bluuebunny/crossref_metadata_2025 huggingface dataset:
High-purity Ge x-ray detectors: Sensitivity factors and usefulness
Authors: Steel E. B.
Published: June 2020

High Purity Germanium (HPGe) x-ray detectors are now commercially available for the analytical electron microscope (AEM). The detectors have superior efficiency at high x-ray energies and superior resolution compared to traditional lithium-drifted silicon [Si(Li)] detectors. However, just as for the Si(Li), the use of the HPGe detectors requires the determination of sensitivity factors for the quantitative chemical analysis of specimens in the AEM. Detector performance, including incomplete charge, resolution, and durability has been compared to a first generation detector. Sensitivity factors for many elements with atomic numbers 10 through 92 have been determined at 100, 200, and 300 keV. This data is compared to Si(Li) detector sensitivity factors.

The overall sensitivity and utility of high energy K-lines are reviewed and discussed. Many instruments have one or more high energy K-line backgrounds that will affect specific analytes. One detector-instrument-specimen holder combination had a consistent Pb K-line background while another had a W K-line background.
Finding out more and more about less and less—fifty years of milestones in microanalysis
Authors: Wittry D.B.
Published: June 2020

During the past half century, a wide variety of techniques of microanalysis have been developed to a practical stage and many of these are presently undergoing refinement and improvement. In fact, practically every means of bombarding a specimen with radiation and observing signals from the interaction of this radiation with the specimen has been explored, as shown in Fig. 1. Many of the techniques used in microanalysis today are based on physical principles that were known for many years. But they became practicable only with improved technology, e.g. improved vacuum systems, sources, detectors, lenses, spectrometers, signal amplifiers and computers.

A "road map" of the history of microanalysis would contain some of the milestones along the way, similar to the list of significant events in the history of microscopy published in the EMSA Bulletin in Fall of 1983. My own (and highly subjective) list is given in the Table. It is not surprising that many of the key figures contributors on this list have been previous recipients of the EMSA Distinguished Scientist Award (names printed in bold face).
Structural and electronic properties of defects in semiconductors
Authors: Batstone J.L.
Published: June 2020

The development of growth techniques such as metal organic chemical vapor deposition (MOCVD) and molecular beam epitaxy during the last fifteen years has resulted in the growth of high quality epitaxial semiconductor thin films for the semiconductor device industry. The III-V and II-VI semiconductors exhibit a wide range of fundamental band gap energies, enabling the fabrication of sophisticated optoelectronic devices such as lasers and electroluminescent displays. However, the radiative efficiency of such devices is strongly affected by the presence of optically and electrically active defects within the epitaxial layer; thus an understanding of factors influencing the defect densities is required.

Extended defects such as dislocations, twins, stacking faults and grain boundaries can occur during epitaxial growth to relieve the misfit strain that builds up. Such defects can nucleate either at surfaces or thin film/substrate interfaces and the growth and nucleation events can be determined by in situ transmission electron microscopy (TEM).
Automated electron tomography: from data collection to image processing
Authors: Liu Weiping , Fung Jennifer , de Ruijter W.J. , Chen Hans , Sedat John W. , Agard David A.
Published: June 2020

Electron tomography is a technique where many projections of an object are collected from the transmission electron microscope (TEM), and are then used to reconstruct the object in its entirety, allowing internal structure to be viewed. As vital as is the 3-D structural information and with no other 3-D imaging technique to compete in its resolution range, electron tomography of amorphous structures has been exercised only sporadically over the last ten years. Its general lack of popularity can be attributed to the tediousness of the entire process starting from the data collection, image processing for reconstruction, and extending to the 3-D image analysis. We have been investing effort to automate all aspects of electron tomography. Our systems of data collection and tomographic image processing will be briefly described.

To date, we have developed a second generation automated data collection system based on an SGI workstation (Fig. 1) (The previous version used a micro VAX). The computer takes full control of the microscope operations with its graphical menu driven environment. This is made possible by the direct digital recording of images using the CCD camera.
Advances in image simulation for high-resolution TEM
Authors: O'Keefe Michael A.
Published: June 2020

The original high-resolution transmission electron microscope (HRTEM) image simulation program was written as a tool to confirm interpretation of HRTEM images of niobium oxides. Thorough testing on known structures showed that image simulation could reliably duplicate the imaging process occurring in the HRTEM, and could thus be confidently used to interpret images of unknown structures. Mainstream application of image simulation to routine structure determination by HRTEM was ushered in by the establishment of the wide applicability of the SHRLI (simulated high-resolution lattice image) programs. Structure determination of the mineral takéuchiite by HRTEM and image simulation was the first such determination accepted by the KJCr without x-ray data. Of course, once the reliability of image simulation had been established, it was realized that the technique could be put to work for applications other than structure determination. Early on, simulations were used to explore various HRTEM imaging parameters, including specimen ionicity, validity of the projection approximation, and the resolutionlimiting effects of incident-beam convergence. Since the inception of HRTEM image simulation, its range of uses has continued to expand, and so has the number of programs available; distribution of the SHRLI code spawned improved versions as well as some new programs.
New applications of near-field optical storage
Authors: Kino G. S. , Hayashi S. , Ichimura I.
Published: June 2020

Some time ago, we described a new type of near-field imaging system using the Solid Immersion Lens. A confocal microscope using this principle has demonstrated sub-100 nm resolution with visible light. In this paper, we will describe how this device is being applied to increasing the density of optical storage in CD ROMs and magneto-optical storage systems.

The SIL is placed between the objective and the disk. As illustrated in Fig. 1(a), if the SIL is in the form of a hemisphere, rays enter it along its radii and converge at its center. If the refractive index of the SIL is n, the wavelength in this material is reduced by 1/n and consequently increases the effective NA of the objective lens by the refractive index n and decreases the spot size by 1/n. With this configuration, we were able to obtain good quality images of a grating with 100 nm gaps and strip widths.
High-resolution Transmission Electron Microscopy of dislocations in intermetallic compounds
Authors: Mills M.J.
Published: June 2020

The fine structure of dislocations plays a critical role in determining the macroscopic mechanical behavior Intermetallic compounds. Many of the technologically important characteristics of these compounds, an example their strength at high temperatures, appear to be determined by intricate details of dislocation stucture at the atomic level. High resolution transmission electron microscopy (HREM) offers the etential to obtain structural information at this level by observing these line defects in an "end-on" configuration.

Samples of HREM images of several important dislocation types in Ni3Al and TiAl are shown in Figures through 3. Each of these particular dislocation types (i.e. Burgers vectors and line directions) tend to be longly favored in these compounds, indicating that along these line directions the dislocations are likely have either low mobility or low energy.
Photoelectron diffraction and holography: new directions in imaging atoms near surfaces
Authors: Fadley Charles S.
Published: June 2020

Photoelectron spectroscopy is by now a widely applied characterization technique in physics, chemistry, and materials science in which the energy, direction, and perhaps also spin of electrons ejected from a solid surface are measured, thereby providing a broad range of information on atomic composition and electronic, atomic, and magnetic structure. However, further measuring the directional dependence of electrons excited from core levels yields what has been termed photoelectron diffraction, a versatile probe of near-surface atomic positions and magnetic order. Photoelectron diffraction has been used to study a wide variety of surface structure problems, including adsorption, epitaxial growth, and surface structural and magnetic phase transitions. This technique is also unique in permitting the separate study of chemically, structurally, or magnetically distinct atoms of a given type, through high-resolution measurements of core binding energy shifts and multiplet splittings in openshell systems. Such diffraction data can also be analyzed with a holographic fourier-transform methodology, thus yielding the exciting prospect of direct three-dimensional images of both atomic positions and magnetic order.
Advanced microscopy—the new high-resolution zone-plate microscope at the advanced light source in Berkeley
Authors: Meyer-Ilse W. , Medecki H. , Magowan C , Balhorn R. , Moronne M. , Attwood D.
Published: June 2020

A new x-ray microscope (XM-1) has been installed at the Advanced Light Source in Berkeley. This transmission microscope uses zone-plates for a resolution exceeding visible light microscopies. Samples can be as thick as 10 microns, for wet or dry specimens. These features make x-ray microscopy a valuable complement to other advanced techniques.

There are two types of x-ray microscopes, scanning and conventional (imaging) microscopes. The scanning type minimizes radiation dose to the sample and is convenient for high resolution use of fluorescent labels; however, it requires a spatially coherent x-ray source and as a result involves long exposure times. The conventional type provides a higher potential for ultimate resolution as there is no scanning stage needed, and it can operate with an incoherent light source. It therefore has a shorter exposure time, but does require a higher radiation dose due to lens inefficiencies. The new XM-1 is of the second type. Its optical layout is very similar to the Gottingen x-ray microscope operated at the BESSY facility in Berlin, Germany.
Multiple plasmon scattering contributions to CBED contrast
Authors: Marthinsen Knut , Høier Ragnvald , Holmestad Randi
Published: June 2020

One of the most successful applications of quantitative convergent beam electron diffraction (CBED) which have developed over the last years are methods for accurate determination of low-order structure factors. Obvious applications are determination of electron charge densities and bonding effects. However, the use of these methods is still not straight forward, and they are demanding and expensive both experimenatlly and computationally. The experiments have in general to be based on digital intensity recording and energy filtering for partly removing the background of inelastically scattered electrons. Computationally the methods are based on multi-parameter least squares fitting between experiment and theory, and since the complexity of the problem is O(n3), where n is the number of beams included in the calculations, one of the central problems here is to limit n without loss of accuracy. The present work is focused on a theoretical description of the multiple inelastic scattering contributions, in particular plasmon scattering contributions, to CBED contrast.
Chemical sensitivity of convergent beam electron diffraction on the stoichiometry of GaN
Authors: Liliental-Weber Zuzanna , Kisielowski Christian , Washburn Jack
Published: June 2020

III-V nitride thin film growth has attracted considerable attention because it now seems feasible to engineer semiconductor band gaps between 2.1 and 6.2 eV. One of the challenges coming with this development is related to the fact that structural perfection seems not to correlate directly with optical properties such as the emission of blue-green or UV light in GaN. In order to better understand this material High Resolution Transmission Electron Microscopy (HREM) and Convergent Beam Electron Diffraction (CBED) experiments were used to study structural defects in GaN thin films. Experiments were performed with a Topcon 002B and ARM operating at 200 and 800 KeV, respectively, and were guided by image simulations. Results of parallel luminescence studies will be published elsewhere.

Plan-view micrographs of GaN grown on the (0001) basal plane of A12O3 with a lattice mismatch of 14% show small angle grain boundaries which divide the layer into large subgrains of about 800 nm diameter. Other defects visible in the plan-view micrographs are threading dislocations and planar defects lying parallel to the {1010} planes of the GaN.
Structure factor measurement in TiAl and silicon
Authors: Swaminathan S. , Wiezorek J. M. , Jones I. P. , Zaluzec N. J. , Maher D. M. , Fraser H. L.
Published: June 2020

The accurate measurement of low order structure factors is required for the determination of the electron charge density distribution in crystals. In this work the energy-filtered convergent beam electron diffraction (CBED) rocking curve method has been used for accurate structure factor measurements. This CBED method for structure factor refinement involves matching of the experimental CBED intensities to those calculated using dynamical electron diffraction theory. The CBED experiments were conducted with a Philips EM420 Transmission Electron Microscope coupled with a custom built energy-filtering attachment enabling single electron counting. The theoretical pattern matching was performed using FORTRAN programs which were developed by Swaminathan. Initially the experimental plan involved an attempt to refine structure factors of TiAl by two dimensional Bloch wave calculations. The results of this project have been reported elsewhere. Subsequently it proved impossible to obtain results with sufficient precision for TiAl reproducibly, i.e. less than 0.1%, from samples of different thicknesses.
Electron Microscope investigation of crack path selection and crack interface interactions in a W-ZrO2(Y2O3) directionally solidified eutectic (DSE)
Authors: Isabell T.C. , Dravid V.P. , Hill D.N.
Published: June 2020

Metal-ceramic composites play a vital materials role in many technologically important industries due to their unique electrical, thermal and structural properties. The mechanical properties of metal-oxide materials are largely controlled by the properties of the metal-ceramic interface, specifically its structure and chemistry which govern the bonding between the constituents. For a brittle matrix composite, the fracture properties of the interface can determine the failure response of the composite as a whole.

The W-ZrO2(Y2O3) directionally solidified eutectic was grown by a skull melting technique described elsewhere. Composites were grown with 10 mol % yttria and ~ 6 w% tungsten. Figure 1 is a scanning electron micrograph showing that the tungsten grows as parallel fibers approximately lujn in diameter in a zirconia matrix. Selected area diffraction of the composite (Figure 2) reveals the growth direction to be: <110>zrO2 // <11l>w.

Electron microscopy of microindentation cracks, of pre-existing microcracks due to thermal expansion anisotropy and of short cracks inadvertently introduced during specimen preparation shows four different crack-interface interactions:
Martensitic transformation in zirconia-alumina nanolaminates
Authors: Gajdardziska-Josifovska M. , Aita C. R.
Published: June 2020

With an eye towards developing transformation-toughening ceramic coatings, we grew multilayers of polycrystalline zirconia and amorphous alumina in which the layer spacing was scaled to insure nanosize zirconia crystallites. In this manner, nanolaminates with a high volume fraction of tetragonal zirconia (t-ZrO2) were produced, independent of the deposition parameters and without the use of dopants.

For a coating to be of practical use, not only must it contain a significant amount of t-ZrO2, but this phase must also transform locally to the monoclinic phase (m-ZrO2) m response to stress. In bulk zirconia-alumina composites, with dopant stabilized tetragonal zirconia, the martensitic t → m transition is auto-catalytic, resulting in widespread transformation of the parent phase. Twinning and slip are the recognized transformation mechanisms. In this work, we study the transformation mechanism in zirconia-alumina nanolaminates using high resolution electron microscopy (HREM).

The multilayers were grown by reactive sputter deposition in a multiple target if diode system.1 Si (111) wafers were used as substrates for the multilayers studied by microscopy.
Nanocomposite processing via infiltration of mesoporous silica
Authors: Srinivasan U. , Homma I. , Chun C. M. , Dabbs D. M. , Hajduk D. A. , Gruner S. M. , Aksay I. A.
Published: June 2020

Synthesis of materials with nanoscale (1~100 nm) organization is important in various applications. Recently, scientists at Mobil described a new family of mesoporous molecular sieves. These materials have regular arrays of uniform pore channels ranging from 1.6~10 nm in diameter in contrast to other mesoporous solids such as amorphous silicas and modified layered clays and silicates. A surfactantsilicate co-assembly model has been proposed to explain the formation of these materials. According to this pathway, the matching of the charge density at the organic-inorganic interface controls the assembly of the mesophases and four distinct silica mesophases have been observed, lamellae, hexagonally packed tubes, and two bicontinuous structures of cubic symmetry. Different phases are constructed by varying the synthesis parameters such as the surfactant/silicate ratio and the acidity. Here, we report the synthesis of a new amorphous mesoporous phase with short range order and with no long range crystallinity. Due to its interpenetrating network structure, this amorphous mesoporous silica can be used as a matrix for nanocomposite processing. Here, we use it as a host to process ruby glass.
Crystallization of nano-size thallous oxide during ion irradiation of Tl-Ba-Ca-Cu-O high-temperature superconductors
Authors: Newcomer P. P. , Wang L. M. , Miller M. L. , Ewing R. C.
Published: June 2020

The Tl-Ba-Ca-Cu-O class of type-II high temperature superconductors (HTS) have Tc's as high as 125K. Although they have good critical current values, when a field is applied the weak pinning and consequent flow of magnetic vortices are a major impediment to the usefulness of these materials. Ion irradiation has been shown to enhance the pinning. High quality single crystals, as determined with x-ray precession and HRTEM, with sharp HTS Meissner signals, were irradiated with 1.5 MeV Kr+ and Xe+ ions using the HVEM-Tandem facility at Argonne National Laboratory. Ion beam microstructural modification was studied in-situ using electron diffraction and after irradiation using HRTEM and nano-beam EDS on Tl-1212 and Tl-2212 (numbers designate the stoichiometry Tl-Ba- Ca-Cu-O) single-crystal HTS. After irradiation, microstructure was studied using the JEOL 2010 in the Earth and Planetary Science Department at the University of New Mexico in order to characterize the resulting irradiation-induced nano-size precipitates.
In Situ hot-stage high-resolution Transmission Electron Microscope studies of the mechanisms and kinetics of precipitation reactions
Authors: Howe James M.
Published: June 2020

In situ hot-stage high-resolution transmission electron microscopy (HRTEM) provides unique capabilities for quantifying the mechanisms and kinetics of precipitation reactions at the atomic level. Such information is required to understand phase transformations and the behavior of material interfaces. This paper provides a brief summary of the in situ hot-stage HRTEM technique and illustrates the use of this technique to obtain information about heterogeneous nucleation processes in precipitation and crystallization reactions. Examples of other types of in situ HRTEM studies can be found in previous papers by Sinclair et al. and Howe et al.

The specimen and microscope requirements for in situ hot-stage HRTEM are the same as those for static HRTEM except that one must have a hot-stage specimen holder and equipment for recording and analyzing dynamic images. A high-resolution television-rate camera connected to a standard videocassette recorder (VCR) can be used to store hours of data for low cost. The dynamic images can then be analyzed directly during playback or sent to a computer for image processing and analysis.
Analytical ultra high-voltage Electron Microscope equipped with EDS and energy-filtered imaging system at NRIM
Authors: Furuya K. , Osaki M. , Hagiwara S. , Saito T.
Published: June 2020

The ultra high voltage transmission electron microscope (UHV-TEM) having an acceleration voltage of 1000 kV or more has been used for the observation of atomic structure of materials because of its high resolution approaching to 0.1 nm. Few effort has been done to develop an analytical UHV-TEM with energy dispersive x-ray spectroscope (EDS) for in-situ experiments such as ion irradiation, because high density of hard x-ray accompanied with primary electrons is supposed to prevent to measure the characteristic x-ray from the specimen. However, the observation of the heterostructures and interfaces requires analytical capability of determining the local chemical composition compatible with high resolution electron microscopy. This paper describes about a new analytical UHV-TEM (AHV-TEM) equipped with EDS and energy filtered imaging system and its application to Ni silicide thin film.

The AHV-TEM in this study is based on JEM-ARM1000 with a side entry goniometer. Figure 1 shows the comparison of calculated CTF and optical diffractogram of amorphous Ge taken near Scherzer defocus with E=1000 keV, Cs=2.6 mm, Cc=3.4 mm and Qi=0.3 mrad.
Quantitative elemental concentrations by energy-filtered imaging
Authors: Bentley J. , Hall E. L. , Kenik E. A.
Published: June 2020

There is widespread interest in elemental distribution maps produced from energy-filtered core-loss images obtained wim commercial imaging energy-filters and slow-scan charge-coupled device (CCD) cameras on transmission electron microscopes (TEMs). Earlier work on the feasibility of mapping solute segregation in stainless steels by energy-filtered imaging confirmed the utility of jump-ratio images (created by division of a post-edge image by a pre-edge one) for rapid assessments of elemental distributions. The effects of diffraction contrast and thickness variations are largely corrected for in such images. However, quantitative compositional information requires the use of net core-loss intensities following subtraction of an extrapolated background. Such core-loss intensities are influenced by diffraction contrast and thickness variations; corrections for these effects may be necessary for a quantitative interpretation. In the present work, energy-filtered images are treated similarly to quantitative electron energy-loss spectrometry (EELS) data. An image showing number of atoms per unit area, nx, is obtained by dividing the core-loss intensity image, Sx(Δ,β), by the low-loss image, J1(Δ,β), obtained with identical energy window Δ and collection half-angle β, and by the partial ionization cross-section, σx(Δ,β). Further normalization by specimen thickness, t, yields an image showing elemental concentration in atoms per unit volume:
Atomic and electronic structure of a 60° misfit dislocation
Authors: Batson P.E.
Published: June 2020

Strained Si quantum wells provide high electron mobility channels for devices within the standard Si-based technology. These wells consist of 8-12nm thick layers, epitaxially grown over relaxed Si-Ge alloys. The 1.4% lattice mismatch between Si and a Ge40Si60 alloy produces a Si layer strained in tension in the plane of the layer and in compression in the direction perpendicular to the layer, splitting the Si conduction band into a higher energy four-fold degenerate band and a lower energy two-fold degenerate band. The latter band is a high mobility channel for electron conduction. If the Si layer is made thicker than the critical thickness for epitaxy, misfit dislocations result to accommodate the strain. For growth of Si on (001) Ge40Si60 these are of the 60° type, dissociated into a 30° partial dislocation at the Si/alloy interface, a 90° partial some tens of Angstroms away in the alloy, and a connecting stacking fault. In the presence of this strain relieving structure, the electron mobility is degraded.
Where are the limits to spatial resolution in the HRTEM?
Authors: O'Keefe Michael A.
Published: June 2020

In discussing resolution limits, it is important to distinguish between the resolution of a microscope and the resolutions of the images produced by the microscope. The spatial resolution of a high-resolution transmission electron microscope (HRTEM) is an upper bound on the resolution of images that can be produced by that microscope, but there is no guarantee that any particular image from the microscope will attain this bound. In addition to instrumental limits, properties of the specimen will act to degrade image resolutions. For specimens that beam-damage rapidly, image resolution depends upon electron energy and electron dose. For small-cell crystalline specimens, Bragg's law mandates that allowable resolutions be quantized, preventing image resolution from reaching microscope resolution. However, improving the resolution of a HRTEM gives it the capability to produce higher resolution images.

Image “resolution” is a measure of the spatial frequencies transferred from the image amplitude spectrum (specimen exit-surface wavefunction) into the image intensity spectrum (Fourier transform of the image intensity).
High spatial resolution x-ray microanalysis of interfaces
Authors: Michael J. R.
Published: June 2020

X-ray microanalysis in the analytical electron microscope (AEM) refers to a technique by which chemical composition can be determined on spatial scales of less than 10 nm. There are many factors that influence the quality of x-ray microanalysis. The minimum probe size with sufficient current for microanalysis that can be generated determines the ultimate spatial resolution of each individual microanalysis. However, it is also necessary to collect efficiently the x-rays generated. Modern high brightness field emission gun equipped AEMs can now generate probes that are less than 1 nm in diameter with high probe currents. Improving the x-ray collection solid angle of the solid state energy dispersive spectrometer (EDS) results in more efficient collection of x-ray generated by the interaction of the electron probe with the specimen, thus reducing the minimum detectability limit. The combination of decreased interaction volume due to smaller electron probe size and the increased collection efficiency due to larger solid angle of x-ray collection should enhance our ability to study interfacial segregation.
Practical limits on the spatial resolution in energy-filtered mapping
Authors: Crozier P.A.
Published: June 2020

One parameter of importance in energy-filtered elemental mapping is the achievable spatial resolution. In practice, the resolution in a particular experiment depends on the energy loss used to form the image. Moreover, the importance of critical factors for defining the resolution, namely quantum localization, chromatic aberration and statistics, change with energy loss.

The fundamental limit on the spatial resolution in any energy-loss experiment is determined by the localization of the inelastic scattering process. Kohl and Rose (1985) have undertaken detailed quantum mechanical calculations of the influence of inelastic scattering on high resolution images. Fig 1 shows the results from these calculations for the change in spatial resolution as a function of energy loss for typical experimental conditions on the Zeiss 912.

Chromatic aberration in the electron optical column causes electrons of different energy to be focused in different planes causing image blurring. The resulting diameter d of the disk of least confusion depends on the energy and angular spread of the beam through the equation:
Atomic resolution determination of the structure and chemistry of ceramic grain boundaries
Authors: Browning N. D. , McGibbon M. M. , Chisholm M. F. , Pennycook S. J.
Published: June 2020

Characterization of grain boundaries in ceramics is complicated by the multicomponent nature of the materials, the presence of secondary phases, and the tendency for the grain boundary plane to “wander” on the length scale of a few nanometers. However, recent developments in the scanning transmission electron microscope (STEM) have now made it possible to correlate directly the structure, composition and bonding at grain boundaries on the atomic scale. This direct experimental characterization of grain boundaries is achieved through the combination of Z-contrast imaging (structure) and electron energy loss spectroscopy (EELS) (composition and bonding). For crystalline materials in zone-axis orientations, where the atomic spacing is larger than the probe size, the Z-contrast technique provides a direct image of the metal (high Z) columns. This image, being formed from only the high-angle scattering, can be used to position the electron probe with atomic precision for simultaneous EELS. Under certain collection conditions, the spectrum can have the same atomic spatial resolution as the image, thus permitting the spectra to be correlated with a known atomic location.
Three-Dimensional analysis of oxide-oxide directionally solidified eutectic interfaces by high-resolution Microscopy and Electron Energy Loss Spectroscopy
Authors: Dickey E.C. , Dravid V.P. , Revcolevschi A.
Published: June 2020

It is well appreciated that the strength of heterophase interfaces in ceramic composites plays an extremely influential role in the macroscopic mechanical behavior of the bulk material. It is therefore useful to understand the structure of such interfaces in order to make structure/ property relationships between interface structure and mechanical behavior. High Resolution Electron Microscopy (HREM) is an extremely useful technique for elucidating the atomic structure of heterophase interfaces in ceramic materials, but HREM has typically been used to image lattice planes along only one zone axis. Often, however, it is useful to obtain three-dimensional information about the interface in order to fully appreciate and understand the complete relaxation and structure of the interface. Directionally solidified eutectics (DSEs) offer a unique opportunity to study heterophase interfaces in three dimensions, because they contain numerous, identical interfaces with consistent crystallographic orientation relationships between the two phases. Of particular interest are those eutectics that have lamellar morphologies, because the planar interfaces may be viewed along two orthogonal directions (Fig.l).
Impurities and grain boundaries in sintered titanium diboride
Authors: Pettersen G. , Bardal A. , Høier R.
Published: June 2020

In conventional Al-electrolysis the electrodes suffer from degradation when used in the harsh environment of an aluminium electrolysis cell. The carbon cathode, which is placed at the cell bottom, is not well wetted by aluminium, and must be covered by a pad of liquid Al in order to establish a good electrical contact. To avoid short circuiting of the cell the anode-to-cathode distance (ACD) must be kept above 4-6 centimetres. Replacing the carbon cathode with a new, inert cathode, well wetted by liquid aluminium, would allow new cell designs where only a thin film of aluminium covers the cathode during cell operation, thereby allowing the ACD to be lowered. This in turn opens for substantial reductions in the energy consumption of an electrolysis cell, and combined with an inert anode the outlet of CO2 and fluorides harmful to the environment could be reduced.

The most promising candidate for use as an inert cathode is titaniumdiboride (TiB2), a ceramic material which exhibits promising properties such as a high electrical conductivity, sufficient mechanical strength, good resistance to chemical attack and low solubility in liquid aluminium, and which is also well wetted by liquid aluminium.
TEM of grain growth and phase transformations during creep of SCS-6 silicon carbide fibers
Authors: Giannuzzi L. A. , Lewinsohn C. A. , Bakis C. E. , Tressler R. E.
Published: June 2020

The SCS-6 SiC fiber is a 142 μm diameter fiber consisting of four distinct regions of βSiC. These SiC regions vary in excess carbon content ranging from 10 a/o down to 5 a/o in the SiC1 through SiC3 region. The SiC4 region is stoichiometric. The SiC sub-grains in all regions grow radially outward from the carbon core of the fiber during the chemical vapor deposition processing of these fibers. In general, the sub-grain width changes from 50nm to 250nm while maintaining an aspect ratio of ~10:1 from the SiC1 through the SiC4 regions. In addition, the SiC shows a <110> texture, i.e., the {111} planes lie ±15° along the fiber axes. Previous has shown that the SCS-6 fiber (as well as the SCS-9 and the developmental SCS-50 μm fiber) undergoes primary creep (i.e., the creep rate constantly decreases as a function of time) throughout the lifetime of the creep test.
Characterization of modified ceramic fiber surfaces using AFM
Authors: Amold C. L. , More K. L. , Lara-Curzio E.
Published: June 2020

Several models have been developed to describe the interfacial behavior of fiber-reinforced ceramic matrix composites. However, these models are limited in that they do not take into account the effect of fiber surface roughness on the fiber sliding resistance. Clearly, the fiber surface roughness will play an important role in extensive fiber/matrix debonding and fiber pull-out behavior which are characteristic of a toughened composite. In this study, a Topometrix TMX2010 Atomic Force Microscope (AFM) was used to quantitatively evaluate the surface topography of a SiC fiber subjected to a series of surface modification treatments. The relationship between interfacial properties determined from fiber push-out tests and the surface roughness will be used to modify existing mathematical models.

In order to systematically study the effect of surface roughness on the interfacial properties of ceramic matrix composites, a “model” single fiber composite having varying degrees of fiber surface roughness was developed. This was accomplished by using a single manufacturer's ceramic fiber which was subjected to a series of treatments in order to alter the surface.
High-resolution TEM study of ion beam irradiation induced amorphization in ceramic materials
Authors: Wang L.M. , Ewing R.C. , Weber W.J.
Published: June 2020

Radiation damage of nuclear materials (e.g. fast- or fusion-neutron damage in reactor structural components, fission-fragment damage in nuclear fuels and alpha decay damage in nuclear waste forms) has been one of the major challenges faced by the material science community. Ion beam irradiation and implantation experiments have been used extensively in the past few decades not only for simulating these damaging process in materials but also for improving material properties for many technological applications.

As an energetic particle traverses a crystalline target, it loses its energy predominantly through electronic (ionization) and nuclear (elastic collision) interactions with the atoms in the lattice. The target atom which receives sufficient energy from the interactions may get displaced from its lattice site and may further displace other target atoms, thus creating a displacement cascade which is usually a few nanometers in scale. Just at the end of the collision phase, which lasts for only a few tenths of a picosecond, a displacement cascade contains a very dense cluster of point defects and the region may be considered amorphous.
Crystal structure of Tl-substituted HG-1223 superconductor with critical temperature of 138K under atmospheric pressure
Authors: Feng Y. , Larbalestier D.C. , Sun G.F. , Xin Y. , Wong K.W. , Osofsky M.S. , Tom L.E. , Ikeda S. , Fujii H. , Kumakura H. , Togano K.
Published: June 2020

Since the discovery of the Hg-Ba-Ca-Cu-O superconductors, several members of the system bearing the formula HgBa2Can−1CunO2n+2+x (n=l,2,3) were synthesized. The highest critical temperature Tc of 133.5K under atmospheric pressure was achieved from the Hg-1223 compound (n=3). The Hg-compounds are structurally analogous to the single-layer Tl-based compounds TlBa2Can−1CunO2n+2+x. In Hg-1223, oxygen is almost absent in the Hg-O plane at the stoichiometric (x=0) composition. In contrast, the oxygen sites in the Tl-O plane are nearly fully occupied. The difference in oxygen occupancy of the corresponding rock-salt Hg-O and Tl-O planes in Hg- 1223 and Tl-2223 is due to the difference in valence of Hg2+ and Tl3+.

To create a necessary fractional oxygen occupation in the Hg-O planes, a partial substitution of Tl for Hg was carried out and the Tc of the Tl-substituted sample raised up to 138K. We report here on the crystal structure of the new compound. Synthesis and properties has been published elsewhere.
Electron holography of catalysts
Authors: Datye A. K. , Kalakkad D. S. , Allard L. F. , Völkl E.
Published: June 2020

The active phase in heterogeneous catalysts consists of nanometer-sized metal or oxide particles dispersed within the tortuous pore structure of a high surface area matrix. Such catalysts are extensively used for controlling emissions from automobile exhausts or in industrial processes such as the refining of crude oil to produce gasoline. The morphology of these nano-particles is of great interest to catalytic chemists since it affects the activity and selectivity for a class of reactions known as structure-sensitive reactions. In this paper, we describe some of the challenges in the study of heterogeneous catalysts, and provide examples of how electron holography can help in extracting details of particle structure and morphology on an atomic scale.

Conventional high-resolution TEM imaging methods permit the image intensity to be recorded, but the phase information in the complex image wave is lost. However, it is the phase information which is sensitive at the atomic scale to changes in specimen thickness and composition, and thus analysis of the phase image can yield important information on morphological details at the nanometer level.
Observation of grain superstructure in thin aluminum films by orientation imaging microscopy
Authors: Alvis Roger , Dingley David , Field David
Published: June 2020

The correlation of aluminum alloy reliability data to microstructure has long been the goal of those scientists seeking to model electromigration behavior of interconnects. Traditionally, microstructural information has been acquired through x-ray diffraction , and transmission electron microscopy (TEM). However, each of these techniques is capable of delivering only part of the characterization whole. We describe the application of orientation imaging microscopy (OIM) to thin aluminum alloy films and demonstrate its versatility in providing the key microstructural reliability parameters: namely texture and grain size, as well as providing insight to the microstructure of grain boundaries.

OIM was performed on an electromigration test structure (figure 1). The Al-alloy was deposited on titanium and capped with an anti-reflective titanium nitride. Subsequently, the test structure was patterned and capped with a multilayer blanket consisting of silicon nitride (SiN), and SiO2. The structure was annealed after the SOG deposition at 450° C for 90 minutes, seeing no electrical stressing. The die was removed from the package and deprocessed before the OIM was acquired.
Strain measurement in In0.2Ga0.8As/GaAs quantum wires by convergent beam electron diffraction
Authors: Hillyard S. , Chen Y.-P. , Reed J.D. , Schaff W.J. , Eastman L.F. , Silcox J.
Published: June 2020

The positions of high-order Laue zone (HOLZ) lines in the zero order disc of convergent beam electron diffraction (CBED) patterns are extremely sensitive to local lattice parameters. With proper care, these can be measured to a level of one part in 104 in nanometer sized areas. Recent upgrades to the Cornell UHV STEM have made energy filtered CBED possible with a slow scan CCD, and this technique has been applied to the measurement of strain in In0.2Ga0.8 As wires.

Semiconductor quantum wire structures have attracted much interest for potential device applications. For example, semiconductor lasers with quantum wires should exhibit an improvement in performance over quantum well counterparts. Strained quantum wires are expected to have even better performance. However, not much is known about the true behavior of strain in actual structures, a parameter critical to their performance.
Evolution of the microstructure of Cu(Ti)/SiO2 layers annealed in NH3
Authors: Liu J. , Theodore N. D. , Adams D. , Russell S. , Alford T. L. , Mayer J. W.
Published: June 2020

Copper-based metallization has recently attracted extensive research because of its potential application in ultra-large-scale integration (ULSI) of semiconductor devices. The feasibility of copper metallization is, however, limited due to its thermal stability issues. In order to utilize copper in metallization systems diffusion barriers such as titanium nitride and other refractory materials, have been employed to enhance the thermal stability of copper. Titanium nitride layers can be formed by annealing Cu(Ti) alloy film evaporated on thermally grown SiO2 substrates in an ammonia ambient. We report here the microstructural evolution of Cu(Ti)/SiO2 layers during annealing in NH3 flowing ambient.

The Cu(Ti) films used in this experiment were prepared by electron beam evaporation onto thermally grown SiO2 substrates. The nominal composition of the Cu(Ti) alloy was Cu73Ti27. Thermal treatments were conducted in NH3 flowing ambient for 30 minutes at temperatures ranging from 450°C to 650°C. Cross-section TEM specimens were prepared by the standard procedure.
TEM characterization of subsurface damage in silicon carbide substrates
Authors: Qian W. , Skowronski M. , Augustine G. , Glass R.C. , Hobgood H. McD. , Hopkins R.H.
Published: June 2020

Because of its wide band gap and physical stability, silicon carbide is an important semiconductor material for high power, high temperature solid state devices. In such applications, any surface damage introduced during wafer fabrication is detrimental to optimum device fabrication and operation. A typical wafer fabrication procedure consists of mechanical lapping and polishing, followed by chemical etching for removal of any residual mechanical damage. However, SiC is a refractory material with strong atomic bonding and high mechanical hardness, chemical etching of its surface is often difficult. Mechanical polishing is thus the crucial step during wafer preparation. Though a number of techniques are currently in use for assessment of polishing induced surface damage, such as grazing incidence xray diffraction and Rutherford backscattering, none of them is effective for studying the hidden damage beneath the polished surface. In the present work cross-sectional transmission electron microscopy (XTEM) was used to observe directly the nature and extent of subsurface damage in 6HSiC substrates after different stages of mechanical polishing, and to elucidate the possible mechanism for material removal by the abrasive treatments.
Interpretation of HREM images of m-barium ferrite taken under dynamical scattering conditions
Authors: Kwon Dongchul , Rabenberg Lew
Published: June 2020

In HREM analyses of extended structural defects in complex compounds, it is desirable to be able to image atomic columns composed of light elements as well as those composed of heavy elements. For the thinnest possible specimens, HREM image contrast tends to be dominated by the heavy elements, however, it is possible to increase the contribution of the light elements to the image by imaging specimens of somewhat greater thicknesses. This paper presents results from a HREM study of extended defects in M-barium ferrite in which this approach has been successfully applied.

Hexagonal ferrites, of which M-barium ferrite, BaFe12O19, is an example, form a versatile class of compunds built up from varied stackings of simpler structural units denoted R, S , and T. Mbarium ferrite takes the magnetoplumbite structure - a simple alternation of R blocks and S blocks. HREM techniques have been widely used to charcterize defects in stacking sequences, intergrowths, and polytypes in these materials.
Direct observation of mechanical twinning in pure iridium
Authors: Chen C. L. , Song S. G. , Mitchell T. , Gray G. T. , Tsong T. T.
Published: June 2020

Mechanical twinning in crystalline solids is understood according to a recent study to occur via two distinct mechanisms; i.e. a step-wise (athermal) and a dislocation pole (thermal) mechanism. In f.c.c. structures, the two twinning mechanisms are both operational. Twinning by a dislocation pole mechanism normally takes place at elevated temperatures since thermal activation is needed in structures requiring a high passing stress. When twinning occurs by the step-wise mechanism, the selection of {111} planes as twin boundaries to form a coherent interface between the twin and the matrix lattice is limited. In the past twenty years, Field Ion Microscopy (FIM) has successfully been used to analyze many microstructural defects. However, there has been no detailed analysis of mechanical twin morphology using FIM techniques. We present here the FIM observations of deformation twins in pure Ir and compare the results with predictions of twin thickness and boundary structures according to the two twinning mechanisms.
Identification of non-martensitic transformation products(NMTP) in a carburized 8620 steel
Authors: Donlon William T. , Dowling William E.
Published: June 2020

Additions of Cr and Mn to steel are intended to increase hardenability (the ability to form martensite on cooling from austenite) and thereby improve the mechanical properties. However, conventional gas carburization of alloy steels containing Cr and Mn as well as Si will produce oxides of these elements (internal oxidation) near the surface (due to the oxygen potential of the carburizing atmosphere). Additionally, the oxidation of these elements locally reduces the hardenability of the alloy, creating the potential to produce non-martensitic transformation products (NMTP) near the surface. These oxides and the associated NMTP have been shown to decrease the fatigue resistance of carburized steels if they are not removed by subsequent machining operations. The objective of this study is to characterize the oxides, identify the NMTP and assess the degree of local alloy depletion in a carburized 8620 steel (0.21 C, 0.93 Mn, 0.023 S, 0.12 Si, 0.49 Cr, 0.38 Ni and 0.17 Mo).