bluuebunny/crossref_metadata_2025 huggingface dataset:
The Control of Power for Efficient Batch Mixing
Authors: Layton R. A. , Murray W. R. , Garbini J. L.
Published: May 2005

In the batch mixing of composite solid propellants, small variations in the mixing process can lead to unacceptable variability in the properties and performance of the propellant grain. A new closed‐loop mixing strategy is proposed to improve the robustness of the mixing process with respect to these small variations, and thereby to reduce the variability of the finished grain from batch to batch. The new mixing strategy is based on the hypothesis that repeatability of mixing results can be improved by doing the same amount of work on each batch and that mixing efficiency can be improved by continuously controlling power. Justification of the hypothesis is given. The effectiveness of the new mixing strategy is demonstrated through simulations, using a process model based on measurements and analysis of an existing process for the batch mixing of an ammonium nitrate composite solid propellant. Results indicate that the new strategy improves the repeatability of the mixing process by reducing mixing power fluctuations and by eliminating variations in work done on the mixture from batch to batch. The new mixing strategy is shown to be feasible. Because the new mixing strategy is successful with wide robustness margins for this specific difficult mixing process, the strategy should be effective in the batch mixing of a wide range of composite solid propellants.
Synthesis and Explosive Properties of Dinitrobitriazole
Authors: Licht H. H. , Ritter H.
Published: May 2005

Dinitrobitriazoles were obtained from aminotriazoles by diazotation, coupling with methazonic acid and subsequent cyclization. They proved to be highly energetic materials. The chemical, physical and explosive properties have been investigated.
QM/MM modeling the Ras–GAP catalyzed hydrolysis of guanosine triphosphate
Authors: Grigorenko Bella L. , Nemukhin Alexander V. , Topol Igor A. , Cachau Raul E. , Burt Stanley K.
Published: May 2005

The mechanism of the hydrolysis reaction of guanosine triphosphate (GTP) by the protein complex Ras–GAP (p21ras – p120GAP) has been modeled by the quantum mechanical—molecular mechanical (QM/MM) and ab initio quantum calculations. Initial geometry configurations have been prompted by atomic coordinates of a structural analog (PDBID:1WQ1). It is shown that the minimum energy reaction path is consistent with an assumption of two‐step chemical transformations. At the first stage, a unified motion of Arg789 of GAP, Gln61, Thr35 of Ras, and the lytic water molecule results in a substantial spatial separation of the γ‐phosphate group of GTP from the rest of the molecule (GDP). This phase of hydrolysis process proceeds through the low‐barrier transition state TS1. At the second stage, Gln61 abstracts and releases protons within the subsystem including Gln61, the lytic water molecule and the γ‐phosphate group of GTP through the corresponding transition state TS2. Direct quantum calculations show that, in this particular environment, the reaction GTP + H2O → GDP + H2PO can proceed with reasonable activation barriers of less than 15 kcal/mol at every stage. This conclusion leads to a better understanding of the anticatalytic effect of cancer‐causing mutations of Ras, which has been debated in recent years. Proteins 2005. © 2005 Wiley‐Liss, Inc.
Structure of the tetrameric form of human L‐Xylulose reductase: Probing the inhibitor‐binding site with molecular modeling and site‐directed mutagenesis
Authors: El‐Kabbani Ossama , Carbone Vincenzo , Darmanin Connie , Ishikura Syuhei , Hara Akira
Published: May 2005

L‐Xylulose reductase (XR) is a member of the short‐chain dehydrogenase/reductase (SDR) superfamily. In this study we report the structure of the biological tetramer of human XR in complex with NADP+ and a competitive inhibitor solved at 2.3 Å resolution. A single subunit of human XR is formed by a centrally positioned, seven‐stranded, parallel β‐sheet surrounded on either side by two arrays of three α‐helices. Two helices located away from the main body of the protein form the variable substrate‐binding cleft, while the dinucleotide coenzyme‐binding motif is formed by a classical Rossmann fold. The tetrameric structure of XR, which is held together via salt bridges formed by the guanidino group of Arg203 from one monomer and the carboxylate group of the C‐terminal residue Cys244 from the neighboring monomer, explains the ability of human XR to prevent the cold inactivation seen in the rodent forms of the enzyme. The orientations of Arg203 and Cys244 are maintained by a network of hydrogen bonds and main‐chain interactions of Gln137, Glu238, Phe241, and Trp242. These interactions are similar to those defining the quaternary structure of the closely related carbonyl reductase from mouse lung. Molecular modeling and site‐directed mutagenesis identified the active site residues His146 and Trp191 as forming essential contacts with inhibitors of XR. These results could provide a structural basis in the design of potent and specific inhibitors for human XR. Proteins 2005. © 2005 Wiley‐Liss, Inc.
Conformational characteristics of the complete cequence of group A streptococcal M6 protein
Authors: Fischetti Vincent A. , Parry David A. D. , Trus Benes L. , Hollingshead Susan K. , Scott June R. , Manjula Belur N.
Published: May 2005

M protein is considered a virulence determinant on the streptococcal cell wall by virtue of its ability to allow the organism to resist attack by human neutrophils. The complete DNA sequence of the M6 gene from streptococcal strain D471 has allowed, for the first time, the study of the structural characteristics of the amino acid sequence of an entire M protein molecule. Predictive secondary structural analysis revealed that the majority of this fibrillar molecule exhibits strong alpha‐helical potential and that, except for the ends, nonpolar residues in the central region of the molecule exhibit the 7‐residue periodicity typical for coiled‐coil proteins. Differences in this heptad pattern of nonpolar residues allow this central rod region to be divided into three subdomains which correlate essentially with the repeat regions A, B, and C/D in the M6 protein sequence. Alignment of the N‐terminal half of the M6 sequence with PepM5, the N‐terminal half of the M5 protein, revealed that 42% of the amino acids were identical. The majority of the identities were “core” nonpolar residues of the heptad periodicity which are necessary for the maintenance of the coiled coil. Thus, conservation of structure in a sequence‐variable region of these molecules may be biologically significant. Results suggest that serologically different M proteins may be built according to a basic scheme: an extended central coiled‐coil rod domain (which may vary in size among strains) flanked by functional end domains.
Localization of hydrogen‐bonds within modules in barnase
Authors: Noguti Tosiyuki , Sakakibara Hirofumi , Gō Mitiko
Published: May 2005

Proteins in eukaryotes are composed of structural units, each encoded by discrete exons. The protein module is one such structural unit; it has been defined as the least extended or the most compact contiguous segment in a globular domain. To elucidate roles of modules in protein evolution and folding, we examined roles of hydrogen bonds and hydrophobic cores, as related to the stability of these modules. For this purpose we studied barnase, a bacterial Rnase from Bacillus amylolique‐faciens. Barnase is decomposed into at least six modules, M1–M6; the module boundaries are identified at amino acid residues 24, 52, 73, 88, and 98. Hydrogen bonds are localized mainly within each of the modules, with only a few between them, thereby indicating that their locations are designed to primarily stabilize each individual module. To obtain support for this notion, an analysis was made of hypothetical modules defined as segments starting at a center of one module and ending at the center of the following one. We found that the hydrogen bonds did not localize in each hypothetical module and that many formed between the hypothetical modules. The native conformations of modules of barnase may be specified predominantly by interactions within the modules. © 1993 Wiley‐Liss, Inc.
An analysis of the conformational paths of citrate synthase
Authors: El‐Kettani Mohammed Anass Ech‐Cherif , Zakrzewska Krystyna , Durup Jean , Lavery Richard
Published: May 2005

Previous simulation studies have provided reaction pathways leading from the closed to the open form of citrate synthase. We now undertake a detailed analysis of these pathways using a variety of different tools including backbone dihedral angles, P‐Curves helicoidal parameters, inter‐helix geometrical parameters, and accessibility calculations. The results point to a relatively small number of residues, mostly in loop regions, which are responsible for the majority of the conformational changes observed. An important role is attributed to transient changes in the backbone which facilitate movement along the reaction coordinate. Comparisons between the two pathways show that they share many common features despite the different algorithms used to generate them. © 1993 Wiley‐Liss, Inc.
Steric and conformational features of the aconitase mechanism
Authors: Lauble Hanspeter , Stout Charles David
Published: May 2005

Crystal structures of mitochondrial aconitase with α‐methylisocitrate and with sulfate bound have been solved and refined at 2.0 Å resolution with R factors of 18.2 and 16.8%, respectively. The steric factors and conformational effects observed in both new structures support the proposed mechanism for the overall reaction catalyzed by aconitase. The alternate substrate α;methylisocitrate is derived from α;methyl‐cis‐aconitate during crystallization and is observed to bind in the active site in a manner very similar to that observed for isocitrate. The methyl group is accommodated by favorable contact with Ile‐425. However, the other potential hydration product of α;methyl‐cis‐aconitate,α;methylcitrate, cannot be accommodated in the active site due to steric conflict of the methyl group with Asp‐165. The results are consistent with the requirement that cis‐aconitate must bind in two ways, in the citrate mode and in the isocitrate mode. Crystals of aconitase with sulfate bound are isomorphous to those with isocitrate bound. However, the structure displays significant conformational changes, providing a model for the substrate‐free state of enzyme. Three water molecules bind in place of the Cα; and Cβ‐hydroxyl and carboxyl groups of isocitrate, while sulfate binds in place of the Cγ;carboxyl Group. Side chains of Ser‐642 and Arg‐447 in the active site rotate to pair with other side chains in the absence of substrate. The new conformation of Arg‐447 triggers a concerted set of shifts which transmits conformational change to the surface of the protein, 30 Å from the active site. In the absence of substrate, a chain segment containing the [4Fe‐4S] ligand Cys‐358 also shifts, resulting in the net translation and reorientation of the Fe‐S cluster. © 1995 Wiley‐Liss, Inc.
Purification and crystallization of a schistosomal glutathione S‐Transferase
Authors: McTigue Michele A. , Bernstein Susan L. , Williams DeWight R. , Tainer John A.
Published: May 2005

The 26‐kDa glutathione S‐transferase from Schistosoma japonica (Sj26), a potential antischistosomal vaccine antigen, has been crystallized in an unligated form. Sj26 was recombinantly produced in E. coli without using a glutathione affinity column to facilitate preparation of unligated enzyme. The recombinant protein contains all 218 residues of Sj261,2 and an additional 13 residues linked to the C‐terminus. Crystals of recombinant Sj26 were obtained by the vapor diffusion method using ammonium sulfate as the precipitant at pH 5.6. The crystals belong to the hexagonal space group P6322 with unit cell dimensions a = b = 125.2 Å and c = 72.0 Å and contain one Sj26 monomer per asymmetric unit. A complete native diffraction data set has been obtained to 2.4 Å resolution. © 1995 Wiley‐Liss, Inc.
Cation distribution and magnetic properties of nickel–chromium ferrites NiCrxFe2–xO4 (0 ≤ x ≤ 1.4)
Authors: Rais A. , Gismelseed A. M. , Al‐Omari I. A.
Published: May 2005

Nickel–chromium ferrites NiCrxFe2–xO4 (0 ≤ x ≤ 1.4) were studied using X‐ray diffraction, magnetization measurements and Mössbauer spectroscopy. X‐ray diffraction patterns show that all samples have cubic spinel structure. The temperature dependent magnetic measurements revealed that a magnetic compensation point appears at chromium concentration x = 0.9, 1.2 and 1.4. Moreover, it was observed that the Curie temperature TC decreases and approaches the compensation temperature TK as Cr3+ substitution for Fe3+ increases. The magnetization data at all concentrations are discussed in the light of Néel's molecular field model taking into account the cation distributions obtained using the analysis of Mössbauer spectra. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Location of epoxy rings in a long chain acetogenin by fast‐atom bombardment and linked scan (B/E) mass spectrometry of lithium‐cationized molecules
Authors: Laprévote Olivier , Girard Christian , Das Bhupesh C. , Laugel Thierry , Roblot François , Leboeuf Michel , Cavé André
Published: May 2005

Fast‐atom bombardment desorption combined with mass spectrometry (using linked scans at constantB/E) of a lithium‐cationized long‐chain acetogenin was used to determine the position of two epoxy rings in thhe alkyl chain. Analysis of metastable and collision‐induced dissociations gave structurally useful information which could not be obtained by other spectroscopic methods such as nuclear magnetic resonance. A direct effect of lithium of thhe observed decomposition pathways was demonstrated.
Accuracy and precision of gas chromatography/combustion isotope ratio mass spectrometry for stable carbon isotope ratio measurements
Authors: Wong William W. , Hachey David L. , Zhang Shide , Clarke Lucinda L.
Published: May 2005

We evaluated the precision, accuracy and linearity of three commercial gas chromatography/combustion isotope ratio mass spectrometry (GC/C‐IRMS) instruments in regard to stable carbon isotope ratio measurements of fatty acids with 13C enrichment levels ranging from natural abundance to 924‰, in comparison to measurements by conventional gas isotope ratio mass spectrometry (GIRMS). Memory effect was also evaluated with a fatty acid mixture containing methyl myristate and methyl stearate at natural abundance levels of 13C but methyl palmitate at 13C enrichment levels of 460 or 924‰. At natural abundance, the δ13C values of fatty acids measured by the GC/C‐IRMS instruments were reproducible to within 0.34‰ (range: 0.11‰ to 0.32‰) and accurate to −0.38±0.40‰ (mean difference ± standard deviation; range: −0.03±0.25‰ to −0.84±0.39‰). At enrichment levels of 13C (23 to 924‰), the δ13C values were reproducible to within 1.48‰ (range 0.20‰ to 1.00‰) and accurate to −1.11±3.16‰ (range: −1.02±3.23‰ to +4.56±13.42‰). Stable carbon isotope ratio measurements by all three GC/C‐IRMS instruments were found to be linear from −30 to 924‰ (r2 > 0.9999; p ⩽ 0.004) in comparison to those measured by GIRMS. Significant memory effect was found in only one system. Based on our data, the GC/C‐IRMS instruments can provide linear, precise and accurate stable carbon isotope ratio measurements and require only pico‐and nanogram quantities of samples.
Effects of chemical state on quantitative AES of metal–sulfur compounds
Authors: Griffis D. P. , Linton R. W.
Published: May 2005

A quantitative approach to AES is illustrated for various metal–sulfur compounds involving: (a) intensity measurements via integral areas of background subtracted N(E) spectra (including sample probe potential biasing to improve background subtraction); (b) low primary electron dose, pulse‐count spectrum acquisition to minimize primary electron beam damage and charging artifacts; (c) corrections to spectral intensity for variations in electron backscattering and inelastic Auger electron mean free path for each metal–sulfur compound matrix; (d) XPS quantitative analysis to correct for differences in surface vs. bulk stoichiometries. Although the above approach results in improved analytical precisions, a residual difference of greater than a factor of 2 remains in the Auger elemental sensitivity factor for sulfur (LMM) in corresponding metal sulfate vs. sulfide compounds. This suggests a chemical state dependent Auger electron yield (core level ionization cross section times the Auger transition probability). Accurate AES quantification, therefore, may require chemical state specific sensitivity factors, particularly for valence shell transitions.
Inelastic electron tunnelling spectroscopy of silane coupling agents
Authors: Brewis D. M. , Comyn J. , Oxley D. P. , Pritchard R. G. , Reynolds S. , Werrett C. R. , Kinloch A. J.
Published: May 2005

Inelastic electron tunnelling (IET) spectra are reported and assigned for some trialkoxysilanes adsorbed on aluminium oxide. Spectra of the triethoxysilanes have many common features, and there is some evidence that these compounds are attached to the oxide surface by their ethoxy groups. There are differences in the trimethoxysilane spectra which may be due to a reaction at the oxide surface during junction preparation. In particular, IET spectra of 3‐glycidoxypropyltrimethoxysilane show that the epoxide group reacts to produce magnified image groups.
Characterization of contamination layers by emission angle dependent XPS with a double‐pass CMA
Authors: Hofmann S. , Sanz J. M.
Published: May 2005

The use of non destructive depth profiling by emission angle dependent XPS analysis is demonstrated for a thin contamination layer consisting of carbon, hydrogen and hydride‐bonded oxygen on top of an anodic oxide of Nb2O5 on Nb. Using a double‐pass CMA with an angle resolved aperture and measured intensity ratios of O 1s (hydroxide)/O 1s (oxide) and O 1s (hydroxide‐/C 1s) as a function of the emission angle, the thickness (d = 3.3 nm) and composition are determined.
XPS: Energy calibration of electron spectrometers. 1—An absolute, traceable energy calibration and the provision of atomic reference line energies
Authors: Anthony M. T. , Seah M. P.
Published: May 2005

Atomic standards of binding energies are presented for the calibration of X‐ray photoelectron spectrometers. The binding energies are measured using a VG Scientific ESCA 3 Mk II for which the photoelectron peak positions can be established with a measurement precision standard deviation of 5 meV. The absolute calibration of the voltage scale is established with an accuracy of 11 ppm over the binding energy range 0–1250 eV, using a measurement chain traceable to the NPL primary voltage standards. The zero of energy is set to ±11 meV on the differential of the Ni Fermi edge using Mg Kα12 radiation and absolute binding energies, for the Cu 2p3/2, Cu L3MM, Cu 3p, Ag 3d5/2, Ag M4NN and Au 4f7/2 peaks, are established with errors of 0.01 to 0.02 eV. An analysis is made of literature calibrations to assess their zero setting and voltage scaling errors. Preliminary tests have been made to show that the calibrations may be reproduced on instruments outside NPL using a simple work procedure.
Status report on the ASTM E‐42 Committee on surface analysis
Authors: Nelson G. C.
Published: May 2005

Committee E‐42 on Surface Analysis was formed by the American Society for Testing and Materials in 1976 from its predecessor, Subcommittee E‐02.02, to advance the quality of standard practices, standard materials, and reference data in the area of surface analysis. These objectives are accomplished through sponsoring symposia and workshops at the Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy in the spring and the National Symposium of the American Vacuum Society in the autumn of each year as well as through the development of recommended practices, standard materials, round robin comparisons, and publications. Subcommittees which are currently active are Editorial, Terminology, Standard Reference Materials, Ion Beam Sputtering, Energetic Ion Analysis, Auger, ESCA, ISS, and SIMS. This report summarizes their progress to the end of 1983.
The role of electron spectroscopy in the evolution of long‐range industrial R&D illustrated by AES studies in adhesion, catalysis and corrosion
Authors: van Ooij W. J. , Visser T. H. , Biemond M. E. F.
Published: May 2005

The improvement in spatial resolution of scanning Auger spectroscopy in recent years has increased its applicability to industrial problems markedly, as is illustrated by several case studies in adhesion, corrosion and related areas. It is shown that the analytical capabilities of AES are enhanced if complemented by simultaneous energy‐dispersive x‐ray analysis. Suggestions for further development of AES instruments for use in industrial R&D are given.
The adsorption of diethyldithiophosphate on cuprous sulphide
Authors: Mielczarski J. , Minni E.
Published: May 2005

The adsorption of diethyldithiophosphate (DTP) from its aqueous solutions has been studied on cuprous sulphide (chalcocite) surfaces by measuring the characteristic changes in the positions and relative integrated intensities of C 1s, P 2p, S 2p, O 1s and Cu 2p3/2 XPS lines and by observing the changes in the in situ internal reflection IR (infrared) spectra at various stages of adsorption. A multistage model is suggested for DTP adsorption on a freshly formed chalcocite surface. During adsorption components preadsorbed on the surface are removed. The DTP ions are initially distributed on the surface without any special orientation but later form islands. The degree of orientation increases with coverage and later, a well oriented close packed monolayer is found. When the adsorption continues beyond this stage the additionally deposited molecules form a randomly oriented layer on the close packed oriented monomolecular layer.
Quantitative XPS: The calibration of spectrometer intensity—energy response functions. 1—The establishment of reference procedures and instrument behaviour
Authors: Seah M. P. , Anthony M. T.
Published: May 2005

The ASTM E‐42 committee round robin on XPS measurements found, in a simple survey, that the intensity‐energy response of electron spectrometers was unacceptably unreliable. In this paper new, high accuracy, reference procedures are developed to define the relative intensity‐energy response function of spectrometers, for the constant ΔE and ΔE/E modes, for analysts to calibrate their own instruments. Two procedures are developed, one involving the measurement of peak areas, for Cu, Ag and Au, carefully specified to reduce the effects of measurement noise, and the second, for use on well‐designed spectrometers, through the measurement of the spectrum background. The measurements on Cu, Ag and Au reference foils show that intensity ratios are reproducible to within 2% standard deviation and, from preliminary tests, that the ratio of the response functions of a VG Scientific ESCALAB I and the NPL ESCA 3 Mk II is proportional to E0.094, except for the low pass energy of 20 eV in the ESCALAB I where the proportionality changes to E−0.156. Similarly the ratio of the functions for a Perkin‐Elmer PHI 550 and the VG Scientific ESCA 3 Mk II is proportional to E−0.244 over the normal XPS measurement range to an accuracy of 2%.
X‐Ray photoelectron spectroscopic studies of the surface of sputter ion plated films
Authors: Robinson Kevin S. , Sherwood Peter M. A.
Published: May 2005

X‐ray photoelectron spectroscopic analysis of a reactively sputter ion plated titanium nitride film showed the surface to be oxidised to TiO2, with a sub‐layer of oxynitride. Argon ion etching gave a depth profile of the film, but it preferentially sputtered titanium nitride, and caused mixing of TiO2 and TiN phases to form titanium oxynitrides. Titanium oxynitride was also produced by nitrogen ion implantation into titanium metal with a surface layer of titanium dioxide.
The inelastic mean free path of electrons in some semiconductor compounds and metals
Authors: Jablonski A. , Mrozek P. , Gergely G. , Menhyárd M. , Sulyok A.
Published: May 2005

The elastic backscattering probability Pe of electrons is proportional to the product of the inelastic mean free path (IMFP), effective backscattering cross section (σeff), and atomic density (N). Thus, experimental evaluation of Pe, e.g. from the elastic peak intensity measurements, enables the determination of the IMFP. σeff can be calculated by integrating the differential elastic scattering cross sections using a simplified model based on the first Born approximation and the Thomas–Fermi–Dirac atomic potential. No significant difference in the values of σeff was found using the Thomas–Fermi, the Thomas–Fermi–Dirac and the Hartree–Fock atomic potentials or integrating the scattering cross sections tabulated by Fink et al. From the experimental values of Pe reported by Schmid et al. and by Gergely the IMFP was determined for a number of elements. A good agreement was found with the data on the IMFP published in the literature. Comparing the elastic peak of two samples and using the data of Ashley and Tung as reference values, the IMFP has been determined for GaP, GaSb, InP, InSb and Si3N4 samples. Good agreement with the data of Ashley and Tung was obtained for Si, Ge, SiO2 and GaAs.
Ionicity of metallic oxide surfaces on metals as observed by Auger (XPS) spectroscopy
Authors: Ascarelli P. , Moretti G.
Published: May 2005

Research relevant to the understanding of polymer–metal adhesion led us to an oxygen Auger (KLL) study on metal oxide surfaces. This was done in order to analyse the ionicity and strength of ‘Lewis sites’ on oxide surfaces grown on metals as compared to their bulk metal oxide counterparts. Following some suggestions contained in earlier works by Wagner we show that relative Auger (KLL) oxygen energies are a sensitive probe of oxygen valence electron population and hole relaxation. A semi‐empirical model is discussed to justify these findings. Furthermore it is shown that this ‘observable’ feature is also influenced by the metal oxide thickness at the metal surface.
Facet development and its influence on depth resolution during sputtering of Si
Authors: Carter G. , Nobes M. J. , Abril I. , Garcia‐Molina R.
Published: May 2005

A model is developed, assuming mutation of facet lengths to larger values, to explain the experimental observations of the change in the population distribution of the lengths of facets developed during ion bombardment sputtering erosion of Si. The ensuing Gaussian facet length distribution, with mean length increasing linearly with ion fluence, is then used to show that the depth resolution δz/z0 of interface broadening first increases as z and then tends towards a constant value with increasing z0.
Energy calibration secondary standards for X‐ray photoelectron spectrometers
Authors: Evans Stephen
Published: May 2005

The selection of elementary calibration standards for X‐ray photoelectron spectrometers is discussed; it is suggested that Zn and Ga may be more satisfactory routine single‐element standards than Cu, Ag or Au. Binding energies for the 2p3/2 and 3d photoelectron peaks from elemental Zn, Ga (and Ge) and for the most intense LMM Auger peaks from Zn and Ga are reported and relevant energy separations compared with published Lα X‐ray energies. The instrumental voltage scale was calibrated to a precision of 0.0035% (one standard deviation, SD) by reference to published data for Cu and Au and the SD of the measured peak energies were generally ⩽0.03 eV. Taking residual voltage scaling uncertainties into account, the largest energy separations in the data for Zn and Ga should be accurate to 0.05 eV (one SD).
Results of an ISS round robin sponsored by ASTM committee E‐42 on surface analysis
Authors: Miller A. C.
Published: May 2005

Results are reported for a round robin involving ion scattering peak positions and FWHM measurements from seven cylindrical mirror analyzer (CMA) based instruments from the same manufacturer. The specimen used in the round robin was a Cu–Ag–Au ternary alloy. The ion scattering data were obtained using 4He and 20Ne ions at 1 and 2 keV. Within the set of data for any given peak, the spread in the FWHM values was >70%, and the variation between the maximum and minimum CMA voltages was ∼8.5% A comparison of the experimental data with the results of calculations involving the dispersion characteristics of a CMA and the scattering equation suggests that much of the spread in the peak position is associated with the position of the specimen with respect to the CMA geometry. The cause of the spread in the FWHM measurements is unknown. Further analysis of the data indicates an inelastic energy loss of ∼3% for 20Ne scattering from Ag at 2 keV.
Convolutional smoothing algorithms in electron spectroscopy
Authors: Evans Stephen , Hiorns Anthony G.
Published: May 2005

Multiple application of the convolutional smoothing algorithm of Savitsky and Golay to electron spectra leads to an undesirable distortion of the lineshape. The use of a single convolution of the data with a suitably‐chosen Gaussian function gives superior results with a large saving in computation. The distortion introduced by this procedure merely simulates the effect of widening the spectrometer slits.
The use of an electron flood gun when adopting monochromatic AgLα radiation for the XPS analysis of insulators
Authors: Edgell M. J. , Paynter R. W. , Castle J. E.
Published: May 2005

To combat the problem of specimen charging when analysing insulators with a high energy monochromatic AgLα x‐ray source for XPS in the VG ESCA3, the application and use of a low energy electron flood gun is investigated. It is found that individual specimens can require widely differing ‘optimum’ conditions for the satisfactory management of surface charging. However, the use of an accelerating voltage of at least 6 V, together with an emission current of at least 0.25 mA, appears to be satisfactory for the majority of specimens. It is concluded that an electron flood gun, when properly set‐up, can play an important role in gaining chemical state information from non‐conducting materials using XPS, though it is noted that the use of secondary binding energy referencing may still be necessary.
Analysis of polymer surfaces by SIMS 6—detection of cyclic oligomer on the surface of poly(ethylene terephthalate) film
Authors: Briggs D.
Published: May 2005

The dominant oligomeric species in poly(ethylene terephthalate) (PET) is cyclic trimer. Comparison of the SIMS spectra of pure polymer and cyclic trimer shows a markedly more intense peak at 577 daltons in the positive ion spectrum from the trimer, since this is the mass of the quasi‐molecular ion. This difference can be used to semi‐quantitatively analyse for cyclic trimer which has migrated to the surface of PET film.
An AES/SEM study of reed blades
Authors: Vanden Berghe R. , Vlaeminck R. , Van Paemel R. , Saillé M.
Published: May 2005

The soft Reed consists of two Au coated Fe/Ni blades sealed in a glass tube filled with nitrogen. The desired properties of the contact area of the Reed blades (hardness, contact resistance etc. …) can be obtained either by diffusion‐annealing (in vacuum or in an inert atmosphere) or by ‘arcing’ and ‘furbishing’. In this paper the compositional changes of the contact layer, resulting from diffusion annealing are related to the annealing time and temperature, and compared with those obtained by ‘arcing’ and ‘furbishing’. Arcing and furbishing are performed in the sealed Reed switch in which a glow discharge is ignited by applying an alternating tension between the blades, first when the blades are stationary, without making contact (arcing), and second when the switch is activated intermittantly (furbishing). The modifications of the surface composition, due to arcing and furbishing are compared with those obtained by annealing in nitrogen or in nitrogen/oxygen mixtures. A possible relation between the surface composition of arced and furbished Reed switches and the measured contact resistance is examined. These investigations are performed using SEM and AES techniques.
Surface studies of keratin fibres and related model compounds using ESCA, 2—intermediate oxidation products of cystyl residues on keratin fibre surfaces and their hydrolytical stability
Authors: Baumann H. , Setiawan L. D. , Gribbin D.
Published: May 2005

S 2p binding energies of the surfaces of keratin fibres oxidized to different degrees under industrially applied oxidative wet finishing conditions have been estimated using ESCA. With the help of S 2p data obtained from chosen model compounds qualitative identification of the oxidation products of cystyl residues on the surfaces of partially oxidized wool has been made. The oxidation products identified are the residues of cystine monoxide, cysteine sulphinic acid and sulphonic acid. The hydrolytical stability of the intermediate oxidation products of cystyl residues on the fibre surface seems to be comparable with that of the model compounds (cysteine sulphinic acid>cystine monoxide>cystine dioxide). The reaction conditions determine the partial oxidation products which are analysed on the fibre surface. However, in the present study a conclusive evidence for the existence of dioxycystyl residues cannot be given.
Practical surface analysis: state of the art and recent developments in AES, XPS, ISS and SIMS
Authors: Hofmann Siegfried
Published: May 2005

This review considers the well established and most frequently applied surface analysis techniques: AES, XPS, ISS and SIMS in a comparative manner, confronting fundamental principles and present instrumental performance with the requests of the scientist. The primary goal of surface analysis is the determination of the elemental composition of the outermost atomic layer of a solid. In addition, characterization of binding states, of homogeneity and of structural details will often be required. Whereas the information gathered generally contains also contributions from deeper layers, the inherent high in depth resolution of the techniques allows thin film analysis with high precision. Thus, surface analysis includes the analysis of interfaces and thin films by depth profiling. Recent progress has led to improvements e.g. in sensitivity, spectral resolution and data acquisition and handling. With the trend to high spatial resolution, surface analysis is becoming a special branch of microlocal analysis. Quantification is of primary interest. However, the variety of approaches and their dependence on instrumental parameters hamper interlaboratory comparisons, pointing out the need of standardized methods and correction procedures, of well characterized test samples and of accurate data banks. Advance in precise quantification will depend on future progress in our understanding of matrix effects and beam‐sample interactions.
Distribution of hydrogen in the NPL standard ta2O5 films
Authors: Bishop H. E.
Published: May 2005

The NPL has produced well characterized tantalum pentoxide anodized films for use as a thickness and depth resolution standard for profiling in surface analytical techniques. Very sharp interfaces for these films have been demonstrated using AES. Studying these films by dynamic SIMS in the CAMECA IMS 3F, well defined profiles with a sharp interface were obtained with an oxygen primary beam. More complex profiles were obtained with argon and caesium primary beams, apparently showing the presence of hydroxide at the metal/oxide interface and a high concentration of hydrogen in the metal near the surface. However an argon primary beam with an oxygen flood gave the same type of profile as that obtained with an oxygen primary beam. Elastic Recoil Detection Analysis confirmed that there was no high concentration of hydrogen at the metal‐oxide interface and showed that hydrogen in the tantalum was present at 1 at %.
XPS and ISS examinations of electrode surfaces and passive layers with a specimen transfer in a closed system
Authors: Haupt S. , Calinski C. , Collisi U. , Hoppe H. W. , Speckmann H.‐D. , Strehblow H.‐H.
Published: May 2005

The application of UHV surface analytical methods to the study of electrodes and surface layers may be affected by changes introduced by contact with the laboratory atmosphere. Therefore, a specimen preparation and transfer in a closed system with its specifications is described. Three examples of its application are discussed: the examination of the electrode – electrolyte interface on Cu and the study of the formation of passive anodic oxides on Fe and on FeCr alloys in 1 M NaOH.
Ion scattering spectroscopy studies of zirconium dioxide thin films prepared in situ
Authors: Martin P. J. , Netterfield R. P.
Published: May 2005

Low energy ISS has been used to investigate, in situ, thin films of zirconium dioxide deposited by evaporation and ion‐assisted deposition. It is shown that when a film is deposited to an average thickness of 0.3 nm ± 0.03, as measured by in situ ellipsometry, complete coverage of the substrate occurs. Ion‐assisted films have detectably higher Zr surface concentrations and reduced low‐energy sputter peaks. Inelastic tailing effects in the Zr scattering peak for 2 keV 4He+ are found to come from particles scattered from approximately the first 7 nm of the oxide surface. The influence of primary ion energy on the Zr/O ratio is also examined.
Angle‐resolved X‐ray photoelectron spectroscopy of epitaxially grown (100) β‐SiC to 1300 °C
Authors: Wheeler Donald R. , Pepper Stephen V.
Published: May 2005

The (100) surfaces of three β‐Sic crystals grown epitaxially on Si substrates were analyzed by angle‐resolved x‐ray photoelectron spectroscopy (XPS). The specimens were heated by direct current for 2 min in 25 °C increments from 900 to 1300 °C. After each anneal, Si 2p, C 1s and O 1s spectra were obtained for 28° and 64° photoelectron takeoff angles. After annealing below 1150 °C, the Si 2p spectrum has three main lines. One is assigned to SiC, one to SiO2 and the other to a suboxide. The angular dependence of the intensities of the three features is consistent with 22 A of SiO2 over 10 Å of suboxide on the SiC substrate. After annealing above 1150 °C, the O 1s and the oxide lines in the Si 2p spectrum gradually decrease, while the C 1s spectrum develops a second line which proved to be due to surface graphite. After heating at 1175 °C the surface was free of oxide and nearly free of graphite. For this surface, C 1s and Si 2p spectra were obtained for electron takeoff angles between 8° and 64°. Comparison of the Si 2p/C 1s ratio with that calculated from a layer model of β‐SiC indicates that the top layer in this state is primarily Si rather than C. After heating above 1200 °C, the second characteristic line in the C 1s spectrum grows. Both the binding energy and characteristic loss features of the new carbon line developed after annealing at high temperatures indicate that it is due to graphite. The angular dependence of the intensities of the two C 1s features indicate that 18 Å of graphite is formed on the surface heated to 1300 °C for 8 min.
Energy spectra of electrons transmitted through aluminium films
Authors: Tung C. J.
Published: May 2005

The transmission of electrons through aluminium films has been studied. Several physical quantities including the energy loss, the pathlength, the angular deflection and their distributions were calculated. Theoretical models have been used to estimate the inelastic and elastic differential cross‐sections for electrons in aluminium. The calculated spectra were compared with available experimental data.
Modification of the electrical and mechanical properties of AlGaAs interfaces induced by low energy electron irradiation
Authors: Gazecki J. , Williams J. S. , Cozzolino C.
Published: May 2005

Changes in the AlGaAs Schottky characteristics after low energy (20 keV) and low fluence (<1017 cm−2) electron irradiation have been investigated and correlated with film adhesion enhancement which also results from electron bombardment. The electrical and mechanical characteristics were measured as a function of irradiation dose. The observed lowering of the barrier height after irradiation can be related to an induced positive charge in the interfacial layer. It is suggested that this positive charge may be partly responsible for the adhesion enhancement of the Al film to the GaAs substrate.
Quantitative AES study of Fe/P alloys using a calibration curve after fracture in UHV
Authors: Hirokawa Kichinosuke , Oku Masaoki
Published: May 2005

Quantitative AES is commonly used in the field of surface analysis. It has been found for Fe/P alloys that when appropriate references for a calibration curve could be obtained, quantification could be carried out with interesting metallographical information.
Investigation of a passive film on an ironchromium alloy by AES and XPS
Authors: Mischler S. , Mathieu H. J. , Landolt D.
Published: May 2005

Passive films formed on a Fe24Cr alloy in 0.5 M H2SO4 at 0.7 V are characterized by AES depth profiling and XPS. Obtained results and evaluation procedures are critically compared. It is found that correction for electron escape depth significantly improves the accuracy of AES profile data. The use of low energy peaks in AES allows metallic species to be distinguished from oxidized species and profiles with good depth resolution to be obtained. Quantification is impeded by peak overlap. XPS results depend significantly on the background subtraction and peak deconvolution procedure employed. From the different data it is concluded that the ratio Cr/Cr + Fe in the passive film studied is approximately 0.9 compared to 0.26 for the bulk alloy. The film thickness is 1.5 ± 0.3 nm. Within the precision of present XPS data the metal composition of the layers adjacent to the film is the same as that of the bulk.
Quantitative analysis of the inelastic background in surface electron spectroscopy
Authors: Tougaard Sven
Published: May 2005

Recent progress, in the quantitative analysis of the distortion of surface electron spectra, resulting from inelastic electron scattering, is reviewed.

A physical model for the problem is formulated and based on this, basic deconvolution formulae are found. In the formulae, detailed information on the differential inelastic electron scattering cross‐section K is essential. Methods to determine,K are studied and developed. One method is based on a dielectric response calculation. Furthermore, it is found that for the noble and transition metals, K is sufficiently similar that a simple ‘universal’ cross‐section can be defined. In addition, methods for experimental determination of cross‐sections are found and in particular a formula is derived which allows the extraction of direct quantitative cross‐section information through a simple analysis of REELS spectra.

The importance of proper background correction is investigated for model electron spectra. Experimental XPS spectra are also studied and it is found that for both the simple and the noble metals, the primary excitation spectra extend 2–3 inelastic scattering events, i.e. ∼50 eV, below the peak energy. Beyond this energy, the spectra are of zero intensity over a wide energy range. Besides, experimental spectra are analysed on the basis of experimentally determined cross‐sections and the results are discussed, in relation to the analysis based on theoretical cross‐sections.

The importance of defining simple procedures for routine analysis of spectra is stressed and it is demonstrated that the proposed ‘universal’ cross‐section provides a very simple method for approximate spectral analysis.

Finally, some important issues to be considered in the near future are pointed out.
The inelastic mean free path of electrons in the ordered Al48Ni52 alloy
Authors: Mrozek P. , Jablonski A. , Sulyok A.
Published: May 2005

A new method for determining the inelastic mean free path was applied to the ordered polycrystalline AlNi alloy. The results obtained agree well with the literature data.
XPS studies of the thermal behaviour of passivated Zircaloy‐4 surfaces
Authors: Kaufmann R. , Klewe‐Nebenius H. , Moers H. , Pfennig G. , Jenett H. , Ache H. J.
Published: May 2005

The composition and the chemical states of components of Zircaloy‐4 (zirconium alloy) surfaces were studied in the temperature range between room temperature and 500°C. Each sample was kept at constant temperature (25, 100, 200, 300, 400, 500°C) for up to 16 hours. The changes of composition and chemical states of the Zircaloy‐4 surface during heating were monitored by x‐ray photoelectron spectroscopy (XPS). Originally, the components form well‐defined layers elucidated by angle‐resolved x‐ray photoelectron spectroscopy (ARXPS). In contrast to depth profiling using ion sputtering, ARXPS is non‐destrutive. However, it is applicable for layers of up to a few nanometres thickness only.

The experiments showed a decomposition of the ZrO2 coverage above 200°C accompanied by oxygen diffusion into the bulk. These processes lead to the reduction of ZrO2 to metallic zirconium on the surface at 300°C and higher temperatures. The oxygen diffusion into the bulk was indicated by AES depth profiles. The layered structure observed up to a heating temperature of 200°C could not be seen at higher temperatures. After Zr metal appears at the surface during the heating process, a reaction with the adsorbed hydrocarbons takes place, leading to the formation of zirconium carbide.

Though the depth resolution of an AES depth profile does not permit identification of layers with thicknesses in the nanometre region, the temperature‐dependent behaviour of oxyen is reflected by its AES profiles, showing features in accordance with the results from ARXPS, especially with respect to the fact that well‐defined layers vanish above 200°C.
Characterization of silica overlayers deposited on ZrO2 and TiO2 by CVD of Si(OC2H5)4
Authors: Jin T. , White J. M.
Published: May 2005

Silica, derived from Si(OC2H5)4, was studied on high surface area titania and zirconia powders using ion scattering spectroscopy (ISS) and Auger electron spectroscopy (AES) with depth profiling. After a large exposure and thermal processing of Si(OC2H5)4, more silicon was detected by AES on TiO2 (Si/(Si + Ti) = 50%) than on ZrO2 (Si/(Si + Zr) = 40%). With ISS, however, the reverse was found; the Si signal was 92% of the total metal on ZrO2 but only 70% on TiO2. Moreover, when the silica‐covered oxide surfaces were depth‐profiled with Ar+ (2 kV, 4 μA), the fraction of silica, based on ISS, decreased rapidly from 92% to 55% during the initial 100 s for ZrO2 but remained about 70% over the first 150 s for TiO2. The results strongly support a model in which Si(OC2H5)4 decomposes to form a thin film of SiOx which completely covers ZrO2, while on TiO2, particles of SiOx and/or mixed oxide layers form which leave titania exposed. On ZrO2, the estimated thickness of the SiOx film is 0.24 nm.
Combined EBIC—Auger analysis of AuGeNi/n‐GaAs ohmic contact formation
Authors: Hill I. R. , Lau W. M. , Yang G. R. , North R. A.
Published: May 2005

Electron beam induced current imaging has been used to monitor the dynamic changes of the metal–semiconductor interface of AuGeNi/n‐GaAs during annealing at 300°C. The reacted interface was then revealed by argon ion etching of the metal overlayer, and analyzed by secondary electron and Auger electron imaging. The combined EBIC–Auger imaging of the reacted interface indicates that the formation of the ohmic contact starts at localized areas where small Ni‐ and As‐rich grains are formed. The results also show that this combined EBIC–Auger imaging technique is particularly suitable for investigating the mechanism of degradation of Schottky contacts.