bluuebunny/crossref_metadata_2025_split huggingface dataset:
Vacancy-ordered superstructures in YBa2Cu3Ox
Authors: Reyes-Gasga J. , Krekels T. , Van Tendeloo G. , Van Landuyt J. , Amelinckx S. , Verwey M. , Bruggink W. H. M. 
Published: June 2020

YBa2Cu3Ox samples with different oxygen content were prepared in bulk form by the constant stoichiometry method. All material was initially equilibrated at 840°C during one hour in order to remove traces of CO2 and water. The temperature is subsequently lowered to 340°C for a four hour anneal. Afterwards different samples are brought at different equilibration temperatures between 340°C and 940°C. Final cooling to room temperature is done at a rate of 240°C/h. keeping the weight obtained at the equilibration temperature constant; this is performed by monitoring the oxygen partial pressure. The method decouples oxygen contents and cooling rates (and hence the degree of order). Material was prepared with an accurate oxygen content of x=6.25, 6.5, 6.625, 6.75, 6.875 and 6.98.Apart from the X=6.25 material, all investigated samples had an orthorhombic structure with a b/a ratio increasing with the oxygen content. Such samples are characterised by the presence of (110) twinning.
Electron microscopy of explosively fabricated copper oxide superconductors
Authors: Murr L. E. , Pradhan M. , Sudarsan U. , Niou C. S. 
Published: June 2020

Efforts to fabricate useful devices or fixtures from copper oxide superconductor powders, especially YBa2Cu3O7, have been somewhat critically dependent upon structural and microstructural information provided by electron microscopy (especially SEM and TEM). In our own research, which involves the fabrication of monolithic structures encapsulating copper oxide superconducting, powdered material within a metal matrix such as copper, powder morphology, size and size distribution (Fig. 1) as well as powder microstructure (Fig. 2a) have been of concern in optimizing reliable superconducting products. Residual microstructures, including grain boundaries (inter-particle interfaces), are also critical features which control or influence mechanical behavior as well as superconductivity (especially transport supercurrent).The fabrication process involves significant features of both explosive welding and explosive consolidation, and optimization requires optimizing the welding of the metal matrix and simultaneous consolidation of the superconducting powder. In a copper matrix, one important optimum seems to lie within a narrow region of explosive detonation velocity (VD) ranging from 1.8 to 2.2 km/s.
High-resolution x-ray elemental images
Authors: Lyman C. E. , Hepburn J. S. , Stenger H. G. , Michael J. R. 
Published: June 2020

Field-emission electron sources and digital image collection techniques produce x-ray emission images of elemental distributions (maps) with far higher quality than those obtained by conventional x-ray dot mapping. Without a field-emission source the useful upper magnification of an x-ray image is only a few times 104X with the resolution rarely exceeding 100 nm. The images described below are routinely collected at 1,000,000x with a resolution of better than 5 nm. Such images are collected at quite low x-ray intensities and over long time periods compared to electron images. This means that the effects of x-ray background at each pixel and of image drift become important issues in the collection of meaningful images.The instrument used in this work was the Vacuum Generators HB-501 STEM equipped with a Link Systems LZ-5 windowless energy dispersive x-ray detector of 146 eV energy resolution. This instrument is equipped with a gun lens to provide several times more current in the small probe than the normal HB-501. The electron beam was 1.8 nm in diameter (FWHM) and the beam contained about 0.9 nA. The digital x-ray maps shown here were obtained with 128x128 pixels and 100 ms dwell time per pixel. With this small electron beam the image magnification should be at least 400,000x to allow the beam to fill each pixel and avoid underscanning (beam smaller than the pixel).
Field ion microscope investigations of atomic processes at surfaces
Authors: Kellogg G. L. , Schwoebel P. R. 
Published: June 2020

Although no longer unique in its ability to resolve individual single atoms on surfaces, the field ion microscope remains a powerful tool for the quantitative characterization of atomic processes on single-crystal surfaces. Investigations of single-atom surface diffusion, adatom-adatom interactions, surface reconstructions, cluster nucleation and growth, and a variety of surface chemical reactions have provided new insights to the atomic nature of surfaces. Moreover, the ability to determine the chemical identity of selected atoms seen in the field ion microscope image by atom-probe mass spectroscopy has increased or even changed our understanding of solid-state-reaction processes such as ordering, clustering, precipitation and segregation in alloys. This presentation focuses on the operational principles of the field-ion microscope and atom-probe mass spectrometer and some very recent applications of the field ion microscope to the nucleation and growth of metal clusters on metal surfaces.The structure assumed by clusters of atoms on a single-crystal surface yields fundamental information on the adatom-adatom interactions important in crystal growth. It was discovered in previous investigations with the field ion microscope that, contrary to intuition, the initial structure of clusters of Pt, Pd, Ir and Ni atoms on W(110) is a linear chain oriented in the <111> direction of the substrate.
The structure of partially expanded erythrocyte spectrin
Authors: McGough Amy M. , Josephs Robert 
Published: June 2020

In vivo the red cell suffers elastic deformation during its turbulent passage through the vasculature. Although the physical process responsible for the cell’s elasticity is still unknown, it is generally regarded as being a property of the erythrocyte skeleton. The skeleton, a two-dimensional network located on the cytoplasmic side of the membrane is composed of dodecamers of actin interconnected by spectrin molecules. Understanding the elastic properties of the skeleton in terms of the molecular properties of its component proteins is a major unsolved problem in red cell biology. Our work has focused on spectrin since it alone, of the skeleton proteins, appears to be able to undergo the reversible changes in structure necessary to account for the elastic properties of the red cell.Spectrin is highly alpha-helical and highly charged. Consequently the molecule can reversibly expand or condense in response to changes in ionic strength. Spectrin forms tetramers which are 2000 Å long when fully extended. The conformation actually assumed by spectrin in the cell is not known; however, calculations based on the number of molecules per unit area of membrane indicate that in the erythrocyte the average end to end distance of the molecule is only 700 Å.
Surface facetting in small ceramic particles
Authors: Bonevich John E. 
Published: June 2020

The structural morphology of small particles has long been of interest in the field of catalysis. Aluminum oxide serves the dual purpose of being a desirable support material for catalytic reactions and also a engineered ceramic material. In an effort to understand the sintering process on an atomistic scale, the structures of small alumina particles have been investigated and their surfaces characterized. We present here the preliminary results of the surface facetting of alumina particles as related to their thermodynamic Wulff constructions.Small particles of aluminum oxide were formed by means of an arc discharge. A bell jar was roughed to 20 millitorr and then a mixture of Ar-20%O2 was bled into the chamber to a total pressure of about 50 torr. The aluminum electrode configuration consisted of a wire anode and a plate cathode with an electrode gap of 1 mm; arcing occurred at 780 V for 5 minutes.
Influence of ion-milling on the T2 phase in Al-2.5%Li-2.5%Cu alloy
Authors: Reed J. R. , Michel D. J. , Howell P. R. 
Published: June 2020

The Al6Li3Cu (T2) phase, which exhibits five-fold or icosahedral symmetry, forms through solid state precipitation in dilute Al-Li-Cu alloys. Recent studies have reported that the T2 phase transforms either during TEM examination of thin foils or following ion-milling of thin foil specimens. Related studies have shown that T2 phase transforms to a microcrystalline array of the TB phase and a dilute aluminum solid solution during in-situ heating in the TEM. The purpose of this paper is to report results from an investigation of the influence of ion-milling on the stability of the T2 phase in dilute Al-Li-Cu alloy.The 3-mm diameter TEM disc specimens were prepared from a specially melted Al-2.5%Li-2.5%Cu alloy produced by conventional procedures. The TEM specimens were solution heat treated 1 h at 550°C and aged 1000 h at 190°C in air to develop the microstructure. The disc specimens were electropolished to achieve electron transparency using a 20:80 (vol. percent) nitric acid: methanol solution at -60°C.
A variety of morphologies in diblock copolymer/homopolymer blends
Authors: Thomas Edwin L. , Winey Karen I. 
Published: June 2020

A wide range of morphologies and thereby physical properties can be achieved in block copolymer/homopolymer blends by varying the copolymer composition, copolymer concentration and molecular weights. Recently we investigated micelle shape transitions in diblock copolymer with homopolymer blends at low copolymer concentration. In this paper we study the microstructure over a wider concentration range for a polystyrene-polybutadiene (PS/PB) diblock copolymer of molecular weight 20.5 × 103/20.5 × 103 blended with 17.2 × 103 molecular weight homopolystyrene (hPS).Figure 1 shows schematically a possible spectrum of microdomain structures dependent on the copolymer concentration of a lamellar PS/PB and hPS. Below the critical micelle concentration (CMC) the block copolymer is molecularly dispersed in the homopolymer exhibiting a homogeneous phase. As diblock concentration increases the minority (i.e. PB) forms spherical and/or cylindrical micelles randomly dispersed in the hPS. Further increases in diblock concentration induces long range ordering of various microdomains. In addition three biphasic regions are proposed in which two phases coexist: isotropic cylinders with ordered cylinders, ordered cylinders with ordered bicontinuous double diamond (OBDD), and OBDD with swollen lamellae.
Microdomain and inorganic cluster formation in block copolymers of poly(styrene) and poly-(2-vinylpyridine)
Authors: Kunz M. , Möller M. 
Published: June 2020

Selforganization of polymer molecules into ordered supramolecular structures provides a general route for the preparation of materials with new optical, electrical and mechanical properties. In the present paper we we report on glassy diblock copolymers of poly(styrene) and poly(2-vinylpyridine) where the poly(2-vinylpyridine) block was modified by quaternization and by coordination to various transition metal salts. Electron spectroscopic imaging (ESI) and electron energy loss spectroscopy (EELS) were used to localize and to identify the different phases and elements. It has been studied whether the different systems can be used for the formation and stabilization of ultrasmall clusters of inorganic semiconductors.Diblock copolymers of nearly monodisperse molecular weight were synthisized by sequential polymerization of styrene and 2-vinylpyridine. Quaternization with methyliodine resulted in formation of salt groups. Bulk materials were obtained by slow solvent evaporation at elevated temperatures. Ultramicrotomed specimens were examined with a ZEISS CEM 902 operated at 80 kV. An integrated electron energy loss spectrometer allowed to record element specific images as well as electron energy loss spectra.
On resolving fine periodic microstructures in the optical microscope
Authors: Putnam W.S. , Viney C. 
Published: June 2020

Many sheared liquid crystalline materials (fibers, films and moldings) exhibit a fine banded microstructure when observed in the polarized light microscope. In some cases, for example Kevlar® fiber, the periodicity is close to the resolution limit of even the highest numerical aperture objectives. The periodic microstructure reflects a non-uniform alignment of the constituent molecules, and consequently is an indication that the mechanical properties will be less than optimal. Thus it is necessary to obtain quality micrographs for characterization, which in turn requires that fine detail should contribute significantly to image formation.It is textbook knowledge that the resolution achievable with a given microscope objective (numerical aperture NA) and a given wavelength of light (λ) increases as the angle of incidence of light at the specimen surface is increased. Stated in terms of the Abbe resolution criterion, resolution improves from λ/NA to λ/2NA with increasing departure from normal incidence.
EELS white line intensities calculated for the 3d and 4d metals
Authors: Ahn C. C. , Pearson D. H. , Rez P. , Fultz B. 
Published: June 2020

Previous experimental measurements of the total white line intensities from L2,3energy loss spectra of 3d transition metals reported a linear dependence of the white line intensity on 3d occupancy. These results are inconsistent, however, with behavior inferred from relativistic one electron Dirac-Fock calculations, which show an initial increase followed by a decrease of total white line intensity across the 3d series. This inconsistency with experimental data is especially puzzling in light of work by Thole,et al., which successfully calculates x-ray absorption spectra of the lanthanide M4,5white lines by employing a less rigorous Hartree-Fock calculation with relativistic corrections based on the work of Cowan. When restricted to transitions allowed by dipole selection rules, the calculated spectra of the lanthanide M4,5white lines show a decreasing intensity as a function of Z that was consistent with the available experimental data.Here we report the results of Dirac-Fock calculations of the L2,3white lines of the 3d and 4d elements, and compare the results to the experimental work of Pearson et al. In a previous study, similar calculations helped to account for the non-statistical behavior of L3/L2ratios of the 3d metals. We assumed that all metals had a single 4s electron. Because these calculations provide absolute transition probabilities, to compare the calculated white line intensities to the experimental data, we normalized the calculated intensities to the intensity of the continuum above the L3edges. The continuum intensity was obtained by Hartree-Slater calculations, and the normalization factor for the white line intensities was the integrated intensity in an energy window of fixed width and position above the L3edge of each element.
Transition metal oxides revisited: ELNES of metal L2,3 and oxygen K edges
Authors: Krivanek Ondrej L. , Paterson James H. , Poppa Helmut R. , Rez P. 
Published: June 2020

When examined at 0.5 eV or better energy resolution by electron energy loss spectroscopy (EELS), many inner shell loss edges begin to show new fine structures. Recently, we have been able to acquire inner shell loss spectra routinely at about 0.4 eV resolution, using the Gatan PEELS™ on the VG HB501 STEM. We have therefore decided to reinvestigate the energy-loss near-edge structure (ELNES) of oxygen K and metal L2,3 edges in first row transition metal oxides.Figure 1 shows the metal L2,3 edges from vanadium oxide, chromium oxide, manganese oxide, iron oxide, cobalt oxide, nickel oxide, and copper oxide. Except for the chromium oxide sample, which was prepared by crushing and dispersing grains of crystalline Cr2O3, samples were made by vapor-depositing a thin metal film onto rock salt, heating it in air at about 400° C while still on the substrate, and subsequently floating it off. The resultant thin oxide films were from the same sample batches as those used for the EELS Atlas, where they were identified as VOx, MnO2, Fe2O3, CoO, NiO, and CuO.
Effects of accelerating voltage and thickness on the signal-to-noise ratio in Electron Energy Loss Spectroscopy (EELS)
Authors: Botton Gianluigi , L′Espérance Gilles 
Published: June 2020

The advantages of medium accelerating voltages (200-400KV) for EELS have been considered to be an improved jump ratio of edges and an improved signal to background ratio for an increased range of thiknesses. However, very little experimental data of the Signal to Noise Ratio (SNR) as a function of incident electron energy (Eo) can be found in the literature. The interest in performing such measurements is to investigate the effect of accelerating voltage on the detectability limits in EELS since SNR can be related to the minimum detectable fraction. In this paper, measurements made on NiO samples show an improved SNR with increasing Eo at a constant thickness value. Changes in the angular distribution of scattering are considered to be responsible for the improved SNR.The NiO sample studied was prepared by evaporation on a copper supporting grid. Uniform areas of different thicknesses (t) caused by the superposition of the film were analysed. Values of mean free path (λ) for NiO were found in the literature. All analyses were carried out with a Philips CM30 and a GATAN 666 Parallel EEL spectrometer (PEELS) coupled to a Link AN10000 MCA. Spectra were transfered on to an external computer for SNR calculations.
In situ Transmission Electron Microscope observations of mesotaxial silicide formation in the CoSi2/Si system
Authors: Hull R. , White A.E. , Short K.T. , Yalisove S.M. , Loretto D. 
Published: June 2020

A new technique for synthesis of buried epitaxial metal silicide layers in Si (“mesotaxy”) by high-dose implantation of Co and Ni into Si surfaces has been developed. Subsequent to implantation at energies in the few hundred keV range and doses in the 1017Cm−2 regime, thermal annealing at temperatures up to 1000°C results in the formation of well-defined and relatively high quality Si/metal disilicide/Si structures.The exact implantation and processing conditions are crucial in determining the structure and quality of the buried silicide layer. In this work, we describe transmission electron microscope experiments which illuminate the silicide formation process both by static studies of as-implanted and annealed structures, and dynamical in-situ experiments where as-implanted structures are annealed inside the microscope to mimic the ex-situ annealing conditions. The structure geometry in these materials turns out to be close to ideal for such in-situ experimentation: typical implantation conditions for formation of a contiguous silicide layer result in tlqe metal layers being of the order a few hundred to a thousand Å and buried about 600-1000 Å below the Si surface. In-situ annealing in the plan-view geometry inhibits surface diffusion across the interfaces, which would be expected in the cross-sectional geometry (5). The typical penetration depths attainable in Si with 200 keV electrons, say ~ 1 micron, allow a significant thickness, hsubthin of Si substrate below the metal layer, thickness hm, to be retained during the in-situ experiment such that hm ≪hsubthin. This is important, as it ensures that the film stress condition (which arises because of the difference in bulk lattice parameters between the Si and metal silicide layers) is reasonably representative of the stress conditions relevant for the case of annealing on the unthinned substrate.
A new look at absorption in high-energy electron diffraction
Authors: Bird D.M. , King Q.A. 
Published: June 2020

People seldom take absorption very seriously in electron diffraction calculations. Since the work of Hashimoto et al. it has been common practice to set the absorbative part of the potential coefficient V′g to be one tenth of the elastic part Vg. Although this may not be a bad approximation in simple metals, there is no reason why it should apply to more complicated structures. Here, Vg may be small because of interference between different atoms in the unit cell, but the same cancellation might not occur in V′g because the individual atomic contributions to Vg and V′g need not scale in the same way. In fact, the absorbative contribution increases more rapidly with atomic number than the elastic part. This effect is particularly marked in non-centrosymmetric crystals, where V′g and Vg need not have the same phase. Both V′g and Vg are now complex numbers which we write as(1)The squared modulus of the total potential coefficient now becomes(2)If g → −g, ϕ and ϕ′ change sign, so if the phase difference is non-zero the overall magnitude of the +g and −g potential coefficients are not equal. The standard assumption is that |V′g| = 0.1|Vg| and ϕg − ϕ′g = 0, which ignores corrections to the magnitude of Vg of order | V′g/Vg|.
GexSi1-x/Si superlattices grown on (100)-, (111)-, and (110)-oriented Si substrates
Authors: Kuan T. S. , Iyer S. S. , Yeo E. M. 
Published: June 2020

GexSi1-x/Si heterostructures have been studied extensively because of their potential device applications. Previous GexSi1-x/Si heteroepitaxy studies have been mostly confined to growth on (100) surfaces and have focused on how growth temperature and GexSi1-x layer thickness affect growth morphology and defect generation. In this work we compare the quality of GexSi1-x/Si superlattices grown on (100)-, (111)-, and (110)-oriented Si substrates. We find that these three growth directions give rise to different growth morphologies and defect structures. Strained GexSi1-x layers in a (100) GexSi1-x/Si superlattice annealed at 450 – 500°C have recently been reported to exhibit a CuPt-type long-range order. Thus, another objective of this work is to explore whether growth along the <110> and/or <111> directions can promote or suppress the onset of ordering.Superlattices consisting of 18 layers of alternating Ge0.5Si0.5 (5 nm) and Si (20 nm) were grown by molecular beam epitaxy (MBE). Before growing the superlattice, a 3D-nm-thick Si buffer layer was grown on the Si substrate.
ALCHEMI studies on the location of zinc in GaAs
Authors: Christenson K. K. , Eades J.A. 
Published: June 2020

The diffusion of Zn in GaAs is anomalous in that the diffusion coefficient D is proportional to the Zn concentration squared. Further, the diffusion rate of the column III species in III-V layer structures (ie. Ga and Al in GaAs-GaAlAs) can be increased by 105 with the addition of doping levels of Zn3. The column V sites are not affected. As an aid to understanding the diffusion process we have located the position of the Zn in the GaAs lattice.There are four high symmetry positions in the zincblende structure that the Zn could occupy: Ga, As, T (Tetrahedral interstitial, located at 1/2 1/2 1/2 with four nearest neighbors at 0.433 a0) and H (Hexagonal interstitial, located at 5/8 5/8 5/8 with six nearest neighbors at 0.415 a0). Interstitial diffusion involves hopping between alternating T and H sites with the energy barrier to diffusion being equivalent to the difference in the potential energy of the two sites. Figure 1 indicates the possible low-index orientations for ALCHEMI studies which can differentiate between these sites.