bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structure and chemical composition of nanophase particles in Mg-based alloys
Authors: Radmilovic V. , Thomas G. 
Published: June 2020

Conventional and high resolution transmission electron microscopy, as well as microchemical analyses, are playing an important role in identifying precipitates in Mg based alloys for aerospace applications, especially for nanometer sizes. During aging of Mg-Al-Nd-Zn based alloys, Al-Nd-Zn based particles precipitate which affect the mechanical properties. These alloys, which serve as the metal matrix for MMC materials containing SiC particulates as reinforcement, are processed by rapid solidification/powder metallurgy techniques, and they are designed for relatively high temperature (250-300° C) applications.Figure 1 shows the typical structure of second-phase particles in the Mg-based matrix. The spread in the particle size range is quite large, e.g., roughly between 70 and 100 nm. Close examination of these particles shows (Fig. 2) that there is no coherency with the Mg-based matrix, and no specific crystallographic relationship has been established. In some cases the growing direction of large particles was found to be within 5° of the C-axis of the Mg matrix.
Multislice calculations of RHEED patterns from vicinal Si (001)
Authors: Lordi Scott 
Published: June 2020

Vicinal Si (001) surfaces are interesting because they are good substrates for the growth of III-V semiconductors. Spots in RHEED patterns from vicinal surfaces are split due to scattering from ordered step arrays and this splitting can be used to determine the misorientation angle, using kinematic arguments. Kinematic theory is generally regarded to be inadequate for the calculation of RHEED intensities; however, only a few dynamical RHEED simulations have been attempted for vicinal surfaces. The multislice formulation of Cowley and Moodie with a recently developed edge patching method was used to calculate RHEED patterns from vicinal Si (001) surfaces. The calculated patterns are qualitatively similar to published experimental results and the positions of the split spots quantitatively agree with kinematic calculations.RHEED patterns were calculated for unreconstructed (bulk terminated) Si (001) surfaces misoriented towards [110] ,with an energy of 15 keV, at an incident angle of 36.63 mrad ([004] bragg condition), and a beam azimuth of [110] (perpendicular to the step edges) and the incident beam pointed down the step staircase.
UHV-TED study of clean Si(100) surface structures
Authors: Jayaram Ganesh 
Published: June 2020

Detailed information about the structure of silicon surfaces is very important prior to deposition of metal contacts. Though transmission electron diffraction is sensitive to the atomic structures of both the surface and the bulk, under appropriate conditions, information on the structure of the surface can be obtained from a careful analysis of the diffraction spot intensities.Since Si(100) surface is highly reactive (sticking coefficient for water = 1), preparation and observation of clean surfaces necessitates ultra-high vacuum (UHV) conditions. A thin sample of Si(100) (B doped to 1 ohm-cm) was prepared for observation inside a Hitachi UHV-H9000 300keV electron microscope (stable operation pressure ∼9xl0-11 Torr). It was mechanically polished, dimpled and ion-milled before being transferred into a UHV surface science chamber attached to the microscope. In situ sample preparation carried out inside this chamber involved a combination of sputtering using 2-4 keV argon ions (to clean the surface) and electron-gun annealing cycles (to order the surface).
Development of a 300 kV field emission TEM
Authors: Ishida Y. , Bando Y. , Kitami Y. , Tomita T. , Kersker M. 
Published: June 2020

The 300 kV analytical electron microscope, as compared with the 100 to 200 kV instruments, have excellent features such as the high resolution of TEM images, high P/B ratio of EDS and PEELS, and high spacial resolution in analysis.We hereby report the principal specifications of an ultrahigh sensitivity and ultrahigh resolution field emission type electron microscope, which, capable of giving full play to the above-mentioned features of the 300 kV analytical instrument, allows elemental analysis at the single atomic layer level (nm regions).Its electron gun, simply operated by CPU control, allows emission current to be obtained at the touch of a single button. As the emitter, a W (100)-TF emitter, which can be used simply, stably, and for a long period of time, is employed. After build-up, this emitter can obtain about 10 times the angular current density of the W (310) emitter. Around the emitter are provided three electrodes to make emission current variation and electrostatic lens function independent of each other.
Observation of crystal structures by image restoration in electron holography
Authors: Tanji Takayoshi , Ishizuka Kazuo 
Published: June 2020

Off-axis electron holography has been applied to crystal structure images using digital image processing.Three important factors pertaining to the correction of aberrations in electron holography are:(1)interference fringes narrower than one third of the required resolution,(2)a Signal to Noise (S-N) ratio in the hologram which is high enough for high resolution reconstruction, and(3)the estimation of the amount of aberrations.We have obtained interference fringes with a spacing of below 0.03 nm , which is sufficient for a resolution of 0.1 nm in the reconstructed image. The S-N ratio depends on the instrument used to record the hologram and whether the specimen causes strong scattering or weak scattering.Some ways of estimating the amount of aberration have been proposed. Here we adopted an algorithm which involves minimizing the contrast of the reconsturcted image by optimizing the processing parameters (Cs and df), because it is applicable not only to weak phase objects but also to general phase objects and, in principle, only one hologram is needed to determiner the parameters.
A novel UHV-REM as applied to observation of reconstruction of Pt(100) surface
Authors: Takeguchi Masaki , Akita Tomoki , Takai Yoshizo , Shibata Kichiro , Shimizu Ryuichi 
Published: June 2020

Direct observation of surface reconstruction under reflection electron micros-copy(REM) provides an intimate insight into basic processes on the surface, leading to more comprehensive understanding of surface physics in atomic scale. For this purpose we have developed a special UHV-specimen chamber, which allows various types of attachments, e.g., evaporator, ion gun, cooling facility, gas inlet and STM if necessary, to be mounted. This chamber was mounted in a 200kV transmission electron micro scope(TEM), Hitachi H-700H, to construct a novel UHV-REM for surface study.Fig.l shows a schematic diagram of the UHV-TEM constructed in the present work. The specimen chamber is evacuated with turbomolecular pump and Ti sublimation pump to the vacuum pressure of ~10-9 Torr. Some additional ports for, evaporator, gas-inlet, etc. are also attached around the specimen stage. Feedthrough metal bellows for driving system allows specimen holder to be translated in X- and Y-directions and to be tilted against electron beam without deterioration of vacuum pressure.
TEM observations of surface-step and hole-edge faceting in acid-etched and annealed MgO thin foils
Authors: King Simon , Barry Carter C. 
Published: June 2020

Surface-steps formed during the cleavage of MgO on {100} planes, the smaller steps of which may be of atomic height, have been observed in Reflection-Electron Microscopy investigations to be accurately aligned along <001> directions. Steps of atomic height also have been identified on MgO smoke-particle platelets; these steps may be curved or straight, with the straight steps showing evidence for faceting along <001>. Reference also is made to faceting along <011> and <012> directions. Straight steps ∼2 unit cells high, with edges along <100> also have been imaged by High-Resolution Profile-Imaging at the peripheries of MgO smoke microcubes. After etching in aqua-regia and annealing in air, however, high densities of “large” steps several unit cells high, as well as numerous holes, are formed. It is faceting in these foils that is reported here.As can be seen in fig 1, obvious faceting of the surface-step traces is extremely rare in these foils, in marked contrast to substrates such as LaAlO3 and SrTiO3, on which surface-step traces facet readily after a similar preparation treatment.
Imaging microstructural contact damage in silicon
Authors: Morris Jonathan C. 
Published: June 2020

The indentation of single crystal silicon has been shown to produce a metal to semiconducting structural phase transformation. This phase transformation dominates the effect of contact damage from both indentation and scratching at low loads and hence affects the results of related mechanical tests. We are examining the microstructure of contact damage in silicon in order to understand better the mechanisms which control its low-load mechanical and tribological behavior. Extensive transmission electron microscopy (TEM) as well as scanning electron microscopy (SEM) have been used to characterize both morphological and structural changes brought about by contact damage.The plan-view bright field image in Figure 1 exhibits strong crystallographic contrast outside of the indented area. The indented area as well as the extrusions emanating from it are amorphous as evidenced by their lack of crystallographic contrast regardless of tilt as well as their diffuse illumination in dark field. Small bits of fragmented polycrystalline silicon are visible at the indentation borders as well as at the tip of one extrusion.
Characterization of the oxidation-sulfidation of a preoxidized ODS FeCrAl alloy
Authors: Pint B. A. , Banks B. M. , Duncan J. C. , Garratt-Reed A. J. , Hobbs L. W. 
Published: June 2020

Preoxidation is a common technique used to protect alloys from environmental degradation. A dense, adherent oxide is grown on an alloy before placing it into a more aggressive environment. Thus, under conditions such as the mixed O-S atmosphere found in coal gasification, the rapid formation of sulfide can be avoided.While several studies have looked at the formation of protective alumina scales in mixed H2-H2O-H2S environments, none of these studies have considered the formation of less-protective, metastable aluminas on the oxidation behavior at temperatures less than 1000°C where θ-Al2O3 is commonly formed. This is especially important because in order to form an adherent alumina scale, an oxygen-active element such as Y, Ce, Hf or Zr is routinely added and these types of elements have been found to stabilize the lower-temperature alumina phases and inhibit the transformation to α-Al2O3. Furthermore, the transformation from θ- to α-Al2O3 involves a 13% volume reduction and cracking through the scale which could compromise the protectiveness of the scale.
A high-resolution EM study of grain boundaries in Pr and Co-doped ZnO ceramics
Authors: Solórzano I.G. , Vander Sande J.B. , Baek K.K. , Tuller H.L. 
Published: June 2020

Metal oxide varistors are multijunction materials whose nonlinear current-voltage characteristics derive from the electrical activity of their grain boundary regions. The high degree of nonlinear-ity in polycrystalline ZnO has been attributed to the synergistic action of two types of cations added in sufficient concentrations: transition metals, such as Co and Mn which have ionic radii similar to that of the ZnO matrix, and dopants with large ionic radii, such as Bi and Pr which segregate at grain boundaries and usually form intergranular phases. The present investigation was undertaken with the objective to clarify the role of dopants in an electrically active Pr and Co doped ZnO ceramic by studying the structure and chemistry of individual grain boundaries through high-resolution electron microscopy (HREM) and analytical electron microscopy (AEM).Bulk specimens containing 1 mol% Pr and 1 mol% Co were prepared by conventional sintering at 1400° C. Some samples followed an oxidative anneal at 650° C for 3 h to further enhance their electrical activity.
Coherency-induced morphological instability in NiAl-type precipitate
Authors: Ghosh G. , Olson G. B. , Fine M. E. 
Published: June 2020

In many commercial alloys, phase transformation involves nucleation and growth of coherent precipitates. The elastic strain fields around individual coherent precipitates and the overlap of such strain fields constitute an “elastically constrained system” in which the precipitates exhibit shape transition and anomalous coarsening behavior. Results of classical γ-γ’ system shows that an individual precipitate may split into two parallel plates (or doublet) or eight smaller cuboids (or octate) with their faces parallel to the {100} directions. Theoretical modeling of such shape transitions imply that the process is governed by the competition between interfacial and elastic energies. Here, we report the shape transitions observed in an elastically constrained system involving bcc structures.Polycrystalline specimens of Fe-6.42Al-14.8Ni (alloy#l) and Fe-8.08Al-12.2Cr-18.2Ni (alloy#2) were studied. Alloy#l was solution treated at 1100°C followed by continuous cooling at 0.01°C/s to 950°C and subsequently helium quenched. Similarly, alloy#2 was solution treated at 1200°C and continuously cooled at 0.01875°C/s to 1065°C and helium quenched to room temperature.
Study of factors affecting corrosion of aluminum automotive wheels
Authors: Plummer H. K. , Simmons R. N. , Ocobock R. W. , Honey T. A. , Paputa Peck M. C. 
Published: June 2020

Aluminum automotive wheels, which have been used since the mid 1970’s, have proven to be very rugged, but early wheels discolored with time. Since 1976 the machined “bright” exterior surfaces, have been coated with a chromium based “conversion” pretreatment, and painted with a “clearcoat” of polyester or acrylic to preserve appearance. These coated wheels can exhibit “filiform” corrosion between the Al surface and the clearcoat (Fig. 1). The corrosion is filamentous and closely follows aluminum grain boundaries. Corrosion results from oxidation of the aluminum (anode) in the presence of water and oxygen at a break (cathode) which intrudes through the clearcoat and conversion coat into the aluminum (Fig. 2). Current specifications require ≤ 1.6 mm filiform corrosion from a scratch after 400 h of accelerated corrosion testing. This paper correlates accelerated corrosion with the composition of the clearcoat paint, the UV absorbance of the paint and the microstructure of the Al / Cr conversion coat / clearcoat interface to learn the necessary parameters to produce Al wheels with enhanced protection. Production Al wheels, from a variety of sources, wheels prepared to our specifications and a design of experiments (DOE) wheel series prepared in our laboratories were examined.The accelerated corrosion test exposes the test piece to UV weathering (400 h) with four water spray cycles every 23 h. After UV exposure the surface is scratched through the surface layers into the Al metal with a carbide scribe, followed by exposure to HCl vapor (1 h).
Microstructure of superconducting Y1Ba2Cu3O7-x/Nd1.85Ce0.15CuO4-y bilayer films
Authors: Prasad Beesabathina D. , Salamanca-Riba L. , Mao S. N. , Xi X. X. , Venkatesan T. 
Published: June 2020

Superconducting bilayers of Y1Ba2Cu3O7-x(YBCO) and Nd1.85Ce0.15CuO4-y (NCCO) are of particular interest for the study of the interaction between p-type superconductors(YBCO) and n-type superconductors for possible device applications. The microstructural study is crucial since the crystallinity and interface quality of the bilayers effect the characteristics of heterojunctions. In this report, we present details of the microstructure of superconducting NCCO/YBCO bilayers.NCCO/YBCO bilayers were deposited on three different single crystal substrates of (001) LaAlO3, (001) SrTiO3, and (001) Y-ZrO2(YSZ) using pulsed laser depositon. The details of the deposition and superconducting properties are reported elsewhere. The samples reported in this report have typical YBCO thickness of 2000 A and NCCO thickness of 4000 A.Figure 1(a) shows a bright field image of a NCCO/YBCO bilayer grown on YSZ and exhibits a Moire’ fringe pattern in some regions of the NCCO film. The Moire’ fringes have a spacing of ∼ 31.01 Å.
Cryomicroscopy of low-Tg latex particles via freeze drying
Authors: Reffner J. R. 
Published: June 2020

Transmission Electron Microscopy (TEM) is a powerful tool for investigating the structure of latex particles. However, examining low Tg (glass transision, Tg < room temperature) latex particles requires special techniques due to the significant deformation which occurs if the particles are dispersed onto a substrate at room temperature. Here a freeze drying (FD) technique is presented which permits individual emulsion particles, including stained particles, to be examined in a manner that minimizes deformation by maintaining the particles at temperatures below Tg.Typically, particle morphology is determined from images of individual latex particles dispersed onto a supporting ultra-thin substrate or from images of ultra-microtomed sections of films cast from the latex. Examining particles dispersed onto a substrate is often advantageous, allowing direct determination of particle shape and characterization of the morphology prior to the film formation process. Although low Tg materials can be examined using this technique, information about the size, shape and morphology of phase separated domains can be obscured by the deformation which occurs when the particles are examined at room temperature.
Dirac-fock calculations of scattering factors and mean inner potentials for neutral and ionised atoms
Authors: Rez David , Rez Peter 
Published: June 2020

Tables of X-ray and electron scattering factors are essential for programs that calculate diffraction intensities or simulate images. These tables are calculated from atomic charge densities derived from Hartree Fock programs for atoms. The most frequently used results are those due to Doyle and Turner who used Coulthard's relativistic Hartree Fock program. They did not calculate scattering factors for all elements and other results using different programs were used to complete the tables given in the International Tables for Crystallography. As microscopy and diffraction become more quantitative it has become important to reexamine the calculation of atomic scattering factors using more recent Hartree Fock codes to quantify more precisely differences due to solid state effects. We also feel it is desirable to calculate all naturally occuring elements, and their common ionised states, using the same program.The charge densities were calculated using the Multi-Configuration Dirac-Fock code of Grant et al.
Electron microscopy and diffraction of crystalline dendrimers and macrocycles
Authors: Buchko C. J. , Wilson P. M. , Xu Z. , Zhang J. , Lee S. , Moore J. S. , Martin D. C. 
Published: June 2020

The synthesis of well-defined organic molecules with unique geometries opens new opportunities for understanding and controlling the organization of condensed matter. Here, we study dendrimers and macrocycles which are synthesized from rigid phenyl-acetylene spacer units, Both units are solubilized by the presence of tertiary butyl groups located at the periphery of the molecule. These hydrocarbon materials form crystalline and liquid crystalline phases which have been studied by differential scanning calorimetry, hot stage optical microscopy, and wide-angle x-ray scattering (WAXS).The precisely defined architecture of these molecules makes it possible to investigate systematic variations in chemical architecture on the nature of microstructural organization. Here we report on the transmission electron microscopy (TEM), selected area electron diffraction (SAED), and high resolution electron microscopy (HREM) studies of crystalline thin films formed by deposition of these materials onto carbon substrates from dilute solution. Electron microscopy is very attractive for gaining structural information on new molecules due to the scarcity of material to grow single crystals suitable for conventional crystallography.
Improvement of amplitude-divided electron holography
Authors: Ru Q. , Endo J. , Tonomura A. 
Published: June 2020

Compared with the wavefront-divided electron holography obtained by an electron biprism, the amplitude-divided one proposed by Matteucci et al. has some essential advantages: less necessary coherency, wide interference area and available to most of transmission electron microscopes. In order to confirm and achieve these advantages in practical use, we introduce some improvements in both hologram formation and reconstruction steps. Two electron-optical setups and experimental results are presented for small objects (<1 μm) and much large objects (>1 μm), respectively.The electron-optics for taking the holograms of small objects is illustrated in Figure 1. A single crystal thin film (gold film of 0.2nm lattice spacing is used in our experiment) is placed on the objects (latex particles of 120 nm on a thin carbon film are used here) with a certain gap. In fact, the gap is spontaneously made by the microgrids of the specimen film and the crystal film.
Direct imaging of nucleic acid conformation in water by scanning tunneling microscopy
Authors: Lindsay S.M. , Nagahara L. , Thundat T. 
Published: June 2020

We have developed methods for imaging biopolymers under water by scanning tunneling microscopy (STM). The STM gives fairly high resolution images of small biopolymers. Larger polymers may be imaged with the atomic force microscope. Both techniques allow biological processes to be studied as they occur. Both suffer limits on resolution which are a consequence of the distortion of soft biological molecules by the contact force of the probe. The chemical sensitivity of the STM can be exploited to overcome this limitation, and we will discuss methods for nucleic acid sequencing.A number of images of nucleic acids in various configurations are displayed on the following page. All are perspective projections looking into the substrate at an angle of about 45° with respect to the axes. (A) shows a random-sequence fragment of double helical DNA. The 36Å helix repeat is clearly visible. (B) shows a single strand of poly (rU). (C) Shows (left side) three complete 146 base-pair fragments of DNA from the nucleosome. (D) shows a kinked nucleosome fragment.
Current and future directions of on-line Transmission Electron Microscope image processing and analysis
Authors: O’Keefe Michael A. , Kilaas Roar 
Published: June 2020

Image processing and analysis are increasingly employed in order to extract the maximum amount of useful information from transmission electron micrographs. Whereas most processing is carried out a posteriori, i.e. from images that have been recorded on film then digitized for computer processing, it is obviously useful to be able to improve the on-line image in near-real time for the benefit of the microscope operator. In addition, interfacing an external computer to the internal controls of modern TEMs allows on-line image analysis to provide the first step in algorithms designed to assist the operator in adjustment of microscope parameters such as alignment, astigmatism and defocus.The hardware required for on-line image processing can be as simple as a detector coupled to a TV camera, the signal from which is digitized, stored and averaged by a set of cards controlled by a host computer, with a monitor displaying the image stored in the memory card.