bluuebunny/crossref_metadata_2025_split huggingface dataset:
TEM study of melt-processed “123” YBaCuO containing excess “211”
Authors: Yan Y. , Stobbs W. M. , Cardwell D. A. , Campbell A. M. 
Published: June 2020

High Jc values of 104~106 A cm-2 are generally required in the use of YBCO. In this context the commonly used sintering method for making bulk high-Tc superconductors has the disadvantage that grain boundaries in such material tend to act as weak links. Melt processesing of the YBaCuO “123” phase has been found to be effective in reducing the problem. In order to understand the mechanisms involved, the physical properties (Tc, Jc, etc.) of YBa2Cu3O7-x (“123”), with varying additions of Y2BaCuO5 (“211”), are being compared and correlated with associated changes in the structure.TEM analysis indicates that the melt processed material contains well aligned tabular “123” platelets with near to common c axis orientations (the preferred orientation for grain growth is in the a-b plane), trapping more equiaxed “211” phase particles of varying sizes. Electron diffraction (Fig.la inset) has shown that there are no large orientation changes between platelets throughout the whole specimen despite their being interconnected by “gaps” where there are phase changes.
Prospects for atom-probe analysis in biology and medicine
Authors: Panitz J. A. 
Published: June 2020

The atom-probe field ion microscope may be the ultimate microanalytical tool because a single atom, chosen from its neighbors at the discretion of the experimenter, can be visualized in atomic resolution and then identified by its mass-to-charge ratio. Although the analysis procedure is destructive;the lateral and depth resolution of the atom-probe is impressive, exceeding 0.5 nm under favorable conditions. Despite these attributes, atom probe analysis has been largely confined to problems in the materials sciences. The atom probe has made no impact in biology or medicine, largely because of restrictions imposed by the technique on the preparation, imaging, and analysis of biological samples. Recent developments in each of these areas has made atom probe analysis of biological samples a more viable prospect.Biological Sample PreparationThe atom-probe technique places severe restrictions on the type of sample that can be analyzed. Field ionization is used to image a surface in atomic resolution, and field desorption provides a source of ions for analysis. These processes occur with a high probability only in electric fields greaterthan 100 MV/cm. Electric fields of this magnitude (and the nature of the imaging process) require theuse of a needlelike substrate, known as a field-emitter "tip".
Atomic-level characterization of defects in microalloyed NiAl: An atom probe investigation
Authors: Jayaram R. , Miller M. K. 
Published: June 2020

Nickel aluminides have been studied in great depth in recent years on account of their potential application in advanced aircraft and land-based turbines. Although the low density and high melting point of NiAl are particularly attractive features, its poor ductility and fracture toughness at ambient temperatures limit its technological application. Since mechanical behavior is largely governed by microstructural features, a careful microanalytical characterization is crucial to the understanding of structure-property relationships in NiAl. Defect features such as dislocations, substitutional solutes and solute segregation to grain boundaries play important roles in influencing mechanical properties. The atom probe field ion microscope (APFIM) is particularly well suited to the characterizationof such types of microstructural features.The atom probe has been used to provide a quantitative explanation of the changes in yield stress when NiAl is doped with boron, carbon, or beryllium. An enormous increase in the yield stress is observed in boronand carbon-doped NiAl in contrast to beryllium-doped NiAl which shows only a modest increase. The matrix was severely depleted of the solute in the boron- and carbon-doped NiAl, whereas almost all of the beryllium was in solid solution. The excess boron and carbon atoms scavenged trace metallic impurities and formed highly stable ultrafine (= 2 nm diameter) precipitates with compositions that were consistent with the stoichiometry of MB2 and MC, respectively. Estimates of the yield stress increase due to a precipitation hardening mechanism were obtained based on atom probe measurements of particle size and number density. These estimates have been shown to be in agreement with experimental values.
Transmission Electron Microscopy of AlxGa1-xN/SiC multilayer structures
Authors: Pike W. T. , George T. , Khan M. A. , Kuznia J. N. 
Published: June 2020

The potential of wide-band-gap III-V nitrides as solar-blind ultraviolet sensors and light emitters has prompted an increasing amount of work recently, including the fabrication of the first UV sensors from as-deposited single crystal GaN. We have used high resolution transmission electron microscopy (TEM) to study the microstructure of two novel developments of wideband-gap III-V nitrides: the growth of ultra-short period GaN/AlN superlattices (digital alloys); and the incorporation of SiC layers into AlxGa1-xN structures. By varying the relative periods in a GaN/AIN superlattice, it should bepossible to tailor the band gap of the composite to lie between the elemental values of 365nm for GaN and 200nm for AIN. The group IV semiconductor, SiC, has a close lattice match (< 3%) to AlxGa1-xN forgrowth on the basal plane. Demonstration of epitaxial growth for AlxGa1-xN/SiC multilayers could enable an extension of direct band-gap material towards the visible.The superlattice samples were grown by low-pressure metalorganic chemical-vapor deposition (MOCVD)using a unique switched atomic-layer-epitaxy (SALE) procedure (as first used by Dapkus et al. for GaAs). GaN was grown on the basal-plane sapphire substrates above a thin AlN layer, which has been foundto maximize the crystalline quality of the GaN film.
TEM characterization of WSix films
Authors: Kannan V. C. , Merchant S. M. , Irwin R. B. , Nanda A. K. , Sundahl M. , Rambabu B. , Singh A. K. 
Published: June 2020

Metal silicides such as WSi2, MoSi2, TiSi2, TaSi2 and CoSi2 have received wide attention in recent years for semiconductor applications in integrated circuits. In this study, we describe the microstructures of WSix films deposited on SiO2 (oxide) and polysilicon (poly) surfaces on Si wafers afterdeposition and rapid thermal anneal (RTA) at several temperatures. The stoichiometry of WSix films was confirmed by Rutherford Backscattering Spectroscopy (RBS). A correlation between the observed microstructure and measured sheet resistance of the films was also obtained.WSix films were deposited by physical vapor deposition (PVD) using magnetron sputteringin a Varian 3180. A high purity tungsten silicide target with a Si:W ratio of 2.85 was used. Films deposited on oxide or poly substrates gave rise to a Si:W ratio of 2.65 as observed by RBS. To simulatethe thermal treatments of subsequent processing procedures, wafers with tungsten silicide films were subjected to RTA (AG Associates Heatpulse 4108) in a N2 ambient for 60 seconds at temperatures ranging from 700° to 1000°C.
STEM study of the high-pressure oxidation of GeSi
Authors: Lee Tan-Chen , Theodore N. David , Silcox John 
Published: June 2020

GeSi alloys are of interest because of their potential applications in optical and electronic devices. Understanding the growth of thermal oxide is very important for the GeSi system if an adaptationof the existing Si technology is going to be used. Thermal oxidation of GeSi leads to a Ge-rich layerat the GeSioxide interface. By sufficiently speeding up the rate of oxidation at a given temperature,such as with high pressure oxidation, it is possible to convert both Ge and Si into oxide and suppress the Ge pile-up at the oxide front. This was observed in the oxidation of GeSi films (Ge concentration 5-17 at.%) using pure oxygen at 600 atm and 550 °C. The segregation of Ge oxide from Si oxideand the Ge pile-up in high pressure oxidized GeSi, which are difficult to observe with other techniques, were studied by using a dedicated STEM.An epitaxially grown Si (2500 Å)/Ge.15Si.85 (500 Å) hetero-structure on Si(100) was oxidized in a wet ambient at 750 °C and 25 atm. It was then made into anXTEM (cross-sectional transmission electronmicroscope) sample and characterized using a VG HB 501A STEM equipped with EELS (electron energy lossspectrometry) and a windowless X-ray detector. STEM BF (bright field) and ADF (annular dark field) images are shown in Fig. 1(a) and 1(b). STEM BF images are similar to conventional TEM BF images. Fig. 1(a) shows that three layers of oxides are grown on the Sisubstrate.
Specimen preparation of irradiated materials for examination in the atom probe field ion microscope
Authors: Russell K. F. , Miller M. K. 
Published: June 2020

The atom probe field ion microscope (APFIM) is well suited to the characterization of the fine scale features and defects that are formed in materials due to exposure to neutron irradiation. However, in order for the technique to be effective, suitable specimens are required. Atom probe field ion microscopy specimens are in the form of ultrasharp needles that are usually produced by a series of mechanical and chemical or electrochemical methods. These needles have a typical end radius of approximately 10 to 50 nm and a taper angle of between 1 and 5. The small dimensions mean that the specimens are extremely fragile and difficult to handle and do not easily lend themselves to remote operations in a hot cell. The small size and mass of the APFIM specimen has the advantage that the amount of material required is minimal.A concept in working with irradiated materials is to keep exposure to the operator "as low as reasonably achievable" (ALARA).
Microstructural characterization of sol-gel coating on PET films
Authors: Chen R. T. , Norwood R.A. 
Published: June 2020

Sol-gel processing has been used to control the structure of a material on a nanometer scale in preparing advanced ceramics and glasses. Film coating using the sol-gel process was also found to be a viable process technology in applications such as optical, porous, antireflection and hard coatings. In this study, organically modified silicate (Ormosil) coatings are applied to PET films for various industrial applications. Sol-gel materials are known to exhibit nanometer scale structures which havepreviously been characterized by small-angle X-ray scattering (SAXS), neutron scattering and light scattering. Imaging of the ultrafine sol-gel structures has also been performed using an ultrahigh resolution replica/TEM technique. The objective of this study was to evaluate the ultrafine structures inthe sol gel coatings using a direct imaging technique: atomic force microscopy (AFM). In addition, correlation of microstructures with processing parameters, coating density and other physical properties will be discussed.The materials evaluated are organically modified silicate coatings on PET film substrates. Refractive index measurement by the prism coupling method was used to assess density of the sol-gel coating.AFM imaging was performed on a Nanoscope III AFM (by Digital Instruments) using constant force mode. Solgel coating samples coated with a thin layer of Ft (by ion beam sputtering) were also examined by STM in order to confirm the structures observed in the contact type AFM. In addition, to compare the previous results, sol-gel powder samples were also prepared by ultrasonication followed by Pt/Au shadowing and examined using a JEOL 100CX TEM.
Visualization and quantitation of cellular and tissue anatomy by 3D light microscopy
Authors: Turner J. N. , Roysam B. , Holmes T. J. , Szarowski D. H. , Lin W. , Bhattacharyya S. , Ancin H. , Mackin R. , Becker D. 
Published: June 2020

Many areas of biomedical research require the visualization and quantitation of 3D micro- and tissue level anatomy. Both are possible by utilizing confocal or wide-field light microscopy in combination with computational methods, including deblurring and 3D image analysis. The three-dimensionality of the specimen, required image resolution, and parameters to be quantitated dictate the methods of choice. Applications under study by our group range from automatically quantitating a few cell layers in cervical/vaginal smears, or hundreds of cell nuclei or immunologically labeled cells in thick brainslices, to tracing individual neurons for long distances in 3D space. Examples of our wide-field deconvolution methods and automated detection and counting of nuclei in thick tissue are shown.Image restoration by blind deconvolution of portions of the axonal fields of two rat hippocampal pyramidal cells injected with biocytin and contrasted with horseradish peroxidase and diaminobenzidine6 is shown in Figure 1. The original data is projected along and perpendicular to the optic axis in Fig. 1a while 1b is a similar set of restored image projections.
An algorithm for estimation of chromosome motion in Four-Dimensional microscopic images
Authors: Marshall Wallace , Agard David , Sedat John 
Published: June 2020

Analysis of the three-dimensional organization of chromosomes within the nucleus has revealed a number of characteristic structural features. Yet imaging of living nuclei indicate that chromosomes undergo considerable random motion. Maintenance of nuclear organization in the face of such motion is thought to involve the attachment of chromosomes to the nuclear envelope or matrix. Yet while such attachments have been proposed to play a variety of functional roles as well as maintain nuclear organization, direct evidence for the existence of these mechanical interactions in vivo has been lacking. One way to demonstrate such attachment directly would be to estimate the motion of chromosomes and attempt thereby to demonstrate the presence of fixed points, which would indicate attachment of chromatin to some fixed superstructure.We have previously presented a motion estimation algorithm that is designed for tracking the motion of nonrigid and featureless objects such as chromosomes. This algorithm starts with a structural representation for the set of chromosomes at each time point, and then finds a correspondence between elements of the representations at successive time points.
Analysis of co-deposited Ti-Hf thin film on (0001)6H-SiC by HREM, energy-selected and hollow-cone images
Authors: Bow J. S. 
Published: June 2020

Solid solution binary alloys are attractive for defect-free thin film semiconductor contacts because lattice matching can be obtained by composition adjustment, but chemical homogeneity is required. Highly composition sensitive energy-selected and hollow cone (HC) dark field imaging were evaluated for heterogeneity detection in Ti-Hf films using an Ω filter/Zeiss 912 TEM. Conventional HREM, which relatively insensitive to spatial composition variations in this case, was used to observe structural defects in the films near the interfaces.Thin films of pure Ti deposited via UHV electron beam evaporation at room temperature on n-type, vicinal (0001) 6H-SiC showed good epitaxy. This contact displayed rectifying characteristics. The interface was both structurally and chemically sharp. However, misfit dislocations at “stand off” positions were found, due to 4 % mismatch between the basal parameters of Ti and SiC. same column with Ti in the periodic table and has hexagonal crystal structure, but larger lattice parameter (aHf = 3.196 Å, and aTi = 2.950 Å). The Ti-Hf solid solution system obeys Vergard's law well, that is, the lattice parameters of this alloy change linearly with composition.
Studies of poorly conducting samples by the low-loss electron method in the SEM
Authors: Wells O. C. , Rishton S. A. 
Published: June 2020

The low-loss electron (LLE) image in the scanning electron microscope (SEM) shows stronger topographic contrast, less sensitivity to specimen charging and a shallower information depth in comparison with the more familiar secondary electron (SE) imaging method. When working with a poorly conducting or insulating sample the beam energy must be reduced to typically ~1.5 keV to minimise the net charging current at the surface of the specimen. Even if this is done correctly the topographic contrasts in the LLE image can still be considerably stronger than in the SE image.Fig. 1(a) shows the original LLE detector in which the sample is inclined at 45° to the electron beam. Fig. 1(b) shows a new detector which operates with a specimen tilt of 20°. Both have been used in a Cambridge Instrument Co. S250 Mk.III SEM.The possibility of obtaining a LLE image with a 20° specimen tilt is demonstrated with uncoated photoresist in Fig. 2 (tungsten filament) and with a “Crystal“ image store to capture and replay the image.
AFM of phospholipid membranes: From ripples to domains to interdigitation
Authors: Shao Zhifeng , Yang Jie , Mou Jianxun , Czajkowsky Czajkowsky 
Published: June 2020

In the past few years, a great deal of effort was made in many laboratories in the development of suitable specimens and better instrumentation for biological applications of atomic force microscopy (AFM) for its promise of high spatial resolution imaging of biological samples under physiological conditions. This effort has resulted in the publication of a number of excellent and reproducible images of various bio-macromolecules. Most notables include plasmid DNA and DNA fragments at, gap junction plaques, and cholera toxin, among others. However, the majority of these work were aimed at the methodology and the characterization of the AFM. Very little information was actually revealed about the biological systems being studied. This has been one of the major criticisms from many biologists and electron microscopists, that nothing new was learned by biological AFM.This situation has started to change recently. Rees et al. showed by AFM in air that the DNA template at the site of DNA-RNA polymerase complex bent differently in the presence of open or elongation promoter.
Indications of flux pinning by chemical defects in 123
Authors: Li D.J. , Zhang J.P. , Qin L.C. , Marks L. D. 
Published: June 2020

A problems with bulk high temperature superconductors for some time has been obtaining specimens which show high critical currents; typical critical currents in bulk materials lie in the range of 103 Amps/cm2 whereas thin film specimens now routinely reach the 106 Amps/cm2 range. There has recently been indications of higher critical currents in some materials, with suggestions that there is flux pinning by 1/3(301) type defects. We have previously studied in some detail bulk materials with excess copper that contain large number of such defects. In the light of the recent results, we have returned to these materials to study the critical current in addition to the structure.Details of the specimen preparation will be reported elsewhere. The key point is that with the correct preparation conditions, the bulk materials show a fairly sharp transition at 9IK and magnetization measurements indicate (reproducibly) a Jc of more than 106 at 4.5K, using the total size of the specimen and not a smaller grain size.
Dislocations in YBa2Cu3O7−δ (δ = 0.77)
Authors: Zhu Yimei , Zhang Hong , Moodenbaugh A.R. , Suenaga M. 
Published: June 2020

Abundant dislocations and dislocations associated with stacking faults were observed and characterized in YBa2Cu3O7−δ (δ= 0.77). The crystallographic orientation of the dislocation and the fault were analyzed using Kikuchi patterns matched with computer generated Kikuchi maps. The Burgers vector of the dislocation and the displacement vector of the fault were determined by using the g·b = 0 and g · R=0 criteria.Bulk samples of YBa2Cu3O7 were produced by standard pressing and sintering up to 970 °C. Samples were heated in air, then quenched into liquid nitrogen to reduce oxygen content. Subsequent anneal at 200 ° C took place with samples sealed in silica with 1/2 atm. of argon. TEM specimens were thinned by ion mill and examined in a JEOL 2000FX electron microscope operating at 200kv.X-ray powder diffraction and convergent beam electron diffraction with 200 Å spot size show that YBa2Cu3O6.23 has a tetragonal structure.
Structural and superconducting study of the system (Pb,Bi)-Sr-Ca-Cu-O
Authors: Aurisicchio C. , Calestani G.L. , De Blasi C. , Fiorani D. , Manno D. , Palmisano M. 
Published: June 2020

The results of a study of the structural and superconducting properties performed on a (Pb, Bi) - Sr - Ca - Cu - O systei by x rays, transmitted electron aicroscopy (CBED) and magnetic susceptibility measurements are reported.The sample was prepared by solid state reaction of a mixture of Bi2O3, PbO, SrCO3, CaCO3 and CuO, according to the starting composition Bi2PbO.4Sr2Ca3Cu4Ox. A slight excess of Ca and Cu, with respect to the stoichiometric formula (Bi, Pb)2Sr2Ca2Cu3Ox was utilized in agreement with in order to minimize the reaction time required for the obtainment of the c= 3.7 nm phase and to avoid the presence of the c-shorter phase (−3.1 nm) in the final product. The mixture was ground, heated at 780 oC for 8h and then cooled to room temperature in air and annealed again at 840 oC for 60h. Finally a textured sample was obtained by pressing the powder into a pellet which was annealed at 840 oC for 8h.
Effect of Microstructures on Properties of YBa2Cu3O7-x
Authors: Xiang-yun Song , Shulin Wen , Mei-yu Zhao , Zhen-en Li 
Published: June 2020

The purpose of this investigation is to reveal the correlation between microstructures and curitical current density (Jc) in YBCO ceramic superconductors by TEH. Further analyses have shown that these microstructural features are denpendent on Cu-O planes behaviour of two dimensions and key to explain the mechanism of the relation between microstructure and Jc. Three YBCO samples which have the same composion but different processing were measured and compared. The Tc values of three samples were approximately the same (90K) but the Jc values were quite different:30A/cm2 for sample S1 300A/cm2 for sample S2 and 2000A/cm2 for sample S3. Hundreds pictures for three samples were randomly taken in low magnification by TEM. Using the statistical method, the microstructural information were measured from TEM pictures.A number of observations by TEM have found that three kinds of microstructural features, including the grain of c/a≥3 (grain length c, width a),the grain boundary between parallel-straight grains and the grain with twin domains play a major role in YBCO ceramics superconductors as shown in Fig. 1. The results of investigation have been shown that their content increases as Jc value are increased and as a function of Jc as shown in Fig. 2.
Short-range order in amorphous FeTb
Authors: Tewes M. , Zweck J. , Hoffmann H. 
Published: June 2020

The importance of amorphous rare-earth/transition-metal (Re-TM) alloys for use as magneto-optic (MO) storage media has been shown first in 1973. First atomic structural data of amorphous Fe2Tb were given in 1974 and compared with those of a crystalline counterpart, which is the well-known Laves phase. Significant differences of short range order (sro) in amorphous and crystalline Fe2Tb have been found. Similiar results were given in 1986 for a composition Fe79Tb21, to be used for MO-recording.In this work we present pair distribution functions (PDF’s) determined from electron diffraction data for amorphous FeTb alloys. It has been shown that Fourier transformation of the experimental observed diffraction intensities gives the original infinite lattice of an investigated (crystalline) specimen multiplied by its selfcorrelation-function. Therefore the PDF approaches zero for r-values greater than the distance ro representing the mean dimension of a crystal.