bluuebunny/crossref_metadata_2025_split huggingface dataset:
Imaging magnetic microstructure with SEMPA
Authors: Kelley M. H. , Unguris J. , Celotta R. J. , Pierce D. T. 
Published: June 2020

By measuring the spin polarization of secondary electrons generated in a scanning electron microscope, scanning electron microscopy with polarization analysis (SEMPA) can directly image the magnitude and direction of a material’s magnetization. Because the escape depth of the secondaries is only on the order of 1 nm, SEMPA is especially well-suited for investigating the magnetization of ultra-thin films and surfaces. We have exploited this feature of SEMPA to study the magnetic microstrcture and magnetic coupling in ferromagnetic multilayers where the layers may only be a few atomic layers thick. For example, we have measured the magnetic coupling in Fe/Cr/Fe(100) and Fe/Ag/Fe(100) trilayers and have found that the coupling oscillates between ferromagnetic and antiferromagnetic as a function of the Cr or Ag spacer thickness.The SEMPA apparatus has been described in detail elsewhere. The sample consisted of a magnetic sandwich structure with a wedge-shaped interlayer as shown in Fig. 1.
Digital processing of high-resolution electron holograms
Authors: Völkl E. , Allard L. F. 
Published: June 2020

Electron Holography has been shown to be an useful tool in high resolution imaging for obtaining more information from the electron image than is possible in conventional microscopy. In our laboratory we presently record our images on photographic material, and then digitize them by using a 4096 pixel line scan by EKTRON. Digitizing photographic material and correcting for its nonlinearities is a time consuming process which will soon be alleviated by the installation of the GATAN retractable slow-scan CCD-camera. Both camera and microscope will be operated from a Macintosh computer using the software “Digital Micrograph®” and “Advanced Acquisition®”, the first of which is used already for image processing of our negatives.From an electron hologram, e.g. an hologram of a PMN ferroelectric material (FIG. 1a), the diffraction pattern of the object (FIG. 1b) can be obtained and evaluated from areas as small as one unit cell.
Origin of the defect structures in oxygen-implanted silicon-on-insulator material
Authors: Venables D. , Krause S.J. , Lee J.D. , Park J.C. , Roitman P. 
Published: June 2020

Silicon-on-insulator material fabricated by high-dose oxygen implantation (known as SIMOX) has been used for high speed and radiation hard devices and is under consideration for use in low power applications. However, a continuing problem has been crystalline defects in the top silicon layer. SIMOX is fabricated by two distinct methods: a single oxygen implant to a dose of 1.8×l018 cm-2 followed by a high-temperature anneal (≥1300°C, 4-6 hr) or by multiple lower dose implants (∼6×l017 cm-2) with high-temperature anneals after each implant. To date, there has been no systematic comparison of the defect structures produced by these two fabrication methods. Therefore, we have compared the defect structure and densities in multiple vs. single implant wafers. In this paper we describe the origin and characteristics of the defect structures in SIMOX and show how their densities are controlled by the processing method and conditions.Silicon (100) wafers were implanted in a high current implanter at ∼620°C to doses of 1.8×l018 or 0.6/0.6/0.6×l018 cm-2 and annealed at 1325°C, 4 hr in 0.5% or 5% O2 in Ar. Cross-section (XTEM) and plan-view (PTEM) samples were studied with bright field and weak beam dark field techniques in a transmission electron microscope operating at 200 keV.
Characterization of NiO thin films on α-Al2O3 before and after heat treatment
Authors: Kotula Paul G. , Barry Carter C. 
Published: June 2020

The NiO-α-Al2O3 system is of interest as a model system for the study of phase boundaries and reaction kinetics in oxide ceramics. Such a system is of new importance when one of the constituents is a thin film because the reaction kinetics and its dependence on film microstructure is not well understood. Additionally, solid-state reactions between a thin film and single-crystal substrate can be used to produce buffer layers for heterojunctions.In the present study, thin films of NiO have been grown on single-crystal α-Al2O3 substrates by pulsed-laser ablation (PLA). The PLA system used a KrF (248nm) excimer laser operating at 350 mJ per pulse with a pulse repetition rate of 10 Hz. The laser beam was focused to a spot 1×2mm on the surface of rotating NiO pellet. Films were grown at nominal substrate temperatures of 750°C and oxygen pressures of about 10 mTorr. Films were grown both on bulk substrates for which 6000 laser pulses was used to produce 1000Å films and electron-transparent substrates for which 500 laser pulses was used to produce 80Å films.
Electron microscopy of natural and epitaxial diamond
Authors: Posthill J.B. , George T. , Malta D.P. , Humphreys T.P. , Rudder R.A. , Hudson G.C. , Thomas R.E. , Markunas R.J. 
Published: June 2020

Semiconducting diamond films have the potential for use as a material in which to build active electronic devices capable of operating at high temperatures or in high radiation environments. Ultimately, it is preferable to use low-defect-density single crystal diamond for device fabrication. We have previously investigated polycrystalline diamond films with transmission electron microscopy (TEM) and scanning electron microscopy (SEM)e.g.1 and homoepitaxial films with SEM-based techniquese.g.2. This contribution describes some of our most recent observations of the microstructure of natural diamond single crystals and homoepitaxial diamond thin films using TEM.We are developing techniques to thin diamonds to electron transparency in the region of interest; particularly as diamond is difficult to mechanically thin. One simple (but time consuming) approach for the fabrication of plan-view diamond TEM samples is to thin only by ion milling. Figs. 1 and 2 show TEM micrographs taken from a (100) natural type IIb (semiconducting) diamond crystal and a (100) natural type la diamond that have been ion milled to electron transparency.
Advantages of FE-TEM for convergent-beam electron diffraction
Authors: Kaneyama T. , Tomita T. , Ishida Y. , Kersker M. 
Published: June 2020

Many electron microscopes equipped with a field-emission gun (FE-TEMs) are now used for the purpose of improving the spatial and the energy resolution in energy dispersive x-ray spectroscopy and electron energy loss spectroscopy. For the convergent-beam electron diffraction techniques, FE-TEMs have greater advantages than conventional electron microscopes with a thermal LaB cathode. We discussed these advantages using JEM2010F and JEM2010, which have equivalent specifications except for the electron source and the condenser lens system.High spatial resolutionThe brightness of an FE-gun (∽ 5 × 108A cm-2 sr-1) is about 100 times that a conventional LaB6 cathode. The gun can obtain enough current for taking CBED patterns in an exposure time of a few seconds even with an electron probe less than 1 nm in diameter (FIG. 1). Steep wedge shapes and rapid bends within the illuminated area deteriorate the accuracy of quantitative CBED analysis. Improvement of the spatial resolution by a small probe reduces these inevitable averaging effects.
Quantitative analysis of convergent-beam electron diffraction patterns
Authors: Lin Xiwei , Zhu Jing , Dravid Vinayak P. 
Published: June 2020

In recent years, there have been great advances in electron crystallography by quantitative convergent beam electron diffraction (QCBED). From the distribution of dynamical diffraction intensities, QCBED can determine the Fourier components of the crystal potential accurately and completely, enabling direct measurement of phases of crystal structure factors. Given the combination of small probe size in CBED and the high accuracy of the quantitative analysis (e.g. determination of bonding charge distributions in covalent crystals), QCBED is a powerful experimental methods for detection of a small change in the crystal potential of a few nanometer structure (e.g. near grain boundaries/defects).More recently, interest has shifted towards the possibility of the automated matching of experimental and theoretical CBED patterns by optimization for speed and even higher accuracy. In this work, the combined variable matrix algorithm is used to automate the least-squares refinement. The program was tested by calculated intensities randomized with Gaussian distribution as experimental data.
A photoelectron microscope study of surfaces
Authors: Engel W. , Kordesch M. , Bradshaw A. M. , Zeitler E. 
Published: June 2020

Photoelectron microscopy is as old as electron microscopy itself. Electrons liberated from the object surface by photons are utilized to form an image that is a map of the object's emissivity. This physical property is a function of many parameters, some depending on the physical features of the objects and others on the conditions of the instrument rendering the image.The electron-optical situation is tricky, since the lateral resolution increases with the electric field strength at the object's surface. This, in turn, leads to small distances between the electrodes, restricting the photon flux that should be high for the sake of resolution.The electron-optical development came to fruition in the sixties. Figure 1a shows a typical photoelectron image of a polycrystalline tantalum sample irradiated by the UV light of a high-pressure mercury lamp.
PHAX-SCAN: Functional integration of a Scanning Electron Microscope and an energy-dispersive x-ray analyser
Authors: Peeters Marc H. , Otten Max T. 
Published: June 2020

Over the past decades, the combination of energy-dispersive analysis of X-rays and scanning electron microscopy has proved to be a powerful tool for fast and reliable elemental characterization of a large variety of specimens. The technique has evolved rapidly from a purely qualitative characterization method to a reliable quantitative way of analysis. In the last 5 years, an increasing need for automation is observed, whereby energy-dispersive analysers control the beam and stage movement of the scanning electron microscope in order to collect digital X-ray images and perform unattended point analysis over multiple locations.The Philips High-speed Analysis of X-rays system (PHAX-Scan) makes use of the high performance dual-processor structure of the EDAX PV9900 analyser and the databus structure of the Philips series 500 scanning electron microscope to provide a highly automated, user-friendly and extremely fast microanalysis system. The software that runs on the hardware described above was specifically designed to provide the ultimate attainable speed on the system.
EM-002B computer control development
Authors: Chang M. , Kamewari T. 
Published: June 2020

The EM-002B is an ultrahigh resolution TEM with unique TEM-probe analytical capabilities. In its standard configuration, one set of lens current parameters along with 20 specimen stage XY coordinate sets can be stored in a non-volatile memory. The first stage in implementing computer control of the microscope involves extending the ability to store and recall multiple lens parameter and stage position sets.This has been accomplished by adding a standard RS-232C communications channel to the EM-002B and developing a state-of-the-art window software package to run on an IBM AT PS2 or compatible computer. This package accepts the commands from a mouse input and allows storage and automatic setting of lens current and stage position sets. After transfer to the computer parameter, sets are assigned a file name and may be stored on a floppy or hard disk. These files are easily modified and transferred via the communications channel to the EM-002B.
Development of 200kV ultrahigh-resolution analytical electron microscope
Authors: Kaneyama T. , Naruse M. , Ishida Y. , Kersker M. 
Published: June 2020

In the field of materials science, the importance of the ultrahigh resolution analytical electron microscope (UHRAEM) is increasing. A new UHRAEM which provides a resolution of better than 0.2 nm and allows analysis of a few nm areas has been developed. [Fig. 1 shows the external view] The followings are some characteristic features of the UHRAEM.Objective lens (OL)Two types of OL polepieces (URP for ±10' specimen tilt and ARP for ±30' tilt) have been developed. The optical constants shown in the table on the next page are figures calculated by the finite element method. However, Cs was experimentally confirmed by two methods (namely, Beam Tilt method and Krivanek method) as 0.45 ∼ 0.50 mm for URP and as 0.9 ∼ 1.0 mm for ARP, respectively. Fig. 2 shows an optical diffractogram obtained from a micrograph of amorphous carbon with URP under the Scherzer defocus condition. It demonstrates a resolution of 0.19 nm and a Cs smaller than 0.5 mm.
Electron-beam damage and the 3-D structure of negatively stained ompF porin
Authors: Dorset Douglas L. , Massalskl Andrew K. 
Published: June 2020

A 20Å resolution 3D electron microscopic structure analysis of negatively-stained crystalline sheets of ompF porin was instrumental in demonstrating the existence of a physical water-filled pore which spans the membrane bilayer. It also suggested that the three separate channels in a trimer actually converge near the interface of two stacked membranes to form a single cylindrical outlet. Immediately this structure was criticized in terms of its probable transport properties.An additional inconsistency was found with the 3D structure of the genetically related phoE porin, which revealed no such convergence of the negative stain-filled pores. The possible role of radiation damage in this discrepancy will be shown.Electron micrographs of the small hexagonal porin sheets (a=79Å, plane group p3) stained with 2% uranyl acetate had been photographed with “normal” beam doses and the images of specimens tilted ±45° were digitized so that the phases and amplitudes of the Fourier transforms could be used to construct a 3D representation of the structure.
An epi-fluorescent spinning-disk confocal microscope
Authors: Cheng P. C. , Chen V. K.-H. , Kim H. G. , Pearson R. E. 
Published: June 2020

The confocal microscope offers a number of advantages over the conventional light microscope in improvement in spatial resolution optical sectioning by rejecting out-of-focus signals. The applications of confocal microscopy in biology will be greatly expanded if real-time imaging can be achieved.A real-time epi-fluorescent confocal microscope based on a spinning disk design has been constructed at our laboratory (Fig. 1). Different from Petran's tandem scanning configuration, but similar to Kino's, our microscope has both the illumination and the detection rays sharing the same pinholes (Fig. 2). As a result, the optical arrangement is simpler and much easier to align. The spinning “Nipkow disk” used in our microscope has 194,400 pinholes (25х25μm) arranged in 90 interleaved spirals (Fig. 3). The minimum and maximum spacing between adjacent pinholes are 90μm and 207μm respectively. When the disk is spun at 1000rpm, we achieved a frame rate of 1500f/sec with 1440 lines/frame. The disk is spun by a simple mechanism mounted on a X-Y linear slide (Fig. 4). The disk was fabricated by lithography on a 4 inch glass substrate (Fig. 5). At the present time, a 5W Argon ion laser or a 200W high pressure mercury arc lamp is used as the light source. By a set of mechanical slides, the microscope operates not only in epi-fluorescent and reflective confocal modes, but also in conventional epi-fluorescent and transmitted modes (i.e. bright field, phase contrast etc.). The low intensity confocal fluorescent image is amplified by the use of a TV-coupled second generation image intensifier. Then, the TV signal from the video camera is digitized and processed by a frame store interfaced to a 80386 microcomputer. In addition, the fine focus control of the microscope is driven by a stepping motor via the same computer.
3-D image analysis of serial focal sections from confocal scanning laser microscopy
Authors: Russ J. Christian , Russ John C. 
Published: June 2020

The Confocal Scanning Laser Microscope (CSLM) is used in two quite different imaging modes: reflection and transmission. Most instruments maintain their confocal optics only when operated in reflection mode, in which light reflected or emitted from points in the sample or on its surface, lying in the focal plane of the microscope, is detected to form an image. Point elevations can be measured by scanning through a range of focal distances. Recording in memory the maximum brightness at each pixel forms an image containing the “in-focus” information for the entire irregular surface or object (Figure 1). These are powerful capabilities and account for much of the current use of confocal microscopes for metrology of rough surfaces, and for use with fluorescent dyes.True transmission confocal imaging can be achieved by passing the light from the source through the specimen to a mirror, reflecting it back through the specimen again (maintaining the focus in the same plane), and thence to the detector. This is shown schematically in Figure 2. This is only possible with monochromatic light, because of sample-induced chromatic aberrations.
Ordered Structures in Gd2CuO4 and isostructural cuprates
Authors: Mitchell T. E. , Roy T. , Fisk Z. , Cheong S-W , Thompson J. D. , Cheng T. T. 
Published: June 2020

INTRODUCTION.The lanthanide cuprates Ln2CuO4 (Ln = Pr, Nd, Eu, Gd, etc.), have a a triple perovskite unit cell.The structure is tetragonal, 14/mmm, a ∼ 0.39nm, c ∼1.19nm, with layered nets of [CuO4] squares. By contrast, the structure of La2CuO4, which also has a triple perovskite cell, contains layers of [CuO6] octahedra. La2CuO4 becomes superconducting by doping with SrO while Ln2CuO4 becomes superconducting by doping with CeO2 for Ln = Pr, Nd and Sm. Both La2CuO4 and YBa2Cu3O7 have a tetragonal-to-orthorhombic transformation while Ln2CuO4 remains tetragonal.The present study was undertaken to investigate microstructures in the lanthanide cuprates.EXPERIMENTAL. The Ln2CuO4 single crystals were grown as plates from a PbO or CuO flux. Specimens for TEM were prepared by ion milling using a liquid nitrogen specimen cooler. High resolution electron microscopy (HREM) was performed on either a Philips CM3OST at 300kV or a JEM4000FX at 400kV.
Scanning Electron Microscope Study of Superconducting Transport in a YBa2Cu3O7-δ thin film
Authors: Farrow R. C. , Monroe Don , Brocklesby W. S. , Hong M. 
Published: June 2020

By combining electron probing with current biasing at low temperatures a map of the transport characteristics of a mixed phase thin film superconductor can be obtained. The electron beam of a scanning electron microscope (SEM) acts as a local heat source. Under the proper conditions of temperature, bias current, and beam current, variations in the superconducting state can be mapped and compared to microstructure and chemical phase information. This method has recently been applied to high Tc superconductors to map critical currents and to identify weak links in superconducting paths. We discuss here the possible application of the technique to identify the superconducting phase within a matrix of non-superconducting material.The sample was an ∼1 μm thin film that was grown by sputtering from a YBa2Cu3O7-δ target onto a [001] SrTiO3 substrate. A more detailed description of the growth procedure is given elsewhere. The morphology, crystallinity, and stoichiometry of the samples were characterized in the SEM. The film had several chemical phases and a morphology consisting of large rectangular platelets (typical size 200х50 μm), covering ∼20-30% of the surface.
Electron radiation damage in YBa2Cu3O7
Authors: Roy T. , Sickafus K. , Clinard F. W. , Mitchell T. E. 
Published: June 2020

Some potential applications of high temperature superconductors involve radiation environments with possible deleterious effects on properties. In addition, radiation introduces point defects and defect clusters which could possibly pin flux lines and raise the critical current density. The present research was undertaken to characterize the damage produced by electrons in situ by TEM.Thin specimens of YBa2Cu3O7 were prepared either by crushing or by ion-milling. Irradiations and observations were performed in either a Philips EM400T at 120kV, a Philips CM30 at 300kV, or a JEM2000EX at 200kV.The main effect of electron irradiation is to cause the fading of the twins which are ubiquitous in YBa2Cu3O7 (Fig. 1). The twins themselves are the result of the tetragonal-to-orthohombic phase transformation and represent regions in which the Cu-O chains (and oxygen vacancies) are ordered along either of the a axes of the original tetragonal cell.
High-resolution observations of nanometer-sized cavities in rapidly solidified 304 stainless steel
Authors: Kelly Thomas F. , Shin Keesam , Bae Jung Chan , Flinn John E. 
Published: June 2020

Recent theoretical work by Wolfer and Adams has predicted, and experimental work by Bae et al. has confirmed, that void-like cavities are produced in rapidly solidified materials during post-melting heat treatment. Studies of a 304 stainless steel using conventional TEM have shown that 8 nm voids are present in a material that wgs consolidated from centrifugally atomized powder by hot extrusion at 900°C. After heat treating the material at 900° C for one hour, 1 × 1021m−3of the 8 nm voids are found. When heat treated at 1200° C for one hour, however, there is a large increase in the number density of 8 nm voids to 5 × 1021m−3.Since this increase in void volume cannot be explained as void swelling because there is insufficient gas present, there must be a source of additional void volume in the material. Conventional TEM out-of-focus imaging can be used to image voids down to about twice the point resolution of an instrument. It was reasoned, then, that the extra void volume might then be present as small voids that were to small to be detected in the conventional TEM. In order to image these small voids, we decided to use a high-resolution TEM so that the smallest possible void could be imaged.
Analytical Electron Microscopy study of two vehicle-aged automotive exhaust catalysts having dissimilar activities
Authors: Kim Sooho , D’Aniello M. J. 
Published: June 2020

Automotive catalysts generally lose-agtivity during vehicle operation due to several well-known deactivation mechanisms. To gain a more fundamental understanding of catalyst deactivation, the microscopic details of fresh and vehicle-aged commercial pelleted automotive exhaust catalysts containing Pt, Pd and Rh were studied by employing Analytical Electron Microscopy (AEM). Two different vehicle-aged samples containing similar poison levels but having different catalytic activities (denoted better and poorer) were selected for this study.The general microstructure of the supports and the noble metal particles of the two catalysts looks similar; the noble metal particles were generally found to be spherical and often faceted. However, the average noble metal particle size on the poorer catalyst (21 nm) was larger than that on the better catalyst (16 nm). These sizes represent a significant increase over that found on the fresh catalyst (8 nm). The activity of these catalysts decreases as the observed particle size increases.