bluuebunny/crossref_metadata_2025_split huggingface dataset:
The use of high-resolution FESEM to study solid-state phase transformations and reactions
Authors: Kotula P. G. , Erickson D. D. , Carter C. B. 
Published: June 2020

High-resolution field-emission-gun scanning electron microscopy (FESEM) has recently emerged as an extremely powerful method for characterizing the micro- or nanostructure of materials. The development of high efficiency backscattered-electron detectors has increased the resolution attainable with backscattered-electrons to almost that attainable with secondary-electrons. This increased resolution allows backscattered-electron imaging to be utilized to study materials once possible only by TEM. In addition to providing quantitative information, such as critical dimensions, SEM is more statistically representative. That is, the amount of material that can be sampled with SEM for a given measurement is many orders of magnitude greater than that with TEM.In the present work, a Hitachi S-900 FESEM (operating at 5kV) equipped with a high-resolution backscattered electron detector, has been used to study the α-Fe2O3enhanced or seeded solid-state phase transformations of sol-gel alumina and solid-state reactions in the NiO/α-Al2O3system. In both cases, a thin-film cross-section approach has been developed to facilitate the investigation. Specifically, the FESEM allows transformed- or reaction-layer thicknesses along interfaces that are millimeters in length to be measured with a resolution of better than 10nm.
Digital image acquisition for the Hitachi S-900 field-emission SEM
Authors: Erlandsen S. L. , Telega P. , Chi E. , Dobson W. , Egelman E. 
Published: June 2020

Users of the Hitachi S-900 field emission SEM attempting to do high resolution topographical studies of cell surfaces (or macromolecular assemblies) and correlative localization of colloidal gold probes are handicapped by imaging conditions related to contamination or radiation damage of the specimen surface since secondary (SE) and backscatter (BS) electron imaging must be done consecutively.We have developed a digitial acquisition system for the S-900 FESEM using an analog/digital conversion board on the VME bus of a Silicon Graphics IRIS, using the conventional and graphics memory for image storage, rather than using a frame grabber with its internal A/D and frame memory. A DT-1492-G board from Data Translation with a 250 kHz throughput was used for the 12-bit A/D circuitry. We collect data at 12-bit resolution, and use the frame buffer memory on the IRIS for separately converting, and then displaying as 8-bit (greyscale, 256 levels) SE and BS electron images.
Microscopy of latex film formation
Authors: Ming Yaqiang 
Published: June 2020

Latex here denotes a stable colloidal dispersion of polymer in solvent. The solvent usually is water. Large tonnages of latices are used in paper coatings, paints, and growing numbers of other waterbased coatings. All these applications require the latices to be film-forming, at least to a degree. Despite past investigations, the mechanisms of film formation are not well understood and are now being studied intensively in several places.Our goal is to understand how a suspension of latex particles in water or other solvent becomes a continuous film, one monolayer or multiple layers deep. Several techniques have been employed: transmission electron microscopy ( TEM ) including replication, freeze-fracture, and microtome sample preparations, small angle neutron scattering ( SANS ); cryogenic scanning electron microscopy ( Cryo-SEM ), and atomic force microscopy ( AFM ). TEM is tedious and requires small thin samples; SANS is expensive, time consuming, and difficult to interpret; AFM is easy to use, but images must be interpreted with caution because artifacts can prevail.
Measuring intermolecular binding forces with the Atomic-Force Microscope: The magnetic jump method
Authors: Hoh J. H. , Hillner P. E. , Hansma P. K. 
Published: June 2020

The atomic-force microscope (AFM) can measure forces between atoms and molecules with a sensitivity of <10−12 N. By coating the AFM tip with specific molecules the types of interactions that can be examined will be greatly extended. Recently tips with biotin attached have been used to probe surfaces coated with avidin or streptavidin, to measure the respective bond strength.We have developed a novel approach to measuring intermolecular forces with the AFM that employs paramagnetic beads coated with one of the molecules to be studied. Beads are incubated with a surface coated with the second molecule, and allowed to form a specific bond. A small magnet glued to an AFM cantilever is then advanced toward the bead until the bond with between the two molecules breaks and the bead “jumps” to the magnet. The deflection of the cantilever provides a direct readout of the interaction force at the “jump,” and thereby a measure of the bond strength.
HREM of interfaces between YBa2Cu3O7 thin films grown on LaGaO3
Authors: Roy T. , Mitchell T. E. 
Published: June 2020

Thin films of superconducting YBa2Cu3O7 have been grown successfully on a number of different substrates by a variety of techniques. Superconducting transition temperatures Tc are as good as the best bulk material. More importantly, critical current densities Jc are higher in the best thin films than in material made by any other technique. Thin films grown on single crystals with the perovskite structure, e.g. SrTiO3, LaAlO3 and LaGaO3, have been particularly successful. In the present paper, HREM has been used to study the interface between YBa2Cu3O7 and the LaGaO3 substrate.Electron beam evaporation of Cu and Y and thermal evaporation of BaF2 onto (001) LaGaO3 single crystal substrates produced an almost amorphous precursor. This was subsequently annealed in wet and dry O2 at 850°C followed by a further anneal in dry O2 at 400°C. Typical values of Jc were better than 107A/cm2 at 7K. Cross-sectional TEM specimens cut parallel to the (110) plane were prepared by the sandwich technique with the final ion-milling being performed at liquid nitrogen temperatures to minimize damage.
Electron Microscopy study of thallium-based superconducting oxides
Authors: Yang D.Y , Hu J.J , Li F.H. 
Published: June 2020

Some Tl-based superconducting oxides are usually not homogeneous in composition, structure and microstructure so that X-ray and neutron diffraction analyses are powerless. This paper reports some results of electron microscopy study on Tl-Sr-Ca-Er-Cu-O and Tl-Ba-Al-Ca-Cu-O superconducting oxides.The samples of nominal compositions TlSr2CaEr0.5Cu3Oy and Tl0.4BaAl0.6Ca3Cu3Oy were prepared by solid reaction. The sintered pellets were crushed into fine fragments and dispersed in CCl4. The suspension was dropped onto microgrids. The specimens were observed with JEM-200CX high resolution electron microscope and H- 9000NA analytical electron microscope.Two phases are identified in TlSr2CaEr0.5CU3Oy by electron diffraction analysis. The lattice parameters are a=b=0.386nm, c=2.92nm(phase 1) and a=b=0.379nm, c=3.54nm(phase 2). The two phases are intergrown as shown in the lattice image taken with electron beam along the direction(Fig.1). In the image with a higher magnification(Fig.2) dark bands correspond to Tl-O layers and bright bands to perovskite blocks and both of them may vary in their spacings.
Modulated structures in Nd2−xCexCuO4
Authors: Li D.J. , Zhang J.P. , Marks L.D. 
Published: June 2020

The recent discovery of an n-type superconductor of general formula Nd2-xCexCuO4 has opened up the possibility that there exists a new family of high temperature superconductors. Initially identified as having a Nd2CuO4-type structure, more recent reports have mentioned a second phase which contains a superstructure. Although the diffraction data presented in both these later papers is very similar, the exact form of the modulation is presented as different. Important questions are which phase is the active superconductor; what is the structural and chemical relationship between the modulated an unmodulated phases and what is the correct interpretation of the modulated unit cell. In addition, it has been suggested that the modulations are due to ordering of oxygen defects, a point which needs to be rigorously tested.Two Nd2-xCexCuO4 compounds were prepared by the identical solid-state reaction, followed by sintering at 1170° C for 12 hours.
On the 2√2 a × 2√2 a supestructure phase
Authors: Reyes-Gasga J. 
Published: June 2020

Recently Reyes-Gasga et. al. have studied the superstructures phases produced by the ordering of vacancies (or oxygen) in the YBa2Cu3Ox, supercondutor compound. In these papers they also discussed briefly a posible interpretation of the diffraction pattern based on a square unit cell with edges 2√2 a × 2√2 a, where a=0.38nm (fig. 1e), and suggested that this pattern might not be due to a pure vacancy ordered structure but should presumably be attributed to a deformation modulated superstructure of a highly oxygen deficient perovskite phase. This diffraction pattern was studied previously in detail and it has been attributed to a number of oxygen vacancy ordered orthorhombic structures with different oxygen content. In this report I shall inform about some experiments concerning with the formation conditions and temperature behavior of the phase that produces this pattern.Heating the YBa2Cu3O7, superconductor compound in situ in the TEM is possible to obtain not only diffuse streaks and superstructure spots unless also new arrays of superstructure spots. Therefore the experimental procedure consists in the in situ heating of this compound in the JEDL 200C TEM using a heating holder. It is well known that the exact temperature value in this kind of experiments is hard to specify and here only an average temperature range is reported.
Structural studies of small amorphous volumes by electron diffraction
Authors: Moine Pierre 
Published: June 2020

Qualitatively, amorphous structures can be easily revealed and differentiated from crystalline phases by their Transmission Electron Microscopy (TEM) images and their diffraction patterns (fig.1 and 2) but, for quantitative structural information, electron diffraction pattern intensity analyses are necessary. The parameters describing the structure of an amorphous specimen have been introduced in the context of scattering experiments which have been, so far, the most used techniques to obtain structural information in the form of statistical averages. When only small amorphous volumes (< 1/μm in size or thickness) are available, the much higher scattering of electrons (compared to neutrons or x rays) makes, despite its drawbacks, electron diffraction extremely valuable and often the only feasible technique.In a diffraction experiment, the intensity IN (Q) of a radiation, elastically scattered by N atoms of a sample, is measured and related to the atomic structure, using the fundamental relation (Born approximation) : IN(Q) = |FT[U(r)]|.
Multislice calculations for quasi-periodic and non-periodic objects
Authors: Herrera R. , Gómez A. 
Published: June 2020

Computer simulations of electron diffraction patterns and images are an essential step in the process of structure and/or defect elucidation. So far most programs are designed to deal specifically with crystals, requiring frequently the space group as imput parameter. In such programs the deviations from perfect periodicity are dealt with by means of “periodic continuation”.However, for many applications involving amorphous materials, quasiperiodic materials or simply crystals with defects (including finite shape effects) it is convenient to have an algorithm capable of handling non-periodicity. Our program “HeGo” is an implementation of the well known multislice equations in which no periodicity assumption is made whatsoever. The salient features of our implementation are: 1) We made Gaussian fits to the atomic scattering factors for electrons covering the whole periodic table and the ranges [0-2]Å−1 and [2-6]Å−1.
Crystallisation kinetics and microstructural evolution of Ni24Zr76 amorphous alloy
Authors: Ghosh G. , Chen F.R. 
Published: June 2020

Apart from technological applications, scientifically amorphous —> crystal transformation is very important in understanding the atomic processes involved. For in-depth understanding of the crystallisation process, it is necessary to employ a combination of a number of experimental techniques. In this investigation, the details of the crystallisation of Ni24Zr76 amorphous alloy has been studied by differential scanning calorimtry (DSC), transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). This amorphous alloy undergoes eutectic crystallisation i.e., it transforms to (α-Zr) + NiZr2 crystals. It is our interest to study the kinetics of the crystallisation as well as the different steps involved in the evolution of equilibrium microstructure.Ribbons of 2-3 mm wide and 25-30 μm thick were produced by melt-spinning technique. Dynamic as well as isothermal crystallisation were studied in a Du-pont DSC 910 cell coupled with computer controlled thermal analyser (TA9900) having system control and data acquisition capabilities.
Long-period modulated superstructures in Pd-12.5 at.%Ce and Pd-15 at.%Ce alloys
Authors: Kuwano Noriyuki , Itakura Masaru , Oki Kensuke 
Published: June 2020

Pd-Ce alloys exhibit various anomalies in physical properties due to mixed valences of Ce, and the anomalies are thought to be strongly related with the crystal structures. Since Pd and Ce are both heavy elements, relative magnitudes of (fcc-fpd) are so small compared with <f> that superlattice reflections, even if any, sometimes cannot be detected in conventional x-ray powder patterns, where fee and fpd are atomic scattering factors of Ce and Pd, and <f> the mean value in the crystal. However, superlattices in Pd-Ce alloys can be analyzed by electron microscopy, thanks to the high detectability of electron diffraction. In this work, we investigated modulated superstructures in alloys with 12.5 and 15.0 at.%Ce.Ingots of Pd-Ce alloys were prepared in an arc furnace under atmosphere of ultra high purity argon. The disc specimens cut out from the ingots were heat-treated in vacuum and electrothinned to electron transparency by a jet method.
Observation of discommensuration arrays in transition metal substituted TaTe4
Authors: Bennett J.C. , Boswell F.W. , Corbett J.M. , Prodan A. , Kohara S. 
Published: June 2020

TaTe4 is a quasi-one-dimensional crystal in which chains of Ta atoms along the c-axis are centered within extended cages of Te atoms in square antiprismatic coordination. The subcell structure is tetragonal with axes (axaxc). At room temperature, the crystal is modulated by a commensurate charge-density wave (CDW) which gives rise to a supercell with axes (2ax2ax3c). Transition metal doping of TaTe4 causes the modulation to become incommensurate.A series of mixed crystals (Ta1−xMx)Te with M = Nb, Ti or Zr have been examined using electron diffraction and electron microscopy. In each case, the modulation periodicity (as measured from the positions of the satellites in electron diffraction patterns) remains commensurate until a threshold concentration ( x ∼ .3 for Nb, ∼ .1 for Ti and Zr) is reached and then jumps discontinuously to an incommensurate value. Upon further substitution by Nb, the modulation periodicity varies with x, approaching that of NbTe as x approaches 1.0.
Toughening ceramics and Electron Microscopy
Authors: Hannink Richard H.J. 
Published: June 2020

In the last one and a half decades great progress has been made in the development and understanding of tough ceramics. The principal advance has been in the micro- structural tailoring of ceramic systems and in this area electron microscopy has played a major role.Increased toughness in ceramics is most readily achieved by mechanisms which reduce the effective driving force on a crack. Microstructural mechanisms which promote such reductions are said to impart “crack tip shielding” and ultimately R-curve behaviour. These mechanisms can generally be divided into two broad classes: process zone shielding and bridging or contact zone shielding. Phenomena which contribute to process zone shielding include transformation and micro-crack toughening while bridging or contact zone shielding includes fibre and whisker reinforcement. In reality however, a number of mechanisms will be operating within the same material.This presentation will describe the development and microstructural aspects of, predominantly, process zone shielding mechanisms. The salient microstructural features for the successful application of fibre reinforced ceramics will also be described.
Study of surface plasmon excitation of nanometer size metallic particles in the STEM
Authors: Ouyang F. , Batson P. E. , Isaacson M. 
Published: June 2020

The study of small particles or microclusters has been very active in recent years. When the particle size becomes smaller, its electronic properties deviate from those of bulk material and become size dependent. This phenomenon is referred to as the quantum size effect. In order to study the electronic states of small particles, the excitation energies of the surface plasmon (SP) have been measured by optical absorption spectroscopy and by broad beam angular resolved electron energy loss spectroscopy (EELS). Changes in the SP excitation energy were observed when the particle diameters were smaller than 40 Å.With the high spatial resolution of the scanning transmission electron microscope (STEM), we hope to overcome the difficulties associated with effects of particle size distribution encountered in previous broad beam measurements. For particles with diameters ranging from 100 Å to 200 Å, the SP energy was found decreasing with decrease of the particle size.
AEM-investigations disclose the structure of metal-graphite reagents
Authors: Fürstner A. , Hofer F. , Weidmann H. 
Published: June 2020

Compared to the great utility due to the high reactivity of metal-graphite compounds, found to be useful catalysts as well as most favourable reducing agents little was hitherto known of their structural features. The conflicting reports, viewing these reagents as products of intercalation on the one hand or merely as graphite supported finely dispersed metals on the other were seemingly resulting from factors such as the mode of preparation, work-up procedure, and last not least the limited reliability of a single analytical technique.With the reduction of metal halides by potassium-graphite laminate (C8K) in THF a generally applicable method was at hand which readily and reproducibly allowed the formation of various kinds of metal-graphite combinations suitable for a comprehensive study by analytical electron microscopy in combination with X-ray diffraction (XRD) and photoelectron spectroscopy (XPS).
TEM-nanometer-area electron diffraction of interfaces in semiconductor superlattices
Authors: Tanaka Nobuo , Mihama Kazuhiro , Kakibayashi Hiroshi , Ito Kazuhiro 
Published: June 2020

Recent progress of transmission electron microscope(TEM) enables us to perform electron diffraction from nm-sized areas(nano-diffraction) with a good correspondence with HREM. Nano-diffraction is useful for obtaining local structural information. One of the present authors (NT) applied the method to interfaces of GaAs/AlGaAs superlattices for detection of compositional variation of aluminum(Al) and to nm-sized γ-iron crystallites in MgO for analysis of the strain. Although nano-diffraction has been performed successfully in STEM instruments by Cowley and others, the method in TEM has an advantage in a good compatibility with the structure-imaging method and the established bright and dark-field(BF & DF) imaging methods. In the present paper we report for the first time the detection of lattice strain around interfaces of InP/InGaP strained superlattices as well as results of GaAs/InGaAs, GaAs/AlGaAs and Ge/Si superlattices by using the TEM nano-diffraction method.The nano-diffraction was performed with 200 kV transmission electron microscopes of Cs = 1.2 mm(JEM-2000FX) and Cs = 0.5mm(JEM-2010L Before focusing an election probe, HREM and DF images of the interfaces were taken in the [100] zone axis at 100-400 k in direct magnification.
Misfit accommodation in epitaxial Ge films on Si
Authors: Chisholm M. F. , Pennycook S. J. 
Published: June 2020

Electron microscopy is well suited for the study of the initial stages of misfit dislocation nucleation and of dislocation reactions. High-resolution Z-contrast imaging has the added advantages of producing intuitively interpretable images with chemical sensitivity. This technique has been used to study film formation and misfit accommodation in epitaxial Ge films grown on Si. The epitaxial Ge films studied herein were produced by steam oxidation of Ge-implanted (001) Si. The implanted Ge is rejected by the growing SiO2 layer and has no time to diffuse into the Si. The partitioned Ge forms a distinct strained epitaxial layer on Si. With this growth process the Ge films are constrained to grow layer-by-layer instead of the normally observed island mode. The growth morphology in turn governs the interfacial misfit dislocation nucleation, location, and character.Figure 1 shows a cross-section view of a dislocation-free 5-nm thick Ge film on (001)Si produced by the oxidation of a Ge (2×l016 ions/cm2) implanted Si wafer. This is three to six times thicker than the observed critical thickness for Ge films grown on Si by more conventional growth processes. Ge normally grows as islands on Si and, after the equivalent of six monolayers of Ge is deposited, dislocations are introduced at the island parameters to relieve the misfit strains.
Growth of hematite on (0001) and {1102} sapphire substrates
Authors: Tietz Lisa A. , Summerfelt Scott R. , Barry Carter C. 
Published: June 2020

Defects in thin films are often introduced at the substrate-film interface during the early stages of growth. The interface structures of semiconductor heterojunctions have been extensively studied because of the electrical activity of defects in these materials. Much less attention has been paid to the structure of oxide-oxide heterojunctions. In this study, the structures of the interfaces formed between hematite (α-Fe2O3) and two orientations of sapphire (α-Al2O3) are examined in relationship to the defects introduced into the hematite film. In such heterojunctions, the oxygen sublattice is expected to have a strong influence on the epitaxy; however, defects which involve only the cation sublattice may be introduced at the interface with little increase in interface energy.Oxide heterojunctions were produced by depositing small quantities of hematite directly onto electrontransparent sapphire substrates using low-pressure chemical vapor deposition. Prior to deposition, the ionthinned substrates were chemically cleaned and annealed at 1400°C to give “clean”, crystalline surfaces. Hematite was formed by the reaction of FeCl3 vapor with water vapor at 1150°C and 1-2 Torr. The growth of the hematite and the interface structures formed on (0001) and {102} substrates have been studied by bright-field, strong- and weak-beam dark-field imaging techniques.