bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of interface structure and bonding at atomic resolution in the STEM
Authors: Pennycook S. J. , McGibbon A. J. , McGibbon M. M. , Browning N. D. , Chisholm M. F. , Jesson D. E.
Published: June 2020

Theo scanning transmission electron microscope can now routinely produce a probe of atomic dimensions, 2.2Å at 100 kV and 1.3Å at 300 kV. This capability opens up a new strategy for determining the structure and bonding of materials at the atomic scale, which is particularly advantageous for complex interfaces such as grain boundaries. The Z-contrast image allows the high-Z column locations to be determined by direct inspection, and quantified through maximum entropy methods to a positional accuracy of currently ~0.2Å. With the same electron probe, located to sub-Ångstrom precision with reference to the Z-contrast image, parallel detection EELS can determine light element coordination from core edge fine structure, in principle around a single atomic column.

The attractive features of this approach are the increased resolution associated with incoherent imaging, 0.44 Cs1/4 λ3/4 compared with 0.66 Cs1/4 λ3/4 for phase contrast imaging, and the highly local nature of the image, which makes possible a greatly extended regieme of intuitive image interpretation, and also permits column-by-column spectroscopy without beam broadening.
HREM study of NiO electrochromic film and interace with ITO layer
Authors: Song X. Y.
Published: June 2020

Electrochromic nickel oxide films are of interest in the development of electrochromic devices (“smart windows”) for a variety of applications including architectural and automotive glazings. Structural characterization of NiO films has been performed by Lampert and Agrawal et. al using transmission electron microscopy (TEM), although only in plan view of NiO films which had been deposited on carbon-coated copper grids. However, finer structural features in the NiO electrochromic film and the interface between the NiO film and the indium tin oxide (ITO) layer have not been reported. The purpose of this investigation is to characterize nanometer scale structures in NiO films and the NiO/ITO interface using cross-sectional high resolution electron microscopy (HREM).

The NiO films were deposited using a JS-450D rf sputtering coater. A nickel target of 99.9% purity with a 100 mm diameter was used. ITO coated glass with a sheet resistance of 40 ohm/sq. was used as a substrate, and both target and substrate were water cooled and were separated by 50 mm.
The changes caused by activation and reaction conditions on the morphology of iron catalysts
Authors: Kalakkad D. S. , Shroff M. , Datye A. K.
Published: June 2020

Iron is considered to be one of the most active/low cost catalysts for Fischer-Tropsch synthesis (FTS) used to produce higher order hydrocarbons and synthetic fuels from coal. One of the biggest obstacles faced by the industry in the use of iron is that of rapid deactivation and attrition. While it is generally accepted that deactivation occurs due to carbon deposition or “coking”, the actual steps involved in the formation and deposition of carbon have not yet been thoroughly understood. Also, the causes for attrition in these catalysts have not yet been established.

Our present study involves use of transmission electron microscopy to find the effect of various pretreatment and reaction conditions on the microstructure of Fe catalysts and scanning electron microscopy to study the problem of attrition. The transmission electron microscopy was performed on a 200 kVJEOL JEM 2000FX microscope and the SEM was done using a Hitachi S800 microscope.
Observation of the evolution of 55-atom icosahedral Ag clusters by coherent electron nanodiffraction in a UHV stem
Authors: Liu J. , Spinnler G. E.
Published: June 2020

The morphology of metallic nano particles fluctuates and rapidly changes under the influence of electron beam irradiation. Structural transformations of small Au particles and disordering of small Pt clusters have been reported. Although the existence of a quasimolten state in nano particles has been experimentally observed there are still many unanswered questions concerning the onset of this unstable state. The previous experiments were carried out in non-UHV microscopes and the particles were prepared ex situ. We report preliminary observations of the evolution of clean Ag nano particles in a UHV scanning transmission electron microscope (STEM).

The experiments were performed on a UHV STEM (VG HB-501S), known by the acronym MIDAS (Microscope for Imaging, Diffraction and Analysis of Surfaces). The probe size used for nanodiffraction was approximately 1 nm in diameter with a beam current density of 104 A/cm2. Silver nano particles were formed by evaporating Ag onto a pre-cleaned thin (< 5 nm in thickness) carbon film inside the UHV specimen preparation chamber attached to the MIDAS column.x
Oxygen vacancy clustering in YBa2Cu307-x (x < 0.15)
Authors: Storey B. G. , Kirk M. A. , Marks L.D.
Published: June 2020

There have many studies of oxygen vacancy ordering in highly oxygen deficient YBa2Cu3O7-x (YBCO) however little has been done to investigate oxygen vacancies for x<0.15. Information on defects in asgrown fully oxygenated YBCO is important when generating flux pinning defects by irradiation damage. It has been found that samples with little flux pinning before irradiation have the best flux pinning after irradiation. It is believed that pre-existing defects interfere with the production of irradiation induced defects, therefore, there is a great interest in the behavior of the oxygen vacancies. There is also a hypothesis that oxygen vacancy clusters could be low temperature flux pinners.

It is well known that YBCO is generally oxygen deficient and that at large deficiencies the oxygen vacancies have a long-range order. If the oxygen loss and/or disorder is great enough the material will undergo an orthorhombic to tetragonal phase transition. Most studies of oxygen vacancies have been of materials with x>0.2, however if Tc>90K then x<0.15.
Atomic-force microscopy of a fractured rubber-toughened epoxy
Authors: Shaffer O. , Qian J. , Dimonie V. , Pearson R. , El-Aasser M.
Published: June 2020

Atomic force microscopy (AFM) is a powerful scanning probe technique, which is capable of imaging polymer surfaces. This technique is complementary to the scanning electron microscope (SEM) but because of the AFM's sensitivity in the z direction surfaces that are too smooth to image by SEM can easily be imaged by AFM. This study utilizes transmission electron microscopy(TEM) to image the morphology of the latex rubber particles; SEM and AFM are used to study the degree of dispensability of the latex particles in the epoxy, and the fatigue-fracture surface of the rubber modified epoxy.

Core-shell latex particles were prepared with a core of poly(butadiene-styreiie) |P(B-S)| and a shell Poly(methyl methacrylate)(PMMA). In order to study the interaction between the core/shell particles and the epoxy matrix, the shell is systematically varied in terms of chemical bonding, physical interaction and the extent of these interactions by incorporating acrylonitrile(AN). glycidyl-methacrylate(GMA). and crosslinking agent divinylbenzene(DVB) of varying concentrations in the shell.
Correlation of micro-structural, micro-chemical and micro-magnetic properties of longitudinal recording media using CM20FEG Lorentz TEM
Authors: Nolan T. P. , Sinclair R. , Yamashita T. , Ranjan R.
Published: June 2020

Cobalt alloy on chromium thin film magnetic media are used in industry computer hard disk drives because of their large values of coercivity (Hc), remanent magnetization (Mr), squareness (S*), and relatively low noise. The magnetic performance depends strongly on processing conditions and the resulting nanometer scale microstructure.

A complete structure-processing-properties analysis requires effective measurement of magnetic and microstructural properties. To date, most structure-properties analyses have involved correlation of bulk magnetic (hysteresis loop) properties and magnetic recording measurements with physical microstructures observed by high-resolution SEM and TEM.

The nanoscale microstructural features that dramatically affect magnetic properties are difficult to observe but careful TEM analysis has been used to observe subtle, important differences in the atomic scale physical microstructure. Even these impressive capabilities are becoming insufficient for continued development of improved magnetic recording media. Microstructural design is moving into a regime where appropriate control of magnetic properties requires control of elemental composition and second phase formation as well as crystallography and morphology, at near-atomic levels.
Quantitative image analysis of polymer blends
Authors: Zhang X. , Berry V. K.
Published: June 2020

Quantitative image analysis is important in understanding the role of microstructure in polymer blend properties, as revealed by the TEM. This paper presents an example of the application of the image analysis method to the study of structure/property relationship of an acrylonitrile-butadiene-styrene (ABS) polymer.

ABS is a rubber-toughened two-phase polymer blend. As shown in Figure 1, the microstructure of ABSconsists of small rubber particles embedded in a styrene-acrylonitrile copolymer (SAN) matrix. The morphologies of these blends, which depend on the polymerization conditions, play a key role to the overall physical and mechanical properties of the blends. The quantitative characterization of the rubber phase involves measuring its volume fraction as well as the particle size distribution.

Four ABS samples, available commercially, with different levels of styrene butadiene rubber (SBR),were used in this study. The samples were block stained, using osmium tctroxide (OsO4) solution, and thin sectioned in an ultramicrotome.The thin sections were examined in a JEM-100CX II TEM, operated at 60KV. The representative images were acquired on a SEMICAPS Imaging System using a GATAN CCD TV rate camera.
AEM and AES of radiation-induced segregation in proton-irradiated stainless steels
Authors: Kenik E. A. , Carter R. D. , Damcott D. L. , Atzmon M. , Was G. S.
Published: June 2020

Irradiation-assisted stress corrosion cracking (IASCC) of stainless steels has been attributed in part to radiation-induced segregation (RIS) of both major alloying and impurity elements at grain boundaries. There are phenomenological similarities observed between IASCC and intergranular stress corrosion cracking (IGSCC) of thermally-sensitized stainless steels. One concern for both IGSCC and IASCC is the localized loss of corrosion resistance associated with chromium depletion at grain boundaries. In order to avoid complications related to the long-term, induced radioactivity of neutron-irradiated specimens, four type 304L alloys were irradiated to 1 dpa (displacements per atom) with 3.4 MeV protons at 400°C. Both analytical electron microscopy (AEM) in a Philips EM400T/FEG and Auger electron spectrometry (AES) in a Perkin Elmer (PHI) 660 were employed to measure composition at or near grain boundaries in unirradiated and irradiated specimens of four controlled purity alloys [ultra-high purity (UHP), UHP+S (0.03 at.%), UHP+P (0.08 at.%), and UHP+Si (0.87 at.%)]. A sufficient number of boundaries were analyzed via AEM and AES to result in the standard deviation of the mean boundary composition of less than -0.5 at.%. Further experimental details are presented elsewhere.
High-resolution annular dark-field STEM imaging
Authors: Hillyard Sean , Silcox John
Published: June 2020

Annular dark field STEM imaging has become an important tool as both a high resolution imaging technique showing Z-contrast, and as a way to locate the probe on the specimen while simultaneously recording other data such as electron energy loss spectra. It is intrinsically quantitative since image data can be recorded directly from linear detectors into digital memory Experiments on simple samples,and a multislice simulation approach backed by experimental evidence has been used to explore the image dependence on experimental factors such as inner detector angles and other elements in the imagingprocess Earlier work demonstrated marked thickness dependence in high Z specimens.

In annular dark field imaging, the resolvable spatial resolution is roughly equal to the size of the electron probe One important factor in forming a small probe, and therefore in getting high resolution images, is an electron gun with a small virtual source size. An example is shown in Figure 1, which plots the relativestrengths of the 2.9Å and 2.1 Å fringes taken from experimental images of InP (100) What is seen is that the 2.1Å fringe intensity, at the extreme limits of resolution for this probe (approx 2.2Å in size), changes greatly in comparison with the more easily resolvable 2.9Å fringe as the source demagnification, in effect the source size, is changed.
Fantome: A calculation of the dielectric function from the plasmon excitation
Authors: Normand L. , Thorel A. , Montardi Y.
Published: June 2020

Electron Energy Loss Spectroscopy is now a well known method for chemical analysis(light elements especially), qualitative analysis of trace elements, EXELFS, etc. The low energy part of the spectrum can also be used in order to perform thickness evaluation and dielectric function determination. When EELS coupled with Transmission Electron Microscope, it presents the great interest of performing all measurements with a spatial resolution of the magnitude of the beam size. In the case of the dielectric function, we can then avoid any average effects due to macroscopic measurements. We then have access to the role of defaults, chemical heterogeneities, grain boundaries, anisotropy which can introduce major modifications in the macroscopic properties. The dielectric measurements are based on Kramers-Kronig analysis of the plasmon excitation (1, 2) ; A program (“Fantome”) has been written to process the EELS spectra. Results have been obtained on barium titanate.
Dual-stage choreography of bulk biological specimens by Schottky field-emission SEM: Quality imaging at all magnifications
Authors: Apkarian R. P.
Published: June 2020

The utility of a dual stage scanning electron microscope boasting a Schottky field emission (FE) source, for imaging bulk biological samples is its versatility to select the quality of the secondary electron signal. The detector placement and the specimen staging, either in or below the final probe forming lens, results in two distinct secondary electron images dominated by either the backscatter electron (BSE) component or by specimen specific secondary electrons (SE) that generate a high resolution image. It is only the voltage range to operate the FESEM and whether or not to enhance the SE-I contrast from biological specimens, with the coating of an ultrathin continuous fine grain metal film, which need to be determined for successful image recordings. Our facility has employed 1 nm chromium films on bulk biological specimens in order to restrict the electron beam interaction volume and generate a more intense SE-I signal contrast. Due to the extreme stability and minimal 1 nm beam diameter of the Schottky FESEM operated at high voltage (20-30 keV), very high resolution images of membrane ectodomains composed of hydrocarbons <10 nm in diameter (not colloidal gold markers) were recorded when the specimen was coated with Cr.
Limits of SEM resolution
Authors: Joy D. C.
Published: June 2020

Over the past decade the achievable resolution of the scanning electron microscope (SEM) in secondary electron (SE) imaging mode has improved by about one order of magnitude. In fact, instruments capable of demonstrating a resolution of one nanometer and exhibiting a probe size of less than 0.6nm are now available. Continued improvements in electron-optics, electron sources, and in electronic and mechanical stability promise even smaller probe sizes that still contain adequate current for imaging. It is therefore relevant to consider what resolution might ultimately be achievable with an SEM in SE mode.

The contrast detail in an SE image depends on two factors, the generation of secondaries, and their subsequent escape from the specimen. Changes in either, or both, of these factors will change the number of secondaries collected, and the spatial scale over which this change is accomplished will set the effective resolution of the image (assuming that the physical probe size is small enough to be neglected).
Atomic-Force Microscopy with piezoresistive cantilevers
Authors: Tortonese M. , Giessibl F. J.
Published: June 2020

The atomic force microscope (AFM) works by measuring the deflection of a cantilever as it is scanned over a sample. A sharp tip at the end of the cantilever is responsible for the high lateral resolution achieved with the AFM. There are several ways to measure the deflection of the cantilever. The technique used to measure the deflection of the cantilever most often dictates the mechanical complexity and stability of the instrument. Electron tunneling, interferometry and capacitive sensors have been used successfully. The most common way to measure the cantilever deflection is by means of an optical deflection detector.

The piezoresistivc cantilever offers a new way to measure the deflection of the cantilever, with performances comparable to the performances of other deflection detectors, and with the advantage that the sensor is incorporated in the cantilever. This simplifies the design and operation of the microscope In particular, the piezoresistive cantilever facilitates the use and often improves the performances of an AFM when operated in ultra high vacuum (UHV), at low temperature, or when used to image large samples.
Imaging of the P-glycoprotein in normal and multidrug-resistant small-cell lung carcinoma cells with the Atomic-Force Microscope(AFM)
Authors: Tsai J. M. , Sadava D. , Gould S. A. C.
Published: June 2020

Cancer is characterized by the often rapid and uncontrolled rate of cell growth. This alteration in growth pattern causes normal cells to become tumor cells. After undergoing a period of chemotherapy, some tumor cells become resistant to a variety of drugs, a phenomenon known as the multidrug resistance (MDR). One explanation for this change is the overexpression of P-glycoprotein in the drug-resistant cells. This membrane protein is capable of pumping drugs into the extracellular medium. Since the drugs do not accumulate, the tumor cells are not killed. In order to examine this protein, a contact mode AFM was used to image the cell membranes of both the normal and the MDR tumor cells. The four figures provided show the topographical information of the membranes and suggest that there are differences between the cell lines.
HRTEM study of modulated structures in superconducting Bi2Sr2NdCu2Oy and non-superconducting Bi2Ca2FeOy
Authors: Matsui Yoshio , Ono Akira , Shoda Kaoru , Lee Uk , Horiuchi Shigeo
Published: June 2020

Phenomena of incommensurate modulation in BSCCO superconductors, Bi2Sr2Can−1CunOy (n=1 to 3), have effectively been investigated by high-resolution transmission electron microscopy and it was revealed that periodic compression and expansion of lateral Bi-Bi distance is induced in (BiO)2 layers with a periodicity b=4. 8bg, where bs is a lattice parameter of tetragonal substructure. Longer modulation periodicity is obtained by replacing part of Bi with Pb, while shorter periodicity by replacing Sr (Ca) with La, Y etc. Commensurate modulation structure with shorter periodicity of b=4bs is also found in Bi2Sr2CoOy. In the present study, we examined the modulation structures of two related compounds, superconducting Bi2Sr2NdCu2Oy and non-superconducting Bi2Sr2NdCu2Oy. Electron diffraction and HRTEM observations are made by JEOL's JEM-4000EX type of machine in NRIM (Tsukuba, Japan) with point-to-point resolution of about 0. 17 nm at 400kV.
Extended defects in plastically deformed superconducting ceramics
Authors: Kuroda K. , Yoshida T. , Murase T. , Saka H.
Published: June 2020

Extended defects introduced by high temperature deformation into high Tc superconducting ceramics have been characterized by means of transmission electron microscopy.

Single crystals of YBa2Cu3O7−x (YBCO) were grown from melting mixtures of yttria, barium carbonate and copper oxide contained in alumina boats. Crystals having tetragonal symmetry grew as platelets with dimensions up to 10×10×0.1 mm3 and the (001) broad surface. Crystals were deformed by Brinell indentation with an indenter of Y-doped zirconia between 550 and 900 °C in air. Most indents were done with a load of 70 grf and a loading period of up to 24 h. Thin specimens were prepared by back-thinning technique using an Ar ion beam at 4 kV.

Polycrystals of Bio. 8Pbo. 2SrCa1. 1Cu1. 6Ox (BSCCO) were prepared by sintering process. Rectangular specimens 3×3×8 mm were sectioned from the sintered materials. They were deformed in commpression at 800 °C using strain rate of 1.3×10−5 s−1. Specimens could be deformed to as large as 90 % in a nominal compressive strain.
Incommensurate nature of the “decagonal” Phase Al65Cu20Co15 in the Al-Cu-Co ternary system
Authors: Ramani Atul S. , Song Shihong , Ryba Earle R. , Howell Paul R.
Published: June 2020

The discovery of a phase in Al-14 at% Mn alloys which displays forbidden icosahedral symmetry spurred a massive effort towards synthesis, characterization and theoretical modeling of the so - called “quasicrystalline” phase. Subsequendy, “decagonal” phases in Al-Mn and Al-Fe, having diffraction patterns characteristic of a periodic stacking of two-dimensional “quasicrystalline” structures, have been discovered. The present paper, reports preliminary results of our investigation of the “decagonal” phase first discovered by He et al. in an Al65Cu20Co15 alloy.

High purity metals (Al, Cu, Co) were arc-melted in an argon atmosphere into alloy buttons of nominal composition Al65Cu20Co15. Specimens for TEM were prepared by ion-beam milling in a Gatan ionmilling system operated with an argon ion-beam, at an accelerating voltage of 4 kV and at specimen current of 1 μA. The thin foils were examined in a Phillips EM 420T microscope operating at 120 kV. Selected alloy buttons were fractured and prepared for examination on an ISI - SX 40 SEM operated at 25 kV.
Towards quantitative analysis of nanometer-sized helium bubbles in irradiated steels using parallel-detection EELS in a STEM
Authors: McGibbon A. J. , Brown L. M.
Published: June 2020

The stress rupture properties of high nickel austenitic alloys and austenitic stainless steels used in the nuclear industry are strongly affected under irradiation by the formation of helium from boron by means of an n-α reaction. As the congregation and growth of helium bubbles (typically 20-50nm diameter) at grain boundaries can cause embrittlement in stressed steels, it is important to gain an understanding of embrittlement mechanisms in the material. Consequently, an accurate measurement of quantities such as bubble pressure and metal surface energy is highly desirable. However, this can only be achieved if the number of helium atoms per unit volume is known. In this work, we report on the use of parallel-detection electron energy loss spectroscopy (PEELS) on a VG HB501 scanning transmission electron microscope (STEM) as a powerful technique for characterising helium bubbles in irradiated steels. In addition, we suggest a simple analytical process that could be used to quantify the amount of helium present in each bubble.
Twinning in ternary Ti50Ni(50−x)Mx alloys
Authors: Moberly Warren J. , Sinclair Robert , Duerig Tom W.
Published: June 2020

Twinning in materials results from one of two different effects. Firstly, thermal changes may give rise to growth twins during solidification, annealing twins during recrystallization, or martensitic twins during solid-state phase transformations. Secondly, shear stresses can activate mechanical twinning as a deformation mode other than dislocation slip. TiNi alloys are unusual in that they exhibit both types of twinning. Due to the submicron dimension of both types of twins, transmission electron microscopy (TEM) is used to characterize the resulting structures.

TiNi is well-known for its shape memory properties resulting from a martensitic transformation of the cubic B2 structure to the monoclinic B19' structure upon cooling. Minor concentrations of various third elements can be added to modify different shape memory properties. In the case of TiNiCu ternary alloys, up to 30% Cu is substituted for Ni while retaining the shape memory effect. For small Cu concentrations the B2 austenite phase transforms, upon cooling, to the B19' monoclinic martensite typical of the binary alloy.
Quantitative stress determination in SiC reinforced Al2O3
Authors: Caspers Bernhard , Mader Werner , Angelini Peter
Published: June 2020

Whisker and fiber reinforced ceramic composites offer the potential for increased fracture toughness and fracture strength. However, differences in thermal expansion between whisker and matrix generate residual stresses which may affect the mechanical properties of such composites. The microscopic stress can be determined by analyzing the strain contrast around SiC whiskers quantitatively, similar to the strain analysis performed on ZrO2 inclusions in AI2O3. Previously obtained experimental TEM results on strain contrast around SiC whiskers embedded in Al2O3 were only qualitatively. In the present study the experimental observations are quantitatively evaluated.

Contrast simulation requires the knowledge of the matrix displacement field in the vicinity of the whisker. Due to two force-free surfaces adjacent to the inclusion, Eshelby’s method for an inclusion in an infinite matrix can not be used for the evaluation of the elastic field in a TEM foil. Therefore, the Green’s function method was applied to fulfill the elastic boundary conditions for both surfaces neglecting only the elastic interaction between the surfaces.
Toughening mechanisms in abalone shell
Authors: Gunnison Katie E. , Sarikaya Mehmet , Aksay Ilhan A.
Published: June 2020

Abalone shell (Haliotis Rufescens) is a naturally ocurring ceramic/polymer composite material. The system displays a unique laminated structure of calcium carbonate (aragonite) crystals in a matrix of biological macromolecules. The CaCO3 crystals and the organic matrix are arranged in a miniature “brick and mortar” structure referred to as nacre. Figure 1 is a TEM bright field micrograph illustrating the high degree of order observed in this microstructure.

Although the nacre region of the shell is more than 95% CaCO3 by volume, the natural matrix material and the arrangement of the microstructure lead to a substantial increase in the observed mechanical properties. Mechanical tests performed on the nacre region show a fifty-fold increase over that of pure bulk CaCO3 (Fig. 2), which also compares with other ceramic and cermet systems.

Vickers microhardness testing was performed on samples polished for optical microscopy. Crack propagation features were observed by standard SEM techniques and analyzed in an attempt to identify the possible toughening mechanisms that are operating in the nacre structure. The cracks generally travel by a tortuous path, often displaying microcracks and crack branching. However, these mechanisms alone are not sufficient to account for the observed mechanical properties.
The influence of annealing on the topography of (100) and (111) surfaces of MgO
Authors: Gajdardziska-Josifovska M. , Crozier P. A. , Cowley J. M.
Published: June 2020

The atomic structure and topography of MgO surfaces are of considerable interest because of the frequent use of MgO crystals as substrates for epitaxial growth of metal films, high Tc superconductors and model catalyst systems. In recent years, a large number of studies have appeared employing broad beam techniques to characterise MgO surfaces prepared under different conditions. However, very little has been done to characterise the topography of such surfaces using reflection electron microscopy (REM) techniques. A few studies have appeared on cleaved (100) MgO surfaces but there are no microscopy studies of the (111) surface. We have examined cleaved (100) surfaces and have investigated the effect of high temperature annealing on the surface topography of both the (100) and (111) surfaces.

Single crystal MgO cut along the <010> direction was ground down to a thickness of approximately 150 μm and then cleaved with a razor blade along the (100) plane. The bulk terminated (111) surface of MgO is a polar surface and thus is not an easy cleavage direction.
Surface microstructure on Raney nickel catalysts
Authors: Bradke M. V. , Schnurnberger W. , Seybold I.
Published: June 2020

Raney nickel is a favorite electrocatalyst for alkaline water electrolysis and fuel cells. The good electrochemical properties of this material result from its very fine porosity giving the electrodes a large effective surface. Usually the microstructure is formed by chemical etching of a nickel alloy, leaving back a highly porous electrode consisting of nearly pure nickel. It is well known that the total effective surface can considerably vary depending on the etching process, but up to now the understanding of the influence of all etching parameters on the resulting pore structure is quite ambiguous. Consequently, the study of the microporosity on Raney nickel is an important task within the scope of the development of electrocatalytic electrodes.
Structure and composition of metal particles in Pt-Sn/Al2O3 bimetallic catalysts
Authors: Sachdev A. , Schwank J.
Published: June 2020

Platinum - tin bimetallic catalysts have been primarily utilized in the chemical industry in the catalytic reforming of petroleum fractions. In this process the naphtha feedstock is converted to hydrocarbons with higher octane numbers and high anti-knock qualities. Most of these catalysts contain small metal particles or crystallites supported on high surface area insulating oxide supports. The determination of the structure and composition of these particles is crucial to the understanding of the catalytic behavior. In a bimetallic catalyst it is important to know how the two metals are distributed within the particle size range and in what way the addition of a second metal affects the size, structure and composition of the metal particles. An added complication in the Pt-Sn system is the possibility of alloy formation between the two elements for all atomic ratios.
Structure imaging of grain boundaries in F.C.C. metals
Authors: Krakow William
Published: June 2020

One can now extract information about the projected atomic structure of tilt grain boundaries in metals from zone axes orientations which are not the most open structures as in previous lower voltage microscopic studies of a few years ago. This has been made possible in part by the development of intermediate voltage microscopes capable of a point resolution exceeding 2Å level For these studies it was also necessary to develop techniques for fabricating tilt boundary structures from epitaxially grown Au thin films placed in contact. Analysis of grain boundary micrographs further required that Fourier image filtering and enhancement be applied to the original micrographs. Subsequent computer modelling of the dynamical diffraction processes and images was also necessary to insure the proper image interpretation.

An example of a ∼80Å thick thin film containing a symmetrical tilt boundary corresponding to a Σ = 17/[001]28.1° (410) is displayed in Fig. 1. There is a [100] tilt axis common to both grains and the {200} crossed sets lattice planes on each side of the interface require a resolution level of 2.03Å which is well beyond the {111} planar spacings of 2.3Å of the most open [110] orientation in Au. Here the atom columns are designated by either open circles or crosses corresponding to a two layer repeat. The boundary dislocation cores are designated by structural units of capped trigonal prisms or the same with one cap modifying to contain a rhombohedron unit.
Electron holography for magnetic property study of materials
Authors: Tonomura Akira
Published: June 2020

An electron beam is often modulated, only in phase and not in intensity. When the beam passes through a magnetic field or a ferromagnetic thin film which can be regarded as pure phase objects. Therefore, great defocusing is indispensable for magnetic domain observation in Lorentz microscopy. Electron interference microscopy, however, can directly display the phase distribution of an electron beam in an in-focus electron micrograph, and consequently should provide direct information about magnetic fields.

The development of a coherent field emission electron beam has opened a way to such a possibility using electron holography in which the phase-amplified phase distribution can be displayed as an interference micrograph. In addition, contour fringes have been interpreted as in-plane magnetic lines of force. Such an intuitive interpretation is possible for the following reason (Fig.1). An incident wavefront is displaced by the vector potential circulating around a magnetic field.
Dark-field electron spectroscopic imaging of aged microstructures in an aluminium lithium base alloy
Authors: Solórzano I. G. , Probst W.
Published: June 2020

The examination of microstructures make very high demands on the imaging quality and, therefore, on the instrumentation. In Al-Li base alloys it is of great interest to determine parameters such as size, distribution, morphology and coherency of precipitate phases as they dictate their mechanical behavior. In order to reveal morphological features with high quality the electron spectroscopic imaging (ESI) in dark field mode has shown to be quite a powerful technique.

The ESI technique in the TEM is based on the possibility that accelerated electrons can be elastic and inelastically scattered by the sample atoms, as recently reviewed. The electron distribution in the transmitted and diffracted beams through a crystalline sample is such that both energy loss and elastic electrons will enter a typical objective aperture and thus contribute to both bright field and dark field images. The effect of the polyenergetic electrons is that the image is affected by chromatic aberration of the objective lens. In CTEM’s this effect is enhanced the lower the accelerating voltage and the thicker the sample.
In situ high-resolution Electron Microscopy
Authors: Sinclair Robert
Published: June 2020

In recent years, there have been many dramatic recordings of dynamic behavior, taken at the atomic level by high-resolution electron microscopy. However in the majority of cases, reliance has been placed on the imaging electron beam to bring about the changes in question. There are many disadvantages to this approach, not the least of which is the lack of experimental control available to the operator. Accordingly we have developed the application of a heating holder to achieve stable elevated temperatures at which reactions can be followed under atomic imaging conditions. This article briefly reviews our progress to-date.

Our microscope system is quite conventional, showing that there is no major impediment to hot-stage HREM. We have employed a Philips EM 430 ST (300kV) instrument equipped with a Gatan image pick-up device and a commercial video-recorder. The heating holder is the Philips single tilt sideentry model (PW 6592) which we have found works well up to about 875°C. Of course a double tilt holder is preferable but we overcome the tilting limitations by judicious positioning of cross-section specimens. Image stability can be achieved by heating to a temperature below that of the observation for several minutes before "ramping up" to the desired level.
High-resolution Transmission Electron Microscopy study of metastable CxSi1-x epitaxial alloys grown on silicon
Authors: Posthill I.B. , Rudder R.A. , Hudson G.C. , Hattangady S.V. , Fountain G.G. , Markunas R.J.
Published: June 2020

In addition to the obvious advantages of low temperature semiconductor processing, the potential exists to fabricate new compounds that would not normally be accessible via conventional deposition techniques. For example, we have recently demonstrated the feasibility of growing CxSi1-x (x ≃ 0.03) epitaxial alloys oil Si(100) using remote plasma-enhanced chemical vapor deposition (RPECVD) without the formation of SiC. It is our hypothesis that the band gap of these metastable alloys will depend on carbon concentration and lie between the values for silicon (Eg = 1.1 eV) and β-SiC (Eg = 2.3 eV). The potential would then exist for using these metastable epitaxial alloys for the emitter of a Si-based heterojunction bipolar transistor (HBT). However, the details and limits of metastable carbon incorporation still remain to be elucidated. In this context, the microstructural examination of this novel electronic materials system takes on added importance and relevance. Diffraction contrast and high-resolution transmission electron microscopy (HRTEM) results are presented from metastable CxSi1-x epitaxial alloys that have been grown on Si(100) by RPECVD.
A crystallographic analysis of the CoSi/Si(111) interface using Transmission Electron Microscopy
Authors: Daykin A.C. , Kiely C.J. , Pond R.C. , Batstone J.L.
Published: June 2020

When CoSi2 is grown onto a Si(111) surface it can form in two distinct orientations. A-type CoSi2 has the same orientation as the Si substrate and B-type is rotated by 180° degrees about the [111] surface normal.One method of producing epitaxial CoSi2 is to deposit Co at room temperature and anneal to 650°C.If greater than 10Å of Co is deposited then both A and B-type CoSi2 form via a number of intermediate silicides .The literature suggests that the co-existence of A and B-type CoSi2 is in some way linked to these intermediate silicides analogous to the NiSi2/Si(111) system. The phase which forms prior to complete CoSi2 formation is CoSi. This paper is a crystallographic analysis of the CoSi2/Si(l11) bicrystal using a theoretical method developed by Pond. Transmission electron microscopy (TEM) has been used to verify the theoretical predictions and to characterise the defect structure at the interface.
HREM investigations of Si/SiO2/poly-si compositions
Authors: Maksimov S.K.
Published: June 2020

Application of poly-silicon conductive films in integrated circuits promises a number of advantages. In poly-Si technology, however, there are many unsolved problems. In particular, the cause of anomalously high current gains (β) observed by many authors is now being discussed. For their explanation two hypotheses are mostly put forward: according to the first the effect is accounted for by tunneling carriers through the boundary layer of SiO2. according to the second - it is associated with clustering the impurites at the interface. The present paper is an attempt to explain the effect by investigating the structure of the interfaces in Si/SiO2/poly-Si compositions.

Layers of poly-Si 0.3μm thick were deposited at 620° on the Si (001) surface prepared by various ways: by etching in HF:H2O/(1:50).using a natural oxide or thermal oxide layers of different thickneses. Then Part of samples was doped with As+ ions with energy of 75 keV at dose 1×1016 cm-2 . The samples were annealed at 850° C during 1 hour; part of them were subjected to a repeat annealing during 30 min at 1000°C.
TEM study of epitactically grown GaAs/ScxEr1−xAs/GaAs heterostructures
Authors: Zhu Jane G.
Published: June 2020

The incorporation of metal layers into semiconductors is attracting growing attention due to potential applications in novel electronic devices and new physics of very thin metal films in semiconductors. This paper reports the growth of GaAs/ScxEr1−xAs/GaAs (x=0 and ∼0.3) on (100) GaAs substrates by molecular beam epitaxy (MBE) and the characterization of these heterostructures by transmission electron microscopy (TEM). ErAs, ScAs and many other rare-earth arsenides have the rock-salt crystal structure, which is different from the zinc-blende structure of GaAs. The difference in the crystal structure substantially affects the heteroepitactic growth. The lattice mismatch between ErAs (ScAs) and GaAs is 1.6% (-3.3%). Lattice-matched growth of ScxEr1−xAs/GaAs can be obtained at x=0.32. TEM has been used in this study extensively to characterize the microstructure and the growth-related defects. Both cross-section and plan-view samples have been studied using strong-beam, weak-beam dark-field and high-resolution imaging, as well as selected-area diffraction.
High-resolution Electron Microscopy of GaInAsP: Implications for the study of interfaces and decomposition phenomena
Authors: Bons A.J. , Schapink F.W. , Schryvers D.
Published: June 2020

The quaternary semiconducting compound GaxIn1-xAsyP1-y has important applications in optoelectronic devices, in the form of heterostructures and quantum wells. Lattice matching between two materials with a composition difference (Δx,Δy) is achieved if Δy≈2.2Δx. Furthermore, decomposition structures have been described in these compounds; the decomposition is expected to follow Δy≈=Δx (Fig. 1). In the present study the sensitivity of high-resolution electron microscope (HREM) images for these composition variations is investigated.

GaxIn1-xAsyP1-y layers lattice-matched to InP (x=0, y=0) have been studied with HREM in [001] plan view specimens, and in <110> and <100> cross-sections. The experimental images were interpreted using image simulations. The observations can be summarized as follows:
(1) Even small differences in composition between lattice-matched layers (Δx≈0.17, Δy≈0.37) lead to appreciable HREM-image contrast in <100> cross-section specimens (Fig. 2). <110>-orientations are less sensitive, but interfaces associated with Δx≈0.26, Δy≈0.56 still show good composition contrast (Fig. 3).
TEM characterization of Au/Polysilicon interactions
Authors: David Theodore N. , Allen Leslie H. , Barry Carter C. , Mayer James W.
Published: June 2020

Metal/polysilicon investigations contribute to an understanding of issues relevant to the stability of electrical contacts in semiconductor devices. These investigations also contribute to an understanding of Si lateral solid-phase epitactic growth. Metals such as Au, Al and Ag form eutectics with Si. reactions in these metal/polysilicon systems lead to the formation of large-grain silicon. Of these systems, the Al/polysilicon system has been most extensively studied. In this study, the behavior upon thermal annealing of Au/polysilicon bilayers is investigated using cross-section transmission electron microscopy (XTEM). The unique feature of this system is that silicon grain-growth occurs at particularly low temperatures ∽300°C).

Gold/polysilicon bilayers were fabricated on thermally oxidized single-crystal silicon substrates. Lowpressure chemical vapor deposition (LPCVD) at 620°C was used to obtain 100 to 400 nm polysilicon films. The surface of the polysilicon was cleaned with a buffered hydrofluoric acid solution. Gold was then thermally evaporated onto the samples.
TEM study of very thin InGaAsP layers grown by liquid-phase epitaxy
Authors: Bert N.A. , Kosogov A.O.
Published: June 2020

The very thin (<100 Å) InGaAsP layers were grown not only by molecular beam epitaxy and metal-organic chemical vapor deposition but recently also by simple liquid phase epitaxy (LPE) technique. Characterization of their thickness, interfase abruptness and lattice defects is important and requires TEM methods to be used.

The samples were InGaAsP/InGaP double heterostructures grown on (111)A GaAs substrate. The exact growth conditions are described in Ref.1. The salient points are that the quarternary layers were being grown at 750°C during a fast movement of substrate and a convection caused in the melt by that movement was eliminated. TEM cross-section specimens were prepared by means of conventional procedure. The studies were conducted in EM 420T and JEM 4000EX instruments.

The (200) dark-field cross-sectional imaging is the most appropriate TEM technique to distinguish between individual layers in 111-v semiconductor heterostructures.
Microstructure of barium monoferrite BaFe2O4
Authors: González-Calbet J.M. , Nicolopoulos S. , Vallet-Regí M.
Published: June 2020

BaFe2O4 appears at the initial stage of the solid state reaction during the synthesis of hexaferrites with Ba as divalent cation. In the HREM study of this phase, linear defects like crystallographic shear planes are observed which could change the ideal stoichiometry. Crystals are twinned, confirming previously predicted results from X-Ray data.

Although the crystal structure and superstructure of the BaFe2O4 is well established, the microstructure still remains unknown. This phase is always present during the synthesis of several hexaferrites; the study of the microstructure could help to the understanding of the solid state reaction to synthetize new ferrite phases.

A series with nominal composition Ba2Cu2Fe12022 (Y type hexagonal ferrite) was prepared with different annealing conditions for each sample. Details about the thermal treatments and the final products are given elsewhere. From X-Ray powder diffraction data, the presence of BaFe204 is always identificated at the final products.
High Resolution Electron Microscopy of thin Co-Cr films
Authors: Demczyk B. G.
Published: June 2020

Co-Cr thin films have been studied extensively as leading candidates for perpendicular recording media. The development of microstructure in this system has been reported by a number of investigators. These studies have revealed a general growth scenario in which a fine grained, randomly oriented "transition layer" forms first, followed by the development of columnar grains having their hcp c axes textured normal to the film plane. However, it has been found that such columns are not present in very thin (∽10 nm) layers. Also, it has been inferred from electron microdiffraction studies that both c and a axis texturing occurs in these same films. However, direct evidence for this texturing is still needed. In this work, high resolution electron microscopy (HREM) has been employed to examine very thin (5-10 nm) Co-Cr layers.
Sensitivity of various phytates to beam damage during x-ray analysis
Authors: Ockenden Irene , Lott John N.A.
Published: June 2020

Phytic acid (myoinositol hexaphosphoric acid) has 12 hydrolyzable hydrogens and forms salts with a variety of cations. Phytic acid salts are stored in seeds and act as nutrient reserves of elements such as Mg, K, Ca and P. In diets heavily dependent on grains, phytates have been implicated in reducing the bioavailability of elements such as zinc and iron. The complexing properties of phytates have made these compounds useful in a number of medical and industrial procedures.

Phytin reserves in seeds often are localized in electron dense spherical particles called globoid crystals located within protein bodies. The characteristics of globoid crystals remain poorly defined. Energy-dispersive x-ray analysis of individual globoid crystals from various species has shown that there is considerable variation in the relative proportions of Mg, K, Ca and P species-to-species.
Electron irradiation effects in quartz single crystals and polycrystalline materials
Authors: Flörke O. W. , Martin B. , Röller K. , Wirth R.
Published: June 2020

Electron irradiation damage in quartz and irradiation induced amorphism (metamict transformation in α-quartz) have been studied by several authors.

The present investigations are focused on the orientation dependence of the irradiation damage, the influence of the proton and OH−concentration and the behaviour of grain boundaries during electron irradiation. Starting materials were synthetically grown quartz crystals with well defined OH−content and the crystallographic orientations (0001) (c-cut) and (2110) (x-cut). Polycrystalline quartz from metamorphic rocks (Western Alps) were used for studying the influence of electron irradiation on grain boundaries. Samples were prepared from thin sections (thickness about 30 μm) by ion milling and coated with carbon. The irradiation experiments were carried out in a JEOL JEM 200 CX electron microscope at 200 kV acceleration voltage at room temperature and at about 117 K.