bluuebunny/crossref_metadata_2025_split huggingface dataset:
EELS study of bulk Co and CoSi2
Authors: Wong Kaikee 
Published: June 2020

CoSi2 can grow epitaxially on Si and the Si/CoSi2/Si heterostructure has potential uses in metal-based transistors. To fully utilize the device potential of CoSi2, it is important to develop a thorough understanding of its electronic properties. By comparing the Co L2,3 spectra of pure Co and CoSi2, the bonding between Co and Si atoms can be studied.A Si (111) wafer was treated by Shiraki cleaning before 500 Å of Co was deposited in an E-beam evaporator with a base pressure of 10-7 Torr. The wafer was then annealed in an UHV oven with a base pressure of 10-10 Torr at 950°C for 2 hrs. A standard TEM plan view sample was then prepared from the wafer by dimpling and ion-milling, both from the Si side to preserve the silicide. The stochiometry of CoSi2 was confirmed by SAD and EDS. EELS measurements were carried out in a VG-HB501A UHV STEM operating at 100 keV equipped with a serial EELS detector.
Elemental mapping with an energy-selecting imaging filter
Authors: Krivanek O.L. , Gubbens A.J. , Kundmann M.K. , Carpenter G.C. 
Published: June 2020

Imaging filters produce energy-selected images in a few seconds, and chemical maps formed by processing of several images taken at different energy losses in typically less than one minute. On the other hand, imaging filters do not provide detailed spectra from each specimen point, and are vulnerable to artifacts due to variations in specimen thickness, and other effects influencing EELS background extrapolation and subtraction. These include diffraction contrast arising particularly in crystalline samples, edge overlap, and extended fine structures (EXELFS) in the pre-edge region caused by major edges at lower energies. We have therefore been exploring the practical usefulness of imaging filters on a range of specimens from materials science and biology. The results suggest that the imaging capability combined with full paralleldetection EELS performance delivers a very powerful experimental set-up.Figure 1 shows an energy-filtered bright field image of a steel sample containing about 1 % Cu, obtained at 120 keV with the Gatan Imaging Filter (GIF) attached to a Philips CM12ST microscope.
Detection and resolution in infrared microprobe analysis
Authors: Reffner John A. , Martoglio Pamela A. 
Published: June 2020

Detection and resolution are terms commonly used when describing infrared microprobe (IRM) analysis. However, the clear definitions of each are not always understood completely. It is the purpose of this work to define these terms as they apply to IRM analysis.It is a well-known fact that, for optical imaging, the ability to resolve two separate points is dependent upon both the wavelength of radiation and the numerical aperture of the optical system. The implications of this law were first described in terms relevant to IRM analysis in 1987. In order to be visually resolved, the Rayleigh criterion states that two points must be separated by 0.61 l/NA (the radius of the central maximum of the Airy disk; see Figure 1). Since an IRM detects energy outside the central maximum, this criterion is not valid for spectral resolution. With a 15X objective (NA = 0.58) over the spectral range of 600 - 4000 cm-1 (16.7 - 2.5 μm), the diffraction-resolution limit (DRL) ranges from 2.5 - 15 μm.
Strategies for structure determination by electron crystallography: Application to tubulin
Authors: Downing Kenneth H. 
Published: June 2020

Determination of protein structures at the atomic level by electron microscopy has long been a goal, and has finally become a reality. Progress on several protein structures has been steady, but the rapid flow of structures that was anticipated to follow the initial atomic model of bacteriorhodopsin (bR) has not yet appeared. We will discuss here some of the effects that have led to this slow rate of progress and things that still need to be done to speed up the process.The first requirement for doing crystallographic work is the availability of crystals. To date only a small number of proteins have been crystallized to give high-resolution data. Many of the principles of 2-D crystal formation are clear, and the limitations are in the nature of the amounts of protein available for crystallization experiments. With more experience, crystal availability should no longer be a limitation This will be useful because we envision the day when structures can be solved, at least through the data collection and processing stages, in a matter of days rather than the present years.
Kinematical structure factors from dynamical diffraction?
Authors: Eades Alwyn 
Published: June 2020

In convergent-beam diffraction it is a common observation that kinematically forbidden reflections show "dynamical extinctions", also known as Gjonnes-Moodie lines, G-M lines, black crosses or dark bars. These zeros of intensity can be understood as resulting from the pairing of multiple diffraction routes so that each pair cancels. If the multiple diffraction routes for a reflection that is not kinematically forbidden could be paired in the same way, we could locate a position in the convergent-beam disc where the intensity would depend only on the structure factor for that one reflection. This would be extremely valuable because it would provide electron diffraction with a greatly simplified method of solving crystal structures.It turns out that no such condition can be found. Here, an outline of the argument is given. A full account will be given elsewhere.The pairing of the multiple diffraction routes depends on the existence of symmetry relations between different reflections.
Measurement of lattice parameter at the nanometer scale using convergent-beam microdiffraction from a thermal emission source
Authors: Pike W. T. 
Published: June 2020

With the advent of crystal growth techniques which enable device structure control at the atomic level has arrived a need to determine the crystal structure at a commensurate scale. In particular, in epitaxial lattice mismatched multilayers, it is of prime importance to know the lattice parameter, and hence strain, in individual layers in order to explain the novel electronic behavior of such structures. In this work higher order Laue zone (holz) lines in the convergent beam microdiffraction patterns from a thermal emission transmission electron microscope (TEM) have been used to measure lattice parameters to an accuracy of a few parts in a thousand from nanometer areas of material.Although the use of CBM to measure strain using a dedicated field emission scanning transmission electron microscope has already been demonstrated, the recording of the diffraction pattern at the required resolution involves specialized instrumentation. In this work, a Topcon 002B TEM with a thermal emission source with condenser-objective (CO) electron optics is used.
Theory of transmission low-energy electron diffraction
Authors: Qian W. , Spence J.C.H. 
Published: June 2020

Interpretation of the images from a point source electron microscope requires a detailed analysis of transmission low energy electron diffraction. Here we present a general approach for solutions to the mixed Bragg-Laue case in transmission LEED (100-1000eV), based on the dynamical diffraction theory of Bethe. However, the validity of the dynamical diffraction theory to low energy electrons can be justified by its connection to the band theory for low energy crystal electrons.Assume that the incident beam forms a plane wave and the crystal is a thin slab. According to Bethe, the total electron wavefield within crystal can be written as a linear combination of Bloch waves (equation 1). The Bloch wave excitation coefficients b(j) can be determined by matching the boundary conditions, the wave amplitudes Cg(j) and the wave vectors k(j) for each Bloch wave can be obtained by solving the time independent Schrodinger equations (equation 2).
Advances in ultramicrotomy for physical sciences applications
Authors: McMahon G. , Malis T. 
Published: June 2020

As with all techniques which are relatively new and therefore underutilized, diamond knife sectioning in the physical sciences continues to see both developments of the technique and novel applications.Technique Developments Development of specific orientation/embedding procedures for small pieces of awkward shape is exemplified by the work of Bradley et al on large, rather fragile particles of nuclear waste glass. At the same time, the frequent problem of pullout with large particles can be reduced by roughening of the particle surface, and a proven methodology using a commercial coupling agent developed for glasses has been utilized with good results on large zeolite catalysts. The same principle (using acid etches) should work for ceramic fibres or metal wires which may only partially pull out but result in unacceptably thick sections. Researchers from the life sciences continue to develop aspects of embedding media which may be applicable to certain cases in the physical sciences.
Long-term variations in individual particle types in the aerosol of Phoenix, Arizona, as determined using automated electron microprobe analysis and multivariate statistical techniques
Authors: Katrinak Karen A. , Anderson James R. , Buseck Peter R. 
Published: June 2020

Aerosol samples were collected in Phoenix, Arizona on eleven dates between July 1989 and April 1990. Elemental compositions were determined for approximately 1000 particles per sample using an electron microprobe with an energy-dispersive x-ray spectrometer. Fine-fraction samples (particle cut size of 1 to 2 μm) were analyzed for each date; coarse-fraction samples were also analyzed for four of the dates.The data were reduced using multivariate statistical methods. Cluster analysis was first used to define 35 particle types. 81% of all fine-fraction particles and 84% of the coarse-fraction particles were assigned to these types, which include mineral, metal-rich, sulfur-rich, and salt categories. "Zero-count" particles, consisting entirely of elements lighter than Na, constitute an additional category and dominate the fine fraction, reflecting the importance of anthropogenic air pollutants such as those emitted by motor vehicles. Si- and Ca-rich mineral particles dominate the coarse fraction and are also numerous in the fine fraction.
SEM study of structure and formation of the carbon cluster in the arc-discharge deposits
Authors: Zhou Dan , Seraphin Supapan , Jiao Jun 
Published: June 2020

The richly structured surfaces of the graphite electrodes in carbon arc discharges have been the subject of numerous studies in the past, due to the strong technological importance of the carbon arc lamp. However, since they were not known until recently , no attention was paid to the existence of carbon nanocluster which the discharge produces. Our previous results show that the variations of the production processing conditions will affect the properties of the individual carbon nanotube. We present here a scanning electron microscopy (SEM) study of the topography of the deposits at the graphite cathode, and attempt to correlate the growth behavior of nanotubes to the structural elements of the cathode surface.The starting material in this study is the carbonaceous deposit (i.e. slag) formed on the initial flat cathode as the anode is consumed during the arc discharge. The slag was carefully cleaved to make a SEM sample and the topography of the slag was characterized in both top view and cross-section.
Insertion of yttrium carbide into carbon nanoclusters by vapor transport during growth
Authors: Seraphin Supapan , Zhou Dan , Jiao Jun 
Published: June 2020

Carbon nanoclusters have basic features in common, although they vary greatly in shapes. Concentric graphitic layers separated by 0.34 nm surround a hollow core a few nanometers in diameter. Encapsulating materials into this hollow core changes the physical properties drastically. The insertion offers the possibility to study materials of small dimensions in a closed-off environment. Technological promise is given for the production of nanowires, and other applications in which the nanoscale is of importance. Recent work takes a variety of approaches, inserting lead into nanotubes by capillary suction through open ends, or encapsulating microcrystals of LaC2 into the polyhedral cages. We report a method for filling carbon clusters of various shapes in situ through vapor transport from a composite anode of a graphite rod filled with yttrium oxide paste at a center hole.Both materials pass through the arc discharge, and grow as composite carbon nanoclusters at the pure graphite cathode.
Electron sources: Past, present, and future
Authors: Joy David C 
Published: June 2020

The electron source is the most important component of the Scanning electron microscope (SEM) since it is this which will determine the overall performance of the machine. The gun performance can be described in terms of quantities such as its brightness, its source size, its energy spread, and its stability and, depending on the chosen application, any of these factors may be the most significant one. The task of the electron gun in an SEM is, in fact, particularly difficult because of the very wide range of operational parameters that may be required e.g a variation in probe size of from a few angstroms to a few microns, and a probe current which may go from less than a pico-amp to more than a microamp. This wide range of operating parameters makes the choice of the optimum source for scanning microscopy a difficult decision.Historically, the first step up from the sealed glass tube ‘cathode ray generator’ was the simple, diode, tungsten thermionic emitter.
The SEM in present-day semiconductor FABS
Authors: Bennett Marylyn Hoy 
Published: June 2020

Computers, cars, HDTV, and microwave ovens: what great modern conveniences! Why do these marvels of technology work the way they do? The Scanning Electron Microscope has a lot to do with it. For the last decade, the shrinking geometries of integrated circuits have necessitated the use of the Scanning Electron Microscope (SEM) for inspection and metrology. The current device feature sizes in production are as small as 0.5μm, and current feature sizes under development are 0.25μm or smaller. The semiconductor industry depends on the SEM to tell us if our processes, whether production or developmental, are correct. Neither leading edge fabs nor developmental fabs could function very well without the SEM.The uses of the SEM are many and varied, both inside and outside the fab. Inside the fab, there are many inspection steps to be performed. Although the optical microscope is still a viable option for, and is still routinely used for, in-line wafer inspection, the SEM is indispensable for inspection (Fig. 1) of small geometries such as 0.35μm lines and spaces and 0.5μm contact holes.
Effects of a thiol antioxidant on leucocyte adherence to aortic endothelium during atherogenesis: Quantitative SEM assessment
Authors: Robinson Keith A. , Medford Russell M. , Wayne Alexander R. 
Published: June 2020

Dysfunction of arterial endothelial cells (EC) leading to adherence of circulating leucocytes (WBC) is a pivotal step in atherogenesis, preceding fatty streak formation. The attachment process is mediated at least in part by inducible endothelial-leucocyte adhesion molecules (ELAMs) on the EC surface which interact with WBC counterreceptors. Expression of VCAM-1, a monocyte selective adhesion molecule, by IL-1 and TNF stimulated vascular EC in vitro was shown to be inhibited by a thiol antioxidant (pyrrolidine dithiocarbamate, PDTC). In this study we analyzed the effect of PDTC administered to cholesterol-fed rabbits, on WBC attachment to lesion-prone sites of the aorta using SEM morphometry.New Zealand White (NZW) rabbits (2-3 kg) were fed 1% cholesterol for 3 d. The day before feeding, venous cannulas were introduced, and PDTC (20 mg/kg) or vehicle (0.1 M PBS) was given twice daily throughout. The animals were euthanatized at 4 d and the aortas pressure perfusion fixed with buffered 2.5% glutaraldehyde after rinse with Ringer‘s solution containing heparin (10 u/ml).
STEM characterization of a 6Å diameter Mo3Se3 fiber
Authors: Hornbostel M. , DiSalvo F.J. , Hillyard S. , Silcox J. 
Published: June 2020

LiMo3Se3 is a highly anisotropic conductor containing 6Å diameter one dimensional chains of Mo3Se3 triangles. This compound can be dissolved in polar solvents to produce solutions containing micron length Mo3Se3 fibers. Choice of solvent and solution concentrations allows some control of fiber diameters, from a few hundred angstroms down to the molecular limit of a single 6Å diameter chain. These fibers have been deposited from solution on holey carbon substrates by vacuum evaporation of the solvent to produce free-standing, one dimensional wires.High resolution microscopy at 100kV was carried out in a VG HB501A STEM and confirms the presence of many different sized bundles extending all the way down to the single strands. Figure 1a shows an ADF image of a medium sized strand which commonly occured in a sample prepared with the solvent propylene carbonate. The flexibility of the fiber and its seeming attraction to the edges of carbon holes is apparent as it snakes its way along the surface.
Atomic structures of faceted low-energy Pd/Al2O3 interfaces
Authors: Cosandey F. , Lu P. , Brun N. , Hagege S. 
Published: June 2020

Recently, it has been demonstrated that alpha alumina fibers having the stable trigonal structure can be grown in Pd by internal oxidation. The alumina fibers are oriented with respect to Pd and exhibit strong faceting. In this paper, we present HREM results on the atomic structures of the faceted interfaces.Oxidation experiments were done in air at 1000 °C for 48 hrs on a Pd-10.8 at.% Al alloy. Selected samples were subsequently annealed at 1000 °C for 0.5 hrs in an Al vapor. All HREM observations were done using a Topcon-002B high resolution microscope. For image analysis, the interfaces were modeled using EPITAX and multislice image simulations were performed using EMS programs.The alumina fibers grown by internal oxidation, grow along the <110>Pd oxidation front direction. The orientation relationship between Al2O3 fibers and Pd is not unique, however, most fibers are faceted with primary low energy interfaces between Pd and Al2O3 corresponding to (110)//(0001), (111)//(0001) and (111)//(11-20).
“Dynamic” charging of polymers in the LVSEM
Authors: Butler J. H. , Joy D. C. , Bradley G. F. 
Published: June 2020

Recently we have been using a field emission LVSEM with an immersion-type objective lens extensively for the examination of polymers at low (<2 keV) incident beam energies. During the course of these studies it became apparent that, even though operating in the vicinity of E2 (the accelerating voltage at which no electrostatic charge builds up on the sample surface), sample charging effects of a most curious nature do, in fact, abound.In general the LVSEM has been successful in producing a wealth of exciting information. However, when nonconducting polymers are the subject of observation at E2, an unexpected and unusual charge build-up behavior is almost always encountered on the sample surface under irradiation (c.f. Figure 1). Thus for strongly insulating materials, it is not as easy to work in the realm of E2 as earlier predicted. For example, in some polymeric materials, it appears that charging is a function of magnification: at very high magnifications the sample will charge "positively", at lower magnifications (with all other parameters the same) the same sample will charge negatively, and at even lower magnifications the same sample will revert back to a positive charging situation.
Solvent-assisted osmium staining of butyl acrylate and ethylene-propylene-diene in a styrene acrylonitrile matrix
Authors: Hutchins Gudrun A. 
Published: June 2020

In order to optimize the toughening effect of elastomers in engineering polymers, it is necessary to characterize the size, morphology and dispersion of the specific elastomer within the polymer matrix. For unsaturated elastomers such as butadiene or isoprene, staining with osmium tetroxide is a well established procedure. The residual carbon-carbon double bond in these materials is the reactive site and forms a 1,2-dilato complex with the OsO4. Incorporation of osmium tetroxide into the elastomer not only produces sufficient contrast for TEM, but also crosslinks the elastomer sufficiently so that ultramicrotomy can be accomplished at room temperature with minimal distortion.Blends containing saturated elastomers such as butyl acrylate (BA) and ethylene propylene diene monomer (EPDM) cannot be stained directly with OsO4 because effective reaction sites such as C=C or -NH2 are not available in sufficient number. If additional reaction sites can be introduced selectively into the elastomer by a chemical reaction or the absorption of a solvent, a modified, two-step osmium staining procedure is possible.
Incoherence in atomic-resolution Z-contrast imaging
Authors: Jesson D. E. , Pennycook S. J. 
Published: June 2020

Incoherent imaging of atomic clusters, monolayer rafts, or low index crystal projections at atomic resolution in a scanning transmission electron microscope (STEM) offers a number of distinct advantages over coherent imaging methods. These include an improved “interpretable” resolution and no experimental contrast reversals with specimen thickness or objective lens defocus. However, considerable controversy and confusion has arisen concerning the conditions under which the image of a given object can be interpreted using incoherent imaging theory. Here, we attempt to clarify the situation.Firstly, we consider the case of very thin specimens, such as heavy atoms, clusters of atoms, or extremely thin crystals. Experimentally, these specimens demand a relatively low annular detector inner radius to achieve an acceptable signal-to-noise ratio in the image. It is usual, therefore, to match the detector inner radius to the radius of the directly transmitted disc. In this conventional geometry, the annular dark-field signal will be dominated by coherent scattering, and the use of incoherent imaging theory may give rise to appreciable error close to the resolution of the STEM instrument.
Structure of the Σ=5 (310) interface in NiAl
Authors: Fonda Richard W. , Luzzi David E. 
Published: June 2020

The atomic structure of the Σ=5 [001] (310) grain boundary in NiAl was examined by high resolution electron microscopy and multislice image simulation. As in most other intermetallic compounds, the grain boundaries in NiAl are intrinsically brittle at low temperatures. Although there have been few studies on this alloy, the energies of NiAl grain boundaries have been calculated using embedded atom potentials for both stoichiometric and non-stoichiometric structures. These studies are consistent with the results of Bradley and Taylor, which indicate that nickel-rich compositions result from nickel antisite defects on the aluminum sublattice, while aluminum-rich compositions produce constitutional vacancies on the nickel sublattice, and with recent field ion microscopy results on nickel-rich alloys.The Σ=5 grain boundary was prepared by diffusion bonding at 1000 °C. A JEOL 4000EX was used for HREM imaging and the NUMIS multislice simulation program was used to simulated images. Analysis of these images considered the effects of grain boundary expansion, rigid body displacements along the boundary, grain boundary stoichiometry, and point defects at the boundary.