bluuebunny/crossref_metadata_2025 huggingface dataset:
Si(111)-(5x2) Au structure from off-axis high-resolution Transmission
Electron Microscopy
Authors: Plass R. , Marks L. D.
Published: June 2020

Although metal semiconductor interfaces play a major role in semiconductor device performance the basic understanding of the atomic structure of many of these interfaces has been elusive. The submonolayer of gold on silicon (111) system is of special interest as it displays several different surface structures depending on gold coverage and temperature. Substantial light has been shed on one of these structures, the 5×2 present between .1 and .5 gold monolayers, in recent x-ray diffraction and high resolution STM studies, yet the placement of the gold atoms remains unclear. We present here a solution for this structure found using off-axis plan view HREM and digital image restoration in combination with more conventional bright-field, dark-field imaging and diffraction techniques.

Instrumental details related to this experiment have been reviewed by Bonevich and Marks. Si 111 oriented TEM samples with clean, fairly flat surfaces were prepared using Ar+ ion sputter/electron beam annealing cycles.
Analytical Electron Microscopy of Monolayer Surface Segregation in Alloy Nanoparticles
Authors: Lakis R. E. , Lyman C. E. , Stenger H. G.
Published: June 2020

Alumina-supported Pt-Rh alloy catalysts are widely utilized for air pollution control and are particularly effective for the reduction of nitric oxide (NO) at temperatures below 300°C. The alloy particles of interest are present in the size range of l-15nm in diameter. A catalyst that was observed to contain only Pt-rich alloy particles, performed better than catalysts which contained Rh-rich alloy particles or a mixture of Pt-rich and Rh-rich particles. The reaction data suggested that Rh may have segregated to the surface of the individual Pt-rich alloy particles. This observation is consistent with the literature on the Pt-Rh system. However, there are no traditional surface sensitive techniques (e.g. XPS, AES) which possess both the spatial resolution and the depth resolution required to observe surface segregation in 1-15nm particles. The goal of this study is to determine if this segregation could be observed by analytical electron microscopy in a dedicated STEM.

The composition-size distributions of several catalysts were measured using a VG-HB501 scanning transmission electron microscope (STEM).
Structure and chemical composition of Pt-Ru nanoparticle supported on carbon black
Authors: Radmilovic V. , Gasteiger H. , Ross P.
Published: June 2020

The presence of nanoparticles in catalyst systems is essential because their large surface area increases the reaction rate of the catalyst. However, such a small size of the particles causes serious limitations in microstructural characterization, that could be overcome by high resolution electron microscopy (HREM), especially for particle morphology studies, presence of faults, etc. The present study uses HREM, microdiffraction and EDS techniques to characterize the Pt-Ru catalyst supported on amorphous carbon black. In order to get structural information from local region of single particle optical diffraction has been also performed. HREM imaging allows the particle morphology and the presence of various structural defects to be revealed. To avoid contamination, microchemical analysis has been performed at -160°C, using cold stage beryllium holder. The fluorescence effect can be neglected.

Fig. 1 shows that some of Pt-Ru particle in a catalyst containing 20 % of metal mass and having ratio Pt:Ru=3:l, exhibits pronounced microfaceting on 111 and 100 type planes (see Fig. la), forming equilibrium cubo-octahedron shape.
Flux-pinning related defects in YBa2Cu3O7-x thin films grown on miscut LaA1O3 substrates
Authors: Wang Z. L. , Christen D. K. , Klabunde C. E. , Kroeger D. M. , Lowndes D. H. , Norton D. P.
Published: June 2020

Measurements of critical current density in YBa2Cu3O7-x (Y123) thin film grown on slightly (1.6 deg) miscut LaA1O3 {001} substrates have shown an anomalous angular dependence of Jc. A strong, magnetic field-dependent peak in Jc is observed when the magnetic field is oriented between the c-axis (the film normal direction) and the a-b plane, an orientation where flux pinning normally is not strong. Scanning tunneling microscope images of the films showed tilted-platelet microstructures, suggesting that the films might contain highly oriented internal growth defects, induced by the miscutaligned growth. This array of defects may be responsible for the strong flux pinning and high Jc. In this paper, high-resolution transmission electron microscopy (HRTEM) is applied to study the defect structure formed in the films.

HRTEM studies were performed at 300 kV in a Philips CM30 TEM/STEM with image resolution 2.3 Å. The {001} Y123 films of thickness - 0.5 μm were grown on miscut LaA1O3 {001} substrates. Cross-sectional TEM specimens were prepared in order to examine the relationship between the substrate steps with the observed defects.
SEM and SAM observation of S-adsorbed Cu3Au (110) surface
Authors: Huang Y. , Cowley J. M.
Published: June 2020

The behavior of impurities on the surfaces is an important topic in surface science. Cu3Au is a typical ordering bimetalic alloy whose bulk and clean surface have been extensively studied.This make it a good material for studying the effect of impurities such as sulfur on the properties of the alloy surfaces. Some work has been done by the present authors on the structure and compositionchange of the Cu3Au (110) surface with the sulfur adsorption . It was found that when S isadsorbed on the surface the ratio of the surface Au concentration over Cu concentration decreases drastically. The reason of this change was explained as movement of Au atoms into the bulk and Cu atoms from the bulk to the surface due to the difference in the affinity of Au and Cu for S.

The previous observations were based on macroscopic RHEED and AES techniques, the information was averaged over a large area. In order to obtain more localized information such as surface morphology andthe element distribution, secondary electron microscopy (SEM) and scanning Auger microscopy (SAM) were used to study the clean and S-adsorbed Cu3Au (110) surfaces. The experiment was carried out in a modified UHV VG HB501.
The long-period structure on ordering alloy surfaces
Authors: Huang Y. , Cowley J. M.
Published: June 2020

The long-period structure (LPS) has long been known to exist in bulk ordering alloys such as CuAu and Cu3Au. in the structure the ordered lattice shifts back and forth by a vector every M unit cells and forms a super cell 2M unit cells long. The planes where the lattice shifts are usually called antiphase boundaries (APBs) and the LPS can be regarded as periodically arranged antiphase domains. This superstructure can be detected by the splitting (∝1/M) of some superlattice spots in the diffraction panern. One may ask whether the LPS also occurs on the surface; if so, what is its effect onthe diffraction pattern. The answer to them is important to explain some unknown features observed in the RHEED experiment. They also have significance for the surface transition theories.

Ideal termination of a LPS Cu3Au crystal gives a surface first-layer atomic arrangement shown in fig.1a. In this arrangement the basic vectors a and b of the surface hexagonal ordered structure are two bulk {110} vectors. Every M unit cells in a direction the lattice shifts by(1/2)b. This forms the 2-D super unit cell with a size of 2Ma×b. The relatively shifted areas are actually 2-D antiphase domains. The boundaries between them are the periodically arranged linear APBs. All these features indicate that the ideal Cu3Au(111) surface is indeed a 2-D LPS. Fig.1b and 1c show the 2-D reciprocal lattice calculated from the above surface arrangement.
Identifying groups of airborne particles by ordination
Authors: Shlepr M. , Vicroy C. M.
Published: June 2020

The microelectronics industry is heavily tasked with minimizing contaminates at all steps of the manufacturing process. Particles are generated by physical and/or chemical fragmentation from a mothersource. The tools and macrovolumes of chemicals used for processing, the environment surrounding the process, and the circuits themselves are all potential particle sources. A first step in eliminating these contaminants is to identify their source. Elemental analysis of the particles often proves useful toward this goal, and energy dispersive spectroscopy (EDS) is a commonly used technique. However, the large variety of source materials and process induced changes in the particles often make it difficult to discern if the particles are from a common source.

Ordination is commonly used in ecology to understand community relationships. This technique usespair-wise measures of similarity. Separation of the data set is based on discrimination functions. Theend product is a spatial representation of the data with the distance between points equaling the degree of dissimilarity.
Quantification of micromagnetic structure from Lorentz micrographs
Authors: Zweck J. , Herrmann M. , Hoffmann H.
Published: June 2020

Defocused imaging of magnetic domain structures is a well-known technique to observe the micromagnetic structures in ferromagnetic thin films. Nevertheless, Lorentz microscopy images are rarely subject to a quantitative evaluation of micromagnetic parameters. In this paper, we offer a new method for quantitative evaluation of ripple wavelengths and ripple angle from Lorentz microscopy images carried out on soft magnetic Ni81Fe19 films. The work was carried out using a Philips CM30 electron microscope with a combined Twin/Lorentz lens.

The experiments were performed on thin ferromagnetic films of a Ni81Fe19 alloy. Due to the internal magnetic induction within the specimens, the partial electron waves experience a phase shift proportional to the local in-plane magnetic induction , the specimen's thickness t and the lateral distance x from an arbitrarily chosen point of zero phase shift on the specimen. This phase shift can then be imaged using phase contrast methods similar to HREM. Since the phase shifts and the corresponding deflection angles can be very small, a large defocus is necessary to obtain contrast. This large defocus gives rise to an oscillating phase contrast transfer function for the spatial frequencies under observation as well as to a damping envelope for higher spatial frequencies.
Automatic analysis of Kikuchi diffraction patterns
Authors: Weiland H. , Field D. P.
Published: June 2020

Recent advances in the automatic indexing of backscatter Kikuchi diffraction patterns on the scanning electron microscope (SEM) has resulted in the development of a new type of microscopy. The ability to obtain statistically relevant information on the spatial distribution of crystallite orientations is giving rise to new insight into polycrystalline microstructures and their relation to materials properties. A limitation of the technique in the SEM is that the spatial resolution of the measurement is restricted by the relatively large size of the electron beam in relation to various microstructural features. Typically the spatial resolution in the SEM is limited to about half a micron or greater. Heavily worked structures exhibit microstructural features much finer than this and require resolution on the order of nanometers for accurate characterization. Transmission electron microscope (TEM) techniques offer sufficient resolution to investigate heavily worked crystalline materials.

Crystal lattice orientation determination from Kikuchi diffraction patterns in the TEM (Figure 1) requires knowledge of the relative positions of at least three non-parallel Kikuchi line pairs in relation to the crystallite and the electron beam.
Toward a neuroscope: An application of high-performance computing for real-time evaluation of brain function using MRI
Authors: Potter C. S. , Gregory C. D. , Morris H. D. , Liang Z.-P. , Lauterbur P. C.
Published: June 2020

Over the past few years, several laboratories have demonstrated that changes in local neuronal activity associated with human brain function can be detected by magnetic resonance imaging and spectroscopy. Using these methods, the effects of sensory and motor stimulation have been observed and cognitive studies have begun. These new methods promise to make possible even more rapid and extensive studies of brain organization and responses than those now in use, such as positron emission tomography.

Human brain studies are enormously complex. Signal changes on the order of a few percent must be detected against the background of the complex 3D anatomy of the human brain. Today, most functional MR experiments are performed using several 2D slice images acquired at each time step or stimulation condition of the experimental protocol. It is generally believed that true 3D experiments must be performed for many cognitive experiments. To provide adequate resolution, this requires that data must be acquired faster and/or more efficiently to support 3D functional analysis.
Advances in computational fluorescence microscopy
Authors: Carrington Walter A.
Published: June 2020

By combining optical sections of a fluorescently labelled cell with quantitative calibration of the microscope’s blurring in 3-D , we are able to computationally reverse the blurring of the microscope. This computational process is called image restoration or deconvolution We apply this approach to images taken on a conventional wide field microscope using a cooled CCD camera. The resulting computed 3-D images have improved resolution, greater dynamic range, substantially reduced out of focus haze and substantially greater accuracy of fluorescence quantification than the unprocessed images. Requirements imposed by the biology that are addressed by our methods include the need to minimize photodamage and photobleaching and the need to minimize data acquisition time for following high speed events. We address the need for very high resolution with a sub-pixel restoration scheme. We also consider the optical aberrations associated with imaging into living samples with oil immersion objectives. We consider the need for reducing computation time. Finally, we apply our method to a variety of biological samples.
Pattern recognition in HREM analysis of grain-boundary structures
Authors: Paciornik S. , Kilaas R. , Turner J. , Dahmen U.
Published: June 2020

The present study focuses on an application of pattern recognition techniques to the detection of structural units in grain boundaries and in heterophase interfaces. It describes a simple means of extracting the essential characteristics of an interface from a high resolution image, to find the location, repeat distance and degree of similarity between such units and to sum them into an average unit with increased signal to noise ratio. A measurement of the discrimination between different crystallographic structures can also be obtained from a histogram of the processed image.

Usually the procedure is composed of three steps. In the first the user selects a structural unit of interest and the program scans it over the original image to obtain a real-space cross-correlation (CC) coefficient map. This map will consist of bright spots where the template matches the underlying image and dark spots otherwise. In the second step an automatic peak-finding procedure is used to locate the positions of best match.
A review of Schottky and cold field-emission cathode characteristics
Authors: Swanson L. W.
Published: June 2020

Two high brightness, point cathodes currently being used in TEM's and nanometer electron focusing systems are the cold field emission (CFE) and Schottky emission (SE) cathodes. In terms of emission mechanisms, CFE and SE represent two extremes of a continuous change in surface electric field strength F and temperature T of a pointed cathode of work function ϕ. The conditions for CFE and SE emission modes can be stated as follows:

CFE: 4π(2mϕ(1/2 kT/heF < 0.5

SE: he1/4F3/42<2m1/2 < 0.5

When the above conditions are met most electrons are tunnelling from at or near the Fermi level inthe case of CFE and thermally excited over the vacuum barrier in the case of SE. The expressions for the current density J are:

CFE: JCFE = a(F2/ϕ)exp(10.4/ϕ1/2)exp(-bϕ3/2/F)(A/cm2

SE: JSE = 1202exp(-(ϕ - 3.8F1/2)/)kT)(A/cm2)

where a = 1.54×10-6, b = 0.644 and F and ϕ are in units of V/Å and eV respectively.

One important aspect for source optics applications is the energy spread of the emitted electrons for the two emission regimes. Fig. 1 gives the theoretical values of the full width at half maximum (FWHM) of the energy distribution for the case of CFE with ϕ = 4.0 eV, T = 300 K, J = 1×105 A/cm2 and SE with ϕ = 3.0 eV, T = 1800, J = 1×103 A/cm2.
Trace nanoanalysis
Authors: Newbury D. E. , Leapman R. D.
Published: June 2020

Trace constituents, which can be very loosely defined as those present at concentration levels below 1 percent, often exert influence on structure, properties, and performance far greater than what might be estimated from their proportion alone. Defining the role of trace constituents in the microstructure, or indeed even determining their location, makes great demands on the available array of microanalytical tools. These demands become increasingly more challenging as the dimensions of the volume element to be probed become smaller. For example, a cubic volume element of silicon with an edge dimension of 1 micrometer contains approximately 5×1010 atoms. High performance secondary ion mass spectrometry (SIMS) can be used to measure trace constituents to levels of hundreds of parts per billion from such a volume element (e. g., detection of at least 100 atoms to give 10% reproducibility with an overall detection efficiency of 1%, considering ionization, transmission, and counting).
Extending the limits of molecular microanalysis
Authors: Blackson J. H. , Susnitzky D. W. , Beaman D. R.
Published: June 2020

Modern polymer blends are frequently composed of domains and interfacial phases having submicron dimensions. Previously, die characterization of specific unknown submicron polymer phases has been limited to selective staining methods that help to classify the phase but rarely lead to chemical identification. The present procedure uses parallel detection electron energy loss spectroscopy (PEELS) to perform submicron molecular microanalysis on beam sensitive materials. Polymer domains are first differentiated by their elemental composition and then by their characteristic carbon core loss edge structure. These spectra are compared to spectra recorded from polymers of known composition.

A polymer film composed of alternating 0.5 μm layers of polycarbonate (PC) and polymethylmethacrylate (PMMA) was used as a test specimen (Fig. 1). Ultra-thin sections (<50 nm) were prepared by microtomy, collected on unsupported 600 mesh copper grids and examined at −160°C usinga VG HB601UX dedicated STEM fitted with a Gatan 666 UHV PEELS. The combination of beam blanking, simplecontrol of electron dose, UHV, low energy spread FEG, stage stability and the ability to produce a high contrast image at a very low electron dose makes this instrument ideally suited for this experiment.
A new method for quantitative analysis of EELS
Authors: Luo Suichu , Joy David C.
Published: June 2020

Techniques to remove plural scattering from electron energy loss spectra (EELS) are important in bot hmicroanalysis and other quantitative applications of electron spectroscopy. The techniques used are either based on convolution, or Fourier transform deconvolution, methods, in which either the elastic scattering angular correction or both elastic and inelastic angular corrections are not included. In this work we propose a new method based on both angular and energy loss three-dimension Poisson statistics which includes elastic and inelastic mixed angular scattering correction in order to obtain more accurate quantitative analysis for EELS.

The electron scattering distribution determined by angular and energy loss three-dimension Poissonstatistics is given by:

where ITis the total incident electron intensity; t is the sample thickness; λi, λeand λTare inelastic , elastic and total scattering mean free paths; Si(θ) and Se(θ) are normalized single inelastic and elastic angular scattering distributions respectively, F(E) is the single scattering normalized energy loss distribution.
Lattice parameter measurement by convergent-beam electron diffraction
Authors: Howe J. M.
Published: June 2020

Convergent-beam electron diffraction (CBED) should be an ideal technique for determining the lattice parameters of regions as small as a nanometer in size. This capability was first demonstrated about fifteen years ago and CBED has been used in a number of analyses since this time. In general though, the technique has been slow to catch on, except in the semiconductor area, where CBED has been usedextensively to measure lattice parameters in Si/SixGe1-x superlattices. Possible reasons for the slow adoption of this technique by the electron microscopy and materials science communities may be that: 1) CBED is usually dynamical, and it has become apparent that the use of simple kinematical calculations can lead to substantial errors (or at least some uncertainty) in quantitative lattice parameter determination, 2) a standardized procedure for determining the lattice parameters in the most general case, when six parameters are unknown, has not been established, and 3) surface relaxation associated with the thin foils used in transmission electron microscopy (TEM) may distort the sample and cause it to be unlike bulk material. The purpose of this paper is to assess the present status of lattice parameter measurement by CBED, particularly with respect to the three areas just mentioned.
High-resolution charge collection microscopy with high-voltage electron beams
Authors: Hwang D. M. , Tkachenko Y. A. , Hwang J. C. M.
Published: June 2020

Electron-beam-induced-current (EBIC) microscopy has the unique capability of simultaneously providing structural and transport characteristics of semiconductors. However, EBIC is traditionally performed inside an SEM with less than 40 keV electron beam energy. As the result, the applications of traditional EBIC for semiconductor device characterization are limited by either probing depth (0.02 ~0.05 μm with 2 ~5 keV electron beams) or spatial resolution (1-2 um with 20 ~40 keV electron beams). To achieve useful resolution for studying the interface effects critical to today's submicron devices, one would have to prepare the samples by either removing the passivation/metallization layers or making cross sections. In this paper, we report a breakthrough in the art of EBIC using high-voltage electron beams (200 keV and higher) to improve the spatial resolution and probing depth simultaneously. Adopting a JEOL 4000FX AEM for EBIC imaging, a spatial resolution of 0.05 um was demonstrated from structures 0.5 um beneath the surface. Using this technique, we have identified a facet degradation mechanism in strained quantum well laser diodes and hot-electroninduced defects in GaAs metal-semiconductor field-effect transistors (MESFETs).
Energy-filtered chemical mapping: Current applications to materials science
Authors: Crozier P. A.
Published: June 2020

Elemental mapping is a powerful technique for elucidating the distribution of elements on the nanometer scale in materials with complex morphologies. In electron microscopy, mapping is usually performed on a scanning transmission electron microscope (STEM) fitted with a field emission gun (FEG) using the techniques of energy-dispersive x-ray spectroscopy (EDX) or electron energy-loss spectroscopy (EELS). However, recent advances in spectrometer design and digital image recording have stimulated renewed interest in energy-filtered imaging and elemental mapping with a conventional transmission electron microscope. Here, some applications of energy-filtered chemical mapping in materials science are described.

Experiments were conducted on a Zeiss 912 operating at 120 kV with a thermal source and equipped with an omega filter spectrometer. A variable width slit in the spectrometer image plane allows energy-filtered images to be formed on the microscope viewing screen. These images are digitally recorded using a Gatan 679 slow-scan CCD camera with 1024 pixels.
A TEM/STEM and APFIM study of nitrogen distribution in inert-gas-atomized type 304 stainless steels
Authors: Zhou M. , Kelly T. F. , Flinn J. E.
Published: June 2020

The attraction of austenitic stainless steels lies in the combination of their mechanical and physical properties and corrosion resistance. However, a major disappointment is their relatively low strength. Over the years, continued efforts have been made to try to improve the strength of conventionally processed austenitic steels without sacrificing other properties. Using nitrogen as an alloying element can very effectively increase the strength of austenitic stainless steels while maintaining a high toughness. Improved resistance to intergranular corrosion and longer creep-to-rupture time1 werealso reported among nitrogen-containing austenitic steels. Though there is little doubt that interstitial nitrogen is responsible for the improved mechanical properties, the strengthening mechanism by nitrogen can not be explained successfully in a “conventional sense”, i.e. despite its smaller atomic size, nitrogen was found to increase the yield strength at 4K more than carbon does by a factor of about 2. One reason for the lack of understanding of nitrogen strengthening mechanism is because of thedifficulty of detecting low atomic number elements as well as possible short range order that may exist between interstitial and substitutional atoms.
Quantiative analysis of grain boundaries in YBa2Cu3O7-δ using a 20Å high-resolution probe
Authors: Zhu Yimei , Moodenbaugh A. R. , Zuo J. M. , Suenaga M.
Published: June 2020

One challenge for high Tc superconductor research is to overcome the low intergranular transport currents which hinder practical applications. Evidence shows that lattice mismatch at the boundaries contributes to the depletion in charge carriers (holes), while the strain fields surrounding the cores of boundary dislocations suppress the superconducting order parameter. Using high-spatialresolution EDX, EELS and CBED techniques with a 20 Å field emission probe, we studied cation segregation, variations in oxygen/hole content, and lattice parameters at and across grain boundaries for various Σ and near-Σ boundaries in bulk YBa2Cu3O7-δ. The geometry of those arbitrary grain boundaries was modeled using the constrained Coincidence Site Lattice (cCSL) theory, which requires c2/a2 being rational for coincidence boundaries in non-cubic crystals.

In this presentation, we report our quantitative and simultaneous measurements of lattice parameters, and of oxygen/hole content at the boundary regions. The oxygen/hole density was quantified by guassian fitting to the observed oxygen K-edge spectra and comparing them with those from the same batch which had undergone oxygen reduction process (Fig.1).
EELS of colloids in Mg+ implanted MgAl2O4 spinel
Authors: Evans N. D. , Zinkle S. J.
Published: June 2020

Because magnesium aluminate spinel (MgAl2O4) shows a strong resistance to void swelling during neutron irradiation at elevated temperatures, it is a candidate material for specialized applications in proposed fusion reactors. During implantation at 25°C with 2 MeV Mg+ ions to ∼2.8 × 1021 Mg+/m2, dislocation loops are formed at midrange depths (∼0.5 - 1.0 μm) on {110} and {111}. The microstructurc in the implanted ion region (∼1.5 - 2.0 μm) is shown in cross-section in Fig. 1. Within this implanted ion region, small features (4 - 10 nm diam.) were observed in dark field (DF) images using a spinel 222 reflection (Fig. 2). No evidence was found in electron diffraction patterns to suggest these features are (hexagonal) metallic Mg. However, in an earlier study, similar features in Al+ implanted spinel were identified by parallel electron energy loss spectrometry (PEELS) as metallic Al colloids. Phase identification of metallic Al within this spinel by electron diffraction is complicated because the lattice parameter of spinel (0.8083 nm) is almost exactly twice that of aluminum (0.4049 nm) and the phases are oriented cube-on-cube.
EELS of ice, vitrified water, and frozen aqueous solutions
Authors: Leapman R. D. , Sun S. Q.
Published: June 2020

Cryo-electron microscopy is now an established technique in structural biology for studying vitrified macromolecular assemblies. More recently, there has also been interest in using cryo-electron microscopy combined with electron energy loss spectroscopy (EELS) to determine subcellular water content in cryosections of vitrified tissue. Few EELS measurements have hitherto been obtained from vitrified water or from vitrified aqueous solutions of organic compounds at a resolution better that 1 eV. The purpose of this paper is to establish how valence EELS of vitrified (rapidly frozen) water differs from that of hexagonal (slowly frozen) ice, and also to investigate the effects of electron beam damage on EELS from vitrified aqueous solutions. There is also a fundamental interest in determining the energy loss function to help understand the electronic structure of frozen water, i.e., hexagonal ice, cubic ice and vitreous water, which are strong insulators containing solely hydrogen bonds. Some optical reflectivity measurements have previously been obtained from frozen water in the vacuum ultraviolet up to around 25 eV but it is not clear if these data are accurate over the entire energy range.
Coupled thermal diffuse-atomic inner shell scattering in electron diffraction
Authors: Wang Z. L.
Published: June 2020

In electron diffraction patterns, diffuse scattering at high angles is primarily generated by phonon, or thermal diffuse, scattering (TDS). Techniques were introduced to acquire the electron energy-loss spectra (EELS) of high-angle thermal-diffuse-scattered electrons (TDS-EELS) in a transmission electron microscope (TEM). With regards to the scattering mechanism, the TDS-EELS core ionization edge intensity was believed to be generated primarily by TDS - single electron, double-inelastic electron scattering processes. It was concluded from experimental data that the signal from coupled phonon - atomic inner shell excitations is stronger than that from atomic inner shell excitation alone. A formal dynamical theory is presented in this paper to illustrate the theoretical basis of the experimental observations. The theory can be applied to calculate the diffraction patterns of inelastically double-scattered electrons and the signal intensity observed in TDS-EELS.

TDS is actually a statistically averaged, quasi-elastic scattering of the electrons by the crystal lattice of different thermal vibration configurations.
Alchemi of Fe-doped B2-ordered NiAl alloys with different doping levels
Authors: Anderson I. M. , Duncan A. J. , Bentley J.
Published: June 2020

Recently, a formulation of the ALCHEMI technique has been presented that yields exact expressions for bestfit parameters in terms of the ionization localization constants and site distributions of three elements distributed over two sublattices. The application of this formulation to a NiAl-based B2-ordered alloy doped with 10% Fe used a graphical plotting technique to show that the size of the standard error of the best-fit parameters (and therefore of the site distributions) correlates with the extent to which the plotted data define a unique plane. The definition of the plane depends both upon the scatter of the data (Poisson statistics) and the spread of data over the best-fit plane (the variety of channeling conditions sampled). In this paper, the graphical plotting technique is applied to Fe-doped NiAl B2-ordered alloys of composition Ni0.5-xFexAl0.5 with x ∊ {0.02, 0.10}.

Thin foil specimens of each composition were examined in a Philips CM 12 operated at 120 kV and equipped with an EDAX 9900 ultra-thin window energy-dispersive X-ray spectrometer.
A standard organic sample for evaluating the imaging capabilities of Scanning Electron Microscopes
Authors: Echlin Patrick
Published: June 2020

We have been evaluating several digital scanning electron microscopes prior to the eventual purchase of an instrument. Most manufacturers demonstrate the capabilities of their instruments by using test specimens such as ultra-thin films of sputtered or evaporated noble metals, semi-conductors and photo resists and highly polished multi-compositional specimens made up of light and heavy elements. The microscope we need will be used for imaging and analysis by people from bio-medical laboratories and we are particularly interested in the quality of images we can obtain at low voltages and low beam currents from uncoated and coated samples and whether the specimens suffer any contamination and beam damage during examination and analysis. We do not envisage working at accelerating voltages much above 15keV. We needed a standard organic sample which was stable and easy to prepare and representative of the type of material we would be examining in the microscope we will eventually purchase. After investigating polystyrene spheres and a number of more natural bio-organic samples, including coffee creamer, starch, flour, pollen grains and spores we discovered that spray dried milk is an ideal sample to use for these instrumental evaluations.
Doping-induced contrast in secondary electron images of silicon
Authors: Venables David , Maher Dennis M.
Published: June 2020

As device dimensions in integrated circuits continue to decrease to dimensions on the order of 0. 1μm, obtaining two dimensional maps of the dopant distribution becomes increasingly important. In particular, process simulators attempt to predict the extent of both lateral and vertical diffusion of the dopants. However, experimental information on lateral diffusion has been difficult to obtain, although a variety of techniques based on microscopic and electrical data have been attempted. Recently, Perovic et al. showed that direct secondary electron (SE) images of n-i-p-i superlattice structures in Si could be obtained in a field-emission scanning electron microscope (FESEM). They suggested that this “electronic contrast” was due to the difference in band-bending behavior between n and p-type materials at the specimen surface. In this paper, we show that this phenomenon can be exploited to reveal direct two dimensional images of the extent of lateral and vertical diffusion of dopants in patterned silicon wafers. In addition, we show that the contrast exhibited by the doped regions is a strong function of electron beam energy.
The use of high-resolution FESEM to study solid-state phase transformations and reactions
Authors: Kotula P. G. , Erickson D. D. , Carter C. B.
Published: June 2020

High-resolution field-emission-gun scanning electron microscopy (FESEM) has recently emerged as an extremely powerful method for characterizing the micro- or nanostructure of materials. The development of high efficiency backscattered-electron detectors has increased the resolution attainable with backscattered-electrons to almost that attainable with secondary-electrons. This increased resolution allows backscattered-electron imaging to be utilized to study materials once possible only by TEM. In addition to providing quantitative information, such as critical dimensions, SEM is more statistically representative. That is, the amount of material that can be sampled with SEM for a given measurement is many orders of magnitude greater than that with TEM.

In the present work, a Hitachi S-900 FESEM (operating at 5kV) equipped with a high-resolution backscattered electron detector, has been used to study the α-Fe2O3enhanced or seeded solid-state phase transformations of sol-gel alumina and solid-state reactions in the NiO/α-Al2O3system. In both cases, a thin-film cross-section approach has been developed to facilitate the investigation. Specifically, the FESEM allows transformed- or reaction-layer thicknesses along interfaces that are millimeters in length to be measured with a resolution of better than 10nm.
Digital image acquisition for the Hitachi S-900 field-emission SEM
Authors: Erlandsen S. L. , Telega P. , Chi E. , Dobson W. , Egelman E.
Published: June 2020

Users of the Hitachi S-900 field emission SEM attempting to do high resolution topographical studies of cell surfaces (or macromolecular assemblies) and correlative localization of colloidal gold probes are handicapped by imaging conditions related to contamination or radiation damage of the specimen surface since secondary (SE) and backscatter (BS) electron imaging must be done consecutively.

We have developed a digitial acquisition system for the S-900 FESEM using an analog/digital conversion board on the VME bus of a Silicon Graphics IRIS, using the conventional and graphics memory for image storage, rather than using a frame grabber with its internal A/D and frame memory. A DT-1492-G board from Data Translation with a 250 kHz throughput was used for the 12-bit A/D circuitry. We collect data at 12-bit resolution, and use the frame buffer memory on the IRIS for separately converting, and then displaying as 8-bit (greyscale, 256 levels) SE and BS electron images.
Microscopy of latex film formation
Authors: Ming Yaqiang
Published: June 2020

Latex here denotes a stable colloidal dispersion of polymer in solvent. The solvent usually is water. Large tonnages of latices are used in paper coatings, paints, and growing numbers of other waterbased coatings. All these applications require the latices to be film-forming, at least to a degree. Despite past investigations, the mechanisms of film formation are not well understood and are now being studied intensively in several places.

Our goal is to understand how a suspension of latex particles in water or other solvent becomes a continuous film, one monolayer or multiple layers deep. Several techniques have been employed: transmission electron microscopy ( TEM ) including replication, freeze-fracture, and microtome sample preparations, small angle neutron scattering ( SANS ); cryogenic scanning electron microscopy ( Cryo-SEM ), and atomic force microscopy ( AFM ). TEM is tedious and requires small thin samples; SANS is expensive, time consuming, and difficult to interpret; AFM is easy to use, but images must be interpreted with caution because artifacts can prevail.
Differential height characteristics of plasmid and G-wire DNA as determined by AFM
Authors: Marsh T. C. , Vesenka J. , Henderson E.
Published: June 2020

Atomic-Force Microscopy (AFM) has become an effective tool in the three dimensional characterization of biological systems and is capable of Angstrom sensitivity in the vertical dimension. One unresolved dilemma is that the observed height (diameter) of B-DNA being about 10Å, is less than half its x-ray diffraction value. In this paper we attempt to determine the source of this discrepancy by comparing plasmid DNA co-deposited with a novel form of DNA called “G-wires” (Figure 1). G-wires are formed by G-rich sequences. They are composed of G-4 DNA, a quadruple helical structure. X-ray data of G-4 DNA gives a diameter of 27Å, comparable to that expected for B-DNA (20 to 25Å). In the AFM these structures have a significantly greater height (av. = 22 Å) compared to double stranded (av. = 7 Å) or supercoiled B-DNA (av. = 14 Å) (Figure 2). Thus, the apparent height of nucleic acids in the AFM is dependent upon their innate structural characteristics.
Measuring intermolecular binding forces with the Atomic-Force Microscope: The magnetic jump method
Authors: Hoh J. H. , Hillner P. E. , Hansma P. K.
Published: June 2020

The atomic-force microscope (AFM) can measure forces between atoms and molecules with a sensitivity of <10−12 N. By coating the AFM tip with specific molecules the types of interactions that can be examined will be greatly extended. Recently tips with biotin attached have been used to probe surfaces coated with avidin or streptavidin, to measure the respective bond strength.

We have developed a novel approach to measuring intermolecular forces with the AFM that employs paramagnetic beads coated with one of the molecules to be studied. Beads are incubated with a surface coated with the second molecule, and allowed to form a specific bond. A small magnet glued to an AFM cantilever is then advanced toward the bead until the bond with between the two molecules breaks and the bead “jumps” to the magnet. The deflection of the cantilever provides a direct readout of the interaction force at the “jump,” and thereby a measure of the bond strength.
High-resolution images of cobweb threads of black widow spider Lactradectus mactans by Atomic-Force Microscopy
Authors: Nguyen A. N. , Moore A. M. F. , Gould S. A. C.
Published: June 2020

Its unique mechanical properties make spider silk well-suited to the capture of prey. Orb webs capture prey by dissipating kinetic energy of prey; therefore, high strain and low resilience are important properties of the silk. Cobwebs capture prey with thread breakage and entanglement; therefore, other properties may be more important. Studies reveal that orb web silks consists of proteins arranged in anti-parallel beta sheets. X-ray diffractions reveal orderly crystal regions interspersed with amorphous regions. Silks of different functions from the same web consist of similar proportions of amino acids, yet differ significantly in mechanical properties. It has been suggested that the amorphous regions play a role in determining mechanical properties of spider web. Given these differences in types of orb web silk threads from a single web, we expect to find different structural properties in the cobweb. We present our progress in measuring the structural properties of the cobweb of the black widow spider, Lactradectus mactans, at the molecular level. Our initial results consist of high resolution atomic force microscope (AFM) images of the thread.
Microscopy of melt-textured 1-2-3 cuprate superconductors
Authors: Ringnalda J. , Kiely C. J. , Pollard R. , McCartney D.G. , Beanland R.
Published: June 2020

There has been a concentrated effort to increase the critical current (Jc) carrying capabilities of the cuprate 1-2-3 superconductors. The microstructure has been shown to play an important role in this, and one of the main current research thrusts is aimed at tailoring the microstructure in order to get the required (Jc) improvements. However, because of the complex nucleation and growth kinetics of this system, progress towards commercially viable superconductors has been slow. It has been demonstrated that by carefully controlled heating and cooling routines, the microstructure of the material can be successfully textured. The effects of this type of elevated temperature treatment on the microstructure of these materials are detrimental to its compositional homogeneity, i.e. because the material melts incongruently, it is not possible to maintain the 1-2-3 composition uniformly throughout the material. In this work, the microstructure of 1-2-3 has been inspected before and after heat treatments using transmission electron microscopy (TEM).
HREM of interfaces between YBa2Cu3O7 thin films grown on LaGaO3
Authors: Roy T. , Mitchell T. E.
Published: June 2020

Thin films of superconducting YBa2Cu3O7 have been grown successfully on a number of different substrates by a variety of techniques. Superconducting transition temperatures Tc are as good as the best bulk material. More importantly, critical current densities Jc are higher in the best thin films than in material made by any other technique. Thin films grown on single crystals with the perovskite structure, e.g. SrTiO3, LaAlO3 and LaGaO3, have been particularly successful. In the present paper, HREM has been used to study the interface between YBa2Cu3O7 and the LaGaO3 substrate.

Electron beam evaporation of Cu and Y and thermal evaporation of BaF2 onto (001) LaGaO3 single crystal substrates produced an almost amorphous precursor. This was subsequently annealed in wet and dry O2 at 850°C followed by a further anneal in dry O2 at 400°C. Typical values of Jc were better than 107A/cm2 at 7K. Cross-sectional TEM specimens cut parallel to the (110) plane were prepared by the sandwich technique with the final ion-milling being performed at liquid nitrogen temperatures to minimize damage.
Electron Microscopy study of thallium-based superconducting oxides
Authors: Yang D.Y , Hu J.J , Li F.H.
Published: June 2020

Some Tl-based superconducting oxides are usually not homogeneous in composition, structure and microstructure so that X-ray and neutron diffraction analyses are powerless. This paper reports some results of electron microscopy study on Tl-Sr-Ca-Er-Cu-O and Tl-Ba-Al-Ca-Cu-O superconducting oxides.

The samples of nominal compositions TlSr2CaEr0.5Cu3Oy and Tl0.4BaAl0.6Ca3Cu3Oy were prepared by solid reaction. The sintered pellets were crushed into fine fragments and dispersed in CCl4. The suspension was dropped onto microgrids. The specimens were observed with JEM-200CX high resolution electron microscope and H- 9000NA analytical electron microscope.

Two phases are identified in TlSr2CaEr0.5CU3Oy by electron diffraction analysis. The lattice parameters are a=b=0.386nm, c=2.92nm(phase 1) and a=b=0.379nm, c=3.54nm(phase 2). The two phases are intergrown as shown in the lattice image taken with electron beam along the direction(Fig.1). In the image with a higher magnification(Fig.2) dark bands correspond to Tl-O layers and bright bands to perovskite blocks and both of them may vary in their spacings.
Modulated structures in Nd2−xCexCuO4
Authors: Li D.J. , Zhang J.P. , Marks L.D.
Published: June 2020

The recent discovery of an n-type superconductor of general formula Nd2-xCexCuO4 has opened up the possibility that there exists a new family of high temperature superconductors. Initially identified as having a Nd2CuO4-type structure, more recent reports have mentioned a second phase which contains a superstructure. Although the diffraction data presented in both these later papers is very similar, the exact form of the modulation is presented as different. Important questions are which phase is the active superconductor; what is the structural and chemical relationship between the modulated an unmodulated phases and what is the correct interpretation of the modulated unit cell. In addition, it has been suggested that the modulations are due to ordering of oxygen defects, a point which needs to be rigorously tested.

Two Nd2-xCexCuO4 compounds were prepared by the identical solid-state reaction, followed by sintering at 1170° C for 12 hours.
Atomic imaging and spectroscopy of bismuth cuprate high temperature superconductors
Authors: Ramesh R. , Bagley B.G. , Tarascon J.M. , Green S.M. , Rudee M.L. , Luo H.L. , Hetherington C.J.D. , Thomas G.
Published: June 2020

The newly discovered Bismuth cuprate superconductors belong to a general class of oxides that are termed as polytypoids. The different polytypoids have the same general structure but the repeat sequence in the structure changes with the composition, thus the term polytypoid. In these materials, with the general formula of Bi2Sr2Can−1CunOy (where n=1,2,3 or 4), the superconducting transition temperature increases with the value of n (up to n=3). The details of the cationic stacking and defects in the structure of the different polytypoids have been characterized using atomic resolution electron microscopy in conjunction with image simulations, image processing, microdiffraction and fine probe xray microchemical analysis. In sintered samples, the microstructure and consequently the transport properties have been shown to be sensitive to the structural and microchemical details adjacent to grain boundaries.