bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cristal-growth dynamics of n-doped gaAs
Authors: Huong Pham V. , Bouchet Stéphanie , Launay Jean-Claude 
Published: June 2020

Microstructure of epitaxial layers of doped GaAs and its crystal growth dynamics on single crystal GaAs substrate were studied by Raman microspectroscopy with a Dilor OMARS instrument equipped with a 1024 photodiode multichannel detector and a ion-argon laser Spectra-Physics emitting at 514.5 nm.The spatial resolution of this technique, less than 1 μm2, allows the recording of Raman spectra at several spots in function of thickness, from the substrate to the outer deposit, including areas around the interface (Fig.l).The high anisotropy of the LO and TO Raman bands is indicative of the orientation of the epitaxial layer as well as of the structural modification in the deposit and in the substrate at the interface.With Sn doped, the epitaxial layer also presents plasmon in Raman scattering. This fact is already very well known, but we additionally observed that its frequency increases with the thickness of the deposit. For a sample with electron density 1020 cm-3, the plasmon L+ appears at 930 and 790 cm-1 near the outer surface.
Non-resonant multi- and single-photon ionization for the chemical characterization of surfaces
Authors: Welkie David G. 
Published: June 2020

The chemical analysis of surfaces, where the ‘surface’ of a sample refers to the top few monolayers, is most commonly performed using the techniques of Auger electron spectroscopy (AES), secondary ion mass spectrometry (SIMS), and/or electron spectroscopy for chemical analysis (ESCA). For inorganic materials, AES is especially advantageous for quantitative elemental surface analysis at high spatial resolution. At lower spatial resolutions, SIMS generally provides the highest sensitivity, although quantitative interpretation of the results is often difficult or impossible. The primary reason for such difficulties is that the SIMS signal often depends more strongly on the nature of the local chemical environment at the analysis site than on the concentration of the species that is generating the signal. This is commonly referred to as the SIMS ‘matrix effect’.For organic materials, both ESCA and SIMS are used to obtain information on the chemical structure at surfaces. While ESCA can provide unique information on the nature of the chemical bonds between species at a surface, SIMS can provide complementary information on the molecular structures that are present.
Laser microprobe mass spectrometry: A trend analysis
Authors: Kaufmann Raimund , Spengler Bernhard 
Published: June 2020

Within the search for ultimate frontieres in microprobe analysis, sensitivity, selectivity and spatial resolution are amongst the primary criteria to be assessed. During recent years laser microprobe and ion microprobe analysis have been the most promising and competing approaches which not only share a lot of features in common but, by their physical principles are both rather open to further general improvements and dedicated instrumentations.The term desorption for either laser- or particle-induced ion formation has become common use. Both principles are actually intensively explored especially with respect to produce organic ions by “soft” ionization. Some of the key aspects of such ion formation will be addressed with special emphasis on laser desorption.Both principles are equally well suited for spot probing and/or analytical imaging with spatial resolution in the sub 1 μm range. However, while SIMS ion probe techniques have meanwhile achieved some impressive improvements with respect to practical capabilities by introducing e.g. pulsed high brightness ion sources in combination with TOF-MS the state of the art in the available laser microprobe instruments has virtually remained the same since the first introduction of the LAMMA and LIMA instruments more than a decade ago.
Applications and techniques of thickness measurement for sections and thin films
Authors: Heng Yew M. , Simon Gerard T. , Ottensmeyer F. Peter 
Published: June 2020

The thickness of a specimen to be examined in the electron microscope is a significant parameter for many applications. However, due to the lack of ideal methodology for absolute thickness measurement, most quantitative analyses are performed using approaches which are more convenient. For example, theoretical factors, indirect relative thickness or ratio methods are used to eliminate the necessity to obtain the absolute thickness. These alternatives are theoretically valid. However, experimental verification using standards with known thicknesses are still imperative. Since absolute thickness remains indispensable, continuous development and improvement of techniques for thickness measurement are still much needed. The purpose of this study is to critically survey the importance of absolute thickness measurement and assess the available methods for thickness determination.Knowledge of specimen thickness can be applied for both qualitative and quantitative purposes. Specimen thickness can be used to study imaging properties in different electron microscopy modes. Monitoring of film thickness is, for example, essential when coating specimens for high resolution secondary electron imaging, preparing multilayer specimens in material sciences or preparing ultrathin support films.
Microprobe analysis of technetium-mibi accumulation in cultured heart cell mitochondria: Correlation of structure and membrane potential
Authors: Backus Mark , Hockett Daniel , Piwnica-Worms David , Lieberman Melvyn , Ingram Peter , LeFurgey Ann 
Published: June 2020

Hexakis (methoxyisobutylisonitrile)99mTechnetium (Tc-MTBI) is a gamma emitting radiopharmaceutical currently in clinical use for evaluating myocardial perfusion. Because Tc-MIBI exists as a lipophilic cation with a single positive charge, it has been shown to concentrate in mitochondria in response to membrane potential in a Nernstian fashion similar to rhodamine 123. Use of electron probe x-ray microanalysis (EPXMA) for localization and quantitation of the element technetium in mitochondria and calculation of membrane potential allows correlation for the first time between mitochondrial structure and membrane potential in intact cells.Heart cells from 11-day-old chick embryos were cultured into spherical aggregates 50 -100 μm in diameter after Ebihara et al. Aggregates were then incubated for 60 minutes in HEPES balanced buffer salt solution containing either 0, 36,72, or 144 μMTc99-MIBI as well as 20 mCi metastable Tc99m-MIBI. Some aggregates were prepared for conventional fixation and subsequent electron microscopic evaluation, while other aggregates were plunge frozen in liquid propane and cryosectioned for quantitative EPXMA.
Imaging transported and endogenous calcium independently at a subcellular resolution: ion microscopy imaging of calcium stable isotopes
Authors: Chandra Subhash 
Published: June 2020

Ion microscopy, based on secondary ion mass spectrometry (SIMS), is a unique isotopic imaging technique. The use of stable isotopes as tracers and their SIMS localization at a subcellular resolution has introduced a significant new approach for molecular localization and ion transport studies. A molecule of interest may be tagged with stable2H,13C,15N, etc. and imaged with SIMS for its intracellular location. Stable isotopes of physiologically important elements such as calcium and magnesium provide excellent tracers for ion transport imaging studies with SIMS. in a recent study with44Ca, the brush border region in the small intestine was observed to be the main barrier for calcium transport from the intestinal lumen to the lamina propria region in chickens suffering from Rickets, a vitamin D-deficiency condition.An example of the use of44Ca stable isotope for imaging calcium-calcium exchange between the intracellular and extracellular calcium with SIMS is shown in figure 1. 3T3 cells were grown on high purity germanium chips to about 80% confluency.
Problems with oxygen analysis in the system MgO-Al2O3-SiO2 with the electron microprobe
Authors: Fialin Michel , Rémond Guy 
Published: June 2020

Oxygen-bearing minerals are generally strong insulators (e.g. silicates), or if not (e.g. transition metal oxides), they are included within a rock matrix which electrically isolates them from the sample holder contacts. In this respect, a thin carbon layer (150 Å in our laboratory) is evaporated on the sections in order to restore the conductivity. For silicates, overestimated oxygen concentrations are usually noted when transition metal oxides are used as standards. These trends corroborate the results of Bastin and Heijligers on MgO, Al2O3 and SiO2. According to our experiments, these errors are independent of the accelerating voltage used (fig.l).Owing to the low density of preexisting defects within the Al2O3 single-crystal, no significant charge buildup occurs under irradiation at low accelerating voltage (< 10keV). As a consequence, neither beam instabilities, due to electrical discharges within the excited volume, nor losses of energy for beam electrons before striking the sample, due to the presence of the electrostatic charge-induced potential, are noted : measurements from both coated and uncoated samples give comparable results which demonstrates that the carbon coating is not the cause of the observed errors.
Calculation and measurement of electron ionization cross sections for L and M shells
Authors: Luo Suichu , Joy David C. , Dunlap John R. , Wang Xinlei 
Published: June 2020

The ionization of atoms by electrons is a process of great importance in physics, because it is the primary mechanism for energy loss of electron in matter and for X-ray microanalysis. Powell has critically compared various theoretical, semi- or empirical formulations with experiments and it is clear that although calculations and measurements have been carried out previously for K and to a lesser extent for L shells, very little data, both experimental and theoretical, exist for M shells.We have calculated K ,L (L1 and L23 ) and M( M1 ,M23 M45 )shell ionization cross section covering the entire periodic table and spanning the energy range from the critical ionization energy for a particular element up to 100 keV using Hartree-Slater central self- consistent field model. The calculation algorithm is essentially that described in Ref.3 but both exchange and correlation energy effects have been included in the computations to ensure that the computed cross-sections are valid at low overvoltage ratios, and relativistic corrections have also been included for accuracy at high incident energies.
A simple formula for total elastic Mott cross sections
Authors: Gauvin Raynald , Drouin Dominique 
Published: June 2020

The Monte Carlo method is a very powerful method to describe the scattering of electrons in solids. In this computations, the scattering of electrons is often described by the total elastic Rutherford Cross-Sections, given by [1]:where E is the energy of the electron (KeV),Z is the atomic number of the atom responsible for scattering and α is the screening parameter and it is usually given by [2]:Since equation (1) has been obtained using the Born approximation, it is well known that this formula gives innacurate values when the atomic number of the solid is high and/or the energy of the electron is low [3]. In such cases, total elastic cross-sections computed using the Mott's theory are more accurate. Recently, these total elastic cross-sections have been computed [4] using a complex numerical procedure and values for 96 elements for 26 energies ranging from 20 eV to 30 KeV are available.
A simple Monte Carlo model for electron-probe quantitation
Authors: Duncumb Peter 
Published: June 2020

Since the early work of Bishop in the 1960's, many have used Monte Carlo techniques for studying the role of electron scattering in the X-ray production process, but the simulation of individual trajectories has always proved too slow to be of use for online analysis. The paper describes a simple model for calculating the distribution curves of ionisation with depth ϕ(ρz) for a variety of target conditions, which are then characterised by a type of exponential expression capable of much faster computation. This expression is built into a practical correction procedure which can be applied to the analysis of all elements from boron upwards.The Monte Carlo model uses a simple multiple scattering cross-section with 50-step trajectories. This cross-section is adjusted to give the correct variation of backscatter coefficient with target atomic number, as shown in Figure 1, and this is the only physical parameter which it is necessary to fit empirically.
Analysis of size-segregated samples from vehicular exhaust using laser microprobe mass spectrometry
Authors: Hoeft Stephen , Fletcher Robert 
Published: June 2020

Because of their potential adverse health effects, polycyclic aromatic hydrocarbons (PAHs) are significant environmental pollutants. Many studies have demonstrated the presence of PAHs in vehicular exhaust by using chromatographic analysis techniques on filter samples. Most of these studies do not correlate the aerosol size distribution with that of the composition and occurrence of the PAHs, other than collecting the aerosol into a 'coarse' and a 'fine' (< 2.5 μm diameter) fraction and then determining the PAH content for each fraction. The goal of this study is to characterize the 'fine' fraction aerosol by further segregating it into six size fractions and then using laser microprobe mass spectrometry (LMMS) to analyze each fraction.Samples were collected from the exhaust rooms of traffic tunnels at the Fort McHenry Tunnel in Baltimore, Maryland. This highway tunnel complex separates heavy diesels (trucks) from automobiles. Since each traffic tunnel is independently ventilated, it is possible to collect samples of emissions from either type of vehicular traffic.
Use of a thermal gradient and eds mapping to follow the fine details of formation in Tl-"1223" superconductors.
Authors: Morgan Peter E. D. , Doi Toshiya , Yuasa Toyotaka , Housley Robert M. , Porter John R. 
Published: June 2020

The microstructural requirements of a superconducting wire, with a core of high temperature superconductor ceramic (HTSC), are long and platy grains, with good percolation from grain to grain to allow a high critical current. This microstructure is encouraged by growth from a liquid phase.In earlier work in both Tl- and Bi-HTSC, we found that a liquid phase was also necessary to crystallize the three-Cu-layer 2223-types by solution-reprecipitation; without liquid none formed. It was of interest to see if the same type of situation applies to the Tl- 1223 case, which is attracting increasing attention due to its superior flux-pinning properties. The immediately available sample was a gold encapsulated wire with a core of (Pb0.5Tl0.5)(Sr1.6Ba0.4)Ca2Cu3Ox, made by a published technique, and which had been prefired to 800°C. The sample was subsequently fired in a constant temperature gradient furnace (2°C/cm) for 100h. Samples were mounted, sectioned, polished and gold coated for characterization by BSE imaging and EDS elemental mapping.
SAM/EDX analysis of Cu(Nb) alloys
Authors: Bevolo Albert J. 
Published: June 2020

For several years our laboratory has investigated the properties of copper based alloys with transition metals such as Cu80Nb20. When heavily drawn these alloys retain the thermal conductivity of pure copper but acquire strengths usually associated with steels. Niobium dendrites, that are immiscible in the copper matrix in the as-cast form, become very fine, thermally stable filaments when heavily drawn. When heat treated in a diffusion pumped static vacuum chamber the surface unexpectedly acquires a silvery coloration rather than the reddish color expected from the dominant copper constituent. If a flow of inert gas is maintained then the surface becomes reddish. Experiments involving SAM and EDX analyses of cast alloys ex situ and in situ treated in ultra high vacuum (UHV) were performed to investigate this behavior.Auger depth profiles of the ex situ silver colored alloys showed from the Nb (167) Auger transition lineshape that the dominant phase was metallic NbO.
Particle preparation for materials analysis (tutorial)
Authors: Zeissler Cynthia J. 
Published: June 2020

Often, good results in materials analysis depend on good sample preparation. Although sample preparation can often be simple and straightforward, particles sometimes present special challenges. Sometimes just a few tricks make the only difference between the success and failure of sample preparation and analysis. Without adequate insight and care in specimen preparation, there may be loss of sample, over-expended effort and loss of time, contamination (sample or instrument), adverse morphological changes, misrepresentation of elemental composition or phase distribution, and other artifacts. This tutorial will cover a variety of topics dealing with sample preparation methods, the tools, equipment and supplies used, and artifacts primarily of concern to analytical electron beam techniques.The many combinations of numerous parameters that can affect sample treatment and analysis make it difficult to produce a simple flow-chart for sample preparation. Various factors that determine optimal preparation methods include the physical state of the received sample (e.g., bulk, powder or single particle, wet or dry, homogeneous or heterogeneous), and the known chemical properties of the received sample.
Removal of Bragg-Compton Channel Coupling in Electron Compton Scattering
Authors: Jonas P. , Schattschneider P. , Pongratz P. 
Published: June 2020

Electron Compton scattering is inelastic scattering of fast electrons at large angles off core or valence electrons. The energy of the scattered electron is increasingly lowered with scattering angle; the energy distribution can be shown to be an image of the electron momentum density distribution in the ground state.The most dominant problem in ECOSS (Electron Compton Scattering from Solids), is the Bragg-Compton channel coupling. Bragg scattered electrons in the specimen act as new sources for Compton scattering. Since these Compton events correspond to various scattering angles a number of Compton profiles with different maximum and width are superimposed in a measurement.The MethodWe may write the total measured intensity M at a particular energy loss E as a linear combination of coupled Bragg-Compton events. In the case of a systematic row reflection with i excited beams it is always possible to choose n = 2 * (i - 1) angles such that the system of linear equations can be solved with respect to I.
Deconvolution of EELS Spectra Revisited
Authors: Su D.S. , Schattschneider P. 
Published: June 2020

The exact analysis of EELS-data needs a removal of multiple scattering from the measured low energy spectrum. Several methods have been reported. However, only the Fourierlog deconvolution seems to be widely used, inspite of difficuties with correct phase retrieval. Alternatively, a matrix-deconvolution proposed by one of the authors can be applied. The following comparison of the distinct approaches shows for the first time the limitation of the methods. Surprisingly, we find that the Fourier-log method is restricted to D ≤ π/2 (D is given in units of the mean free path) even if the proposed phase correction is applied. But also the method given by Spence, theoretically applicable for any D, fails for D ≥ 3 in our simulation. These failures may have been overlooked because EELS experimenters avoid specimens with D ≥ π/2, in general.We obtained the single loss distribution S from a measured Al plasmon spectrum of a thin film (d = 50nm) using the Fourier-log algorithm.
Some Quantification Problems in Parallel EELS Images
Authors: Botton G. , L’Espérance G. , Ball M.D. , Gallerneault C.E. 
Published: June 2020

The recently developed parallel electron energy loss spectrometers (PEELS) have led to a significant reduction in spectrum acquisition time making EELS more useful in many applications in material science. Dwell times as short as 50 msec per spectrum with a PEELS coupled to a scanning transmission electron microscope (STEM), can make quantitative EEL images accessible. These images would present distribution of elements with the high spatial resolution inherent to EELS. The aim of this paper is to briefly investigate the effect of acquisition time per pixel on the signal to noise ratio (SNR), the effect of thickness variation and crystallography and finally the energy stability of spectra when acquired in the scanning mode during long periods of time.The configuration of the imaging system is the following: a Gatan PEELS is coupled to a CM30 (TEM/STEM) electron microscope, the control of the spectrometer and microscope is performed through a LINK AN10-85S MCA which is interfaced to a IBM RT 125 (running under AIX) via a DR11W line.
STEM Study of Surface Plasmon Excitation in Small Spherical Particles
Authors: UGARTE Daniel 
Published: June 2020

Small particles exhibit chemical and physical behaviors substantially different from bulk materials. This is due to the fact that boundary conditions can induce specific constraints on the observed properties. As an example, energy loss experiments carried out in an analytical electron microscope, constitute a powerful technique to investigate the excitation of collective surface modes (plasmons), which are modified in a limited size medium. In this work a STEM VG HB501 has been used to study the low energy loss spectrum (1-40 eV) of silicon spherical particles [1], and the spatial localization of the different modes has been analyzed through digitally acquired energy filtered images. This material and its oxides have been extensively studied and are very well characterized, because of their applications in microelectronics. These particles are thus ideal objects to test the validity of theories developed up to now.Typical EELS spectra in the low loss region are shown in fig. 2 and energy filtered images for the main spectral features in fig. 3.
Design of a Field-Emission Gun for the Phillips CM20/STEM microscope
Authors: Mul P.M. , Bormans B.J.M. , Schaap L. 
Published: June 2020

The first Field Emission Guns (FEG) on TEM/STEM instruments were introduced by Philips in 1977. In the past decade these EM400-series microscopes have been very successful, especially in analytical electron microscopy, where the high currents in small probes are particularly suitable. In High Resolution Electron Holography, the high coherence of the FEG has made it possible to approach atomic resolution.Most of these TEM/STEM systems are based on a cold field emitter (CFE). There are, however, a number of disadvantages to CFE’s, because of their very small emission region: the maximum current is limited (a strong disadvantage for high-resolution TEM imaging) and the emission is unstable, requiring special measures to reduce the strong FEG-induced noise. Thermal field emitters (TFE), i.e. a zirconiated field emitter source operating in the thermal or Schottky mode, have been shown to be a viable and attractive alternative to CFE’s. TFE’s have larger emission regions, providing much higher maximum currents, better stability, and reduced sensitivity to vacuum conditions as well as mechanical and electrical interferences.