bluuebunny/crossref_metadata_2025 huggingface dataset:
Problems in Thin-Film X-ray Quantification
Authors: Chapman J N , Nicholson W A P
Published: June 2020

Energy dispersive x-ray microanalysis (EDX) is widely used for the quantitative determination of local composition in thin film specimens. Extraction of quantitative data is usually accomplished by relating the ratio of the number of atoms of two species A and B in the volume excited by the electron beam (nA/nB) to the corresponding ratio of detected characteristic photons (NA/NB) through the use of a k-factor. This leads to an expression of the form nA/nB = kAB NA/NB where kAB is a measure of the relative efficiency with which x-rays are generated and detected from the two species.

Errors in thin film x-ray quantification can arise from uncertainties in both NA/NB and kAB. In addition to the inevitable statistical errors, particularly severe problems arise in accurately determining the former if (i) mass loss occurs during spectrum acquisition so that the composition changes as irradiation proceeds, (ii) the characteristic peak from one of the minority components of interest is overlapped by the much larger peak from a majority component, (iii) the measured ratio varies significantly with specimen thickness as a result of electron channeling, or (iv) varying absorption corrections are required due to photons generated at different points having to traverse different path lengths through specimens of irregular and unknown topography on their way to the detector.
Determination of the Lattice parameter for TiCl-x and TiNl-x by Use of HOLZ Lines in CBED [114] zonP Axis Patterns
Authors: Lenvig Hansen Poul , Madsen Kristian
Published: June 2020

TiC and TiN are very hard and wear resistant materials. They are used as thin wear protecting films on tools working in abrasive environments and as powders for grinding. Furthermore, whiskers of TiC and TiN are used as fibre reinforcement in composite materials.
The crystal structure is fcc with lattice parameter a = 0.4240 nm for TiN and a = 0.4328 nm for TiC. Understoichiometric forms, TiN1-x and TiC1-x ( 0 ≤ x ≤ 0.5 ), are common. Their lattice parameter decreases with increasing x. As the understoichiometric forms have inferior mechanical properties compared with the stoichiometric forms, it is of interest to develop methods to measure the composition of the phases.

It is the objective of this paper to show that the HOLZ lines in [114] zone axis CBED patterns can be used to measure the local lattice parameter in TiC and TiN in order to distinguish the two phases and in order to assess understoichiometry.
A Combined IKL-ALCHEMI Technique for atom Configurations in Multinary Ordering Alloys and its Application to Cu-Au-Pd
Authors: Matsumura Syo , Moriraura Takao , Oki Kensuke
Published: June 2020

Diffraction technique of x ray, electron or neutron has been extensively utilized to determine atomic configuration in ordering alloys. The method of analysis has been well established for the binary alloy case. From the diffracted intensities or the values of structure factors, we can straightforwardly determine site-occupancies or pair-correlations of atoms on the fundamental lattice points in a binary alloy. For ternary or multinary alloys, however, it turns impossible to obtain the quantities concerning atomic configuration by the conventinal diffraction technique. This impossibility in the multinary case is due to the fact that the structure factor of a superlattice reflection is a function of two or more independent parameters describing the atomic configuration. In this paper we propose an experimental procedure to break through this impossibility; simultaneous employment of the Intersecting Kikuch-line (IKL) method and ALCKEMI (Atom Location by Channeling Enhanced Microanalysis) enables us to determine the occupation probabilities of constituent atoms on lattice sites in ternary or multinary ordering alloys.
Identification of Several New Ferromagnetic and Antiferromagnetic Rare Earth Cuprates
Authors: Fendorf M. , Keller S.W. , Stacy A.M. , Gronsky R.
Published: June 2020

Several new rare earth cuprates having the chemical form RxCuyOz (where R represents the rare earths La, Nd, Sm, Eu, and Gd) have recently been synthesized using a NaOH flux at 400°C. The materials are polycrystalline, and contain varying amounts of R2CuO4 and CuO. During subsequent susceptibility measurements using a SQUID magnetometer, it was found that the Gd material orders antiferromagnetically at approximately 14K, while the other compounds become ferromagnetic between 18K and 28K. Treatment of the powders with 12M HC1 for several minutes dissolves the impurity R2CuO4 and CuO phases, thus facilitating efforts to determine the composition and crystal structure of the new ferromagnetic and antiferromagnetic cuprates. Details of synthesis and magnetic behavior of these materials are to be published elsewhere. In this study, a first attempt is made to characterize the Eu and Gd materials.

Energy dispersive x-ray analysis carried out during scanning electron microscopy work indicates that the R:Cu ratio in the Gd material is 1:1.70 (close to 3:5) and that in the Eu material is 1:1.96 (close to 1:2).
The Low-Temperature Structure of Magnetite Studied by CBED
Authors: Zuo J.M. , Spence J.C.H. , Petuskey W.
Published: June 2020

Magnetite (Fe3O4) has the cubic inverse spinel structure for T > TV = 119 K and undergoes a firstorder metal-insulator Verwey transition below TV. The transition from hopping conductivity to insulating behaviour below TV is believed to be due to a condensation of localised electrons onto the Fe++ and Fe+++ ions on the octahedral (B) sites. Tetrahedral (A) sites contain only Fe+++ ions. The aim of this research is to determine this unknown charge ordering below TV by CBED, taking advantage of the high sensitivity of low-angle electron diffraction to ionicity. Below TV the c axis of the cubic cell doubles, and there is a small monoclinic distortion.

Previous CBED work established that the space-group is Cc (C centering, glide plane normal to b, displacement along c). Anderson proposed that the building block for the low-temperature structure consists of two Fe++ and two Fe+++ ions per tetrahedron (see, e.g. figure 1).
Analytical Calculation of Complex Lattice Potentials for Electron Diffraction
Authors: Weickenmeier A.
Published: June 2020

For the quantitative interpretation of electron microscopical diffraction patterns it is often indispensable to perform simulations to get insight into the contrast mechanisms. If the inelastic mean free path length is not small compared with the crystal thickness the diffraction patterns are affected by absorption phenomena. In this case a realistic calculation must include these effects. Within the dynamical theory this can be done by adding an absorptive part to the Fourier coefficients Vg of the lattice potential .

Because there are only few experimental data available the absorptive part must be computed. In the most cases the dominant contribution to arises from the thermal diffuse scattering since plasmon excitations and electron excitations contribute in good approximation only to the mean absorption potential .
Then all branches of the dispersion surface are similiar attenuated.

Extensive numerical calculations have been performed by Radi for many crystals. Nevertheless it is impossible to tabulate the for all crystals even for only few temperatures and acceleration voltages.
Progress in design and applications of CCD cameras for Electron Microscopy
Authors: Downing Kenneth H.
Published: June 2020

Over the last several years the long-awaited revolution in direct-digital readout systems has begun, with the introduction of efficient slow-scan CCD cameras. Earlier, the introduction of video cameras to electron microscopes had brought a quantum leap in the speed and efficiency of carrying out a host of operations. The high sensitivity of the video cameras provided the ability to see the image in much more detail and at a lower beam intensity than had been possible previously by viewing the fluorescent screen. The ability to assess, on line, characteristics such as specimen quality and image focus, even qualitatively, gave feedback to the operator that previously took hours to obtain. Due to the low resolution of these video systems, however, they were rarely useful for data recording.

The current generation of CCD cameras goes a long way toward meeting the needs of data recording in many, though certainly not all, applications.
Tele-Presence Microscopy: An Interactive Multi-User Environment For Collaborative Research using High Speed Networks and The Internet
Authors: Zaluzec Nestor J.
Published: June 2020

Tele-Presence Microscopy (TPM) is an advanced concept in the integration of computers and high speed networks with scientific instruments for operation, control, communication and research which makes use of ANL's Advanced Analytical Electron Microscope (AAEM) and Analytical Scanning Electron Microscope (ASEM) as development/testbed sites. The implementation of a Tele-Presence Microscopy Facility allows a user from a remote location to either observe and/or control state-of-the-art instrumentation in a real time interactive mode. Using TPM, a user will be able toactivelyparticipate in scientific investigations at unique resources such as user facilities without being physically present at those locations. Manufacturers would be able to configure demonstration equipment which are accessible via the TPM system and thus allow prospective customers to remotely evaluate instrumentation before purchase. After acquisition, implementation by the manufacturer of a TPM system would allow remote service/diagnostics by a systems engineer who resides at the manufacturing site. Finally in an educational environment, students can initiate tele-presence operation of instruments which may not be available at their host institution, allowing widest possible access to unique facilities, Alternatively, should students have access to local equipment, they will have the opportunity of consulting an advisor or non-local expert in the field in an on-line mode during their actual experimental session, thus freeing valuable time which would be otherwise wasted during unproductive experiments.
Creating a standard method of controlling digital microscopes: the microscope access protocol (map)
Authors: Dodson T. A. , Völkl E. , Allard L. F. , Nolan T. A.
Published: June 2020

The process of moving to a fully digital microscopy laboratory requires changes in instrumentation, computing hardware, computing software, data storage systems, and data networks, as well as in the operating procedures of each facility. Moving from analog to digital systems in the microscopy laboratory is similar to the instrumentation projects being undertaken in many scientific labs. A central problem of any of these projects is to create the best combination of hardware and software to effectively control the parameters of data collection and then to actually acquire data from the instrument. This problem is particularly acute for the microscopist who wishes to "digitize" the operation of a transmission or scanning electron microscope. Although the basic physics of each type of instrument and the type of data (images & spectra) generated by each are very similar, each manufacturer approaches automation differently. The communications interfaces vary as well as the command language used to control the instrument.
Microstructural characterization of AL-8900 superplastic materials using orientation imaging microscopy
Authors: Garmestani H. , Kalu P. , Mehr K. , Dingley D.
Published: June 2020

Electron Backscattered Pattern (EBSP) technique has been shown to be an effective tool for measuring lattice orientation of bulk polycrystalline materials in an SEM. Automation of this technique through Orientation Imaging Microscopy (OIM) opened a new era of materials characterization which had only existed using Transmission Electron Microscope (TEM) for thin foil specimens. Investigation of grain orientation and grain to grain misorientation are among a number of parameters which are crucial in studying the mechanisms of deformation in materials, especially superplastic materials. The microstructure and texture changes corresponding to different stages of Superplastic Forming (SPF) has been traditionally characterized using conventional optical, TEM and X-ray Techniques. TEM analysis of grain structure and subgrain formation could only provide information for individual grains or at best a small region of the microstructure, hence do not provide a global picture. On the other hand, the data obtained by OIM technique and the regeneration of the microstructure based on different definitions of grain boundary can provide a better understanding of Superplasticity.
Thin-foil based TEM screens with electrophoretic deposition of phosphors
Authors: Fan G.Y. , Russ Ben , Talbot Jan B. , Price Jeff , Ellisman Mark H.
Published: June 2020

The availability of 2k×2k or larger format CCD chips has made direct digital imaging more practical in electron microscopy. But the suboptimal performance of scintillating screens, particularly their inferior resolution as compared to film, is still an obstacle to a broader adaptation of digital imaging technology to electron microscopy. Thin-foil substrate screens have improved brightness and resolution over the more commonly used glass substrate screens, particularly at higher operating voltages, but further improvements are required for the optimum performance of the CCD imaging systems. Self-supporting single crystal YAG screens, approximately 30 μm in thickness, provide better resolution and detection-quantum-efficiency as compared to the phosphor screens, but their lower brightness, about 4 - 8 times lower, makes them less than ideal at least for low dose applications. Until brighter single crystal scintillators become available, powder phosphor screens may offer performance advantages for applications where radiation damage to the specimen is a concern.
Semi-automated methods for 3-D reconstruction of macromolecular complexes
Authors: Carragher B. , Whittaker M.
Published: June 2020

Techniques for three-dimensional reconstruction of macromolecular complexes from electron micrographs have been successfully used for many years. These include methods which take advantage of the natural symmetry properties of the structure (for example helical or icosahedral) as well as those that use single axis or other tilting geometries to reconstruct from a set of projection images. These techniques have traditionally relied on a very experienced operator to manually perform the often numerous and time consuming steps required to obtain the final reconstruction. While the guidance and oversight of an experienced and critical operator will always be an essential component of these techniques, recent advances in computer technology, microprocessor controlled microscopes and the availability of high quality CCD cameras have provided the means to automate many of the individual steps.

During the acquisition of data automation provides benefits not only in terms of convenience and time saving but also in circumstances where manual procedures limit the quality of the final reconstruction.
Combining structures from cryo-EM and x-ray crystallography
Authors: Stewart P.L. , Nemerow G.R.
Published: June 2020

Cryo-electron microscopy (cryo-EM) combined with three-dimensional image reconstruction techniques has produced structures of large macromolecular assemblies. Interpretation of low resolution (25-35 A) cryo-EM density can be greatly enhanced by mapping in crystallographic structures of component molecules. Difference imaging between the cryo-EM structure of the human adenovirus particle and a capsid calculated from the crystal structure of the major structural protein, hexon, revealed numerous minor structural components in the viral capsid. In addition, the atomic binding sites of the minor protein components were visualized on the crystallographic structure of hexon.
Current studies are focused on examining the structural events during adenovirus cell entry. The receptor that triggers adenovirus internalization has been shown to be αv integrin. Cryo-EM is being used to solve the structure of adenovirus with bound Fab fragments from a monoclonal antibody that blocks binding of the virus to the receptor (Fig. 1). The antibody recognizes a linear epitope of nine amino acids that includes an Arg-Gly-Asp (RGD) integrin binding motif.
SOPHIE, a helium cooled superconducting Electron Microscope with a Schottky field emitter
Authors: Stark H. , Beckmann E. , Henderson R. , Zemlin F.
Published: June 2020

High-resolution cryo-electron microscopy yielded remarkable results in biological molecular structure research. These successes encouraged to proceed in developing even better instruments and procedures. In our laboratory we built the cryo-electron microscope "SOPHIE", a modified Philips CM 20 FEG. SOPHIE stands as an acronym for Superconducting Objective in a PHIlips Electronmicroscope. The main features of this microscope are the following:

1.

200kV acceleration voltage

2.

Schottky field emitter

3.

Helium cooled superconducting objective

The Helium-cooled cryo-objective from the former microscope SULEIKA was adapted into the column of the original Philips CM20 FEG [Fig. 1], This new SOPHIE microscope, thus, combines two important features: a modern computer controlled electron microscope with a high coherent beam source and the proven advantages of the superconducting cryo-objective. The advantage of the field emission gun at 200 kV over a thermionic cathode at 100 kV can be best visualized while comparing the respective phase-contrast-transfer functions at Scherzer focus [Fig.2]. Moreover, SOPHIE is equipped with the small spot scanning procedure.
Using micro-MRI to watch development live and in 3-D
Authors: Jacobs R. E. , Allman J. , Barr A. , Fraser S. E. , Meade T.
Published: June 2020

The ability of MRI to provide three dimensional images of thick opaque samples in a noninvasive manner has made it an extremely important clinical tool. In addition, the large number of types of contrast mechanisms in a MR experiment offer the clinician and research scientist the possibility of adapting the image contrast to fit the problem of interest. While typical resolutions employed clinically are on the order of a millimeter, the notion of using MRI at microscopic resolutions arose early in the development of this technique. Spatial resolution in biological samples is typically limited by a number of physical effects as well as signal-to-noise ratio (S/N) considerations. Estimates of the theoretical limits of resolution in the MR image arising from these phenomena range from 2 to 0.5 micron. The practical spatial resolution is currently determined by the S/N which is often limited by the amount of time available to actually acquire the image (i.e. the temporal resolution).
A systematic ALCHEMI study of Fe-doped NiAl alloys
Authors: Anderson I.M. , Duncan A.J. , Bentley J.
Published: June 2020

ALCHEMI site-occupation studies of alloying additions to ordered aluminide intermetallic alloys have been performed with varying degrees of success, depending on the ionization delocalization correction procedure applied to the data. Most published studies have been applied to just one or two alloys in order to ascertain qualitatively the site-preference of the alloying element. However, quantitative siteoccupancies can be extracted from carefully performed ALCHEMI experiments as long as the data are properly treated for ionization delocalization and anti-site occupancies. Systematic studies can therefore yield the dependence of site-occupancies in alloys on independent thermodynamic variables. The purpose of the present study is to examine the variation in the site-occupancy of Fe in B2-ordered NiAl as a function of solute concentration and alloy stoichiometry.

Twelve different alloys were prepared for this study with stoichiometrics Ni50-xAl50Fex (Ni-deficient), Ni50-x/2Al50-x/2Fex (intermediate), and Ni50-xAl50Fex (Al-deficient), with x = 0.25, 2, 5, and 10. All alloys were homogenized at 1300°C for 5 h, step-cooled to room temperature, then annealed at 800°C for 72 h and water quenched.
Charge density in TiAl intermetallics studied by quantitative CBED
Authors: Holmestad R. , Zuo J.M. , Spence J.C.H. , Høier R. , Horita Z.
Published: June 2020

The relationship between mechanical properties and charge density topology in TiAI intermetallics has attracted considerable interest during the last few years. TiAI is a candidate for use in the aerospace industry, but a problem is the undesired brittleness at low temperatures. Doping (with i.e. Mn) is known to increase the ductility, and the question is if this doping is followed by detectable changes in the bonding charge density. It has been suggested for example that the largely covalent Ti-Ti bond is diluted by Mn, reducing brittleness, and that the depth of the Peierls valley encountered by dislocations may also be controlled by doping. In this paper we use the systematic row convergent beam electron diffraction (CBED) technique5 to determine low order structure factors in TiAI intermetallics with and without manganese doping. Subsequently, from the structure factors found, electronic bonding charge density maps are made. Also TiAI with other doping elements are now under examination.
Use of direct phasing in determination of atomic co-ordinates of anthanthrene, C22H12
Authors: Leslie C. E. , Fryer J. R. , Gilmore C. J. , Nicolson W.
Published: June 2020

Imaging of organic crystals in the electron microscope is limited by their sensitivity to the electron beam, with even the most stable molecules only giving a resolution of ~3Å. By contrast, electron diffraction requires a lower beam intensity, and so can give much better resolution, down to ~lÅ under favourable conditions. Intensities may be measured directly from the diffraction pattern, and the phase determination problem can be surmounted by applying the maximum entropy method, which chooses phases by likelihood estimation.

It was decided to apply this method to the organic molecule anthanthrene, C22H12 (fig. 1), since x-ray studies found that the crystals were monoclinic with a = 12.10Å, b = 10.34Å, c = 10.74Å, β = 92.2°, space group P21/a and Z = 4, but no details of the atomic co-ordinates were given in the literature. A previous study of the molecule, using KC1 as the substrate, produced epitaxial layers showing the acprojection being most common at room temperature.
Unitarity and the real world: applications of direct phasing to electron diffraction data
Authors: Tivol W. F.
Published: June 2020

The Sayre equation can be derived as a special case of unitarity, and recently it was shown that the derivation applies to dynamical scattering and electron diffraction. Since both the triplet formula and the tangent formula can be derived from the Sayre equation, use of these direct methods to find the phases for electron diffraction amplitudes is fully justified.

The most transparent form of the unitary equation is

where Â is the scattering amplitude operator, f is the final state, i the initial state, and n is a complete set of intermediate states; the sum over these states becomes an integral where the intermediate states form a continuum.

If there is Friedel symmetry, the form of the Sayre equation derived from equation (1) is

The prime on the sum meansK ≠ 0.If Friedel symmetry is violated, Σ' | A(K) |2becomes

This equation is a quantitative relationship which not only has an essentially unique solution for the phases, but which also constrains the magnitudes of the intensities.
High-angle electron scattering from amorphous silicon
Authors: Libera M. , Ott J.A. , Siangchaew K. , Tsung L.
Published: June 2020

Channeling occurs when fast electrons follow atomic strings in a crystal where there is a minimum in the potential energy (1). Channeling has a strong effect on high-angle scattering. Deviations in atomic position along a channel due to structural defects or thermal vibrations increase the probability of scattering (2-5). Since there are no extended channels in an amorphous material the question arises: for a given material with constant thickness, will the high-angle scattering be higher from a crystal or a glass?

Figure la shows a HAADF STEM image collected using a Philips CM20 FEG TEM/STEM with inner and outer collection angles of 35mrad and lOOmrad. The specimen (6) was a cross section of singlecrystal Si containing: amorphous Si (region A), defective Si containing many stacking faults (B), two coherent Ge layers (CI; C2), and a contamination layer (D). CBED patterns (fig. lb), PEELS spectra, and HAADF signals (fig. lc) were collected at 106K and 300K along the indicated line.
Closed graphene nanostructures
Authors: Iijima Sumio
Published: June 2020

Graphene is named a single sheet of graphite, or a 2-D carbon hexagons network. The graphene structure has been observed in partially graphitized carbon which is familiar to electron microscopists and its HRTEM image properties were analyzed previously in detail. C60 molecules, which has brought a great excitements in interdisciplinary fields of science and technology, is basically the same graphene structure with a curvature. The individual C60 molecule can be imaged without difficulty by HRTEM. Many of fundamental problems with the molecule however are not solved by the HRTEM technique. On the other hand, carbon nanotubes, a family of the fullerene and discovered serendipitously by the present author5, are an ideal subject for the HRTEM investigation and in fact their structural details can only be analyzed by this technique. The present talk reviews the carbon nanotubes and related structures with an emphasis of usefulness of the HRTEM.

Search for the multi-shell graphite particles leads to unexpected discovery of carbon nanotubes which grow on a cathode in a carbon-arc chamber for the C60 production.
The breakup of the intermediate gold aggregates
Authors: Yao Nan , Shih Wan Y. , Dabbs Daniel M. , Aksay Ilhan A.
Published: June 2020

The synthesis of nanometer scale gold particles is well known historically. Stable and highly colored suspensions result from the reduction of gold cations in solution. But the formation of the gold particles is not monotonic, that is, the mechanism is not simply nucleation and growth. Rather, the pronounced color changes in the evolving suspension indicate that the mechanism is nucleation, aggregation, deaggregation, and growth. Until recently, the structure of the intermediate aggregate had been assumed to be an aggregation of primary particles, each 4-7 nm in diameter. HRTEM studies have shown that the intermediates are continuous ramified structures (Figure 1) which undergo a desintering process to form the final particles (~24-26 nm diameter). In this paper, we discuss a model which explains the role of the surfactant on the gold intermediate in the breakup of the intermediate structure.

Gold colloids were prepared by reducing AuIIICl3 (aq) with sodium citrate as in previous studies:
Scanning force microscope Z-calibration using steps on chemically etched mica
Authors: Fei L. , Fraundorf P.
Published: June 2020

Obtaining reliable dimensional information in all three directions is very important in scanning force microscopy (SFM). Calibration standards for SFM should be easy to produce and reliable. For example, mica is often used as a lateral calibration standard, because lattice fringes are relatively easy to obtain. However, reliable height information is hard to get. Pits formed by lithography (180 nm in depth) are used for vertical calibration by some SFM manufacturers.1 These standards have 10variability and are large on the size scale of monolayers. Colloidal gold particles have been proposed as one kind of SFM vertical standard, but the size variability of these particles (e.g. ranging from 5 to 24 nm) makes their use of limited practical value.

One solution to the problem is to use chemically etched mica as height calibration standard. Mica has a layered structure, and its c-axis is well denned and weakly bonded. In this study, we used muscovite mica which has c-axis lattice spacing of 10 Å.
In situ Electron Microscopy and its applications to semiconductor reactions at high-resolution
Authors: Sinclair Robert
Published: June 2020

In situ electron microscopy experiments can provide the most revealing insights into material behavior. However, in order to take full advantage of the observations, quantitative measurements are required so that the underlying mechanisms are completely interpreted. This approach also ensures that specimen and environmental artifacts do not play a role and that real “bulk” processes are being studied. These points are illustrated in this paper by reference to work on reactions in semiconductor systems, especially at high resolution.

The technique and practice of in situ microscopy are quite exacting. Thus it is often necessary to record changes in the same specimen area for extensive periods of time (e.g., hours), under identical imaging conditions. One can never be sure when a significant event will take place, or sometimes whether it has actually occurred -- accordingly a high degree of acuity on behalf of the observer is essential. A number of procedures is recommended to check that the results are representative and reproducible, including comparing the structural evolution with that from ex situ samples both qualitatively and quantitatively (e.g., [1]). Some contemporary applications are given in a recent publication.
In Situ Electron Microscopy observations of structural transformations in single crystal lanthanum aluminate
Authors: Grant Norton M. , Bentley James , Biggers Rand R.
Published: June 2020

Single crystals of lanthanum aluminate (LaAlO3) are of interest as substrates to support the growth of films of the superconducting oxide YBa2Cu3O7. In order to facilitate epitaxy the thin films will often be deposited onto heated (T ≥ 700°C) substrates. LaAlO3 has a cubic structure at elevated temperatures and undergoes a transformation on cooling to the rhombohedral crystal structure-the stable form at room temperature. The phase transformation from the cubic to the rhombohedral structure leads to the formation of twins. The twin boundary is predominantly the (100) plane of the pseudo-cubic cell. Several potential problems associated with the phase transformation in LaA1O3 and the concomitant formation of twins have been postulated. Firstly, defects related to the twin boundaries might act as preferred nucleation sites during film deposition. Secondly, on cooling through the transformation temperature, after film deposition, twinning of the substrate might introduce strains into the thin film deposited on the initially untwinned substrate.
Combined x-ray, EELS, microanalysis, and electron holography of electrically active electroceramic interfaces
Authors: Ravikumar V. , Wilcox N. , Rodrigues R. P. , Dravid Vinayak P.
Published: June 2020

A large number of electroceramics derive their useful properties from the presence of electrically active interfaces. Varistors and GB capacitors are examples of important electroceramics where the electrical activity of grain boundary (GB) region controls the macroscopic response of the bulk devices. Electrical activity of GBs is often induced by doping and thermal processing. As a part of a broad program, we are investigating the inter-relationship among GB variables (structure, chemistry, and electronic structure) and GB induced properties in model electroceramics such as SrTiO3.

GB doping of SrTiO3 polycrystals was achieved by infiltrating Mn into the GBs under appropriate thermal processing cycle. A quick survey of the microstructure by SIMS revealed that virtually all GBs are decorated with Mn. Subsequently, thin foils were examined for AEM analysis using Hitachi HF-2000 cold field emission gun TEM (FEG TEM), equipped with an Oxford Pentafet x-ray detector and a Gatan 666 PEELS system. A probe size of ~ 1 nm was utilized for microanalysis.
Decomposition of electron energy loss spectrum-line profiles by target factor analysis
Authors: Splinter S.J. , Bruley J. , Smith D.A.
Published: June 2020

Interfaces play a ubiquitous role in governing the behavior of materials, but the fundamental means by which they exert their influence are surprisingly little understood. EELS offers a path towards elucidating the nature of both the coordination and local chemistry at interfaces; however, successful application requires the development of quantitative techniques for the deconvolution of various contributions to the spectra. The present work describes a first application of Factor Analysis (FA) to this problem. FA is a multiparameter statistical method used to extract subtle information from complicated data sets, the mathematical basis of which has been well documented in the literature. In brief, FA seeks to reproduce a given data set within experimental error using the minimum number of statistically non-zero “factors” or “components”. In this study, FA has been successfully applied to the decomposition of an Al L2,3 spectrum-line profile across a magnesium aluminate spinel/sapphire interface. One of us (JB) recently examined this heterophase structure in detail using multiple least squares decomposition of the two endpoint components (spinel and sapphire).
The measurements of the elastic-inelastic multiple scattering electron intensity in EELS
Authors: Cheng S. C. , Wang Y. Y. , Dravid V. P.
Published: June 2020

The Electron energy loss function in the low energy range is determined by collective excitation of valence electrons and charge carriers, i.e. plasmons, as well as interband and intraband excitations. The explicit dependence of the cross-section on the momentum transfer q allows the observation of nonvertical interband transition and a measurement of the dispersion of plasmon excitations. The drawback of the momentum resolved electron spectroscopy is the multiple scattering, which often obscure the single scattering events. Under relatively small scattering angles, both strong elasticinelastic multiple (E-I-M) scattering and elastic scattering events compared to the inelastic scattering have been reported. In order to find out in what momentum range the E-I-M scattering intensity can be ignored in the momentum resolved electron spectroscopy, we have measured the angular dependency of the intensities of the E-I-M scattering electrons Ie+in. The intensities of the elastic scattering electrons Ie as well as of the inelastic scattering electrons Iin were also measured and are presented in this paper together. A simple relationship between Ie and Ie+in is found.
Interfacial composition analysis of silicon nitride whisker reinforced oxynitride glass systems
Authors: Sun E. Y. , Alexander K. B. , Becher P. F. , Hwang S. L.
Published: June 2020

Microstructural and compositional analysis in many structural ceramics requires sophisticated analytical electron microscopy because of the light elements (O, N, C and B) present in the materials and the nano-scale amorphous phases at the grain boundaries. In the present study, scanning transmission electron microscopy (STEM) combined with energy-dispersive x-ray spectroscopy (EDS) and parallel-detection electron energy-loss spectroscopy (PEELS) was used to analyze the composition at interfaces in β-Si3N4 whisker reinforced oxynitride glass systems. Composition profiles were acquired by either manually stepping the probe across the interface or by sequential integration during slow-rate line-scanning with a < 2.0 nm probe in the STEM mode of a Philips EM400T/FEG microscope.

Silicon nitride, which has been recognized as one of the most promising candidates for high temperature applications, is typically densified by employing various sintering aids such as yttria and alumina. Reaction of the sintering aids and the oxide surface layer on Si3N4 particles forms secondary intergranular phases that are primarily silicon metal oxynitride glasses.
AFM study of the dynamics of α-alumina surface faceting during high-temperature processing
Authors: Bench Michael W. , Heffelfinger Jason R. , Barry Carter C.
Published: June 2020

To gain a better understanding of the surface faceting that occurs in α-alumina during high temperature processing, atomic force microscopy (AFM) studies have been performed to follow the formation and evolution of the facets. AFM was chosen because it allows for analysis of topographical details down to the atomic level with minimal sample preparation. This is in contrast to SEM analysis, which typically requires the application of conductive coatings that can alter the surface between subsequent heat treatments. Similar experiments have been performed in the TEM; however, due to thin foil and hole edge effects the results may not be representative of the behavior of bulk surfaces.

The AFM studies were performed on a Digital Instruments Nanoscope III using microfabricated Si3N4 cantilevers. All images were recorded in air with a nominal applied force of 10-15 nN. The alumina samples were prepared from pre-polished single crystals with (0001), , and nominal surface orientations.
The annealed (0001) α-alumina surface and its influence on thin-film growth
Authors: Bench Michael W. , Kotula Paul G. , Barry Carter C.
Published: June 2020

The growth of semiconductors, superconductors, metals, and other insulators has been investigated using alumina substrates in a variety of orientations. The surface state of the alumina (for example surface reconstruction and step nature) can be expected to affect the growth nature and quality of the epilayers. As such, the surface nature has been studied using a number of techniques including low energy electron diffraction (LEED), reflection electron microscopy (REM), transmission electron microscopy (TEM), molecular dynamics computer simulations, and also by theoretical surface energy calculations. In the (0001) orientation, the bulk alumina lattice can be thought of as a layered structure with A1-A1-O stacking. This gives three possible terminations of the bulk alumina lattice, with theoretical surface energy calculations suggesting that termination should occur between the Al layers. Thus, the lattice often has been described as being made up of layers of (Al-O-Al) unit stacking sequences. There is a 180° rotation in the surface symmetry of successive layers and a total of six layers are required to form the alumina unit cell.
Nucleation of pyroxene and amphibole in glassy veins along interfaces and cracks in ultramafic inclusions from San Carlos, Arizona
Authors: Wirth R.
Published: June 2020

Ultramafic inclusions occur in ellipsoidal bombs in basalt flows. The inclusions of the San Carlos ultramafic inclusion locality have been described in detail by Frey & Prinz (1978). They mainly consist of olivine, orthopyroxene (opx), clinopyroxene (cpx) and Cr-spinel. Ultramafic inclusions are important because they are samples of the upper mantle material, and thus they provide direct insight into the upper mantle processes and composition. Glassy veins are fairly abundant along mineral interfaces and cracks. The glass apparently results from incongruent melting of hydrous phases. The glassy veins are between a few nanometer and several microns wide. Veins with a width > 1 μm exhibit crystals of olivine, pyroxene and feldspar. The narrow veins (< 1 μm) only occasionally show crystallization of small crystals (several hundred nanometer). The early stages of crystallization of pyroxene and amphibole and the chemical composition have been investigated by HRTEM and analytical TEM.

Glassy veins along interfaces: small grains (several hundred nanometer) of opx have nucleated at an opx/glass interface.
A microscopist's view of catalysis
Authors: Targos W.
Published: June 2020

Analytical electron microscopy, AEM, has provided valuable information on the structure, composition, location and size of metal clusters and/or crystallites supported on amorphous or crystalline metal oxide materials. Although this information is vital to the understanding of how a catalyst functions, the catalytic reaction is usually more complex. Many variables must be taken into account to evaluate properly a catalyst. Improper selection of process variables can make a good catalyst perform poorly. Consequently, focusing on specific metal site properties may not always be the appropriate direction to take when evaluating a supported metals catalyst problem.

To help the microscopist appreciate the complexity of the problem, the following examples were chosen to illustrate this point. Reforming catalysis involves a complex set of reactions to convert naphtha feed to high octane gasoline. The catalyst is comprised of highly dispersed Pt on a high surface area alumina with Cl. The catalyst is dual functional requiring both metal site activity for dehydrogenation and acidity for isomerization and cyclization.
Microstructural evolution of γ-alumina supported rhodium catalysts
Authors: Weng-Sieh Zara , Gronsky Ronald , Bell Alexis T.
Published: June 2020

In an era of increasing environmental awareness, stricter federal and state regulation of pollutant emissions are emerging. A major source of pollution arises from automobiles which inadvertently form gaseous products such as nitric oxide (NOx), carbon monoxide (CO), and hydrocarbons (HC). Since the early 1980's, these effluents have been converted to safer forms using a three-way catalytic converter that employs a high dispersion of rhodium and platinum particles supported on a large surface area of transitional γ-phase alumina. Unfortunately such a converter is susceptible to decreased performance over time, and this degradation has been attributed to changes in the catalyst microstructure. The nanoscaled nature of the transition metal catalysts and the submicron-scaled size of the transitional alumina necessitates the use of the high spatial resolution analyses made possible by transmission electron microscopy.
Advantages of modern field emission Electron Microscopes for characterization of catalytic materials
Authors: Allard L. F. , Bradley S. A. , Völkl E. , Pennycook S. J.
Published: June 2020

The ability to characterize the structure of a variety of catalytic materials, especially supported metal catalysts, has been dramatically enhanced in recent years by the improved electron microscopy capabilities provided by the new generation of field emission gun transmission (FE-TEM) and dedicated scanning transmission electron microscopes (d-STEM). Although the reciprocity theorem says that a TEM and a dedicated STEM have equivalent, but reciprocal, electron optical geometries so that imaging conditions in one instrument can, in principal, be duplicated in the other, in reality the TEM and d-STEM offer column geometries that are optimized for different kinds of analytical output. For example, the d-STEM permits introduction of an energy dispersive spectrometer, which collects x-rays at a solid angle of 0.2 sr (but at a low take-off angle). A high take-off angle detector in a TEM may give a collection angle of only 0.013 sr. This x-ray collection efficiency coupled with use of annular dark-field techniques makes the imaging and analysis of nanometer-sized metal clusters on supports more effective.
Studies of surface and structural heterogeneity of carbon supports and carbon-supported catalysts
Authors: Liu J. , Colburn S. M. , Ornberg R. L. , Ebner J. R.
Published: June 2020

Activated carbons are generally used as support materials for precious metal catalysts. Properties of carbon that are important to catalyst preparation and application include composition, surface area, microstructure and pore shape and size distribution. Macropores (> 50 nm), mesopores (2-50 nm) and micropores (<2 nm) generally coexist in activated carbons. The accessibility of metal particles dispersed in microporous systems is of predominant importance, especially for large molecules that exhibit slow diffusion transport in narrow pores. It is desirable to have metal particles highly dispersed in readily accessible locations. As part of an on-going program of the characterization of carbonsupported catalysts we report some preliminary observations of the microstructure of carbon supports by a variety of electron microscopy techniques

Commercial carbon supports and carbon-supported Pt catalysts were used in this study. High resolution secondary electron (SE) microscopy, low voltage backscattered electron (LVBE) microscopy and high-angle annular dark-field (HAADF) microscopy techniques were employed to extract surface and structural information.
Scanning probe microscopy of the activation and sulfur deactivation of Pd model catalysts
Authors: Catani R. , Lee K.-H. , Wolf E.E.
Published: June 2020

Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) are used to image the microstructure of surfaces before and after pretreatment and reaction to establish a correlation between activity/deactivation and morphology. Several surfaces of flat thin Pd films supported on graphite, and single crystals of silica and alumina, show that the morphology of these films is highly sensitive to the method of activating the Pd catalysts. It is shown that the activity and selectivity for the probe reaction, butadiene hydrogenation, of a Pd/graphite film catalyst changes with the film microstructure. It is also shown that catalysts prepared via different procedures leading to the same surface structures exhibited the same reactivity, and vice versa, i.e. different microstrcutures lead to different activity, thus demonstrating a correlation between activity and morphology. The structure can be changed by changing the hydrocarbon to hydrogen ratio which causes significant deactivation due to changes in morphology.
STEM measurement of Ge concentration profiles in Si/GeSi/Si heterostructures with 3 Å resolution
Authors: Lee Tan-Chen , David Theodore N. , Silcox John
Published: June 2020

GeSi alloys are of great interest because of potential applications to high-performance semiconductor devices. For example, the fastest heterojunction bipolar transistor (in Si-based materials) in 1990 was fabricated by using a strained GeSi layer. To accomplish this, it is necessary to keep the Ge concentration and the thickness of the GeSi films below a “critical thickness” to avoid relaxation of the GeSi alloys. It is therefore important to control the Ge concentration and the thickness of GeSi films. When the thickness of the GeSi film is under 10 nm, common characterization techniques such as RBS (Rutherford Backscattering Spectrometry), Auger analysis and SIMS (Secondary Ion Mass Spectrometry) reach resolution limits. The accurate measurement of Ge profiles in GeSi thin films becomes a difficult but important issue. In this paper, we measure Ge concentration profiles by different analytical techniques obtained from STEM and compare them with results from SIMS and Auger analysis.
Microstructure of thin film La0.5Sr0.5CoO3 electrode for microelectronics applications
Authors: Wang Z. L. , Zhang Jiming
Published: June 2020

Increasing circuit densities in dynamic random access memories (DRAMs) is one of the major interests in microelectronics research. In a ferroelectric capacitor memory, conducting electrodes must make intimate and ohmic contact to both sides of the ferroelectric thin film. The bottom electrode serves as the substrate during growth and the top electrode is deposited on top of the ferroelectric film. Single crystalline La0.5Sr0.5CoO3 (LSCO) thin films, which are conductive and low electrical resistivity, have recently grown on both sides of Pb-Zr-Ti-O (PZT) ferroelectric film, which has shown a great potential for making fatigue-free small thickness storage capacitors. The present paper reports the microstructure studies of the LSCO thin films grown on MgO(00l) and LaAlO3(100) (LAO) substrates by the metalorganic chemical vapor deposition (MOCVD) technique.

Cross-section specimens were made to examine the structure of the film and its relationship with the substrate. Select-area electron diffraction (SAD) and high-resolution lattice image show that the LSCO film has an epitaxial relationship with the MgO/LAO substrate.