bluuebunny/crossref_metadata_2025 huggingface dataset:
Uv Raman Microscopy: Spectral and Spatial Selectivity and Even High Sensitivity
Authors: Munro Calum , Pajcini Vasil , Asher Sanford A
Published: July 2020

We have constructed a new UV Raman microspectrometer designed around an Olympus microscope, a single spectrograph and an intensified CCD detector (Fig. 1). We utilize CW excitation from either an intracavity frequency doubled Ar+ laser (257, 244, 229 nm) or a Kr+ laser (206 nm). We optimized the throughput by utilizing specially prepared dielectric coated Rayleigh rejection filters.

In one application we used this instrument to speciate and determine the spatial distribution of non diamond carbon species in CVD diamond samples (Fig. 2). We find that these non diamond carbon species are localized in the interstitial areas between diamond crystals.

In another application we demonstrated the utility of UV Raman microspectroscopy for the rapid, incisive and non-destructive characterization of meteorites and interplanetary dust particles (IDP). In addition to probing the structure and distribution of predominant mineral matrices of these materials, UV excitation enables us to the characterize the small but significant carbonaceous components included within these samples.
Optical Non-Linearities in Infrared Mircospectroscopy: A Preliminary Study into the Effects of Sample Size and Shape on Photometric Accuracy
Authors: Stewart SA , Sommer AJ
Published: July 2020

Several years ago this laboratory reported on the effects of stray light in an infrared microscope and its consequences on the spatial resolution achievable in a typical line scan or mapping experiment of a polymer film. In this study it was demonstrated that unless the size of the sampled area was greater than twice the wavelength of light employed for the analysis, a significant amount of stray light from near neighbors was contained in the sampled areas. Further, this generalization is only valid for sample sizes above the diffraction limit. The results of this study are summarized in Table. The ratio of the sampled area to that of the aperture size (corresponding to expected sample size) can be thought of as a degradation factor in spatial resolution. In this earlier study the sample geometry was chosen to minimize stray light effects arising from the sample size and shape.
Imaging Spectroscopy Using Fiber Optics
Authors: Michael Angel S , Trey Skinner H , Marquardt Brian J
Published: July 2020

Optical fiber probes are routinely used with optical spectrometers to allow measurements to be made on remotely located samples. In most of these systems, however, the optical fibers are used as non-imaging “light pipes” for the transmission of laser light, and luminescence or Raman signals to and from the sample. Thus, while these systems are suitable for remote spectroscopy, they are limited to single-point measurements. In a recent paper, we showed that a small-diameter (i.e., 350 μm) coherent optical fiber bundle can be combined with an AOTF-based imaging spectrometer for fluorescence and Raman spectral micro-imaging with increased flexibility in terms of sample positioning and in-situ capabilities. The previous paper described the operation of the fiber-optic microimaging probe and AOTF imaging system and showed preliminary Raman and fluorescence images for model compounds with 4 μm resolution. We have extended this work to include a discussion of the lateral and vertical spatial resolution of the fiber-optic microprobe in a non-contact proximity-focused configuration.
Exploratory Investigation of Synthetic Zeolites by Near-Infrared Fourier-Transform Raman Microspectroscopy
Authors: Etz Edgar S
Published: July 2020

Zeolites are complex, three-dimensional, hydrated crystalline aluminosilicates that have porous structures with channels or cages of various dimensions. In the simplest way they can be represented by (Na2,K,Ca,Ba) [(Al,Si)O2]nxH2O. They may be either of natural or synthetic origin. As high-surface-area materials, they take on great technological importance, foremost in surface science and catalysis. The structure of the zeolite is critical to its function. Structure information is commonly obtained by x-ray and neutron diffraction, NMR, IR, and Raman spectroscopy techniques. Synthetic zeolites are produced in enormous quantities worldwide and are key to critical technologies. Yet, no real zeolite standards exit that are defined and certified. NIST, with input from industry and academia, has begun a measurement program to certify various physico-chemical properties for a suite of synthetic zeolite powder standard reference materials (SRMs) and research materials (RMs). These proposed "standard" zeolite materials span a range of pore sizes, SiO2/Al2O3 ratios, ring sizes, structural building units, and cage sizes.
Experimental Validation for Infrared Microspectroscopy (IMS)
Authors: Reffner John A , Hornlein Robert W , Hellgeth John W
Published: July 2020

In today’s laboratory environment, it is important that the performance of analytical instruments be tested and validated. In the past, the testing of infrared micro- spectrometers was based solely upon measuring a signal-to-noise (SNR) ratio of the 100% line. This test is insufficient. It is important to test how well the sample area is defined. In all current commercial infrared spectrometer systems, remote image plane masks are used to define specific areas for infrared spectral analysis. A special test specimen has been developed to evaluate the accuracy of the mask’s ability to define the sample area.

IMS resolution test plates were constructed by photolithographic reproduction of a series geometrically shaped thin polymer films on both infrared transparent windows and gold mirrors. First the surface of the plate is coated with a thin, uniform layer of a photoresist polymer. Then this surface is printed with geometrical patterns such as bands, discs and squares.
Auger To The Max: Can We Color The Atoms In Our Stem Images?
Authors: Hembree Gary G
Published: July 2020

A probable future development in materials science is the selective manipulation of structure on an atom by atom basis. Along with the ability to manipulate atoms we will need to be able to tell if the correct ordering has been achieved. Thus the ultimate goal of spectroscopic imaging will be to create a species-labeled two or three dimensional map of the atom positions in the sample. In this paper we will show how far we have progressed towards this goal with Auger electron spectroscopy (AES), how much further we have to go and what the prospects are for overcoming the known obstacles.

AES is inherently surface-sensitive because low energy electrons have very small inelastic mean free paths. This scattering mechanism insures that only those electrons created within a few atomic diameters of the sample surface facing the detector will contribute significantly to the measured signal.
Secondary Ion Mass Spectrometry For The Year 2000 and Beyond: Are There Any Showstoppers?
Authors: Magee Charles W
Published: July 2020

The National Technology Roadmap of Semiconductors (NTRS) shows that future semiconductor processing will require the formation of junctions less than 30nm deep with gate lengths approaching, and becoming less than, 0.lum. Techniques must be available to measure these in-depth, as well as spatial, distributions.

Secondary ion mass spectrometry (SIMS) has long been the technique of choice for measuring dopant profiles in semiconductors. The depth of the junctions formed has, up top now, always been sufficiently deep into the semiconductor that the effects of the analysis on the measured profile (i.e. atomic mixing) could be ignored for the most part. In addition, gate lengths have been sufficiently large that diffusion of LDD implants under the gate have not contributed significantly to short-channel effects. However, the relentless decrease in the required junction depths and gate lengths may mean that the situation may change in the near future.
Interpretation of Changes in Peak Shape and Position of the Oxygen Kα Characteristic X-Ray Line
Authors: Harrowfield I R , MacRae C M , Rajakumar V , Wilson N C
Published: July 2020

Changes in shape and position of long-wavelength X-ray lines measured by wavelength dispersive spectrometry (WDS) reflect changes in the density of bonding states of the emitting atom. However, some features of soft X-ray spectra are not due to bonding. For example, small peaks on the shorter-wavelength side of a characteristic peak probably arise from double ionization, absorption effects must be considered and there may be artefacts from the diffracting crystal itself. Nonetheless, when there are dramatic shape changes, spectrometry of soft X-rays can usefully augment microanalysis particularly in the study of tiny particulates which may be difficult to prepare for transmission microscopy.5 Two examples of spectrometry of O Kα follow.

Oxidation of very fine TiB2 particulates is a problem in the ceramics industry. The backscattered electron (BSE) micrograph in fig. 1 shows a particle section with a central core of TiB2 and a darker, oxidised rim analysing roughly like a borate, interspersed with brighter regions, probably TiO2.
Feasibility of Be Analysis For Geologic Materials Using Epma
Authors: Evensen Joseph , Meeker Gregory P
Published: July 2020

Microanalytical techniques for the analysis of beryllium using the electron probe have been evaluated for Be metal, Be-rich silicate minerals, and three Be-rich synthetic silicate glasses. Despite difficulties typical of ultra-light element analysis in geologic materials, quantitative data for Be may be obtainable through careful analytical measurements, determination of optimal operating conditions, and consideration of parameters such as sample orientation and beam-induced migration.

Analyses for Be were obtained using a layered synthetic microstructure “crystal” (Mo/B4C) on the JEOL 8900 electron microprobe at the USGS, Denver, Colorado. The optimum accelerating voltage for Be detection was determined to be 8kV (Fig.l). Beryllium analyses in glass and mineral phases were successful using a beam current of 30nA and a 50 μm beam diameter. Due to low count rates, peak counting times of 10 minutes (beryl) and 30 minutes (glass) were required in order to achieve reasonable counting statistics and detection limits.
Quality Assurance of Energy Dispersive Spectrometry Systems
Authors: Steel E B , Marinenko R B , Myklebust R L
Published: July 2020

Monitoring the performance capabilities of energy dispersive X-ray spectrometers (EDS) and related x-ray analysis electronics and software is important for determining and improving the reliability, sensitivity, and accuracy of the x-ray analysis system. In addition, there is a growing popularity of quality systems through laboratory accreditation and ISO 9000 related programs that require set quality control procedures for analytical instrumentation. Having similar standard procedures amongst labs would allow direct intercomparison of results. This intercomparison would help labs and manufacturers determine what are normal versus abnormal results and lead to higher quality instruments and analyses. We have been developing a standard operating procedure for the characterization of EDS x-ray analysis systems on electron beam instruments.

We are designing the procedure to maximize the efficiency of each quality control (QC) measurement so that we spend as little time monitoring the analysis system as is possible. We first chose useful QC specimens and then designed data collection methods.
First X-Ray Microprobe and Microspectroscopy Results From The Gsecars Sector At The Advanced Photon Source
Authors: Rivers Mark L , Sutton Stephen R , Eng Peter , Newville Matthew
Published: July 2020

The Advanced Photon Source (APS) at Argonne National Laboratory is a third-generation synchrotron x-ray source, optimized for producing x-rays from undulators. Such undulator sources provide extremely bright, quasi-monochromatic radiation which is ideal for an x-ray microprobe. Such microprobes can be used for trace element quantification with x-ray fluorescence, or for chemical state determination with x-ray absorption spectroscopy. The GeoSoilEnviroCARS (GSECARS) sector at the APS is building an x-ray microprobe for research in earth, planetary, soil and environmental sciences.

The GSECARS undulator source is a standard APS Undulator “A” which is a 3.3 cm period device with 72 periods. The energies of the undulator peaks can be varied by adjusting the gap, and hence the magnetic field of the undulator. The energy of the first harmonic can be varied in this way from approximately 3.1 keV to 14 keV. A measured undulator spectrum is shown in Figure 1.
Quantitative Chemical Analysis of Sub-Micron Phase Segregation In Polyurethane Polymers by Soft X-Ray Spectromicroscopy
Authors: Hitchcock AP , Urquhart SG , Rightor EG , Lidy W , Ade H , Smith AP , Warwick T
Published: July 2020

Phase segregation is important in determining the physical and chemical properties of many complex polymers, including polyurethanes. Achieving a better understanding of the connections between formulation chemistry, the chemical nature of segregated phases, and the physical properties of the resulting polymer, has the potential to greatly advance the development of improved polyurethane materials. However, the sub-micron size of segregated features precludes their chemical analysis by most existing methods. Near edge X-ray absorption spectroscopy carried out with sub micron spatial resolution provides one of the few suitable means for quantitative chemical analysis (speciation) of individual segregated phases. We have used the NSLS and ALS scanning transmission x-ray microscopes (STXM) to record images and spectra of both model and real polyurethane polymers. Relative to energy loss spectroscopy in a transmission electron microscope, STXM has remarkable advantages with regard to a much lower radiation damage rates and much higher spectral resolution (∼0.1 eV at the C ls edge), with a spatial resolution (∼0.1 μm) adequate for many real world problems in polymer analysis.
Correlation Between Functional Recovery From Ischemia and Sarcoplasmic Reticulum Calcium Content Measured by Electron Probe MicroAnalysis
Authors: Barrett LS , Sweet WE , Moravec CS
Published: July 2020

Myocardial ischemia is defined as a cessation of blood flow to the heart, and reperfusion as a return to normal flow conditions following ischemia. It has been shown that contractility decreases immediately during ischemia and diastolic dysfunctiuon may persist during reperfusion. Changes in contractility can be directly attributed to intracellular Ca2+ handling, either by altering the myofilament sensitivity to calcium or by affecting Ca2+ cycling by the sarcoplasmic reticulum (SR). Previous studies have demonstrated that there are changes in intracellular Ca2+ cycling following ischemia and during reperfusion. The goals of the present study were: 1) to assess the effects of varying periods of ischemia on the size of the releasable (diastolic) SR Ca2+ store; 2) to determine whether changes in the size of the SR Ca2+ store are related to ischemia or reperfusion; 3) to correlate changes in the size of the SR Ca2+ store following ischemia with functional recovery of the heart.
Magnesium Content and Distribution During Differentiation of Hl60 Cells
Authors: Di Francesco A , Desnoyer RW , Wolf FI , Covacci V , Cittadini A , Bondt M
Published: July 2020

Mg is present in all living cells as free and bound Mg. Previous observations have shown a positive correlation between total Mg content and proliferative rate in several different cell types (1). To investigate the association between Mg and cell proliferation, we utilized a human promyelocytic leukemia cell line, HL60, that can be induced to differentiate in vitro to neutrophil-like cells, by retinoic acid (RA) and other compounds.

To further investigate this question, we analyzed elemental compartmentalization in HL60 cells before and after differentiation using electron probe microanalysis (EPMA). Differentiation to neutrophil-like cells was induced by culturing the HL60 cells for 96 hours in the presence of 1 μM RA. Cells were washed, pelleted, then rapidly frozen in liquid ethane, cooled to -185°C with liquid N2. Ultrathin cryosections were cut from the surface of the frozen cells, freeze-dried overnight and carbon coated. X ray spectra were collected at -100°C and at 80 keV accelerating voltage in a Philips CM 12 STEM equipped with LaB6 gun and an EDAX 30-mm2 Si(Li) energy dispersive x-ray detector and multichannel analyzer.
Towards The Automatic Segmentation of Multiple Micro Analytical Maps
Authors: Bonnet N
Published: July 2020

Multi-dimensional data sets are now produced by many analytical instruments. They include the series of spectra, the series of images and spectrum-images, which can be considered as a series of spectra at different positions or series of images at different wavelengths.

The automatic (or semi-automatic) handling of such data sets requires that new multivariate analysis methods are made available. For instance, if we restrict ourselves to image sets, there is a need to deduce (from the multiple maps) a single map in which regions of the specimen with approximate homogeneous properties (composition...) can be identified and quantified.

At the present time, only a limited number of software tools are available for this purpose:- the scatterplot allows the display of the correlations between two or three spectra or images,- Interactive Correlation Partitioning (ICP) allows the user to divide the scatterplot into several parts and to reconstitute images with one selected part,-Multivariate Statistical Analysis (MSA) allows us to analyze a data set composed of several images and to identify the different sources of information, and to filter out noise and experimental artefacts.
Multivariate Statistical Analysis of Spectrum Lines and Images
Authors: Anderson Ian M , Bentley Jim
Published: July 2020

Recent developments in instrumentation and computing power have greatly improved the potential for quantitative imaging and analysis. For example, products are now commercially available that allow the practical acquisition of spectrum images, where an EELS or EDS spectrum can be acquired from a sequence of positions on the specimen. However, such data files typically contain megabytes of information and may be difficult to manipulate and analyze conveniently or systematically. A number of techniques are being explored for the purpose of analyzing these large data sets. Multivariate statistical analysis (MSA) provides a method for analyzing the raw data set as a whole. The basis of the MSA method has been outlined by Trebbia and Bonnet.

MSA has a number of strengths relative to other methods of analysis. First, it is broadly applicable to any series of spectra or images. Applications include characterization of grain boundary segregation (position-), of channeling-enhanced microanalysis (orientation-), or of beam damage (time-variation of spectra).
Data Categorization and Neural Pattern Recognition
Authors: Gatts C , Mariano A
Published: July 2020

The natural ability of Artificial Neural Networks to perform pattern recognition tasks makes them a valuable tool in Electron Microscopy, especially when large data sets are involved. The application of Neural Pattern Recognition to HREM, although incipient, has already produced interesting results both for one dimensional spectra and 2D images.

In the case of ID spectra, e.g. a set of EELS spectra acquired during a line scan, given a “vigilance parameter” (which sets the threshold for the correlation between two spectra to be high enough to consider them as similar) an ART-like network can distribute the incoming spectra into classes of similarity, defining a standard representation for each class. In order to enhance the discrimination ability of the network, the standard representations are orthonormalized, allowing for subtle differences betwen spectra and peak overlapping to be resolved. The projection of the incoming vectors onto the basis vectors thus formed gives rise to a profile of the data set.
Application of Nano-Scale Eels Spectrum Lines To Grain Boundaries
Authors: Bruley J , Cho J , Hanner MP , Chan HM
Published: July 2020

Polycrystals containing small quantities of impurity can exhibit dramatically different properties from that of the pure material. One example of this is the tenfold increase in the creep resistance of Y or La doped alumina relative to ultra-pure alumina. Such changes are correlated to grain boundary segregation, however the segregant’s potency to influence properties remains unexplained. Determining the driving force to segregation only partially addresses this issue. A full understanding must take account of the chemical bonding and structural changes occurring at the boundary after segregation. The purpose of this study is to observe the electronic structure associated with the segregating species using EELS spectrum-line profiling. This is accomplished by monitoring the segregation profile along with the characteristic near edge absorption fine structures which reflect changes in the localized density of unoccupied states along that profile. In these experiments a finely focused beam was sequentially stepped across the boundary of interest and a spectrum recorded at each step.
Improved Measurement and Analysis of Series of Valence Electron Energy Loss Spectra and The Local Electronic Structure
Authors: Müllejans H , French R H , Duscher G , Rühle M
Published: July 2020

The local electronic structure of ceramic materials can be determined from valence electron energy loss (Veel) spectra via the dielectric function. The quality of the data is comparable to vacuum ultraviolet spectroscopy with the added benefit of high spatial resolution. We have built and implemented a system for spectrum imaging which not only allows automatic data acquisition but also analysis of the full data set. The system consists of a Gatan PEELS and a Gatan Digiscan fitted to a VG HB501 UX STEM and home-built hardware additions. The hardware extensions allow to acquire 1, 2, 3, 4 or 8 spectra for each pixel and in the case of 2 spectra/pixel to vary the exposure time of the specimen to the primary electron beam by controlling the beam blanker (Fig. 1). The first spectrum (2 to 20 ms) contains an unsaturated zero loss peak and the second spectrum (0.05 to 100 s) at the same position the plasmon peak near to but below saturation (Fig. 2).
Ab-Initio Calculations of Density of States for Ti-Oxide
Authors: Duscher G , Köstlmeier S , Meyer B , Elsässer C , Browning N
Published: July 2020

Electron energy-loss spectroscopy (EELS) has been shown to be a powerful tool to determine not only the chemistry, but also the electronic and atomic structure at grain boundaries by analysing the energy-loss near-edge structure (ELNES). However, as the experimental ability to obtain quality spectra from interfaces with high-spatial resolution is relatively new, the interpretation of ELNES has been mostly qualitative. Here we discuss the ability of ab-initio density of state calculations to perform detailed quantitative analysis at interfaces.

In this methodology, ignoring any multiparticle effects such as excitons, the ELNES can be described as the symmetry projected density of states (DOS) and a matrix element varying slowly with energy. The calculated DOS, which best reproduce the experimental ELNES, are obtained using density functional theory (DFT) in the local density approximation (LDA) (i.e.: Weng et al.). Traditionally, because a high number of atoms (> 60) is needed to reproduce the periodicity of interface structures, more approximate methods such as the real-space multiple scattering method3 and its equivalent in reciprocal space (KKR-method) were used.
Electronic Structure Investigations of γ-Tial.
Authors: Lie K , Holmestad R , Marthinsen K , Høier R
Published: July 2020

The intermetallic compound TiAl is a promising material for applications at high stress and high temperature. It has good balance between lightness, strength and oxidation resistance, but suffers of an intrinsic brittleness at lower temperature. Small, ternary additions of V, Cr or Mn are known to increase the ductility of this material. In the present and a recent study we have used electron energy loss spectroscopy as a sensitive test to investigate the electronic structure in these materials. The near edge structure (NES) may give complementary information to e.g. convergent beam electron diffraction (CBED) about the bonding character in these materials.

EELS spectra were collected using a Gatan 666 spectrometer with parallel recording fitted to a Philips CM 30 transmission electron microscope operating at a nominal voltage of 150 kV. The energy resolution (measured as full width at half maximum) was typically around 1 eV. Spectra from areas of similar thickness, as measured relative to the total inelastic mean free path of the 150-keV electrons were obtained.
Local Temperature Determination Using Elfs Spectroscopy
Authors: Qian M , Sarikaya M , Stern E A
Published: July 2020

ELFS spectroscopy (energy loss fine structure) is used to obtain local atomic structure information It can outperform XAFS (x-ray absorption fine structure) not only because of its low Z element sensitivity, but also because of its high spatial resolution and the capability of combining other high resolution TEM measurements. Although TEM continues to gain importance as an indispensable and unique tool to study nanoscale phenomena by providing simultaneous imaging, diffraction, and spectroscopy information, direct observation and quantitative measurements of physical phenomena are also desirable. This paper gives a first-time demonstration of such a measurement, namely local temperature determination in a TEM sample by ELFS.

The principle is simple and as follows. One can measure, with ELFS, the atomic distances up to ±0.01 Å accuracy for the fist shell (typically around 2 Å ) and the second shell (around 3-4 Å). Atomic distances in a sample will change when its temperature changes, the phenomena that are coupled by the macroscopic temperature dependent lattice expansion.
Imaging of Elastic and Inelastic Electron Scattering in Diamond
Authors: Bell David C
Published: July 2020

The physical properties of diamond are some of the most interesting of natural materials. Electron energy-loss spectroscopy studies of a single crystal diamond wedge allow some of the basic electron matter interactions to be studied. The electron energy-loss spectrum has been examined with particular reference to the plasmon excitations in the crystal. The mean-free path of the electrons through the diamond crystal and the nature of the observed features in the energy-loss spectrum have been examined.

A single crystal of diamond was cut and polished to produce a diamond wedge with a 33° angle making it suitable for observation in a transmission electron microscope (Fig. 1). The determination of the geometrical parameters of the crystal wedge involved the analysis of pendellosung fringes (Fig. 2) and comparisons to bloch wave calculations. The gradient analysis plot shown in Fig. 3 allowed the wedge thickness to be determined at any distance from the edge.
Analytical TEM Study of Nanophase Precipitation in Nial Alloys
Authors: Wilson A W , Howe J M , Garg A , Noebe R D
Published: July 2020

Alloying additions have been found to enhance the mechanical properties of NiAl through solid solution strengthening and the precipitation of 2°d phases. The precipitation of fine, homogeneously nucleated ß' (Ni2Al (Ti,Hf)) has been observed and characterized by dark-field imaging and electron diffraction. The exact composition of these and other precipitates, however, remains unknown. In this study, the composition of the fine ( <20 nm) ß’ precipitates in NiAl alloys is measured and compared to that of well-developed ß’ plates in the matrix.

Two directionally solidified NiAl single-crystal alloys, NiAl-3Ti-0.5Hf and NiAl-7Ti (at.%) were grown by a Bridgeman technique using high purity alumina crucibles. Both ingots were homogenized for 32 h at 1644 K. In addition, the NiAl-3Ti-0.5Hf sample was aged at 1255 K for 6 h and furnace cooled. Samples for transmission electron microscopy were prepared from 3 mm diameter cylinders electro-discharge machined from the heat-treated ingots.
Orientation Analysis by Computer-Aided Diffraction Pattern Matching in The TEM
Authors: Thomas L E , Hugo R C , Stanley J T
Published: July 2020

Electron diffraction patterns taken in transmission electron microscopes are widely used for phase identification and orientation determination of crystallites as small as hundreds or even tens of nanometers in size. The analyses typically require rather tedious measurement of the patterns, and matching of calculated d-spacings and angles with those of known phases. Recently, the analysis of these patterns has been facilitated by powerful desktop computer programs that use digitally captured images for on-line measurement and simulation matching of" the diffraction spot and Kikuchi line patterns. This presentation will illustrate an application of computer-aided pattern simulation and matching for precise determination of crystal orientations.

Two experimental TV camera arrangements were used to record diffraction patterns in a TEM. These included a cooled-CCD camera located on the electron optical axis below the microscope viewing chamber, and a simple TV-rate CCD that recorded directly from the inclined fluorescent viewing screen of the microscope.
Alternative Collection Mode for Rdf Acquisition in Feg-STEM
Authors: Bell David C , Garratt-Reed Anthony J , Hobbs Linn W
Published: July 2020

Overview Radial distribution function (RDF) information obtained from amorphous glasses can provide important near and medium range structure information, determination of this information has important consequences for the encapsulation and the long term stability of nuclear waste material.

RDF data has been obtained from samples of waste glass and amorphous quartz. This data was obtained using a Vacuum Generators HB603 FEG-STEM, equipped with a GATAN Digi-PEELS. Post specimen scanning was employed to minimize the effect of spherical aberration that is present in the incident beam rocking mode.

Previous data obtained using the main-scan coils and rocking the incident beam on the specimen, diffraction information collected from out to 16 nm-1. The intensity of the information falls of rapidly as the inverse forth power of the scattering angle, out to the point where the signal to noise of the detector becomes unity. This point is limited by the sensitivity of the detector and the spherical aberration of the objective lens which limits the ultimate collection angle, regardless of the sensitivity of the detection system.
Surface Structures from Direct Methods Using a Genetic Algorithm
Authors: Landree E , Collazo-Davila C , Marks L D
Published: July 2020

Two two-dimensional atomic models were constructed to test the application of Direct Methods for solving surface crystal structures (atomic positions are listed in Table 1). The use of Direct Methods to solve three dimensional structures from X-ray diffraction has been well established for several years. However to the best of our knowledge never before had this technique been applied to 2-D surface structures. A Genetic Algorithm (GA) search routine was implemented for exploring possible solutions.

The models were constructed using electron scattering factors to calculate the intensities and phases for beams out to 1 Å resolution (Fig. 1). Since electron diffraction from surfaces has been shown to be nearly kinematical X-ray and electron scattering can be handled identically. An error term was applied to the generated intensities to simulate realistic sampling errors. The generated phases for each model were removed and later used to monitor the solutions calculated by the direct methods.
Evaluation of the Structure Factor of Cuprite and Bonding Chracterisitcs
Authors: Kim M Y , Zuo J M , Spence J C H
Published: July 2020

Cu2O is a semiconductor with a band gap of 2.17eV, and its crystal structure is simple cubic. Oxygen atoms form a bcc structure and each oxygen atom is tetrahedrally coordinated by copper atoms, which makes copper linearly coordinated by two oxygen atoms. The structure of cuprite is interesting because the charge state of Cu and oxygen. The most common charge states of Cu is 2+, however, in cuprite for each oxygen there are two Cu atoms which suggest a 1+ charge state of Cu. Charge density of Cu and oxygen are also interesting because of the high Tc superconductors based on copper and oxygen planes and chains. The superconductivity is believed due to the different charge states of copper and/or oxygen in the Cu-oxygen planes due to the doping or oxygen deficiency. by studying the naturally occurring charge states of Cu in Cu2O and CuO, a better understanding of the relationship between structure and bonding can be achieved for the important copper oxides.
Electron Refraction of Amorphous Nanospheres
Authors: Wang YC , Chou TM , Libera M
Published: July 2020

The phase shift imparted to an incident high-energy electron wave in a TEM is related to the specimen’s electron-refractive properties. These, in turn, are related to the electrostatic potential and, by Fourier transform (1), to the electron scattering factors fe  i(s) for the various atom species i in the specimen and scattering vectors s. The average refractive index is determined by the mean electrostatic (inner) potential, Φo, and can be modelled as Φo = (C/Ω) Σfe  i(s0) [equation 1] where C = 47.878 (V-Å2) and the summation runs over all of the atoms in the unit volume Ω (2). Calculated fe  i(s) data are available from the literature (e.g. 3). These calculations have only been done for neutral atoms and some fully ionized cations and anions. They do not account for electron redistribution due to covalent bonding to which Φo is quite sensitive (4).

This research is making Φo measurements using transmission electron holography. Holograms were collected using a 200keV Philips CM20 FEG TEM equipped with a non-rotatable biprism (5) and a Gatan 794 Multiscan camera.
A Direct Phasing Electron Image of Oxygen Atoms in a Ga-In-Sn-O Ceramic
Authors: Sinkler W , Marks L D , Edwards D , Mason T O
Published: July 2020

In solving complex inorganic structures, often the greatest challenge is to obtain good initial atom positions for Rietveld refinement using x-ray diffraction intensities. In this work, a technique is presented which combines direct phasing with HRTEM and exploits dynamical diffraction effects to obtain an image of oxygen atoms. The technique was used in the structure determination of a monoclinic (Ga0.7In0.3)2SnO5 phase to provide accurate first-guess positions for oxygen atoms for subesquent Rietveld refinement.

The solution of the cation positions of the structure relied on HRTEM images. The image in Fig. 1, taken along the crystal’s short b-axis, has a defocus of approximately -50 nm based on the locations of minima in a weak amorphous component in the power spectra of the through-focus image series. Because this is near Scherzer defocus, one expects dark areas of the image to correspond a large projected potential (making the weak phase object approximation). This was used to get successful initial cation positions for a Rietveld refinement of powder x-ray diffraction data. The final refined structure is shown in Fig. 2, including the oxygen positions.
The Use of Electron Diffraction and High Resolution Imaging to Explain why the Non-Dipolar Molecules of l,3,5-Triamino-2,4,6-Trinitrobenzene Display Strong Powder Second Hamonic Generation Efficiency.
Authors: Voigt-Martin Ingrid G , Li Gao , Yakimanski A
Published: July 2020

The exploration of light for applications in optical integrated devices has received world wide attention during the past decade.Organic compounds are of interest because of their large hyperpolarisabilities β and fast response times as well as offering many diferent types of processing geometry. It has been generally understood in the past that the requirements which must be satisfied by the microscopic system (i.e.the molecule) in order for the macroscopic system (i.e. the crystal ) to display second harmonic generation are the following: (a) the molecule must have a dipole moment μ (b) the molecule must have large components of hyperpolarisability β (c) the molecules must adopt a mutual orientation in the unit cell which avoids centro-symmetry.

In practice, TATB was found to have a very large optical susceptibility,although it did not satisfy conditions (a) and (c). With regard to condition (c), it was suggested that structural defects might explain the appearance of second harmonic generation in a centro-symmetric crystal. For this reason we decided to re-examine the problem using electron microscopy and diffraction.
Coherent of PbTe/MgO Bi-Crystals and its Multislice Simulation
Authors: Tanaka N , Egi M , Kimoto K
Published: July 2020

Atomic structure of hetero-interfaces such as semiconductor/oxide is recently much interested from the viewpoints of the device engineering as well as the interface science. Studies of the interface structures have been performed by transmission electron microscopy (TEM)[1], large-angle convergent beam electron diffraction[2] in the cross-sectional observation mode, and by X-ray diffraction[3], TEM[4] and CBED[5] in the plan-view mode. In the present study we applied a coherent convergent beam electron diffraction (c-CBED) technique to the analysis of the rigid-body shift between vacuum-deposited PbTe and MgO (001) thin crystals in the plan-view mode. The c-CBED technique was originated in nano-diffraction experiments by Cowley[6] and the theoretical analysis by Spence[7]. These results suggested a possibility of direct structure-phase determination from the interference fringes formed at coherent overlaps between the diffraction disks. This technique has been recently revived using TEM on SiC by Vine et al.[8] The present study is the first to be concerned with the analysis of interference fringes in c-CBED patterns from epitaxially grown bi-crystals[9].
Nature of In-Plane Phase Transitions in 2D Crystals of the Mitochondrial Porin, VDAC
Authors: Mannella CA
Published: July 2020

VDAC is a voltage-gated ion and metabolite channel that occurs at high density in the mitochondrial outer membrane. Although VDAC is probably related structurally to bacterial porins, small transmembrane voltages cause it to undergo reversible, partial closures that are not seen with the prokaryotic pores. The “closed” states, which are impermeable to ATP, can be induced by effectors, including a synthetic polyanion. There is evidence that closure involves major rearrangements of the pore structure that are difficult to explain in terms of porin-like β-barrels.

The main source of information about the structure of VDAC is electron microscopy of 2D crystals obtained by phospholipase treatment of outer membranes of fungal mitochondria. The unit cell observed after partial lipid hydrolysis (a = 13.3 nm, b = 11.5 nm, γ = 109°) contains six pores which appear to be structurally equivalent at the resolution of correlation averages of crystals embedded in aurothioglucose or vitreous ice (∼1/1.5 nm−1).
Cluster Analysis of Automated Fine-Particle Analysis Using Scanning Electron Microscopy
Authors: O’Keefe CA , Hurley JP
Published: July 2020

Because of analytical advances, submicron particles as small as 0.2 μm can be characterized for chemical composition, size, and shape using scanning electron microscopy (SEM). Once these characteristics are determined, cluster analysis can be used to group the individual particles into categories based on size, shape, and chemical composition.

Submicron particle analysis is important when characterizing the ash to provide information to help solve ash-related problems in coal combustion and gasification systems. Since a combustion system has an excess of oxygen available, the resulting ash is typically easier to characterize than ash from a gasification system. In a gasification system, the lack of oxygen results in additional categories high in Cl and P.

Adequate dispersion of submicron particles for proper analysis of individual particles is required because of the analysis volume of the SEM beam. Therefore, an aliquot of an aqueous solution with a set sample-to-solvent ratio is drawn while being sonicated. A few drops of solution are placed on a vitreous carbon substrate, allowing for particle dispersion on the surface of a smooth substrate. Next, the particles are analyzed by the fine-particle technique (FPT).
High-Energy-Resolution Microcalorimeter Spectrometer for EDS X-ray Micro Analysis
Authors: Wollman D A , Hilton G C , Irwin K D , Dulcie L L , Newbury Dale E , Martinis John M
Published: July 2020

Si(Li) and Ge Energy Dispersive Spectroscopy (EDS) detectors are commonly used for x-ray microanalysis because they are easy to use, inexpensive to operate, and offer both rapid qualitative evaluation of chemical composition and accurate quantitative analysis. Unfortunately, they are limited by energy resolutions on the order of 100 eV, which is insufficient to resolve many important overlapping x-ray peaks in materials of industrial interest, such as the Si Kα and W Mα peak overlap in WSi2. Although WDS spectrometers with excellent energy resolution (typically 2 eV to 10 eV) can resolve most peak overlaps, qualitative WDS analysis is limited by the need to serially scan over the entire energy range using multiple diffraction crystals. There is a need for a new generation of x-ray spectrometers for microanalysis that combines the excellent energy resolution of WDS spectrometers with the ease of use and the parallel energy detection capability of EDS spectrometers.

We are developing a high-energy-resolution x-ray microcalorimeter spectrometer for use in x-ray microanalysis. Our microcalorimeter spectrometer consists of a superconducting transition-edge microcalorimeter cooled to an operating temperature of 100 mK by a compact adiabatic demagnetization refrigerator mounted on a SEM column, read-out SQUID (Superconducting Quantum Interference Device) electronics followed by pulse-shaping amplifiers and pile-up rejection circuitry, and a multichannel analyzer with real-time computer interface.
Development of Atom Counting Technique by Laser Ionization
Authors: Ichimura S
Published: July 2020

The aim of the present study is to discuss the possibility of “counting atoms” by laser ionization technique, which has been applied to post-ionization in sputtered neutral mass spectrometry. The detection of one H2 molecule was tried under an extremely high vacuum (XHV) condition, since the molecule has a higher ionization energy (15.4 eV) than most of elements and the existence probability of it within laser ionization region is less than one under the condition.

Fig.1 shows schematically the experimental setup. The second harmonics (SH) of a picosecond YAG laser was focused with a spherical lens (f=250 mm) into the center of a home-made XHV chamber (Fig. 1a). The focused laser power density (W) is more than 1013W/cm2 for input pulse energy of 30 mJ, and the saturation of H2 ionization can occur under the condition. The repetition rate of the laser was 10 Hz. The XHV chamber can be evacuated to a minimum pressure of 5×10−11n Pa. To the chamber, either an ion counting detector or an ion imaging detector was attached. The ion counting detector (Fig.1b) is composed of ion collecting electrodes, an electron multiplier (EM), and a pulse counter.
Image Formation from Frozen Hydrated Samples in an Energy-Filter-Microscope
Authors: Angert I , Jahn W , Holmes KC , Schröder RR
Published: July 2020

Understanding the contrast formation mechanism in the EM is one of the prerequisites for artefact-free reconstruction of biological structures from images. We found that the normally used correction of contrast formation applied to zero energy loss filtered images corrupted spatial resolution. Therefore the contribution of contrast formed by inelastic electrons was reconsidered, including partial coherence of inelastically scattered electrons and lens aberrations of the microscope. Based on this, a complete description of the zero-loss contrast transfer function (CTF) is now possible.

We used tobacco mosaic virus (TMV), a biological sample known at atomic resolution, for definition of optimum CTF-parameters to reconstruct defocus series from an EFTEM LEO 912. CTF theory as known so far describes image contrast in the weak phase approximation as a linear sum of amplitude and phase contrast. The contribution of amplitude contrast (ratio of amplitude to phase contrast A/P) was determined to be between 7% and 5 % for unfiltered images and 12-14 % for zero-loss filtered images. However, in a filter microscope we remove electrons from the image, so we expect a higher amplitude contrast than in non-filtered images.
Image Restoration and Characteristics of Slow_Scan CCD Camera and Imaging Plates
Authors: Zuo J M
Published: July 2020

The performance of slow scan CCD (SSC) camera [1,2] and imaging plate (IP) [3] for digital recording is limited by resolution and noise. The SSC camera and IP are two digital detectors currently available for transmission electron microscope (TEM). Imaging plates are re-usable flexible sheets, which are used in the standard cassettes. They are readout digitally with a 25 μm pixel size. Both detectors are linear and have large dynamic range. The SSC is a fixed accessory of TEM, images can be acquired, processed and viewed immediately by the microscope operator. The IP fits into a regular film cassette and is used like film except for the processing method. The image plate records electron image by storing electron energy in the potential well of defect states in a photo-stimulable phosphor. The stored image is read out by scanning a laser probe and detecting the stimulated luminescence in a reader. The SSC uses scintillator to convert electrons to photons and detects photons with CCD through optical couplings. The IP has 3000X3760 pixels. The available SSC for electron microscopy ranges from 512×512 to 2048×2048 pixels.
Progress in Computer Assisted Electron Microscopy
Authors: Pan M , Ishizuka K , Meyer C E , Krivanek O L , Sasakit J , Kimurat Y
Published: July 2020

All the lenses, deflectors and stigmators of contemporary electron microscopes are controlled digitally by an internal computer. Control through RS232 serial interface by an external computer has also become a standard feature. This external control has made so-called computer assisted electron microscopy (CAEM) possible and practical. We are developing a CAEM system with two objectives: (1) to free inexperienced microscopists from technical details of operating an electron microscope, especially transmission electron microscopes (TEM); (2) to assist experienced microscopists to operate their microscopes with higher accuracy and efficiency. The features include automated and/or assisted standard operations in focusing, stigmating, and aligning the microscope, and also sophisticated tuning that requires the evaluation of subtle changes in image features such as aligning the incident electron beam direction in the presence of 3-fold astigmatism in objective lens. CAEM can further assist operators in selecting areas or objects and taking images/diffraction/energy spectrum with all the parameters well controlled and catalogued together, thus not only enabling ease-of-use and high accuracy in operation but also yielding more information on the specimen.