bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of sequence–reactivity space for protein–protein interactions
Authors: Li Jiangtian , Yi ZhengPing , Laskowski Michael C. , Laskowski Michael , Bailey‐Kellogg Chris
Published: December 2004

Sequence–reactivity space is defined by the relationships between amino acid type choices at some residue positions in a protein and the reactivities of the resulting variants. We are studying Kazal superfamily serine proteinase inhibitors, under substitution of any combination of residue types at 10 binding‐region positions. Reactivities are defined by the standard free energy of association for an inhibitor against an enzyme, and we are interested in both the strength (the free energy value) and specificity (relative free energy values for one inhibitor against different enzymes). Characterizing the structure of such a space poses several interesting questions: (1) How many sequences achieve particular strength and specificity characteristics? (2) What is the best such sequence? (3) What are some nearly‐as‐good alternatives? (4) What are their common residue type characteristics (e.g., conservation and correlation)? Although these problems are all highly combinatorial in nature, this article develops an efficient, integrated mechanism to address them under a data‐driven model that predicts reactivity for given sequences. We employ sampling and a novel deterministic distribution propagation algorithm, in order to determine both the reactivity distribution and sequence composition statistics; integer programming and a novel branch‐and‐bound search algorithm, in order to optimize sequences and enumerate near‐optimal sequences; and correlation‐based sequence decomposition, in order to identify sequence motifs. We demonstrate the value of our mechanism in analyzing the Kazal superfamily sequence–reactivity space, providing insights into the underlying biochemistry and suggesting hypotheses for further experimental consideration. In general, our mechanism offers a valuable tool for investigating the available degrees of freedom in protein design within a combined computational–experimental framework. Proteins 2005. © 2004 Wiley‐Liss, Inc.
Refinement of X‐ray data on dual cosubstrate specificity of CK2 kinase by free energy calculations based on molecular dynamics simulation
Authors: Setny Piotr , Geller Maciej
Published: December 2004

Free energy differences of binding of adenosine triphosphate (ATP) and guanine triphosphate (GTP) to the protein kinase CK2 (casein kinase 2) were calculated, using molecular dynamics (MD) simulations and the thermodynamic cycle approach. Good agreement with experimental data was obtained. Simulations confirm observations based on crystallographic data that specifically interacting water molecules in the binding site region of CK2 kinase play a key role in its ability to use ATP or GTP as equally efficient phosphate donors. We point out that to obtain quantitatively reasonable results, it was necessary to modify original X‐ray data by assuming the presence of an additional water molecule in the CK2 binding site structure with GTP. Proteins 2005. © 2004 Wiley‐Liss, Inc.
Chemisorption of sulfur dioxide on tungsten and platinum surfaces
Authors: Wu Owen K. T. , Burns Richard P.
Published: December 2004

The chemisorption of SO2 on a W and a Pt surface has been investigated by flash desorption mass spectrometry (FDMS) and AES. AES data indicate that the chemisorbed sulfur dioxide molecules oxidized the W surface, and produced a stable tungsten oxide during the heating (up to 1400 K) process. FDMS data indicate that the decomposition of SO2 yielded elemental and molecular sulfur during the desorption process. FDMS data show that SO2 exists in four binding states (α1, α2, α3 and α4) on a clean Pt surface and in three binding states (α5, α6 and α7) on an oxidized Pt surface. In addition, the coadsorption of SO2 and O2 was carried out on a Pt surface. The coadsorption process can produce SO3 which exists in two different binding states on a Pt surface. The data indicate that the oxidation of SO2 to form SO3 on a Pt surface occurs by means of a Langmuir–Hinshelwood mechanism.
The surface analysis of insulators by SIMS: Charge neutralization and stabilization of the surface potential
Authors: Hunt C. P. , Stoddart C. T. H. , Seah M. P.
Published: December 2004

As part of an ongoing programme of reference work for surface analysis at the NPL, the problem of surface charging when analysing insulators by static SIMS is discussed. Meaningful analysis requires stabilization of the surface potential to a defined reference point, here taken as the potential that would exist if the insulator was a conductor. In SIMS spectra it is shown that both the absolute and relative intensities of peaks depend on the surface potential. It is also shown that, only by the correct design of an electron flood source, can the surface be stabilized to a given constant reference potential. The relevant design principles are illustrated by measurements on isolated targets which define the characteristics of the flood source. Stabilization is effected to within the ±0.5 eV required for static SIMS.
Quantitative auger electron spectroscopy of metal monolayers on metals: Evidence for adsorbate/substrate interface effects
Authors: Rhead G. E. , Argile C. , Barthès M.‐G.
Published: December 2004

A critical appraisal is made of quantitative AES data obtained for some 30 metal monolayer on metal systems, and in particular for lead and tin monolayers on four substrate elements that have Auger emissions in the energy range 62–72 eV: Ni, Cu, Al, Au. The general agreement for a particular set of data tends to confirm the values of various monolayer densities from LEED but there are very significant differences between the attenuation (of the emissions close in energy) produced by the same overlayer on the different substrates. The emissivity of the overlayer metal may also depend on the nature of the substrate. It is concluded that several factors may affect the detected Auger emissions, including the influence of the absorbate/substrate interface on electron scattering and in particular on the back‐emission into the crystal. As a consequence it appears that quantitative analyses via the use of elemental AES emissivities and attenuation factors may be unreliable.
A modulation technique for discrimination against ion induced auger electrons in micro‐area AES
Authors: Ward I. D. , Blattner R. J.
Published: December 2004

Beam brightness modulation Auger spectrometry is shown to be an effective means of eliminating ion induced Auger electrons from Auger electron energy spectra. Modulating the incident electron beam intensity causes the true electron induced Auger electron emission to be modulated at the beam modulation frequency which can be easily separated from the unmodulated ion induced Auger electrons by means of frequency sensitive detection using a lock‐in amplifier. This technique is particularly useful when depth profiling with a high energy ion beam (∼5 kV) and a low current (small spot) electron beam (<100 nA).
Quantitative Auger electron spectroscopy for refractory metal silicides
Authors: Wirth Th. , Procop M. , Lange H.
Published: December 2004

Quantitative AES analysis is carried out on Cr–Si and Mo–Si systems. The treatment is based on the introduction of matrix and sputter correction factors. The matrix correction factors are calculated along the lines outlined in literature and proved to be weakly dependent on composition. Comparison with experimental data obtained on scratched surfaces of MoSi2 and Cr3Si bulk samples showed good agreement between experimental and nominal composition ratios. The sputter correction factors were found to be strongly dependent on composition for both systems. Comparison with theory for the case of preferential sputtering as the dominant ejection mechanism yields agreement with the experiment only for samples with low Si content. This is believed to be due to superposition with recoil location of the heavier component.
A quantification and investigation of surface microporosity in carbon fibres using labelling and XPS
Authors: Dension P. , Jones F. R. , Watts J. F.
Published: December 2004

An investigation is presented into the surface microporosity of Type 1 carbon fibres, with a range of oxidative treatment levels, and in which trichloromethane labelling and XPS analysis is used. Detection of the halogen atoms in molecules retained in the micropores shows that the oxidation‐dependent micropore volume is 2–13 × 10−5 cm3 per gram of fibre, which is in the expected range from results given in the literature. The model of the carbon fibre surface previously reported has been extended and it is proposed that the functional groups are bound to edge carbon atoms in the micropores. This is shown to be consistent with structures given by other workers, from x‐ray diffraction and electron microscopy.
Identification of synthetic metals from the shape of the carbon KLL spectra by the pattern recognition method
Authors: Lesiak B. , Jablonski A. , Zagorska M. , Jozwik A.
Published: December 2004

The aim of the work was to verify the possibility of application of Auger electron spectroscopy in connection with the pattern recognition method to study the polymer surfaces. Synthetic metals were chosen for investigation. The carbon KLL spectra were analysed using the so‐called k‐nearest neighbour rule. Analysis was performed for polyacetylene and polypyrrole doped with Fe(CN) and FeCl4− ions. On the basis of the standard spectra recorded for all polymers the effective recognizing procedure was developed. Noticeable changes of spectra were observed on electrochemical removal of dopants. The analysis made after 90 days of ageing in vacuum revealed some spectra changes in doped polymers. These change may be due to the disappearance of dopants or to the deposition of contaminants. An electron beam of 300 nA at 1000 eV was found to affect the surface of polyacetylene.
Evaluating precursor processing of Ba2 YCu3O7 – y Compounds Using High‐Resolution Scanning Auger Microscopy
Authors: Moore Richard L.
Published: December 2004

Superconducting materials, particularly the rare earth perovskite compounds have been shown recently to be the most promising materials for high Tc applications. Numerous techniques have been utilized to study the composition and structure of these materials. Of particular interest is the microstructure and grain boundaries. Consequently, the analytical technique must have sufficient spatial resolution to distinguish grain boundaries and the ability to characterize those grain boundaries, as well as the adjacent microstructure.

This work will present a study in microstructure and grain boundary composition using high resolution scanning Auger microscopy. Electron‐beam degradation of these compounds was evident. However, using cation ratios circumvented this problem in the scope of this investigation. By correlating electronic properties to a specific microstructure and composition, we can prescribe processing which optimizes the formation of the preferred crystal structure or phase.
Silica coatings on α‐alumina particles: Analysis and deposition mechanism
Authors: Firment Lawrence E. , Bergna Horacio E. , Swartzfager Dennis G. , Bierstedt Paul E. , Van Kavelaar Michael L.
Published: December 2004

Coatings are applied to particulate materials to enhance surface properties while retaining desired bulk properties. Characterization of such coatings presents a challenge. In this paper we present an example of a particle surface analysis and assess how factors such as roughness and coating thickness distributions affect quantitative conclusions. Silica coatings were deposited from aqueous solution on to α‐alumina particles of 150 nm average size. Transmission electron microscopy, x‐ray photoemission spectroscopy and secondary ion mass spectrometry/depth profiling were used to analyze coatings of thicknesses of tens of nanometers to submonolayer. The three techniques were in excellent agreement in the thickness ranges where they overlapped. XPS does not allow assessment of the uniformity or thickness distribution of the coatings. However, depth profiles are quantitatively consistent with a model of random attachment of the silica units to the particle surface during growth, with no preference for the uncoated alumina surface over the previously deposited silica.
The interaction of lithium with sodium and potassium silicate glasses
Authors: Maschhoff B. L. , Armstrong N. R.
Published: December 2004

The interaction of lithium with sodium and potassium glass surfaces in UHV has been characterized with XPS. Earlier studies of the Li/SiO2 system have shown the formation of a partially passivating layer upon initial Li deposition. Following breakdown of this layer, substantial reduction of the glass matrix occurs. In the present study, several compositions of sodium silicate and potassium silicate glasses were found to be more resistant than SiO2 to lithium attack owing to the presence of non‐bridging oxygens in the matrix. The proposed corrosion mechanism involves charge transfer from Li to the modifying cations at the glass surface followed by desorption of neutral Na or K and interdiffusion of Li+ into the glass. For thick (metallic) Li films on sodium silicates, the formation of a dilute Li—Na intermetallic and sodium metal are identified from distinct plasmon structure in the Na(1s) line. Matrix reduction of glasses with low alkali content has been observed subsequent to the atom exchange.
Auger depth profiling of polycrystalline metal films using Xe+ and N2+ ions
Authors: Tanemura M. , Fujimoto S. , Okuyama F.
Published: December 2004

Polycrystalline Al, Mo, Ag and Ta films deposited on mirror‐polished (100) Si wafers were Auger depth profiled using 3 keV Xe+ and N2+ ions as projectiles. In every case, Xe+ sputtering provided a less‐textured surface, and hence a higher depth resolution. This allowed us to conclude that the ion species better suited for practical Auger analysis is Xe+. Tantalum surfaces bombarded with N2+ ions were characterized by very tiny, densely distributed cones, in contrast with Ta surfaces exposed to Xe+ ions displaying no surface protrusion detectable by high‐resolution SEM. This finding was inexplicable by the traditional concept of ‘reactive ion sputtering’, thus the formation mechanism of these tiny cones is discussed. The result of Auger depth profiling of Mo film using Xe+−N2+ mixtures is also reported briefly.
Quantitative AES: Via the inelastic mean free path or the attenuation length?
Authors: Jablonski Aleksander
Published: December 2004

The terms inelastic mean free path (IMFP) and attenuation length (AL) of electrons in solids are described by different definitions and their values may differ profoundly, by >30%. For this reason, it is of crucial importance to decide which term should be used in calculations for quantitative AES analysis. An attempt to answer this question is made in the present work. The Monte Carlo algorithm was developed to simulate the Auger electron transport in metal alloys. Calculations were made for Auger electrons emitted in the Al48Ni52 ordered alloy and the corresponding standards. Comparison with the usual mathematical formalism of AES shows that elastic collisions of Auger electrons can be accounted for by two correcting parameters: (1) a correction denoted by Q, which accounts for the decrease of the Auger electron current; (2) a correction denoted by K, which accounts for the decrease of the depth of analysis. It was proved that the total correcting factor comprises four groups of parameters: atomic densities, back‐scattering factors, inelastic mean free paths and corrections Q. Thus, we obtain the unexpected result that the calculations for quantitative AES require knowledge of the IMFP rather than the AL. The parameter Q is usually close to unity and can be neglected. The use of attenuation lengths in calculations may result in considerable errors. However, it is possible to recalculate values for the AL to obtain the IMFP.
Quantitative analysis of impurities in SIMOX samples using secondary ion mass spectrometry
Authors: Chi P. H. , Simons D. S. , Roitman P.
Published: December 2004

Silicon films produced by the SIMOX process (separation by implanted oxygen) must be annealed at high temperature to remove the crystal damage introduced during implantation of the high oxygen dose. Different annealing gases, temperatures and times have been investigated. In such processes, various impurities present in the hightemperature ceramic furnace tube, as well as annealing gas species, may be incorporated into the samples. Secondary ion mass spectrometry (SIMS) is used as a quantitiative tool to analyze the diffusion of tube components and gases into annealed SIMOX samples. Samples. Samples prepared for this investigation were annealed in nitrogen and argon at temperatures ranging from 1250 to 1350 °C. We found that most impurities are present at low levels and are generally trapped in the surface oxide that is grown during the anneal. SIMS analyses of SIMOX samples annealed in nitrogen showed that nitrogen tends to collect in both the surface oxide band buried oxide layers, piling up at the oxide/silicon interfaces.
Redox processes in polyaniline thin film studied by optical multichannel analysis
Authors: Bernard M. C. , Hugot‐Le Goff A.
Published: December 2004

Optical multichannel analysis (OMA) was used to follow the kinetics of colour changes in electrochromic polyaniline films when the latter are polarized in an electrolytic medium at different potentials. These colour changes, which are related to the transition from one polymer form to another, are very fast. OMA also allowed us to obtain an apparent value of the film absorption coefficient. In the investigated range (300–800 nm), several absorption phenomena can be displayed which are characteristic of the different polymer forms. Two electrolytic media (1 M HCl and 1 M H2SO4) were compared to investigate the role played by the size of the inserted counter‐ion. The overall results allow us to estimate the practical possibility of using polyaniline in electrochromic devices.
Application of transmission Mössbauer effect spectroscopy to the study of electrocatalysis and adsorption phenomena at the nickel hydroxide electrode
Authors: Kamnev Alexander A. , Ezhov Boris B. , Rusanov Ventsislav , Angelov Venelin
Published: December 2004

Mössbauer parameters for ferric hydroxo forms in alkaline matrices, ferric oxyhydroxide and its admixture at the nickel hydroxide electrode surface as well as for ferric hydroxo species absorbed at nickel hydroxides from strongly alkaline solutions have been compared. The feasibility of transmission Mössbauer spectra acquisition for the adsorbed species in the presence of dissolved forms (e.g. in situ) is based on the principle that the latter give no Mössbauer effect at room temperature owing to their diffusional mobility, while the former, being fixed at the adsorbent surface, have been shown to exhibit a sufficient resonant absorption. The effects of adsorption and water have been noted. Some questions connected with anodic oxygen evolution electrocatalysis by iron species involved in the anodic process at the nickel hydroxide electrode are also discussed.
New entries in the XPS fingerprint database for the characterization of precipitated CuZnAl oxide catalysts
Authors: Grohmann I. , Peplinski B. , Unger W.
Published: December 2004

Detailed x‐ray photoelectron spectroscopic data for Cu and Zn observed with well defined reagent grade malachite, precipitated (Zn, Al)‐hydrotalcite and precipitated (Cu, Zn, Al)‐hydrotalcite samples are presented. These data are compared with the respective results observed with CuO and ZnO. Moreover, literature XPS data characteristic of precipitated malachite, CuCO3 and Cu(OH)2 are used for comparison. Relevant copper and zinc data are presented as ‘chemical maps’. Certain results illustrate the analytical potential of a detailed analysis of the Cu2+ 2p satellite parameters which are known to be co‐ordination‐sensitive. The bulk co‐ordinations of Cu2+ and Zn2+ species in malachite, hydrotalcite, CuO and ZnO are briefly reviewed.
Applications of surface‐analytical techniques to aluminium surfaces in commercial semifabricated and finished products
Authors: Amstutz Markus , Textor Marcus
Published: December 2004

The application of surface‐analytical techniques (XPS, SIMS, SNMS) in an industrial R & D department of a company producing aluminium semifabricated and finished products is reviewed. Four different ‘case studies’ are presented related to: (a) composition of oxide films on aluminium foil of commercial purity influencing corrosion resistance and adhesion in packaging products; (b) control of thickness and composition of chromate conversion coatings; (c) surface factors influencing etchability of high‐purity aluminium foil for use in electrolytic capacitors; (d) electrochemical behaviour of AlMgGa alloys in alkaline electrolytes related to use as active battery anodes. Modern surface‐analytical techniques turn out to be a valuable instrument both for product development and problem solving related to surface and interface properties. Specific answers to problems can often only be given based on results of several analytical and structural techniques, including more ‘conventional’ techniques such as wet‐chemical trace analysis or electron microscopy of thin films.
Grain boundary segregation in [100] symmetrical tilt bicrystals of an FeSi alloy
Authors: Hofmann S. , Lejěek P. , Adámek J.
Published: December 2004

The orientation and temperature dependences of the segregation of P, Si and C at [100] symmetrical tilt grain boundaries of an Fe‐3.5 at.% Si alloy were determined by AES analysis ofin situfractured bicrystals. The obtained anisotropy of the segregation enthalpy of all three elements is characterized by its low absolute values for the {013} and {012} boundaries. Both of these boundaries belong to the low classification levels after Paidar and possess high values of interplanar spacing which can be used as a simple geometric criterion of the boundary ‘specialty’. The data are consistent with the construction of the grain boundary segregation diagram showing the dependence of the segregation enthalpy on both the boundary orientation and the maximum solid solubility of the solute.
On the oxidation of γ′‐Fe4N1−x layers; redistribution of nitrogen
Authors: Somers M. A. J. , Kooi B. J. , Sloof W. G. , Mittemeijer E. J.
Published: December 2004

Iron nitride (γ‐Fe4N1−x) layers produced by gaseous nitriding of pure iron in an NH3/H2 mixture at 843 K were gaseously oxidized at 673 K in pure O2. During oxidation an ε‐Fe2N1‐y layer developed between a magnetite (Fe3O4) scale and the parent γ′‐nitride layer. Porosity was observed in the oxide‐adjacent part of the ε‐grains. Scanning Auger microscopical analysis and electron probe microanalysis showed (1) that the occurrence of the ε‐nitride layer is associated with a locally higher nitrogen content, (2) that no nitrogen is incorporated in the oxide layer and no oxygen is dissolved in the nitride layer and (3) that a nitrogen concentration‐depth gradient occurs which corresponds to a change of about 1 at.% N over the thickness of the ε‐layer. From a thermodynamical point of view, formation of N2 gas during the oxidation of γ′‐nitride is more likely to occur than formation of ε‐nitride; the latter reaction appears to be kinetically favoured. Quantitative analysis of the nitrogen redistribution suggests that some of the nitrogen atoms released by conversion of γ′‐nitride into magnetite are transformed into N2 which is present in the pores near the oxide/nitride interface.
Application of glow discharge optical emission spectroscopy to diffusion measurement of copper in ferritic and austenitic iron and steels
Authors: Suzuki S. , Suzuki K. , Kurosawa F. , Kobayashi H.
Published: December 2004

Glow discharge optical emission spectroscopy (GDOS) is a method to analyse the optical emission of elements during sputtering of a solid, providing data on the light intensities of the elements vs. the sputtering time. By correcting the measured light intensities with standard samples, it is possible to obtain the quantitative depth profile up to about 100 μm. In the present research, GDOS was applied to the diffusion measurement of impurity atoms in metals and alloys. After a thin film of copper was coated on iron and steels, the surface film was diffused into the matrix at high temperatures. The penetration curves of copper from the surface were obtained from the GDOS data. Diffusivities of copper in ferritic and austenitic regions of iron were determined from the penetration curves, which were in agreement with previous results. Diffusion of copper in commercial ferritic and austenitic stainless steels was also examined. The diffusivities obtained were comparable with those expected from the temperature dependence of the diffusivities in the ferritic and austenitic phases of pure iron.
Study of concentration–depth profiles in CoSi2 near‐surface layer after ion bombardment
Authors: Vojtusik S. S. , Borodyansky S. E. , Zaporozhchencko V. I.
Published: December 2004

The concentration–depth profiles of Co and Si were investigated in the CoSi2 (100) altered layer after attaining the sputtering steady state by Ar+ ions. The depth profiles were determined from angle‐dependent AES data. Independent measurements of the Co low‐ and high‐energy lines and the Si low‐energy line lead to the conclusion that the concentration–depth profile of elements is not monotonous within the altered layer.
Effects of flame treatment on propylene–ethylene copolymer surfaces
Authors: Sheng E. , Sutherland I. , Brewis D. M. , Heath R. J.
Published: December 2004

The effects of flame treatment on the surfaces of a propylene‐ethylene copolymer have been studied using XPS, contact angle measurement, vapour‐phase derivatization and an adhesion test. The results obtained were compared to those from the homopolymer. An optimum air‐to‐gas ratios of ∼11:1 has been found. Close correspondence between water contact angle and oxygen concentration was found, with the exception of high oxygen concentrations. The orientation or migration of functional groups away from the surface has been proposed to cause the non‐correspondence between water contact angle and oxygen concentration. Diiodomethane advancing contact angle was found to remain constant, independent of flame conditions. XPS analysis in conjunction with vapourphase derivatization with trifluroacetic anhydride (TFAA) suggests that up to 20% and 30% of the oxygen introduced in the surfaces is present as hydroxyl groups for propylene homopolymer and the copolymer, respectively. High adhesion levels of the flame‐treated copolymer with a polyurethane‐based paint were found. In most cases, the adhesion failure was complex, but involved the cohesive failure of the copolymer.
Enhancing the interpretation of x‐ray photoelectron spectra using numerical methods
Authors: Stickle W. F. , Sobol P. E.
Published: December 2004

X‐ray photoelectron spectroscopy (XPS) has long been used as a surface analytical method for the determination of elemental composition and chemistry of a material. Small‐area analysis allows the comparison of different areas of a sample surface, while sputter depth profiling makes it possible to follow the specific chemistry as a function of depth. Often in XPS, peak overlap or subtle changes in chemistry may sometimes make the chemical‐state analysis of the elements in a material difficult. By using a variety of numerical methods, it is possible to enhance the analysis and interpretation of surface analytical data. Such numerical methods would include linear least‐squares and fitting and target factor analysis. By using these methods it is possible to enhance the chemical‐state interpretation and in many cases significantly increase the detection limits of specific elements. Several examples of the application of numerical methods are used to illustrate the enhancement of data interpretation of XPS data, with special emphasis on linescans and sputter depth profiles.
Bethe ionization cross‐sections: A quantitative survey on calculating the backscattering factor in AES
Authors: Lee C. L. , Ong C. K.
Published: December 2004

The objective of this work is to investigate the usefulness of the Bethe cross‐section with Powell parameters for possible future use in quantitative AES. The Powell energy‐dependent parameters are obtained from a least‐squares fit to various experimental and calculated work on ionization cross‐sections and are proven to have an accuracy of better than about 1% for Unl > 4 (Unl = E0/Enl), where E0 is the incident electron energy and Enl is the binding energy of the electrons in the nl‐shell. This cross‐section was quantum mechanically derived from the first Born approximation by Bethe and its use can be extended to lower‐energy ranges as evidenced from the Fano plots available. This means that the cross‐section has the advantages of a closer fit to experimental data and is within the energy range of interest in AES. A simple Monte Carlo approach has been adopted to calculate the backscattering factor and related Auger intensity lines using this cross‐section for C, Si, Cu and Ag elements. Results compared with both recent experimental data and Gryzinski cross‐section results indicate strongly that the Bethe cross‐section can be used for future quantitative analysis in AES.
Activities of the ASTM committee E‐42 on surface analysis
Authors: Powell C. J.
Published: December 2004

The ASTM Committee E‐42 on Surface Analysis was formed in 1976 to advance the field of surface analysis and the quality of surface analyses through the development of appropriate standards (reference procedures, reference materials and reference data), round robins, symposia, workshops and publications. A major function of the Committee is the development of documentary standards or reference procedures. This article contains a brief summary of Committee activities, with emphasis on the reference procedures that have been published and those that are under development.
Evaporated and implanted reference layers for calibration in surface analysis
Authors: Wätjen U. , Bax H. , Rietveld P.
Published: December 2004

The potential of thin reference layers prepared by the Central Bureau for Nuclear Measurements, especially for calibration puposes in surface analysis, is presented. Our special preparation procedure is outlined, making use of an ultrahigh vacuum microbalance with the substitution principle of weighing applied. Our procedure of chracterizing the areal density of the evaporated layers is unique in that it provides for an optimal traceability to the SI unit of mass. Besides thin metal layers evaporated onto vitreous carbon substrates, which can serve for yield calibration in surface analysis, we are making use of thin layers as internal standards on implanted samples in order to perform high‐accuracy determinations of the retained dose through Rutherford backscattering spectroscopy. After sensitive tests of the thickness uniformity, evaporated and implanted thin layers are made available as reference samples.
Correlation of the emission of SIMS cluster ions with composition and structure from the Al2−xCrxO3 Mixed Oxide Series
Authors: Reed Nicola M. , Vickerman John C.
Published: December 2004

The Al2−xCrxO3 mixed oxide series demonstrates that as the composition of the oxide is varied then the distribution of secondary ion clusters is also observed to change. A general model has been proposed to account for these variations in the formation of secondary cluster ions.

It has been shown that at very low chromium concentrations (0–0.1 mole fraction Cr) the incorporation of chromium into the Al2O3 lattice, forming a solid solution, results in an increase in the Al‐O bonding as manifested by the increase in the AlO+ and AlO− species concurrent with the reduction in the Al2+ and Al2O2+ clusters.

At increasing concentrations of Cr (0.1–0.4 mole fraction Cr) these appears to be an increase in the AlO and CrO bonding. This increase is thought to be due to the development of the localized CrCr bonding. This is shown by the increase in the AlO2− and the AlO4− clusters, whilst the influence of the localized bonding is demonstrated by the increased Cr2O+ species. Ther is a decrease in any clusters containing both Al and Cr which is explained in terms of the preference of the chromium to be emitted as part of a chromium pair in this composition range.

At further increased concentrations of Cr (0.4–1.0 mole fraction Cr) a chromium sub‐lattice begins to develop. This formation reduces the localized CrCr bonding which was noted at the lower chromium concentrations, which in turn results in a more delocalized bonding within the chromium lattice. This effect is indicated by the increase in the AlCrOx+ species.

The relative intensities of these cluster ions throughout the composition range, are also shown to reflect the changing oxidation state of the composite oxides across the series.
High‐energy LMM Auger transitions
Authors: Weisz S. Z. , Gomez M. , Resto O. , Many A. , Goldstein Y.
Published: December 2004

We have recently shown that with the commonly available resolution in Auger electron spectroscopy measurements, significant errors can be incurred in the measured Auger line intensities. To overcome this difficulty, a universal relation has been derived theoretically whereby the experimentally measured line intensities can easily be corrected so as to yield good estimates for the true intensities, i.e. those that would have been measured were the resolution infinitely good. The validity of our correction procedure was recently demonstrated for the high‐energy KLL and low‐energy LMM lines of Si, Al and Mg as well as for the high‐energy LMM and low‐energy MNN lines of Cu. In this paper we extend these studies to the high‐energy LMM lines of Zn, Ge, Fe, Co and Ni. We present here the intrinsic lineshapes of these lines as well as the Auger sensitivities relative to silver, measured with different resolutions. The correction procedure applied to the data yields the true sensitivities to a good approximation and is therefore important for quantification and for theoretical calculations of Auger Yields.
Physico‐chemical modifications of solid surfaces by interaction with ion beams
Authors: Pignataro Salvatore
Published: December 2004

The physico‐chemical processes occurring in the particle (ion, photon) bombardment of a surface are reviewed, with particular emphasis on the ion beam–solid interaction. The main factors influencing the chemical reactions which occur by ion bombardment will be discussed in terms of Lindhard–Scharff–Schiøtt (LSS) theory on the basis of experimental data obtained on both organic and inorganic simple systems as well as on polymers. Some typical reaction schemes will be reporte and the modification of the physical properties of the bombarded surface will be shown to be connected with the chemical nature of the products formed as a consequence of the energy deposition of the ion beam. A few examples showing the importance of the above phenomena in the field of surface and interface analysis will be given.
Chemical changes in titanate surfaces induced by Ar+ ion bombardment
Authors: González‐Elipe A. R. , Sanz J. M. , Espinós J. P. , Fernandez A. , Munuera G.
Published: December 2004

The reduction effects and compositional changes induced by 3.5 keV Ar+ bombardment of several titanates (i.e. SrTiO3, Al2TiO5 and NiTiO3) have been quantitatively investigated by XPS.

In all the samples studied here the original Ti4+ species were reduced to lower oxidation states (i.e. Ti3+ and Ti2+), although to a lesser extent than in pure TiO2. On the contrary, whereas Sr2+ and Al3+ seem to remain unaffected by Ar+ bombardment, in agreement with the behaviour of the respective oxides (i.e. SrO and Al2O3), Ni2+ appears more easily reducible to Ni0 in NiTiO3 than in NiO. In addition, other specific differences were observed between the titanates, which reveal the existence of interesting chemical effects related to the presence of the different counter‐ions in the titanates.

In the case of Al2TiO5, its Ar+‐induced decomposition to form TiO2 + Al2O3 could be followed by XPS.
Electron‐irradiation‐induced effects on high‐Tc superconductors analysed by high‐resolution Auger electron spectroscopy
Authors: Seibt E. W. , Zalar A.
Published: December 2004

The change in the surface and bulk compositions of high‐Tc BiPbSrCaCuO and YBaCuO system superconductors caused by electron beam irradiation at room temperature have been investigated using high‐resolution Auger electron spectroscopy (AES). Electrons of energies between 5 and 15 keV were used to study energy‐dependent decomposition phenomena for a wide range of electron radiation doses up to a maximum value of above 1028 electrons m−2. Additionally, irradiations with focused electron beams were carried out on silver‐sheathed Bi1.7Pb0.3Sr2Ca2Cu3O10.2/10 wt.% Ag tape samples with relatively high critical current densities [jc(0 T, 77 K) = 3.3 × 108 A m−2] in order to investigate the radiation‐induced effects on surface and bulk compositions by AES multiplex and sputter depth‐profiling techniques. The results indicate that there are significant changes in composition of the BiPbSrCaCuO samples up to concentration values of about 10 at.% for oxygen and about 12 and 15 at.% for calcium and copper respectively, whereas only small irradiation‐induced decomposition effects are observed for YBaCuO single–crystal and thin film superconductors.
Oxidation of metals by an oxygen ion beam in the MBE process
Authors: Shimizu T. , Nonaka H. , Arai K.
Published: December 2004

X‐ray photoelectron spectroscopy was used to study the oxidation of Cu by oxygen plasma generated from a Kaufman ion gun. It was found that Cu was much less oxidized in co‐evaporation with Ba or Nd compared to Cu‐only evaporation when the total flux density of supplied metals and the oxygen plasma conditions were similar. It was also found that elemental Ba or Nd deposited on a CuO film at room temperature deoxidized the CuO.
Correlation of hydrogen content with properties of oxidic thin films
Authors: Ottermann C. R. , Bange K. , Wagner W. , Laube M. , Rauch F.
Published: December 2004

Hydrogen and hydrogen‐containing species (H2O, OH etc.) play a dominant role in the various properties of glass surfaces and technical oxidic thin films deposited on glass. The amount of hydrogen and its distribution with depth are influenced by preparation and production processes, film materials, density and voids, etc. The 15N nuclear reaction technique, which works quantitatively and non‐destructively, was used to investigate glass surfaces and thin films of TiO2, Ta2O5 and SiO2 produced by sol‐gel processes, reactive evaporation, sputtering and ion plating on glass substrates. An increase or decrease in hydrogen content influences optical and mechanical properties such as the refractive index and adhesion of the films.
Study of the phase composition of iron‐containing Langmuir–Blodgett layers before and after thermal and chemical treatment
Authors: Meisel W. , Gütlich P.
Published: December 2004

Iron‐containing Langmuir–Blodgett mono‐ and multilayers were prepared by depositing ferric stearate onto silicon wafers. Particular care should be taken in order to avoid the presence of alkali ions, which may replace iron ions in the deposited film. By a subsequent heating in air, the fatty acid chains were thermodesorbed. This results in a rather homogeneous coating of the samples by an iron oxide, most probably in the form of crystalline and amorphous γ‐FeOOH, as found by conversion electron Mössbauer, photoelectron and microprobe studies. By a subsequent heating in hydrogen gas or exposure to nascent hydrogen, a partial reduction of the iron oxide layer is possible up to the metallic state (α‐Fe). The Mössbauer spectra show the formation of a mixture of different iron species (Fe3+, Fe2+, Fe0) depending on the reductive treatment.
Surface and in‐depth chemical characterization of sputter‐deposited CrSiO layers by XPS and AES techniques
Authors: Bertóti I. , Tóth A. , Czermann M. , Menyhárd M. , Sulyok A. , Zsoldos E.
Published: December 2004

RF‐sputtered CrSiO cermet films deposited without and with a bias (200 V) have been studied by XPS and AES. Samples as deposited, etched by HF solution as well as annealed at temperatures up to 600°C have been considered. XPS results showed that the surface of the as‐received samples were depleted in Cr and enriched in O with respect to the target composition. Silicon and Cr were present in both oxidized and reduced forms in the surface layer. Ar+ ion sputter profiles revealed that the composition of the subsurface approached that of the target and that Cr was present in the subsurface in reduced and Si in both oxidized and reduced states. AES in‐depth profiling resulted in element concentration trends similar to but element ratios different from those observed by XPS. This was attributed to preferential sputtering coupled with the significantly different sampling depths of the two techniques. Cr3Si was identified by x‐ray diffraction in samples treated at 600°C, but not even traces of it could be detected by this method below 400°C. The Si Auger parameter determined by XPS proved to be more sensitive in identifying silicide‐type bonds in the CrSiO layers studied.
Changes induced in the surface characteristics and catalytic activity of amorphous Cu‐Zr by hydrogen pretreatment
Authors: Katona T. , Molnár Á. , Perczel I. V. , Kopasz Cs. , Hegedűs Z.
Published: December 2004

Hydrogen‐treated amorphous Cu61Zr39 alloy ribbon exhibits the development of characteristic formations (hemispheres) in a circular arrangement (as revealed by SEM) on both sides of the ribbon, in parallel with copper enrichment (determined by AES) and partial crystallization (determined by differential scanning calorimetry). The extrusion of pure copper is considered to be caused by hydrogen diffusing into the bulk through existing surface defects. As a consequence of the surface and structural changes, steady increases in both the copper surface area and the catalytic activity (dehydrogenation of alcohols and isomerization of allyl alcohol and 2‐propyloxirane) are demonstrated.
Use of model depth resolution functions for the deconvolution of depth profiling data
Authors: Makarov V. V.
Published: December 2004

The problem of deconvolution of SIMS depth profiles with model depth resolution function, which may differ from the true resolution function, is considered. The concept of residual depth resolution function is introduced to describe mathematically the result of the deconvolution. The consequences of using a model depth resolution function of double exponential form are explored and the range of exponents over which a deconvolution might give useful information is derived analytically.

It is shown how a depth resolution function of double exponential form distorts the initial profiles of different types. The analytical expressions are obtained for rectangular and exponential initial profiles. It is shown that the convolution of the initial exponential profile with a double exponential resolution function leads to a linear combination of exponential functions containing separately either exponential parameters of the resolution function or that of the initial profile. The resultant inverse of the exponential slope cannot be calculated by direct summation of the characteristic lengths of the initial profile and those of the resolution function.

The asymptotic behaviour of the convolution of the initial Gaussian profile with a double exponential resolution function is explored analytically.
AES study of Si LVV bonding states in various substoichiometric oxide environments
Authors: Lang B. , Khellafi M.
Published: December 2004

Auger electron spectroscopy has been applied to a study of chemical structure effects in silicon oxides caused by changes of the surface or bulk stoichiometry. Ion‐damaged SiO2, vacuum‐deposited SiOx (1 < × < 2) and Si/SiO2 interfaces were investigated. Silicon enrichment causes not only the growth of the elemental Si peak, but also a broadening of the main oxide peak. Detailed comparison of the Si LVV spectra in the three types of samples suggests that the elemental Si component occurs with the same local structure as in bulk silicon.
Si LVV Auger lineshape analysis to study the oxygen chemisorption on TaSi2 thin film
Authors: Sharma J. K. N. , Chakraborty B. R. , Bera Santanu
Published: December 2004

The Si LVV Auger lineshapes of the single‐crystal Si(100) surface and the oxygen chemisorbed and clean TaSi2 surfaces are studied by observing the three Auger transitions that have different final states in the valence band. It is seen from the Si and Ta Auger fingerprints that both Si and Ta form oxides due to chemisorption of oxygen on the silicide surface at room temperature. The variations in the Si LVV fingerprint in silicide and the oxygen‐exposed silicide are explained in term of surface effects and the behaviour of the 3s orbital in the bondings involved. Electron energy‐loss spectroscopy is used to understand the different shallow‐level transitions in Ta and the silicide. The electron impact autoionization spectra for TaSi2 and oxygen‐exposed TaSi2 are also presented and analysed, along with the Ta NNN fingerprint to show the oxidation in Ta.
Sloping shirley‐type inelastic line shapes
Authors: Végh János
Published: December 2004

A simple modification to the Shirley‐type inelastic line shape is proposed. The modification results in a sloping background contribution (‘tail’) and a non‐infinite inelastic tail area. Far from the photopeak the present tail shows Tougaard‐type behaviour, but in the vicinity of the photopeak it deviates significantly from the Tougaard‐type tail. Using the ‘universal’ constants derived in the frame of the Tougaard model, universal ‘tail height’ and ‘tail slope’ parameters are derived.
Photoemission study of an AuPdAu(111) multilayer grown by MBE
Authors: Cole R. J. , Evans J. A. , Gregory D. A. C. , Unsworth P. , Weightman P. , Greig D. , Walker M. J. , Beamson G.
Published: December 2004

An au/Pd/Au(111) multilayer system grown by molecular beam epitaxy has been studied by high‐resolution x‐ray photoelectron spectroscopy. An analysis of the dependence of the relative intensity of the Au and Pd core‐level XPS lines on the take‐off angle indicates that the thickness of the Pd sandwhich layer is ∼5 monolayers. The photoelectron spectra show the presence of more than one chemical environment for each element and suggest that the core‐level photoelectron spectra of Pd atoms in the interfacial layers and the inner layers of the Pd sandwich are split by ∼0.6 eV. The photoelectron spectra of the valence band show that the Pd sandwich retains the high density of states at the Fermi energy that is characteristic of Pd metal.