bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dislocation structures in TiB2/NiAl composites deformed at high temperatures
Authors: Wang L. , Arsenault R.J. 
Published: June 2020

An investigation was undertaken of deformed TiB2/NiAl composites to determine the effect of TiB2 particles on the dislocation density and morphology. Also, the purpose of this investigation was to compare the dislocation structures of the composites with the dislocation structures which had been reported previously in NiAl. The material used in this investigation was produced by the XD process of Martin Marietta and contained 0 and 20V% TiB2 particles in NiAl. The TiB2 particles were about one micron in size, and the grain size of the 0 and 20V% samples is 5 and 1 μm, respectively. In addition to the TiB2 particles, there was also about 10V% aluminum-oxide (α-Al2O3).The samples were tested in compression to 30% deformation at 870° C at various strain rates ranging from 10-4 per sec. to 2×10-2 per sec. The TEM foils were prepared from the deformed and annealed samples and examined in a 100 KV microscope. Also, a 1 MeV HVEM microscope was used.
Shot-noise simulations of HREM images of polymer crystals
Authors: Pradère Philippe , Thomas Edwin L. 
Published: June 2020

High Resolution Electron Microscopy (HREM) is a very powerful technique for the study of crystal defects at the molecular level. Unfortunately polymer crystals are beam sensitive and are destroyed almost instantly under the typical HREM imaging conditions used for inorganic materials. Recent developments of low dose imaging at low magnification have nevertheless permitted the attainment of lattice images of very radiation sensitive polymers such as poly-4-methylpentene-1 and enabled molecular level studies of crystal defects in somewhat more resistant ones such as polyparaxylylene (PPX) [2].With low dose conditions the images obtained are very noisy. Noise arises from the support film, photographic emulsion granularity and in particular, the statistical distribution of electrons at the typical doses of only few electrons per unit resolution area. Figure 1 shows the shapes of electron distribution, according to the Poisson formula :
Electron spectroscopic diffraction at (111) silicon foils
Authors: Reimer L. , Fromm I. 
Published: June 2020

An electron diffraction pattern (EDP) consists of an overlap of patterns of all energy losses in the electron energy-loss spectrum (EELS). Electron spectroscopic diffraction (ESD) in an energy filtering electron microscope (EFEM) allows to separate the contributions of different energy losses to the unfiltered diagram observed in conventional TEM. We report about diffraction experiments with a Zeiss EM902 on (111) silicon foils which show how the EDP of single-crystal foils changes with increasing energy loss and foil thickness. An EDP normally contains the Bragg spots, diffuse streaks by electron-phonon scattering, excess and defect Kikuchi lines when the number of electrons striking the lattice planes is different from opposite sites, a system of excess (bright) Kikuchi bands with an intensity proportional to the probability ψψ⋆ of the Bloch wave field at the nuclei, and defect Ki-kuchi bands when the number of diffusely scattered electrons is equal on both sides of the lattice plane and the intensity becomes proportional to ΣIg.EDPs of thin foils show an increase of contrast of the Bragg spots and the thermal diffuse streaks when comparing an unfiltered (Fig.1a) and zero-loss filtered EDP (Fig.1b). Because the streaks are caused by elastic scattering, they can not be ob served with the plasmon loss (Fig.1c). Bragg spots are also observed at higher energy losses because all delocalized inelastic scattering processes with energy losses less a few hundred eV show intraband transitions which preserve the type of excited Bloch waves.
Electron energy loss near edge structure
Authors: Weng Xudong , Rez Peter 
Published: June 2020

In inner shell absorption spectroscopy, the near edge structure (NES) up to 30 eV above threshold is a prominent solid state effect. It is well known that electron energy loss spectroscopy is advantageous for the study of light elements, like carbon, nitrogen, oxygen, and fluorine. Due to the complexity of the near edge region, it is only recently that a significant amount of research have been carried out to extract information on the solid state effects.The theory to interpret the near edge structure is based on Fermi’s Golden rule. Two methods have been derived which give different and complimentary physical pictures about the inner shell excitation process. Single electron band structure techniques have been successfully applied to the interpretation of x-ray near edge structure. using the projected densities of states (DOS) of L±1 characterpermitted by the dipole selection rule. The multiple scattering method views the near edge structure (XANES) [2.3] as coming from the interference between the outgoing ejected electron wave and renections from neighboring atoms.
Conditions for atomic imaging of mullite
Authors: Epicier T. A. , Thomas G. 
Published: June 2020

Mullite is an aluminium-silicate mineral of current interest since it is a potential candidate for high temperature applications in the ceramic materials field.In the present work, conditions under which the structure of mullite can be optimally imaged by means of High Resolution Electron Microscopy (HREM) have been investigated. Special reference is made to the Atomic Resolution Microscope at Berkeley which allows real space information up to ≈ 0.17 nm to be directly transferred; numerous multislice calculations (conducted with the CEMPAS programs) as well as extensive experimental through-focus series taken from a commercial “3:2” mullite at 800 kV clearly show that a resolution of at least 0.19 nm is required if one wants to get a straightforward confirmation of atomic models of mullite, which is known to undergo non-stoichiometry associated with the presence of oxygen vacancies.Indeed the composition of mullite ranges from approximatively 3Al2O3-2SiO2 (referred here as 3:2-mullite) to 2Al2O3-1SiO2, and its structure is still the subject of refinements (see, for example, refs. 4, 5, 6).
Characterization of thermal barrier coatings formed by electon-beam physical vapor deposition (EB-PVD)
Authors: Unal Ozer 
Published: June 2020

Interest in ceramics as thermal barrier coatings for hot components of turbine engines has increased rapidly over the last decade. The primary reason for this is the significant reduction in heat load and increased chemical inertness against corrosive species with the ceramic coating materials. Among other candidates, partially-stabilized zirconia is the focus of attention mainly because ot its low thermal conductivity and high thermal expansion coefficient.The coatings were made by Garrett Turbine Engine Company. Ni-base super-alloy was used as the substrate and later a bond-coating with high Al activity was formed over it. The ceramic coatings, with a thickness of about 50 μm, were formed by EB-PVD in a high-vacuum chamber by heating the target material (ZrO2-20 w/0 Y2O3) above its evaporation temperaturef >3500 °C) with a high-energy beam and condensing the resulting vapor onto a rotating heated substrate. A heat treatment in an oxidizing environment was performed later on to form a protective oxide layer to improve the adhesion between the ceramic coating and substrate. Bulk samples were studied by utilizing a Scintag diffractometer and a JEOL JXA-840 SEM; examinations of cross-sectional thin-films of the interface region were performed in a Philips CM 30 TEM operating at 300 kV and for chemical analysis a KEVEX X-ray spectrometer (EDS) was used.
Radiation damage characteristics of silicon oxynitride ceramic
Authors: Das Chowdhury K. , Carpenter R.W. , Weiss J.K. 
Published: June 2020

Silicon Oxynitride is a ceramic that often forms during sintering of Si3N4, as a result of reactions with the sintering aid or from oxygen adsorbed on the surface of the powder particles. It is an orthorhombic crystal in which Si is tetrahedrally coordinated, and it is quite susceptible to electron irradiation effects. We present here the first quantitative observations of radiation effects.Time-resolved Electron Energy Loss Spectroscopy (EELS) was used to follow the changes in elemental concentration with irradiation time in crystals of Si2N2O during electron-irradiation at 100kV. The experiments were performed in a Philips EM400ST microscope fitted with a field emission source using a focussed probe and a Gatan 666 Parallel EELS spectrometer. An LN2 cooled specimen holder was used to minimize contamination. Specimens were made from a ceramic containing plate-type Si2N2O microcrystals with long edges parallel to [010], described earlier. The special software for time resolved spectrum acquisition was developed in this laboratory. The Si-L, O-K and N-K edges were acquired as a function of irradiation time at known current density and then individually processed and numerically integrated over a 100eV interval, beginning at edge onset.
Crystallization behavior of Li2O-Al2O3-6SiO2glasses containing Ta2O5
Authors: Hsu J.Y. , Berta Y. , Speyer R.F. 
Published: June 2020

TiO2and ZrO2have been successful nucleating agents in lithium aluminosilicate glass-ceramics, which have applications including cooking ware, heat exchangers, telescope mirrors, and the matrices of fiber reinforced composites. The major crystalline phases, stuffedβquartz ss (solid solution) andβspodumene ss, have very small volume coefficients of thermal expansion, and thus these glass-ceramics have excellent thermal shock resistance. Ta2O5has recently been established as an effective (phase separation inducing) nucleation catalyst in glasses of this system. The effect of varying (re-heating) thermal treatment on microstructure formation in these glasses with Ta2O5additives is discussed herein.Glass samples were prepared in 100 gram batches using SiO2, Li2CO3, Al2O3, and Ta2O5powders as raw materials. The mixture, 1:1:6 in molar ratio of Li2O:Al2O3:SiO2with 4 mol% Ta2O5, was calcined in a Pt - 3.5% Rh crucible at 1350°C for 2 hours, held for another 12 hours at 1650°C, and then quenched onto a copper plate. The glass and devitrified samples were then mechanically thinned and ion-milled using a liquid nitrogen cold stage.
Nonstoichiometry effects on microstructure in amorphous CdGeAs2
Authors: Hong K.S. , Berta Y. , Speyer R.F. 
Published: June 2020

The mechanism of nucleation and growth in amorphous semiconducting CdGeAs2has been demonstrated with the aid of thermal analysis, TEM, and XRD to be: 1) germanium precursor formation, 2) nonstoichiometric chalcopyrite structure crystal growth from the germanium precursor, and 3) solid state transformation of the precursor to the chalcopyrite structure. This crystallization sequence does not follow the pseudo-binary phase diagram which indicates that only in the case of germanium content in excess of stoichiometric CdGeAs2shouldαsolid solution form in equilibrium with chalcopyrite structured CdGeAs2(see Fig. 1). To establish the extent of the germanium precursor nucleation mechanism, samples of deficient (CdGe0.8As2), stoichiometric, and excess (CdGe1.2As2) germanium content were prepared in the bulk amorphous form.Samples were fabricated by water-quenching the molten compound, vacuum sealed in carbon coated (by pyrolysis) fused silica tubes. The amorphous ampoules were broken out of the tubes, sliced to fit the hermetically sealing sample capsule for the differential scanning calorimeter (DSC) and heat treated at 0.5°C/min to various points along the exotherms. The partially devitrified samples were mechanically thinned and ion-milled using a liquid nitrogen cold stage, for examination in the TEM.
Symmetry breaking in convergent-beam diffraction
Authors: Eaglesham D.J. 
Published: June 2020

Convergent Beam Electron Diffraction is now almost routinely used in the determination of the point- and space-groups of crystalline samples. In addition to its small-probe capability, CBED is also postulated to be more sensitive than X-ray diffraction in determining crystal symmetries. Multiple diffraction is phase-sensitive, so that the distinction between centro- and non-centro-symmetric space groups should be trivial in CBED: in addition, the stronger scattering of electrons may give a general increase in sensitivity to small atomic displacements. However, the sensitivity of CBED symmetry to the crystal point group has rarely been quantified, and CBED is also subject to symmetry-breaking due to local strains and inhomogeneities. The purpose of this paper is to classify the various types of symmetry-breaking, present calculations of the sensitivity, and illustrate symmetry-breaking by surface strains.CBED symmetry determinations usually proceed by determining the diffraction group along various zone axes, and hence finding the point group. The diffraction group can be found using either the intensity distribution in the discs
Observation of cerium-oxides in rapidly solidified Ti-4wt% Ce
Authors: Wittig J.E. , Kegley D.R. , Hofmeister W.H. , Bayuzick R.J. 
Published: June 2020

Rapid solidification of Ti rare earth alloys can produce a fine rare earth oxide dispersion. A stable distribution of rare earth oxides in a hexagonal Ti matrix has been shown to increase the flow stress at both room and elevated temperatures. Previous studies have investigated the precipitation phenomena in Ti-erbium Ti-Ianthanum, and Ti-Al-gadolinium alloys. The present research addresses oxide precipitation in a Ti-cerium alloy as a result of rapid solidification processing.Samples of Ti-4 wt% Ce were rapidly solidified by splat quenching 300 mg droplets, after free fall in a 100 m drop tube, onto a copper block. Pyrometer measurements and heat flow calculations estimate that the liquid drop was undercooled approximately 200 K below its equilibrium melting temperature (Tm=1920 K) at impact. Thin foils from the splats were prepared by punching 3 mm diameter discs and twin-jet electropolishing in a solution of 3% perchloric acid, 37% n-butylalcohol, and 60% methanol at 240 K and 34 V. The TEM investigations used a Philips CM12, a CM30, and an EM420T.
Microstructure/property relations in YBa2Cu3O7-x powders
Authors: Thiel B.L. , Sarikaya M. , Javadpour J. , Han C. , Aksay I.A. 
Published: June 2020

We have studied several samples of YBa2Cu3O7-x superconductor with substantially differing electromagnetic characteristics in an effort to relate microstructure with superconducting properties. It is has been shown that the bulk oxygen content of the material can be related to the difference in the a and b lattice parameters which has a linear relationship with the bulk Tc value. Bulk measurements of electronic properties may be misleading as they are complicated by the presence of weak-links in the forms of inter- or intra- granular phases or even oxygen poor regions within a single grain.The samples used were all prepared with the same starting materials but subject to heat treatments which varied the 950°C sintering time and the partial pressure of oxygen in the furnace atmosphere. All of the samples had nominally identical x-ray diffraction patterns (e.g., equivalent bulk Δa/a values as measured by the (103)-(013)/(110) peak splitting) but showed markedly different superconducting properties as measured by the inductance-flux exclusion technique.
UHV microscopy of surfaces: Recent results
Authors: Bonevich J.E. , Zhang J.P. , Jacoby M. , Ai R. , Dunn D. , Stair P.C. , Marks L.D. 
Published: June 2020

In order to examine surfaces of materials, a prerequisite is a microscope which combines ultra-high vacuum (UHV) with surface science cleaning and characterization techniques such as ion beam sputtering, annealing, and Auger spectroscopy. In order to achieve this, we have mounted onto the side of a UHV-H9000 microscope LEED/Auger, an ion gun, and optical heating; in the transfer chamber specimens can be cleaned at a base pressure of 2×10-10 torr and transferred into the microscope which operates at pressures better than 2×10-10 torr. With this marriage, it is relatively simple to prepare and characterize clean surfaces.As an example, thin gold film specimens, textured with the [111] normal to the film, were made in a standard vacuum evaporator and floated onto a gold grid. The transfer chamber was then baked-out at 250°C for about 12 hours to achieve UHV conditions. Figure 1 shows an image taken from the gold film after bakeout.
Quantification of submicron magnetisation structures in thin films using DPC
Authors: McFadycn Ian R. 
Published: June 2020

Differential phase contrast Lorentz. microscopy has been shown to be a powerful technique for studying submicron magnetisation distributions in thin magnetic films. However, the technique has not found wide spread use, perhaps because it is thought to require either a dedicated STEM with a field emission gun, or extensive modifications to the electron optics of a conventional TEM. In this work we have demonstrated that DPC can be implemented on a conventional TEM, in our case a JEOL JEM 2000FX, without recourse to modifications ofthe electron optics ofthe microscope. Some of the controls of the microscope have been modified, but this was for convenience rather than necessity and in no way affects the normal operation ofthe microscope.Figure I illustrates the principle behind DPC. A focused electron probe, of half angle α is scanned across the sample and at each point in the scan, the denection (β1) due to the sample is measured by means of a quadrant detector as follows. Any deflection of the beam can he split into an x-component and a y-component.
In situ TEM studies of deformation and fracture
Authors: Robertson I.M. , Lee T.C. , Dewald D.K. , Birnbaum H.K. 
Published: June 2020

The in-situ TEM straining technique has been used to investigate the micromechanisms of deformation and fracture in several ductile and semi-brittle systems. Attention has been focussed on the dislocation structures ahead of advancing cracks and on the interaction between lattice dislocations and grain boundaries.The deformation experiments were performed in-situ in a transmission electron microscope equipped with a video camera system. The dynamic events were recorded on video tape with a time resolution of l/30th of a second. Static interactions were recorded using the regular microscope plate system. The straining stage deforms the samples in Mode I and can operate at a displacement rate of 4 in sec-1.An example of one of the possible interactions between lattice dislocations and a ∑- 3 ([ll)/60°) grain boundary in 310 stainless steel is shown in the micrograph in Figure 1. The dislocations on slip systems A (a/2[110)1 (ll) 1 ) and B (a/2[101] (11) 1 ) impinge on the grain boundary, generating slip systems C (a/2[l0) 2/(111) 2) and D (a/2[l0) 2/(111) 2). To understand this effect three conditions were considered:
High-resolution hot-stage experiments
Authors: Boyes E.D. 
Published: June 2020

High resolution electron microscopy provides a powerful method for studying controlled dynamic reaction sequences and the development of microstructures on the atomic scale. Temperatures can be controlled with reasonable accuracy using a standard hot-stage, but at elevated temperatures there is some reduction in the contrast, and stability, of images. It is, of course, essential to minimise the effects, including additional heating, of irradiating the sample with a high voltage electron beam in a high vacuum environment, and to take into account the close proximity of two specimen surfaces in designing experiments. TV imaging techniques, in-situ, relocatable ex-situ and environmental methods are being developed for use with two medium voltage side-entry high resolution TEMs, equipped with complementary chemical and structural microanalytical STEM facilities.TV imaging techniques
Dynamic reaction sequences are now mostly viewed with a low-light level TV camera (LLTV) using a thin YAG or YAP pickup screen and recorded on U-matic videotape to facilitate subsequent processing. The results can be improved substantially by using a digital framestore based image processor to enhance the signal to noise ratio of the video signal in realtime. A major element in the SNR is the shot noise statistics of the TEM electron beam.
Quantitative surface damage studies by H.R.E.M.
Authors: Singh S. R. , Fan H. J. , Marks L. D. 
Published: June 2020

Since the original observation that the surfaces of materials undergo radiation damage in the electron microscope similar to that observed by more conventional surface science techniques there has been substantial interest in understanding these phenomena in more detail; for a review see. For instance, surface damage in a microscope mimics damage in the space environment due to the solar wind and electron beam lithographic operations.However, purely qualitative experiments that have been done in the past are inadequate. In addition, many experiments performed in conventional microscopes may be inaccurate. What is needed is careful quantitative analysis including comparisons of the behavior in UHV versus that in a conventional microscope. In this paper we will present results of quantitative analysis which clearly demonstrate that the phenomena of importance are diffusion controlled; more detailed presentations of the data have been published elsewhere.As an illustration of the results, Figure 1 shows a plot of the shrinkage of a single, roughly spherical particle of WO3 versus time (dose) driven by oxygen desorption from the surface.
Crystal structure and stacking faults of myristyl stearate identified by electron diffraction
Authors: Zhang W.P. , Dorset D.L. , Hanlon J. 
Published: June 2020

Although a few X-ray crystal structures of normal-chain esters of long chain acids and short chain alcohols have been carried out, attention has been paid mostly to the long-spacings of waxes synthesized from longer chain alcohols. We have been interested in exploring the crystal structures of the more symmetric waxes via electron diffraction studies.Myristyl stearate thin crystals were epitaxially grown on benzoic acid by the method developed by Wittmann et al. Some samples with or without the presence of the nucleating substrates were annealed at 45°C for 4 hours on a Met tier FP82 hot stage. The thin crystals before or after annealing were examined with a JEOL JEM-100CX electron microscope operated at 100 kV, and selected area electron diffraction patterns from [100] and [110] directions were recorded on Kodak DEF-5 X-ray film. The calibration of the camera length was carried out with a gold Debye-Scherrer diagram. Models of molecular packing were scanned with an Optronics P-1000, and their Fourier transforms were calculated with a program in IMAGIC.
Wavefunction and CBED results of the STEM multislice calculation
Authors: Loane R. F. , Kirkland E. J. , Silcox J. 
Published: June 2020

The multislice algorithm has been used to simulate ADF STEM images. Examination of the evolution of the electron wavefunction as it propagates through the specimen, can provide insight into the sources of contrast in the STEM image. Plots of the wavefunction intensity as a function of position and as a convergent beam electron diffraction (CBED) pattern are two complementary views of the diffraction process. Examples from the large number of these plots that are calculated during the ADF STEM calculations will be presented.The simulated specimen consists of multiples of 47 Å (15 slices) of silicon (111). The slices are 65 Å × 66 Å(512 × 512 pixels) in size, setting the maximum included scattering angle to 95 mrad. The incident probe models a 100 keV VG-HB501 STEM at Scherzer focus with either the low resolution pole piece (Cs=3.3 mm, Δf=1100 Å, αap = 8.2 mrad) or the high resolution pole piece (Cs = 0.7 mm, Δf=510 Å, αap=12.1 mrad). The beam and specimen are aligned exactly along the (111) zone axis (no tilt).