 °C respectively.
Direct phase determination and refinement in the electron crystallography of small structures
Authors: Dorset Douglas L. , McCourt Mary P.
Published: June 2020

The use of electron diffraction intensity data for quantitative determination of crystal structures was largely pioneered by Vainshtein, Pinsker and their co-workers, as recently reviewed, and was shown to produce results consistent with more typical X-ray structure analyses. Despite these encouraging results for a number of representative inorganic and organic materials, it is accurate to say that the technique has not been widely accepted by the crystallographic community. This is probably because, in several of the early analyses, contemporary X-ray structure results were used to provide heavy atom positions, thus providing much of the crystallographic phase information. Since it is also known that correct phases, combined with even scrambled structure factor amplitudes, will lead to a Fourier map that appears to be ’correct’, it is commonly (but incorrectly) thought that noab initioelectron diffraction determinations have been carried out for previously unsolved structures. In addition, the very complexity of n-beam dynamical scattering theory compared to ’primary extinction’ corrections has dampened enthusiasm to continue this work.
HREM study of strong-metal interaction in Pt/TiO2
Authors: Yao Ming-Hui
Published: June 2020

The chemisorption ability and catalytic properties of metal particles supported on reducible oxides are often altered by high temperature reduction(HTR) in a process known as strong metal-support interaction(SMSI). Different models have been proposed to explain the SMSI mechanism. In recent years, experimental evidences have favored the "decoration model", which suggests that SMSI is due to the encapsulation of the metal particles by oxide overlayer species dial have migrated from the support. HREM profile imaging was the most useful tool to directly relate these surface decorations to the SMSI effects. The profile imaging can provide atomic-scale information about supported particles and Uieir surfaces without image being obscured by overlapping contrast from the support.

In the present work, the SMSI effect in Pt/TiO2 and Pt/CeO2 model catalysts have been studied using HREM profile imaging and multislice simulations. HREM observations were made with a JEM-4000EX microscope, operated at 400 kV. Fig. 1(a) shows a typical profile image of TiO2 after HTR in H2 at 923K.
Crystallographic phase identification in the SEM: Backscattered electron kikuchi patterns
Authors: Michael J. R. , Goehner R. P.
Published: June 2020

The use of the recently developed charge coupled device (CCD)-based detector for the acquisition of high quality backscattered electron Kikuchi patterns (BEKP) has allowed on-line crystallographic phase identification studies to be conducted in the scanning electron microscope. High quality patterns suitable for analysis have been obtained in a wide variety of materials with little special specimen preparation. Phase identification through a combination of BEKP and energy dispersive x-ray spectrometry (EDS) is demonstrated by the identification of crystals present on ruthenium oxide thin films on Si. The crystals were identified as RuO2, a tetragonal phase.

The CCD-based detector has been described previously and will only be briefly described here. The detector consists of a scientific grade slow scan CCD coupled to a YAG scintillator by a fiber optic reducer. During operation the CCD is cooled to -40°C by a thermoelectric cooler. This detector allows high quality patterns to be recorded with beam currents as low as 10-10A and exposure times of 1 to 10 seconds.
Scanning Electron Microscope magnification calibration interlaboratory study
Authors: Postek Michael T. , Vladar Andras E. , Jones Samuel N. , Keery William J.
Published: June 2020

The National Institute of Standards and Technology (NIST) is in the process of developing a new scanning electron microscope (SEM) magnification calibration reference standard useful at both high and low accelerating voltages. This standard will be useful for all applications to which the SEM is currently being used, but it has been specifically tailored to meet many of the particular needs of the semiconductor industry. A small number of test samples with the pattern were prepared on silicon substrates using electron beam lithography at the National Nanofabrication Facility at Cornell University. The structures were patterned in titanium/palladium with maximum nominal pitch of approximately 3000μm scaling down to structures with minimum nominal pitch of 0.4μm. Several of these samples were sent out to a number of university, research, semiconductor and other industrial laboratories in an inter-laboratory study. The purpose of the study was to test the SEM instrumentation and to review the suitability of the sample design.
Electrochemical atomic layer epitaxy of semiconductor CdTe thin films
Authors: Huang Baoming M.
Published: June 2020

Semiconductor thin films have important applications in areas such as photovoltaics and luminescent displays. Electrodeposition of these films is a potential low cost, room temperature production technique. Electrochemical atomic layer epitaxy (ECALE) involves alternatively depositing individual element monolayer amount per ECALE cycle, taking advantage of the under-potential deposition (UPD) phenomena.

A series of CdTe thin films have been deposited using ECALE methodology in an electrochemical flow cell system. The 0.5 mM Te4+, Te blank, 5mM Cd2+, and Cd blank solutions are made with purasonic grade TeO2 and CdSO4, research grade electrolyte, and 18 M ohm water. The gold foil substrates are cleaned electrochemically before each experiment. An ECALE cycle starts with depositing monolayer amount Te, rinsing with Te blank, then depositing monolayer amount of Cd, and ending with rinsing with Cd blank solution. The whole flow cell system is controlled by a computer with house-written codes, and the deposition process can be fully programmed.
Interfacial properties of GaSb/InAs superlattices
Authors: Twigg M. E. , Bennett B. R. , Waterman J. R. , Davis J. L. , Shanabrook B. V. , Wagner R. J.
Published: June 2020

Recently, the GaSb/InAs superlattice system has received renewed attention. The interest stems from a model demonstrating that short period Ga1-xInxSb/InAs superlattices will have both a band gap less than 100 meV and high optical absorption coefficients, principal requirements for infrared detector applications. Because this superlattice system contains two species of cations and anions, it is possible to prepare either InSb-like or GaAs-like interfaces. As such, the system presents a unique opportunity to examine interfacial properties.

We used molecular beam epitaxy (MBE) to prepare an extensive set of GaSb/InAs superlattices grown on an GaSb buffer, which, in turn had been grown on a (100) GaAs substrate. Through appropriate shutter sequences, the interfaces were directed to assume either an InSb-like or GaAs-like character. These superlattices were then studied with a variety of ex-situ probes such as x-ray diffraction and Raman spectroscopy. These probes confirmed that, indeed, predominantly InSb-like and GaAs-like interfaces had been achieved.
Domain structures in donor-doped barium titanate ceramics
Authors: Sundaram S. K. , Berta Yolande , Speyer Robert F.
Published: June 2020

The effects of cooling rate and soaking time on the positive temperature coefficient of resistivity (PTCR) of donor-doped barium titanate ceramics have been well studied. Daniels and Wernicke presented a model which predicted that an increasing grain boundary thickness led to a continuous transition from a PTC thermistor to an intergranular capacitor. Common in grain boundary potential layer models of PTC behavior, is the assumption that the polarization vector is parallel to the domain boundary (180° domains). Haanstra and Ihrig observed only 90° domains (perpendicular polarization vectors in neighboring domains) in these materials. They did not observe any intergranular second phase in their microstructures, which had grain boundary thicknesses of 2 - 10 nm. They discarded the potential barrier model proposed by Hoffmann in which a 500 am thick second phase layer (possibly Ti-rich) was assumed to be present at the grain boundary. In the present investigation, the domain structures and grain boundary thicknesses in BaTiO3 PTC thermistor, and the intergranular capacitor specimens were studied.
Electron microscopy of ceramic superconductors
Authors: Grant Norton M. , Barry Carter C.
Published: June 2020

The microstructure of ceramic superconductors plays a crucial role in the transport properties of these materials. For example, it has been shown that high-angle grain boundaries can act as weak links and atomic scale defects can act as pinning centers. The nature and spatial distribution of such defects is related to the way in which the material is processed. Transmission electron microscopy (TEM) is an essential technique for understanding the relationship between microstructure, processing, and properties and for defect characterization. The advantage of TEM is that it is possible to combine various imaging modes with electron diffraction and other analytical techniques such as x-ray energy dispersive spectroscopy in order to obtain both structural and chemical information.

Early measurements of critical current densities (Jc) across individual tilt grain boundaries in YBa2Cu3O7-δ (YBCO) thin films demonstrated that Jc decreased with increasing misorientation angle. More recently, however, it has been observed that this phenomenon may not be the case for all high-angle grain boundaries.
Microstructure of dense MgO penetrated by a silicate liquid
Authors: Ramamurthy Sundar , Mallamaci Michael P. , Barry Carter C. , Duncombe Peler R. , Shaw Thomas M.
Published: June 2020

Grain boundaries control most of the critical properties of ceramic materials and devices. The presence of an intergranular amorphous phase in many polycrystalline ceramic compacts has been reported. Grain boundaries may also involve regions of ordered structure and amorphous (glassy) phase. Dense polycrystalline compacts are processed by liquid-phase sintering routes. The addition of sintering aids such as CaO, MgO and SiO2 influence the densification process substantially. During sintering the grain boundaries are wet by liquid phases, and amorphous films are often found at the grain boundaries and triple junctions in the sintered product. The presence of such films not only influences the sintering behavior but it also affects the final properties in the sintered product. These films have therefore been the subject of intense investigation. Silicate-based compositions are the typical glass phases observed in these materials.

In the present study, polycrystalline, dense MgO cubes have been penetrated by liquid monlicellite (CaMgSiO4) at 1700°C.
Microstructure and phase transformation in KNbO3
Authors: Popoola Oludele O. , Kriven Waltraud M.
Published: June 2020

KNbO3 is a perovskite ferroelectric ceramic material with important electro optical and non linear optical properties. It can be used in an optical parametric oscillator, secondary harmonic generator and photo refractive holographic storage devices. Its macroscopic properties depend on a number of inter-related features such as crystal structure, domain structure, defects and impurity content. KNbO3 has four known solid phases with decreasing symmetry with temperature: Cubic Tetragonal Orthorhombic Monoclinic. The paraelectric to ferroelectric transition occurs during the cubic to tetragonal transformation. The dielectric properties of KNbO3 have been extensively studied and related to the various phase transformations. The aim of this investigation is to study the orthorhombic to tetragonal phase transformations using TEM.

Thin slices were cut from a flux grown crystal and mechanically polished to a thickness of 100 μm with a 1 μm surface finish using diamond paste and isopropyl alcohol as the lubricant.
The Nature of Oxide Surfaces: Topographic and Electronic Structure
Authors: Bonnell Dawn A. , Liang Yong
Published: June 2020

Recent progress in the application of scanning tunneling microscopy (STM) and tunneling spectroscopy (STS) to oxide surfaces has allowed issues of image formation mechanism and spatial resolution limitations to be addressed. As the STM analyses of oxide surfaces continues, it is becoming clear that the geometric and electronic structures of these surfaces are intrinsically complex. Since STM requires conductivity, the oxides in question are transition metal oxides that accommodate aliovalent dopants or nonstoichiometry to produce mobile carriers. To date, considerable effort has been directed toward probing the structures and reactivities of ZnO polar and nonpolar surfaces, TiO2 (110) and (001) surfaces and the SrTiO3 (001) surface, with a view towards integrating these results with the vast amount of previous surface analysis (LEED and photoemission) to build a more complete understanding of these surfaces. However, the spatial localization of the STM/STS provides a level of detail that leads to conclusions somewhat different from those made earlier.
Thickness-dependent annular dark-field STEM
Authors: Hillyard Sean , Silcox John
Published: June 2020

The demonstration of Z-contrast atom structure images and high spatial resolution using annular dark field STEM has drawn considerable interest. This approach is well suited for quantitative image and diffraction pattern acquisition. Experimental data has been used to validate calculations of convergent beam electron diffraction (CBED) patterns in silicon and ADF STEM images of (100) InP. These procedures can be extended to explore the dependence of images on factors such as thickness.

Energy filtered CBED patterns over an angular range of over 150 mrads and covering a range of over four orders of magnitude in intensity from silicon were recorded with a VG HB501A STEM for thicknesses of 217Å, 326Å and 543Å. Simulation using a “frozen phonon” approximation successfully modeled this data provided an accurate phonon amplitude was used. A similar quantitative study for images has been carried out for (100) oriented InP. This sample contains indium columns at the comer of a 2.9Å square and phosphorus atoms at the square center.
Atomic structure of undoped Σ=5 symmetrical-tilt grain boundary in strontium titanate
Authors: Ravikumar V.
Published: June 2020

Strontium titanate is an important electroceramic material which, under appropriate processing and dopant additions exhibits both varistor and Grain Boundary Layer Capacitor (GBLC) behavior. The presence of electrically active grain boundaries is essential for obtaining these properties. The first step towards correlating the grain boundary structure to properties is to determine the detailed atomic structure of the boundary, which includes its geometric structure, chemistry and electronic structure. We present here our TEM investigation of the atomic structure of an undoped (“pristine”) symmetrical tilt grain boundary in SrTiO3. This provides the basic reference structure, changes to which can be studied as a function of doping and/or processing parameters, and correlated to electrical and dielectric properties.

Self-supported TEM samples were made from bicrystals of SrTiO3 through the conventional sample preparation route. Fig. 1 shows a high resolution electron micrograph (Hitachi H9000) of a representative grain boundary region in the sample.
Imaging magnetic microstructure with SEMPA
Authors: Kelley M. H. , Unguris J. , Celotta R. J. , Pierce D. T.
Published: June 2020

By measuring the spin polarization of secondary electrons generated in a scanning electron microscope, scanning electron microscopy with polarization analysis (SEMPA) can directly image the magnitude and direction of a material’s magnetization. Because the escape depth of the secondaries is only on the order of 1 nm, SEMPA is especially well-suited for investigating the magnetization of ultra-thin films and surfaces. We have exploited this feature of SEMPA to study the magnetic microstrcture and magnetic coupling in ferromagnetic multilayers where the layers may only be a few atomic layers thick. For example, we have measured the magnetic coupling in Fe/Cr/Fe(100) and Fe/Ag/Fe(100) trilayers and have found that the coupling oscillates between ferromagnetic and antiferromagnetic as a function of the Cr or Ag spacer thickness.

The SEMPA apparatus has been described in detail elsewhere. The sample consisted of a magnetic sandwich structure with a wedge-shaped interlayer as shown in Fig. 1.
Tunneling stabilized magnetic-force microscopy
Authors: Moreland John
Published: June 2020

Magnetic force microscopy (MFM) can be done by making a simple change in conventional scanning tunneling microscopy (STM) where the usual rigid STM tip is replaced with a flexible magnetic tip. STM images acquired this way show both the topography and the magnetic forces acting on the flexible tip. The z-motion of the STM piezo tube scanner flexes the tip to balance the magnetic force so that the end of the tip remains a fixed tunneling distance from the sample surface. We present a review of some “tunneling-stabilized” MFM (TSMFM) images showing magnetic bit tracks on a hard disk, Bloch wall domains in garnet films, and flux patterns in high-Tc superconductor films. The image resolution of TSMFM is routinely 0.1 μm using Au coated magnetic tips cut from Ni or Fe films. Recent results show that a TSMFM resolution of less than 40 nm is possible with micromachined cantilevers coated with a very thin Au-Fe bilayer.
Digital processing of high-resolution electron holograms
Authors: Völkl E. , Allard L. F.
Published: June 2020

Electron Holography has been shown to be an useful tool in high resolution imaging for obtaining more information from the electron image than is possible in conventional microscopy. In our laboratory we presently record our images on photographic material, and then digitize them by using a 4096 pixel line scan by EKTRON. Digitizing photographic material and correcting for its nonlinearities is a time consuming process which will soon be alleviated by the installation of the GATAN retractable slow-scan CCD-camera. Both camera and microscope will be operated from a Macintosh computer using the software “Digital Micrograph®” and “Advanced Acquisition®”, the first of which is used already for image processing of our negatives.

From an electron hologram, e.g. an hologram of a PMN ferroelectric material (FIG. 1a), the diffraction pattern of the object (FIG. 1b) can be obtained and evaluated from areas as small as one unit cell.
CBED+EBI holography of materials structures
Authors: Herring R.A. , Tanji T.
Published: June 2020

A new method of holography is presented using the CBED+EBI technique of interferomctry. The CBED+EBI method produces interferograms by using an electron biprism to interfere diffracted beams produced from a convergent beam probe. Holography is made possible by the fact that the beams continue to interfere as they are displaced from each other slightly, Fig. 1. This fact enables an object beam to be taken from one part of a crystal (e.g. a crystal defect) and a reference beam to be taken from another part of the crystal (e.g. the perfect crystal). The interference results in a phase shift around the dissimilar region. As well, for small defects which do not disturb or phase shift one beam (say the main beam) significantly but do so with the diffracted beam, directly overlaying the two beams results in a significant phase shift at the small defect. These methods are very easy to apply although the interpretation of phase shifted regions still requires knowledge of the crystal, its diffraction characteristics and interference effects.
Origin of the defect structures in oxygen-implanted silicon-on-insulator material
Authors: Venables D. , Krause S.J. , Lee J.D. , Park J.C. , Roitman P.
Published: June 2020

Silicon-on-insulator material fabricated by high-dose oxygen implantation (known as SIMOX) has been used for high speed and radiation hard devices and is under consideration for use in low power applications. However, a continuing problem has been crystalline defects in the top silicon layer. SIMOX is fabricated by two distinct methods: a single oxygen implant to a dose of 1.8×l018 cm-2 followed by a high-temperature anneal (≥1300°C, 4-6 hr) or by multiple lower dose implants (∼6×l017 cm-2) with high-temperature anneals after each implant. To date, there has been no systematic comparison of the defect structures produced by these two fabrication methods. Therefore, we have compared the defect structure and densities in multiple vs. single implant wafers. In this paper we describe the origin and characteristics of the defect structures in SIMOX and show how their densities are controlled by the processing method and conditions.

Silicon (100) wafers were implanted in a high current implanter at ∼620°C to doses of 1.8×l018 or 0.6/0.6/0.6×l018 cm-2 and annealed at 1325°C, 4 hr in 0.5% or 5% O2 in Ar. Cross-section (XTEM) and plan-view (PTEM) samples were studied with bright field and weak beam dark field techniques in a transmission electron microscope operating at 200 keV.
Characterization of NiO thin films on α-Al2O3 before and after heat treatment
Authors: Kotula Paul G. , Barry Carter C.
Published: June 2020

The NiO-α-Al2O3 system is of interest as a model system for the study of phase boundaries and reaction kinetics in oxide ceramics. Such a system is of new importance when one of the constituents is a thin film because the reaction kinetics and its dependence on film microstructure is not well understood. Additionally, solid-state reactions between a thin film and single-crystal substrate can be used to produce buffer layers for heterojunctions.

In the present study, thin films of NiO have been grown on single-crystal α-Al2O3 substrates by pulsed-laser ablation (PLA). The PLA system used a KrF (248nm) excimer laser operating at 350 mJ per pulse with a pulse repetition rate of 10 Hz. The laser beam was focused to a spot 1×2mm on the surface of rotating NiO pellet. Films were grown at nominal substrate temperatures of 750°C and oxygen pressures of about 10 mTorr. Films were grown both on bulk substrates for which 6000 laser pulses was used to produce 1000Å films and electron-transparent substrates for which 500 laser pulses was used to produce 80Å films.
CBED determinations of step-heights on etched and annealed MgO (100) surfaces
Authors: King Simon , McKernan Stuart , Barry Carter C.
Published: June 2020

The annealing in air of acid-etched (100)-oriented MgO substrates at 1350°C for 10 mins or more, has been shown to promote the formation of relatively large and well-defined surface steps. It is the presence of these surface steps which are thought to result in the improvement in the super conducting properties of thin films, such as YBa2Cu3O7-x (YBCO), deposited onto the surfaces of annealed, as oppose to unannealed, substrates. YBCO, in particular, has been shown to exhibit grapho-epitaxy, in which steps on the surface promote the nucleation of islands and influence the subsequent growth into an interconnected film. The formation of this interconnected film may be influenced by the height of the steps on the substrate, whilst the height of the steps also may play a role in the island nucleation event itself. Therefore, an investigation of the step heights in the acid-etched and annealed substrates employed for the above studies is of paramount importance.
Some comparative observations of carbide precipitation morphology related to coherent twin boundaries and high-energy grain boundaries in stainless steels
Authors: Romero R. J. , Trillo E. A. , Advani A. H. , Murr L. E. , Fisher W. W.
Published: June 2020

Stickler and Vinckier showed more than three decades ago that there is a very consistent relationship between the boundaries upon which carbides (M23 C6) precipitate in 300 series stainless steels (having carbon contents ranging from 0.02 to 0.08 wt%). For example, carbides first appear on regular (high-energy) grain boundaries, then non-coherent boundaries and steps on annealing twins, and finally on coherent twin boundaries at a constant temperature above about 600° C, and at aging times which, correspondingly, change by orders of magnitude (1,10, 100 hrs. respectively at 675°C for 304 stainless steel). We have examined a wide range of precipitation features on these various boundaries in 316 and 304 stainless steels which have not been described previously because there have been limited observations comparing carbide morphologies in the transmission electron microscope (TEM) for high-energy grain boundaries (γgb ∼ 800 mJ/m2), non-coherent steps on twin boundaries (γTB ∼ 200 mJ/m2), and coherent twin boundaries (γtb ∼ 20 mJ/m2) for 316 and 304 stainless steels.
Electron microscopy of natural and epitaxial diamond
Authors: Posthill J.B. , George T. , Malta D.P. , Humphreys T.P. , Rudder R.A. , Hudson G.C. , Thomas R.E. , Markunas R.J.
Published: June 2020

Semiconducting diamond films have the potential for use as a material in which to build active electronic devices capable of operating at high temperatures or in high radiation environments. Ultimately, it is preferable to use low-defect-density single crystal diamond for device fabrication. We have previously investigated polycrystalline diamond films with transmission electron microscopy (TEM) and scanning electron microscopy (SEM)e.g.1 and homoepitaxial films with SEM-based techniquese.g.2. This contribution describes some of our most recent observations of the microstructure of natural diamond single crystals and homoepitaxial diamond thin films using TEM.

We are developing techniques to thin diamonds to electron transparency in the region of interest; particularly as diamond is difficult to mechanically thin. One simple (but time consuming) approach for the fabrication of plan-view diamond TEM samples is to thin only by ion milling. Figs. 1 and 2 show TEM micrographs taken from a (100) natural type IIb (semiconducting) diamond crystal and a (100) natural type la diamond that have been ion milled to electron transparency.