bluuebunny/crossref_metadata_2025_split huggingface dataset:
HREM studies of YBa2Cu3O7-δ prepared from low-temperature precursors
Authors: Dufner D.C. , Ram R.A. Mohan , Clearfield A. 
Published: June 2020

Solid state reactions are the most commonly employed processes for the preparation of high-Tc superconducting ceramic oxides. However, there has been considerable effort expended to prepare the YBa2Cu3O7-δ (1-2-3) superconductor by low-temperature solution methods in order to obtain a more homogeneous oxide mixture resulting in products with superior superconducting properties. Proper processing of the precursors resulting in less preparation time, lower temperature of firing, higher critical current density, higher flux expulsion, etc., is expected.Our laboratory has been preparing low-temperature precursors by sol-gel and other methods. We employed the same methods for the preparation of 1-2-3 superconductors. The precursors were heated at 925°C for 12 hours in flowing oxygen. The resulting powder was found to be superconducting at 92.3K. Superconducting properties were measured by resistivity and impedance measurements.
The future of AEM: Toward atom analysis
Authors: Cliff G. , Kenway P.B. 
Published: June 2020

The ultimate goal of analytical electron microscopy (AEM) is a minimum detection limit, MDL, of one atom! Utilising the small probes and the high current densities attainable using a field emission gun, FEG, in a scanning transmission electron microscope, STEM, the MDL is at present 100 atoms. This discussion will show that an MDL of 1 atom could be achieved with existing engineering technology available on the current generation of AEM instrumentation.Indeed if AEM was like hi-fi an AEM analyst could today combine features of different microscopes to build an AEM capable of atom detection!The parameters affecting the MDL include a) the electron source brightness, b) the detector solid angle, c) the operating voltage and, less frequently discussed, d) the Cs of the probe-forming lens.a) Electron source brightness. The highest brightness electron source is the FEG as used in the dedicated STEM which achieved the MDL quoted above. This is the only source capable of producing the high current density in a small probe required to reduce the MDL to atomic proportions.
Microstructural determination of a metastable phase during rhodium oxidation
Authors: Logan A. David 
Published: June 2020

In heterogeneous catalysis, oxidation of the catalyst is frequently used as a means of removing impurities from the active surface. However, bulk oxidation severely alters the microstructure of the metal due to atom repositioning and valence changes. Transformation of Rh to Rh2O3causes the lattice structure to change from fcc to hexagonal with a resulting volume expansion of 90% due to density changes. This is the reported cause for fracturing of crystallites and variations in reactivity. In this study, microstructural changes during progressive oxidation of 5 nm metal Rh particles have been examined.A 2 wt% Rh/Silica catalyst was prepared using Rh(III)-2,4 pentanedionate as a precursor and nonporous silica spheres as a support. The catalyst was then reduced in flowing H2at 473 K. High resolution electron microscopy (HREM) was performed on a JEM-4000EX having a point resolution of 0.17 nm. The catalyst was oxidized in research purity O2(Matheson 99.99%) using an all glass volumetric chemisorption system.
Characterization of second-phase particles in NiAl-containing trace additions of Zr
Authors: Locci I. E. , Noebe R. D. 
Published: June 2020

X-ray microanalysis and electron diffraction were used to characterize the second phase particles observed in Zr-doped single crystal and polycrystalline NiAl. Zirconium is the most common addition made to NiAl because of its positive effect on the cyclic oxidation behavior of this intermetallic. While the effect of Zr on the oxidation behavior of polycrystalline and single crystal NiAl has been studied in detail, the effect of Zr on the microstructure and mechanical behavior of NiAl has generally been ignored.An intermetallic phase, rich in Zr and Si, was observed in directionally solidified NiAl single crystals. Figure 1 is a dark field and bright field image ofthese precipitates. Diffraction analysis indicated that the second phase was a nickel zirconium silicide (Ni16Zr6Si7). This phase was observed in crystals obtained from two separate sources. All crystals were near stoichiometry in composition and contained 0.1 wt.% Zr as well as an unintentional addition of 0.07-0.10 wt.% Si. Silicon contamination was probably the result of reaction between the NiAl melt and the crucible. The precipitates ranged in size from 10 to 40 nm. Occasionally, strings of precipitates were observed in dislocation paths, suggesting preferential nucleation induced by the presence of crystal defects. Figure 2 illustrates the cuboidal shape of the precipitates as observed near an [011] zone axis; two faces of the cube can be distinguished.
Electron spectroscopic imaging (ESI) on multiphase polymer materials
Authors: Cantow H.-J. , Kunz M. , Möller M. 
Published: June 2020

In transmission electron microscopy the natural contrast of polymers is very low. Thus the contrast has to be enhanced by staining with heavy metals. The resolution is limited by the size of the staining particles and by the fact that electrons with different energy are focused in different image planes due to the chromatic aberration of the magnetic lenses. The integration of an electron energy loss spectrometer into the optical coloumn of a transmission electron microscope offers the possibility to use monoenergetic electrons and to select electrons with a certain energy for imaging. Thus contrast and resolution are enhanced. By imaging only electrons with an element specific energy loss the element distribution in the sample can be obtained. In addition, elastic bright field images and diffraction patterns yield excellent resolution. Some applications of the method on multicomponent polymer materials are discussed.Bulk polymer samples were prepared by ultramicrotoming at room temperature or well below the glass transition temperature. Very thin films for the direct observation of the structure in semicrystalline polymers were obtained by melt-spinning. Specimens were examined with a ZEISS CEM 902 operated at 80 kV.
Characterization of high-performance polymer blends
Authors: Chen R.T. , Rafalko J.J. , Sawyer L.C. 
Published: June 2020

Blending of polymers, a method used to engineer materials to provide specific properties, has been extended to high performance materials being developed for composite applications in the aerospace industry. The high performance requirements of such blends demand a complete understanding of the chemistry and morphology as a function of end-use temperatures. Multidisciplinary protocols for characterization of blends include microscopy, infrared and thermal analysis. The major issues involved in such a study of polymer blends will be described.Recently the Hoechst Celanese polybenzimidazole, [poly-2,2′(m-phenylene)-5,5′ bibenzimidazole], PBI, and the General Electric aromatic polyether imide [poly(2,2′-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane-m-phenylenediimine], Ultem 1000, which are being evaluated for aerospace applications, were found to form miscible blends. The large parts are being fabricated from fibers spun from concentrated solutions (dopes).
The crystalline modifications and the morphology and structure of J-1 polymer spherulites
Authors: Li L. S. , Geil P. H. 
Published: June 2020

The J-1 polymer (Poly(bis 4, 4' dicyclohexylmethane)n-dodecanediamide) (E. I. du Pont)has a well defined chain structure in which cyclohexyl groups and intermolecular hydrogen bonds make the chains rigid. This results in a high melting point for this polymer in the range of 290°C. However, there is also some flexibility in the chains of this polymer due to the -(CH2)10- segments and -(CH2)- groups between every two cyclohexyl groups along the chains. The combination of rigidity and flexibility in the J-1 polymer would lead to a variety of morphologies. In order to varify this we have studied the morphology and structure of the J-1 polymer crystallized from solution.Thin films of J-1 polymer with single crystals and six different kinds of spherulites were prepared by evaporation of solvent from am-cresol solution of J-1 polymer at temperatures of 160°-210°C. The thin films were examined in both polarizing and electron microscopes. A Philips 430 electron microscope was used at 200, 250 or 300 kV accelerating voltages.
Integrated morphometrical and electron energy loss image analysis in cytochemistry
Authors: de Bruijn W.C. , de Jong A.A.W. , Sorber C.W.J. 
Published: June 2020

One aspect of enzyme cytochemistry is, whether all macrophage lysosomal hydrolytical enzymes are present in an active form, or are activated upon stimulation. Integrated morphometrical and chemical analysis has been chosen as a tool to illucidate that cytochemical problem. Mouse peritoneal resident macrophages have been used as a model for this complicated integration of morphometrical and element-related data. Only aldehyde-fixed cells were treated with three cytochemical reactions to detect different enzyme activities within one cell (for details see [1,2]). The enzyme-related precipitates anticipated to be differentiated, were:(1).lysosomal barium and sulphur from aryl sulphatase activity,(2).lysosomal cerium and phosphate from acid phosphatase activity and(3).platinum/di-amino-benzidine( D A B) complex from endogenous peroxidase activity.
A 2-dimensional detection system for Electron Energy Loss Spectroscopy
Authors: von Harrach H.S. , Colling J.A. 
Published: June 2020

A UHV-compatible parallel and serial detection system for electron energy-loss spectroscopy (EELS) has been developed for the VG HB501 field-emission scanning transmission electron microscope (STEM) using a 2-dimensional detector. As pointed out previously the charge coupled devices (CCD) available commercially are vastly superior, in terms of read-out noise, to linear photodiode arrays which are currently used for parallel EELS detection. This feature, together with the ability of operating as an imaging and storage device, makes the 2-dimensional CCD array an attractive choice for parallel EELS and low light-level imaging applications.The system reported here (Fig. 1) is an extension of the VG ELS501 sector magnetspectrometer used for serial EELS with many STEMS. It uses one quadrupole lens to magnify the energy-loss spectrum over a range of 2 to 0.1 eV per detector element. An electromagnetic deflector steers the spectrum to one of three YAG scintillators. Two of these scintillators with suitable masks are used for parallel EELS detection; the third is used for serial EELS and energy filtered STEM imaging via a lightguide and photomultiplier system by scanning the beam across a variable slit as in ELS 501 systems.
Reactions at metal-semiconductor interfaces
Authors: Sinclair Robert 
Published: June 2020

Examination of the architecture of a semiconductor-based microelectronics device shows that metallic, highly conductive components are an integral part of the miniature circuits. As geometries become increasingly small (e.g. at the sub-micron level) the structure at critical interfaces influences the electrical performance to a greater extent. Accordingly metal-semiconductor junctions have significant technological importance, in addition to any natural scientific interest associated with the bonding of two unlike materials. This article reviews some of our recent work on this topic, with particular emphasis on the reactions which can occur either during fabrication of the interface or upon heating in conjunction with device processing or prolonged service.The simplest system consists of an elemental metal and an elemental semiconductor, silicon being the most important example of the latter. Consideration of phase equilibria indicates that such an interface is thermodynamically unstable: upon heating either a reaction can occur to produce a compound phase (i.e. a silicide), or mutual dissolution of the elements within each other takes place to achieve saturated solid solution compositions. Reference to the appropriate binary phase diagram allows prediction of the result if local equilibrium is achieved. Thus although an atomically abrupt metal-semiconductor interface might be grown under specialized circumstances, this situation can be expected to be unusual and moreover it is not stable to elevated temperatures when atomic mobility and diffusion are rapid.
Studies of CoSi2 nano-structures produced by high-dose ion implantation in Si
Authors: Berger S.D. , Loretto D. , Huggins H.A. , White Alice E. , Short K.T. , Bahnck D. 
Published: June 2020

Recently it has been shown that buried layers of single crystal, orientated CoSi2 Can be produced in silicon by implanting high doses of Co followed by a high temperature anneal. This process is known as mesotaxy. The original implant produces a skewed Gaussian distribution of ions. However, on annealing it is found that the distribution sharpens dramatically to give layers which nave flat and abrupt interfaces and are of very good structural and electrical quality.Using a combination of electron beam lithography and reactive ion etching we have fabricated masks which confine the implant dose laterally. In this way we are able to produce discrete structures of CoSi2 with nanometer dimensions. Furthermore, we can now investigate the epitaxial growth process which occurs during the anneal by varying the structure's dimensions, shape and crystallographic orientation with respect to the substrate.
Epitaxial films of CoSi2 on Si (311) and Si (211)
Authors: Batstone J.L. , Phillips Julia M. 
Published: June 2020

Cobalt silicides can be grown epitaxially on silicon by room temperature (RT) deposition of Co onto in-situ cleaned Si in an ultra high vacuum environment. Post-deposition annealing at ∼550°C leads to the formation of CoSi2 which exists in two orientations on Si (111), known as type A and type B. The fractional coverage of type A CoSi2 is critically dependent on the metal thickness. If <10Å Co is deposited at RT, type B CoSi2 is formed. For >10Å Co, intermediate metal-rich silicide phases such as Co2Si and CoSi are formed at low (<450°C) temperatures. At >500°C, mixed A+B type CoSi2 is formed. If higher reaction temperatures are employed, large (∼2000Å) pinholes open up allowing dislocation motion and a conversion of the film to entirely type B CoSi2.Epitaxial growth of CoSi2 on Si (311) has recently been demonstrated. Two orientations, A and B were observed where the B orientation was rotated with respect to the substrate about the inclined (111) axis. Electrically continuous films were obtained at temperatures as low as 500°c with residual resistivities ∽10μΩcm. This work has now been extended to study the effects of substrate orientation on intermediate phase formation in the Co/Si system.
Analysis of transition metal induced surface defects in silicon following apid thermal processing
Authors: Kola R. 
Published: June 2020

Rapid Thermal Processing(RTP) is extensively used in VLSI technology for implant activation, licidation, oxidation, and passivation glass reflow. The diffusion of back-side depositions of transition metals during rapid thermal annealing and the resulting front-side defect formation in silicon has recently been investigated by several authors but a detailed analysis of the defect structure, morphology, and chemistry is lacking. The defect structure and chemistry on both the front and back sides of the wafers ter RTA were investigated by TEM on plan-view and cross-section foils. A Philips EM430 microscope ierating at 300 KeV and a Hitachi H-800 microscope operating at 200 KeV were used. Ni and Cu sputter deposited on the back-side of 4 inch diameter (100) Si wafers were diffused for 10 sec at 1150°C in trogen ambient. The thickness of the metal film was 50 nm. A Heatpulse 2101 RTA system was used.Fig. 1 is a CDF micrograph showing a group of precipitates on the front surface of a sample nickel diffused from the back surface.
Centrosymmetric and nonsymmorphic aluminum oxynitride spinel
Authors: Dravid V. P. , Sutliff J. A. , Weslwood A. D. , Nolts M. R. , Lyman C. E. 
Published: June 2020

There is considerable controversy concerning the point and space group of crystals based on the spinel structure. The debated question is whether the space group of spinel crystals is or . has noncentrosymmetric point group and is symmorphic; has centrosymmetric point group and is nonsymmorphic. One characteristic of the space group that distinguishes it from is that reflections hkl such that h+k, k+l, h+l ≠ 4n, for example {200}, are kinematically forbidden.MgAl2O4 spinel was studied by Steeds and Evans whose observations of {200} reflections in {001} ZAPs lead them to conclude that the space group of this crystal was . de Coomen and Carter also investigated MgAl2O4 spinel and came to the same conclusion. Although these authors do emphasize the importance of a HOLZ contribution to double diffraction, they do not show the effect of changes in accelerating voltage on the HOLZ segment responsible for double diffraction. To clearly show that {200} reflections appear only as a result of double diffraction via HOLZ, it is essential to observe both the {200} reflections and the HOLZ segment as a function of accelerating voltage.
CBED from imperfect crystals: Current achievements and future prospects
Authors: Cherns D. , Jordan I.K. 
Published: June 2020

CBED is usually applied to the study of perfect crystals. However, we have recently shown that CBED can be usefully applied to the study of a range of individual defects (dislocations and stacking faults) and to the study of composition profiles in a range of periodic and aperiodic semiconductor multilayers. In this paper the advantages of CBED for such studies over conventional imaging techniques will be explained and the scope for future work discussed.The application of CBED to the study of dislocations has already been discussed in a series of papers. The technique is to use the large angle method (LACBED) such that a shadow image of a given dislocation is seen in diffraction. The interaction with diffraction contours can then be studied as a function both of deviation parameter and distance from the dislocation core (fig 1). Since in CBED or LACBED we can identify diffraction into higher order reflections than is normally possible in imaging (for example the higher order Laue zone deficiency lines in fig 1), large g.b values are possible with corresponding high sensitivity to the dislocation strain field. One application has been to examine small Burgers vectors, such as those associated with stair-rod dislocations. A further advantage is that, for large g-vectors, image contrast can be explained qualitatively by a simple kinematical model giving the magnitude of the Burgers vector from the number of subsidiary peaks into which the diffraction contour splits. The sign of the Burgers vector follows from the image asymmetry.
Observation of surface morphology by reflection electron holography
Authors: Osakabe N. , Endo J. , Matsuda T. , Tonomura A. 
Published: June 2020

Progress in microscopy such as STM and TEM-TED has revealed surface structures in atomic dimension. REM has been used for the observation of surface dynamical process and surface morphology. Recently developed reflection electron holography, which employes REM optics to measure the phase shift of reflected electron, has been proved to be effective for the observation of surface morphology in high vertical resolution ≃ 0.01 Å.The key to the high sensitivity of the method is best shown by comparing the phase shift generation by surface topography with that in transmission mode. Difference in refractive index between vacuum and material Vo/2E≃10-4 owes the phase shift in transmission mode as shownn Fig. 1( a). While geometrical path difference is created in reflection mode( Fig. 1(b) ), which is measured interferometrically using high energy electron beam of wavelength ≃0.01 Å. Together with the phase amplification technique , the vertivcal resolution is expected to be ≤0.01 Å in an ideal case.
SEM and x-ray EDS studies on the adhesion of novel bisoxazoline-phenolic copolymers to carbon and glass fibers, and metallic filler surfaces
Authors: Deviney M.L. , Brostrom L.R. , Menardi P.J. , Culbertson B.M. , Tiba O. 
Published: June 2020

A very promising new entry into the family of polymers for advanced composites, for aerospace and heavy duty industrial applications requiring high service temperature and/or low flammability, are bisoxazoline-phenolic resins derived from the step-growth copolymerization of 1,3 (or 1,4)-phenylene bisoxazoline (PBOX) and phenol-free phenolic resins. This new resin system offers a very attractive group of properties, including high modulus, high compressive and shear strengths, excellent toughness, high heat distortion temperature, no volatiles evolution and low shrinkage (<1%) during cure, low flammability and low smoke production, good electrical properties, relatively low coefficient of thermal expansion, very good thermal shock resistance and machinability, and excellent adhesion to carbon fibers, fiberglass and powdered (5 to 20 μm) metal fillers (e.g., iron and aluminum).In this paper are presented example scanning electron microscopy (SEM) micrographs of PBOX-phenolic interfacial regions with both reinforcing fibers and metallic fillers. Carbon fiber reinforced composite specimens were examined by SEM (CamScan Series 4 instrument) after testing to failure using standard ASTM shear, flex and compression tests.
Transmission electron microscopy and high resolution scanning electron microscopy of Co-Ni-Pt thin film magnetic recording media
Authors: Chan L. , Yamashita T. , Sinclair R. 
Published: June 2020

In thin film magnetic media, the magnetic hysteresis properties and micromagnetic domain behavior are strongly influenced by both interparticle exchange interactions and by magnetostatic interactions. The exchange interactions are short-range in nature; therefore, they are very sensitive to interparticle separation. Consequently, the magnetic hysteresis properties and the recording behavior of the thin film magnetic media can be drastically altered by the introduction of grain separation during the film deposition process. In this study, thin film media of a CoNiPt alloy of one composition was processed under two different conditions. Transmission electron microscopy (TEM) and high resolution scanning electron microscopy (HRSEM) were used to investigate and explain the difference in magnetic hysteresis characteristics of the films.The structure of the thin film media consisted of a 600 Å thick CoNiPt alloy sputtered on textured 130mm diameter NiP-plated aluminum substrates. A single sputtering parameter was varied to produce two types of films, labelled type I and type II, which exhibited significant differences in their magnetic recording characteristics.
Precipitates in hot pressed Nd-Fe-B magnets
Authors: Chu Tsung-Yao 
Published: June 2020

High-performance permanent magnets based on the Nd-Fe-B ternary system can be prepared by melt-spinning of the molten alloy and subsequent pressing to full density at elevated temperature. The starting composition is always slightly rich in Nd compared to stoichiometric Nd2Fe14B in order to ensure the formation of the Nd-rich grain boundary phase. The excess Nd additions also serve to keep elemental Fe particles from precipitating but, instead, lead to unexpected precipitation within the Nd2Fe14B grains. The current research seeks to fully characterize the structure of the precipitates.Electron transparent specimens for TEM examination were prepared by mechanical grinding of thin sections cut from the hot pressed Nd0.135Fe0.815B0.05 magnets, followed by argon ion beam milling at 6 kV. Most of the samples were studied in a JEOL 1200EX STEM equipped with EDS, operating at 120 kV. A few samples were examined at higher resolution in a JEOL 200 CX TEM operated at 200 kV, employing a side entry goniometer stage and a LaB6 cathode.