bluuebunny/crossref_metadata_2025 huggingface dataset:
High-resolution microscopy of ceramic surfaces
Authors: Bentley J.
Published: June 2020

The characterization of ceramic surfaces plays an important role in understanding a wide variety of properties such as fracture, wear, crack initiation, oxidation, sintering, and thin film growth on substrates. Three major microscopies are employed to obtain nanometer-scale resolution of ceramic surfaces: scanning electron microscopy (SEM), (scanning) transmission electron microscopy (STEM or TEM) especially in the glancing-incidence reflection modes, and scanning tip microscopies - most notably atomic force microscopy (AFM). Each technique has its own set of characteristics, advantages, and disadvantages and is usually complementary to the others.

Conventional SEM is quick and easy to implement. As a mature technique, the contrast mechanisms, although sometimes complex, are largely well understood; computer programs for image simulation are available. The technique is applicable to a wide range of materials and specimen sizes; usually, little specimen preparation is involved. Charging of electrically insulating ceramics has traditionally been overcome by coating but, at high resolution, the faithful representation of the structure then becomes of some concern.
Atomic morphology of the γ/γˊ interface
Authors: Fonda Richard W. , Jin Xuegen , Luzzi David E.
Published: June 2020

Nickel-based superalloys are well known for their high temperature strength. These alloys consist of two phases, γ and γˊ, which in combination produce an alloy of higher strength than either phase alone. A significant factor in this strength increase is the interface between the two phases. The γ phase is a fcc solid solution of nickel, while the γˊ phase has a Ll2 structure based on Ni3Al. The difference in lattice parameter between these two phases is very small, producing large regions of coherent interface between the two phases. This interface between γ and γˊ was examined by high resolution electron microscopy

The nickel-based superalloy (René N4) was generously supplied by Dr. R. Field of GE Aircraft Engines. TEM samples were cut from this oriented single crystal, mechanically thinned, then electropolished in a solution of 10% perchloric acid in ethanol. A Philips 400T TEM was used for conventional imaging and a JEOL 4000EX was used for high resolution imaging.
Structure determination of MBE-grown GaAs(001)-2×4 surfaces by quantitative RHEED analyses
Authors: Ma Y. , Lordi S. , Eades J. A.
Published: June 2020

The GaAs(001) surface is the most widely used gallium arsenide face in the MBE growth of multilayer electronic device structures. Various reconstructions on this face have been reported. They range from the As-rich (2×4) to the Ga-rich (4×2). The As-rich (2×4) surface is the most important one of these, since MBE growth usually starts and ends with this surface. A multislice formalism of Cowley & Moodie with a recently developed edge patching method has been applied to quantitative analyses of the RHEED patterns from MBE grown GaAs(001)-2×4 surfaces. The analyses are based on the ordering of visually estimated spot intensities of the observed RHEED patterns from the GaAs(001)-2×4 surfaces, which is similar to the approach used in early X-ray structure determinations. The surface structure has been proved to be a dimerized vacant 2×4 reconstruction with one dimer of every four missing, which is consistent with previous STM observations.
TEM Study of Co/Pd and Co/Au Multilayers
Authors: De Veirman A.E.M. , Hakkens F.J.G. , Coene W.M.J. , den Broeder F.J.A.
Published: June 2020

There is currently great interest in magnetic multilayer (ML) thin films (see e.g.), because they display some interesting magnetic properties. Co/Pd and Co/Au ML systems exhibit perpendicular magnetic anisotropy below certain Co layer thicknesses, which makes them candidates for applications in the field of magneto-optical recording. It has been found that the magnetic anisotropy of a particular system strongly depends on the preparation method (vapour deposition, sputtering, ion beam sputtering) as well as on the substrate, underlayer and deposition temperature. In order to get a better understanding of the correlation between microstructure and properties a thorough cross-sectional transmission electron microscopy (XTEM) study of vapour deposited Co/Pd and Co/Au (111) MLs was undertaken (for more detailed results see ref.).

The Co/Pd films (with fixed Pd thickness of 2.2 nm) were deposited on mica substrates at substrate temperatures Ts of 20°C and 200°C, after prior deposition of a 100 nm Pd underlayer at 450°C.
Grain separation enhanced magnetic coercivity in Pt/Co multilayers.
Authors: Bertero G.A. , Sinclair R.
Published: June 2020

Pt/Co multilayers displaying perpendicular (out-of-plane) magnetic anisotropy and 100% perpendicular remanent magnetization are strong candidates as magnetic media for the next generation of magneto-optic recording devices. The magnetic coercivity, Hc, and uniaxial anisotropy energy, Ku, are two important materials parameters, among others, in the quest to achieving higher recording densities with acceptable signal to noise ratios (SNR). The relationship between Ku and Hc in these films is not a simple one since features such as grain boundaries, for example, can have a strong influence on Hc but affect Ku only in a secondary manner. In this regard grain boundary separation provides a way to minimize the grain-to-grain magnetic coupling which is known to result in larger coercivities and improved SNR as has been discussed extensively in the literature for conventional longitudinal recording media.

We present here results from the deposition of two Pt/Co/Tb multilayers (A and B) which show significant differences in their coercive fields.
Domains and domain nucleation in magnetron-sputtered CoCr thin films
Authors: Demczyk B. G.
Published: June 2020

CoCr thin films have been of interest for a number of years due to their strong perpendicular anisotropy, favoring magnetization normal to the film plane. The microstructure and magnetic properties of CoCr films prepared by both rf and magnetron sputtering have been examined in detail. By comparison, however, relatively few systematic studies of the magnetic domain structure and its relation to the observed film microstructure have been reported. In addition, questions still remain as to the operative magnetization reversal mechanism in different film thickness regimes. In this work, the magnetic domain structure in magnetron sputtered Co-22 at.%Cr thin films of known microstructure were examined by Lorentz transmission electron microscopy. Additionally, domain nucleation studies were undertaken via in-situ heating experiments.

It was found that the 50 nm thick films, which are comprised of columnar grains, display a “dot” type domain configuration (Figure 1d), characteristic of a perpendicular magnetization. The domain size was found to be on the order of a few structural columns in diameter.
HREM of electron-irradiated silicas
Authors: Qin L.C.
Published: June 2020

Silica (SiO2) crystals exist in various polymorphs which have different densities and different crystal structures, such as quartz, tridymite, and cristobalite, though all of these have in common the network structure which is formed by corner-sharing of SiO4 tetranedra. All these structures are sensitive to electron irradiation. Amorphization occurs when they are irradiated by energetic electrons.

In the present study three polymorphs of silica crystals, α-quartz, α-tridymite and α-cristobalite crystals2 were used as starting materials. Electron irradiation experiments were carried out in situ in the electron microscope. The structural changes of the specimens were monitored using high-resolution electron microscopy (HREM).

The amorphization of α-quartz crystals was found to progress through two morphologies: (a) nucleation and growth of amorphous nuclei with a sharp boundary with the crystalline matrix (figure 1); and (b) crystallinity lost gradually and more uniformly. Figure 2 shows a series of HREM images showing the amorphization of a tridymite crystal.
Deterioration of polysilicon/gate-oxide structures upon H2 annealing
Authors: David Theodore N. , Hung Merit
Published: June 2020

Silicon device-technology makes extensive use of polysilicon layers for capacitors, contact-materials, thin-film diodes, transistors and resistors. In metal-oxide-semiconductor field-effect transistors (MOSFETs) polysilicon is used as the gate electrode on top of a thin gate-oxide layer. The microstructure and stability of the polysilicon and gate-oxide layers can strongly influence electrical behavior of the transistors. Any microstructural deterioration that occurs as a result of processing can result in reduced charge-to-breakdown and lowered breakdown voltages. It is known that interfacial oxides inadvertently present at interfaces of silicon/polysilicon structures break-up as the structures are annealed, Whereas agglomeration of oxide is beneficial in some structures, in MOSFETs such deterioration would be disastrous. The stability of polysilicon/ gate-oxide structures for various processing conditions likely to be used during device-fabrication needs to be characterized. The present study investigates the thermal stability of polysilicon gate-electrode/ gate-oxide structures annealed in a hydrogen ambient at temperatures varying from 800°C to 1050°C.
TEM/HREM study of mechanical alloyed Cu-Zr powders
Authors: Chiou W. A. , Lin C. S. , Liu P.
Published: June 2020

New technologies for the synthesis of materials with unique microstructures and properties have always been of great interest to materials scientists and engineers. It has recently been shown that the preparation of amorphous and nanocrystalline powders by mechanical alloying (MA) can be of great potential. While various mechanisms of amorphization have been proposed, the real process remains unclear. To understand the process/mechanism of amorphization and nanocrystalline formation, investigations of the interfacial regions between collided ball-milled elemental powders is essential. This paper presents an interfacial study of the agglomerated CuZr powders after ball milling.

Samples of commercially produced (AESAR) fine-grained (325 mesh, or 44 μm) Cu (99.3 %) and Zr (99%) powders were weighed to a weight ratio of 1 : 1 (atomic ratio 1.4 : 1) as the starting materials. These powders were mixed together in a steel vial and ball-milled in a SPEX mixer/mill machine. All the process of powder loading/unloading and ball milling were done in an argon gas chamber.
Characterization of microwave-sintered ceramic composites
Authors: Zhang X. , Pan Y. , Meek T.T.
Published: June 2020

Industrial microwave heating technology has emerged as a new ceramic processing technique. The unique advantages of fast sintering, high density, and improved materials properties makes it superior in certain respects to other processing methods. This work presents the structure characterization of a microwave sintered ceramic matrix composite.

Commercial α-alumina powder A-16 (Alcoa) is chosen as the matrix material, β-silicon carbide whiskers (Third Millennium Technologies, Inc.) are used as the reinforcing element. The green samples consisted of 90 vol% Al2O3 powder and 10 vol% ultrasonically-dispersed SiC whiskers. The powder mixture is blended together, and then uniaxially pressed into a cylindrical pellet under a pressure of 230 MPa, which yields a 52% green density. The sintering experiments are carried out using an industry microwave system (Gober, Model S6F) which generates microwave radiation at 2.45 GHz with a maximum output power of 6 kW. The composites are sintered at two different temperatures (1550°C and 1650°C) with various isothermal processing time intervals ranging from 10 to 20 min.
Phase composition and local grain alignment at the Ag/superconductor interface in Ag-sheathed Bi-Sr-Ca-Cu-O tapes
Authors: Feng Yi , Larbalestier D.C. , Babcock S.E. , VanderSande J.B.
Published: June 2020

Texturing of the superconductor phase and proximity to a sourse of silver appear to be crucial to the development of high critical current density tapes of the Bi-Sr-Ca-Cu-O (BSCCO) high-temperature superconductors, yet relatively little is understood about the mechanism(s) by which the [001] texture develops and the complex role that the silver sheath material plays. We have studied the phase composition, alignment, and bonding at the Ag/BSCCO interface for silver-sheathed tapes of both the 2212 and 2223 phases that have been processed under fundamentally different conditions. High-resolution TEM imaging revealed details of the interface that give insight into these important questions.

Ag-sheathed BSCCO tapes with cation compositions Bi2Sr2CaCu2Ox (2212) and Bi1.8Pb0.4Sr2.0Ca2.2Cu3Ox (2223) were prepared by standard powder-in-tube methods. 2212 sample A was heat-treated at 920°C for 15 minutes to melt the superconductor core, then cooled at 240°C/h from 920°C to 840°C and annealed at 840°C for 70 hours.
Short-range order to long-range order transition in a Cu-Ti alloy
Authors: Lee J.S. , Carpenter R.W. , Lim H. , Choo W.K.
Published: June 2020

Cu-Ti alloys have received attention due to their excellent age-hardenability. The age hardening phenomenon of Cu-Ti alloys is closely related to the early stage transformation involving short-range order (SRO), spinodal decomposition, and long-range order (LRO). Despite many researches, the transition from SRO to LRO state in this alloy system is still not understood. Woychik et al. have found {1 1/2 0} SRO reflections in an electron diffraction pattern of an as-rapidly solidified (RS) Cu-15at.%Ti alloy (All indices are referred with respect to the fcc structure in this paper.). with aging, the SRO reflections were replaced by the 4/5{l 1/2 0} LRO (Dla) reflections. Recently, Yoo found the {1/2 1/2 0} spots as well as the {1 1/2 0} spots in an electron diffraction pattern of an as-RS Cu-15at.%Ti alloy. This result may show that some other metastable phases can be present before the formation of the LRO phase. In the present paper, the initial stages of ordering process will be described.
AEM of a Ag-Y-Ba-Cu superconductor precursor material
Authors: Strutt A. J. , Simnad M. T. , Lavernia E. , Vecchio K. S.
Published: June 2020

Analytical electron microscopy (AEM) has been used to characterize a Ag-rich superconductor precursor material whose composition (before oxidation) was based on 10 wt.% of a YBa2Cu3 alloy and 90 wt.% Ag, and the same material after an oxidation heat treatment of 690°C for 24 hours. The material had been produced by a melt spinning process as a metallic alloy to permit deformation of the material (in the metallic state) prior to subsequent oxidation to form the ceramic superconducting Y-Ba-Cu oxide phase.

The microstructure was characterized using a Philips CM30 AEM, at 300 kV, using specimens thinned to electron transparency by ion-milling. Energy dispersive X-ray spectroscopy (EDX) was performed using the same instrument, with a Link Analytical solid-state X-ray detector with an ultra-thin window.

In the as-formed condition, the Y-Ba-Cu alloy phase exists as discrete particles at the triple points of the relatively fine (approx. 250 nm.)
A parametrization of inelastic scattering factors for high-energy electron diffraction
Authors: Seale D. J. , Sheinin S. S.
Published: June 2020

Theoretical images of model structures play a vital role in the analysis of both diffraction and phase contrast electron microscope images. In the theoretical calculations required to produce these images it is important to take absorption, due to inelastic scattering, into account. This is done by including an imaginary part in the Fourier coefficients of the lattice potential, V’g. These coefficients have been presented in a variety of ways. Radi has calculated the absorptive potentials for a number of crystals. He found that the most important contribution to these potentials is due to thermal diffuse scattering (TDS), except for the V’0 term, which does not affect image contrast. The Einstein model, in which all atoms are assumed to vibrate independently of one another, is normally used in calculating the contribution of TDS to the absorption process. This approximation allows one to calculate the absorption potential as a sum of contributions due to the different atoms in the crystal.
A high-resolution fraunhofer in-line electron holography
Authors: Matsumoto Takao , Tanji Takayoshi , Tonomura Akira
Published: June 2020

In-line holography is advantageous in terms of contrast in imaging weak phase objects. However, most of the recent articles on electron holography had an off-axis configuration employing an electron biprism and were applied successfully only to objects with a rather strong phase shift such as magnetic flux and thin crystals. When it comes to the observation of considerably weak phase object, the off-axis method fails. We applied Fraunhofer in-line electron holography to observe an undecagold cluster, the core of which has a diameter of 0.82 nm, and obtained a high resolution image with high contrast that has been obtained neither by off-axis electron holography nor by conventional transmission electron microscopy.

A Hitachi HF-2000 electron microscope equipped with a 200-kV cold field emission gun was used during the experiment. The specimen, Monoamino-Undecagold (NanoProbes, Inc., Stony Brook, N.Y.), was prepared in a highly dispersive form on a thin carbon film supported by a thick holey carbon film.
The effect of core size on the holographic interference images of superconducting fluxons in tilted specimens
Authors: Pozzi G. , Bonevich J.E. , Tonomura A.
Published: June 2020

Recently, observations of quantized flux lines in thin superconducting specimens have been successfully carried out in transmission electron microscopy by means of standard methods of Lorentz microscopy and also by electron holography. The breakthrough with respect to the previous unsuccessful attempts is represented by the fact that the specimen is observed tilted with respect both to the electron beam and the ancillary magnetic field that is used to introduce and stabilize the fluxons in the specimen.

Although a reduction of the phase difference with respect to the optimum situation of fluxons perpendicular to the beam is expected in this set-up, it has nonetheless been possible to ascertain by means of a simple model that this reduction is not below the detectability limit that can be reached by the most advanced phase sensitive methods available today in electron optics, such as electron holography. However calculations have been carried out so far either for the single fluxon case, taking into account also its core structure, or for an array of 25 flux tubes (i.e. fluxons with negligible core size) arranged in a triangular lattice.
Scanning tunneling microscopy/electro-luminescence of III-V and II-VI semiconductors
Authors: Rogers C T. , Gregory S. , Clausen E. M.
Published: June 2020

Scanning tunneling microscopy has proven to be an enormously useful technique for probing the atomic scale electronic structure of clean semiconductor surfaces. In particular, application of STM current-voltage spectroscopy over the last several years has begun to yield detailed information about the energies and spatial locations of electronic bonds at surfaces. Recent work by Kaiser and Bell shows that STM can also be used to elucidate the nature of electronic transport across interfaces buried tens of nanometers beneth the surface. We are attempting to extend the STM current-voltage technique, which has been so successful at addressing near surface electronic properties, to allow the study of the more general class of opto-electronic properties near semiconductor surfaces: We have constructed a novel Scanning Tunneling Microscope/Electro-luminescence apparatus. Our instrument combines a high speed STM with a stationary tunnel tip/collection optics assembly and a standard spectrometer and photodetector. The system allows us to study the spectral composition and intensity of the light generated by various inelastic processes during electron tunneling.
Electron diffraction analysis using a personal computer
Authors: Sutliff J. A. , Notis M. R.
Published: June 2020

The analysis of electron diffraction patterns (EDPs) by manual calculation is difficult in two important cases. The first is when there are many phases that must be included in the search for a pattern’s solution. The second is when, due to the structure of the phases being considered, many solutions for a pattern are possible. In these cases, it is very time consuming to ensure that all possible solutions are found and that the best solution is chosen. A computer can provide tremendous help for the EDP analyst in these situations. Through its ability to make rapid calculations and display data graphically, a computer can relieve the analyst of much of the work involved in a thorough electron diffraction analysis.

In analyzing EDPs a standard procedure is adopted. The analyst first assembles a data base of phases that could be present in the sample being studied. Tables of interplanar spacings and interplanar angles are calculated from crystal structure data on each phase. The positions of spots on experimental patterns are then recorded and radii from the transmitted beam spot to diffracted beams’ spots are measured. Ratios of radii and angles between radii are tabulated.
Comparison of freeze-fractured yeast replicas using conventional TEM and low-voltage field-emission SEM
Authors: Wergin William P. , Erbe Eric F. , Reilly Terrence W.
Published: June 2020

Although the first commercial scanning electron microscope (SEM) was introduced in 1965, the limited resolution and the lack of preparation techniques initially confined biological observations to relatively low magnification images showing anatomical surface features of samples that withstood the artifacts associated with air drying. As the design of instrumentation improved and the techniques for specimen preparation developed, the SEM allowed biologists to gain additional insights not only on the external features of samples but on the internal structure of tissues as well. By 1985, the resolution of the conventional SEM had reached 3 - 5 nm; however most biological samples still required a conductive coating of 20 - 30 nm that prevented investigators from approaching the level of information that was available with various TEM techniques. Recently, a new SEM design combined a condenser-objective lens system with a field emission electron source.
Development of imaging plate for a TEM and its characteristics
Authors: Mori N. , Oikawa T. , Harada Y. , Miyahara J. , Matsuo T.
Published: June 2020

The Imaging Plate (IP) is a new type imaging device, which was developed for diagnostic x ray imaging. We have reported that usage of the IP for a TEM has many merits; those are high sensitivity, wide dynamic range, and good linearity. However in the previous report the reading system was prototype drum-type-scanner, and IP was also experimentally made, which phosphor layer was 50μm thick with no protective layer. So special care was needed to handle them, and they were used only to make sure the basic characteristics. In this article we report the result of newly developed reading, printing system and high resolution IP for practical use. We mainly discuss the characteristics of the IP here. (Precise performance concerned with the reader and other system are reported in the other article.)

Fig.1 shows the schematic cross section of the IP. The IP consists of three parts; protective layer, phosphor layer and support.
Development of 350-KV holography electron microscope equipped with magnetic type field-emission electron gun
Authors: Endo J. , Kawasaki T. , Masuda T. , Tonomura A.
Published: June 2020

A field-emission electron gun is one of the most epoch-making technologies in an electron microscopic world. In a transmission electron microscope, a high brightness of this beam has been effectively employed for electron-holographic measurements, though the value is not still high enough. Development of a higher brightness beam will promise to open up unattained application possibilities of electron holography such as high resolution and high sensitivity interferometry.

We developed the field emission electron microscope for electron holographic applications. Special attentions were paid for high brightness, large beam current and easy operation. Figure 1 is a schematic diagram of the electron gun. In order not to deteriorate the original high-brightness feature of the beam by the aberrations in the gun and the condenser lenses, a magnetic lens was installed between the tip and the extraction anode so that the total aberration effect might be minimized. Field emitted electron beam is converged by the magnetic and the electrostatic lenses, and accelerated in a ten-stage accelerator which is made of porcelain.
A direct measurement of diffusion jump frequency in amorphous materials using VTR-high resolution electron microscopy
Authors: Iijima Sumio
Published: June 2020

Intensity fluctuation in HREM granular images of amorphous thin films such as spattered C and Si films has long been noticed among electron microscopists. The granular images are continuously moving as if they were a bunch of living worms. The origin of the fluctuations is believed to be caused by a charging up effect on the film surface. The present paper introduces for this first time the phenomena using a TV image recording system.

An amorphous oxide thin film used in the present experiment was formed by decomposing a portion of a Tl2Ba2CaCu2O8 superconductor oxide crystal under electron beam irradiation. The structure of the film may be a random network built up by metal-oxygen polyhedra. The HREM images were recorded at a direct magnification 1.2 × 106 times on a real-time TV camera (Getan 622) attached on an electron microscope (ABT-002B, 200keV, Cs 0.4mm, resolution 0.2nm).
A confocal laser scanning microscope for fluorescence and reflection at video rates
Authors: Houpt P.M. , Draaijer A.
Published: June 2020

In confocal microscopy, the object is scanned by the coinciding focal points (confocal) of a point light source and a point detector both focused on a certain plane in the object. Only light coming from the focal point is detected and, even more important, out-of-focus light is rejected.

This makes it possible to slice up optically the ‘volume of interest’ in the object by moving it axially while scanning the focused point light source (X-Y) laterally. The successive confocal sections can be stored in a computer and used to reconstruct the object in a 3D image display.

The instrument described is able to scan the object laterally with an Ar ion laser (488 nm) at video rates. The image of one confocal section of an object can be displayed within 40 milliseconds (1000 х 1000 pixels). The time to record the total information within the ‘volume of interest’ normally depends on the number of slices needed to cover it, but rarely exceeds a few seconds.
Tandem scanning confocal light microscopy as compared with x-ray diffraction for characterizing the behavior of clays in fluid-saturated petroleum reservoir rock
Authors: Stuart C.J. , Viani B.E. , Walker J. , Levesque T.H.
Published: June 2020

Many techniques of imaging used to characterize petroleum reservoir rocks are applied to dehydrated specimens. In order to directly study behavior of fines in reservoir rock at conditions similar to those found in-situ these materials need to be characterized in a fluid saturated state.

Standard light microscopy can be used on wet specimens but depth of field and focus cannot be obtained; by using the Tandem Scanning Confocal Microscope (TSM) images can be produced from thin focused layers with high contrast and resolution. Optical sectioning and extended focus images are then produced with the microscope. The TSM uses reflected light, bulk specimens, and wet samples as opposed to thin section analysis used in standard light microscopy. The TSM also has additional advantages: the high scan speed, the ability to use a variety of light sources to produce real color images, and the simple, small size scanning system. The TSM has frame rates in excess of normal TV rates with many more lines of resolution. This is accomplished by incorporating a method of parallel image scanning and detection. The parallel scanning in the TSM is accomplished by means of multiple apertures in a disk which is positioned in the intermediate image plane of the objective lens. Thousands of apertures are distributed in an annulus, so that as the disk is spun, the specimen is illuminated simultaneously by a large number of scanning beams with uniform illumination. The high frame speeds greatly simplify the task of image recording since any of the normally used devices such as photographic cameras, normal or low light TV cameras, VCR or optical disks can be used without modification. Any frame store device compatible with a standard TV camera may be used to digitize TSM images.
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.
Transmission Electron Microscopy (TEM) of highly dispersed Pt on γ-Al2O3
Authors: Plummer H. K. , Otto K.
Published: June 2020

Methane oxidation was found to be structure sensitive over Pt supported on γ-Al2O3. A method was sought to corroborate the chemical structure of dispersed and particulate Pt, determined indirectly by oxidation studies, with a physical structure i.e., Pt particle geometry and size. TEM allows Pt particles on γ-Al2O3 to be seen and measured, however in the presence of 10 to 50 nm γ-Al2O3 particles a lack of contrast limits detection to ⋍ 2nm. EDS x-ray analysis can only identify Pt particles ≥ 7nm in the TEM.A previous study, using HF dissolution to remove γ-Al2O3, soluble Pt or PtO2, had shown a correlation between non-soluble Pt particle size and temperature pretreatment in oxidizing and reducing conditions. The objective here is to measure, without HF dissolution, Pt particles on γ-Al2O3 at low concentrations, after thermal treatment in oxygen or hydrogen and correlate these observations with methane oxidation kinetics.
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.
Omega-related phases in a Ti-Al-Nb alloy
Authors: Bendersky Leonid A. , Boettinger William J.
Published: June 2020

Study of phase equilibria in the Ti-Al-Nb system is often complicated by the possibility of rapid ordering reactions of a chemical or displacive type during cooling from high temperatures. In the present study we have investigated the decomposition of the high temperature B2 phase of composition Ti-37.5at%Al-12.5at%Nb into “omega-type” phases during either cooling or low temperature annealing. Formation of an “omega-type” phase from the high temperature B2 matrix of composition Ti-27.8at%Al-11.7at%Nb was observed previously by [1]. If the “omega-type” phase forms by pure displacive ordering, i.e. by collapse of (111) plane pairs of the B2 phase, the resulting structure will be as shown in Fig. 1a (termed ω′). The chemical order of the ω′ phase is directly inherited from the B2 structure. The space group of the ω′ phase is P3ml (#164). The same authors suggested a secondary transformation of the ω′ phase to another omega-type phase with the B82 structure shown in Fig.1b The space group for the B82 structure is hexagonal P63/mmc (#194) with reflection conditions such that the 1100 reflection is present, but the 0001 (or 000ℓ,ℓ=2n+l) is absent.
An electron diffraction study of the wholly aromatic copolyester Xydar
Authors: Li L. S. , Geil P. H.
Published: June 2020

It was shown by electron diffraction that p-hydroxybenzoate/m-hydroxybenzoate copolymer (95/5) possesses a three dimensional order with two orthorhombic crystalline modifications coexisting at room temperature. During heating the orthorhombic modifications I and II transform to hexagonal lateral packing of the chains at 290°C and 350°C respectively. The electron diffraction pattern obtained at 350°C can be indexed by a hexagonal unit cell with parameters a = b = 10.74Å, c = 12.34Å, γ = 120°. The observed d-spacings of the reflections and indices are listed in Table I. When the sample was heated to 430°C - 470°C only one broad and diffuse reflection was observed on the equator, while the meridional reflections are still sharp. In order to find out if the high temperature structure of the p- and m-hydroxybenzoate copolymer (95/5) is a general feature for other wholly aromatic copolyesters we have studied a high temperature and high performance resin Xydar SRT 300, which is made from a 1:2:1 molar ratio of following monomers: p, p'-biphenol, p-hydroxybenzoic acid and terephthalic acid.
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.