bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural dynamics of nucleosome core particle: Comparison with nucleosomes containing histone variants
Authors: Ramaswamy Amutha , Bahar Ivet , Ioshikhes Ilya 
Published: December 2004

AbstractThe present study provides insights on the dominant mechanisms of motions of the nucleosome core particle and the changes in its functional dynamics in response to histone variants. Comparative analysis of the global dynamics of nucleosomes with native and variant H2A histones, using normal mode analysis revealed that the dynamics of the nucleosome is highly symmetric, and its interaction with the nucleosomal DNA plays a vital role in its regulation. The collective dynamics of nucleosomes are predicted to be dominated by two types of large‐scale motions: (1) a global stretching–compression of nucleosome along the dyad axis by which the nucleosome undergoes a breathing motion with a massive distortion of nucleosomal DNA, modulated by histone–DNA interactions; and (2) the flipping (or bending) of both the sides of the nucleosome in an out‐of‐plane fashion with respect to the dyad axis, originated by the highly dynamic N‐termini of H3 and (H2A.Z‐H2B) dimer in agreement with the experimentally observed perturbed dynamics of the particular N‐terminus under physiological conditions. In general, the nucleosomes with variant histones exhibit higher mobilities and weaker correlations between internal motions compared to the nucleosome containing ordinary histones. The differences are more pronounced at the L1 and L2 loops of the respective monomers H2B and H2A, and at the N‐termini of the monomers H3 and H4, all of which closely interact with the wrapping DNA. Proteins 2005. © 2004 Wiley‐Liss, Inc.
Synthesis of Functionalised Sulfonamides via Microwave Assisted Displacement of PFP‐Sulfonates with Amines
Authors: Caddick Stephen , Wilden Jonathan D. , Bush Hannah D. , Judd Duncan B. 
Published: December 2004

AbstractA convenient microwave assisted synthesis of sulfonamides from PFP‐sulfonates is described. Reaction of various commercially available amines with pentafluorophenyl (PFP) sulfonate esters under microwave irradiation led to the corresponding sulfonamide products in good yields and without the requirement for chromatographic purification. The data shows that a number of functional groups are tolerated in both the amine and sulfonate ester and that the method can be extended to heterocyclic sulfonamides of potential biological interest.
Quantitative XPS analysis without reference samples
Authors: Ebel Maria F. 
Published: December 2004

AbstractFor approximately ten years there has existed a theoretically based concept of fundamental parameters for XRFA (quantitative X‐ray fluorescence analysis). From a comparison of the differences specific for XRFA and XPS it can be learned that this concept is also applicable to XPS and allows quantitative analysis without reference samples. Additionally, the influence of an overlayer on analytical XPS results is discussed. The theoretical considerations are confirmed by a series of measurements performed on binary and ternary alloys of Ag/Au/Cu and the results are compared with those of earlier measurements with reference samples. An averaged absolute accuracy of approximately ±2 wt% has been found for both methods, but the advantage of an absolute method needs no further comment.
A study of interface problems in polycrystalline GaAs Schotky barrier and MIS solar cells
Authors: Kazmerski L. L. , Ireland P. J. 
Published: December 2004

AbstractAES, SIMS and XPS are used to investigate the interfaces in polycrystalline GaAs Schottky barrier and MIS solar cells. A significant interfacial chemical reaction is found to occur between Au and the GaAs in room temperature fabricated devices, with at least one phase, Ga2Au, identified using chemical peak shifts in XPS. Enhanced interdiffusion is reported at elevated temperatures for these structures. The primary mechanism is identified to be grain boundary diffusion, and the temperature dependence of the diffusion coefficient is estimated from the AES depth‐compositional data. The interface in the Ag/GaAs Schottky barrier is studied for comparison and is found to be stable to 573 K. The measured Schottky barrier heights and photovoltaic performances of these solar cells are correlated with the condition of the metal‐semiconductor interface. The advantage of including a thin oxide layer between the Au and GaAs (MIS structure) in preserving the integrity of the interfaces is demonstrated.
Quantitative measurement of impurities in GaAs layers by secondary ion mass spectrometry
Authors: Clegg J. B. 
Published: December 2004

AbstractA quadrupole‐based SIMS system has been used for the localized impurity analysis of GaAs. Spectral interferences are reduced by using a mass filtered primary ion beam and UHV conditions in the target chamber with energy discrimination of the secondary ions. Practical detection limits for 12 elements have been determined with samples calibrated by other methods. Detection limits for important impurities in GaAs range from 1014 atoms cm−3 for Cr and Mn to 1016 atoms cm−3 for Si, Zn and Sn. Depth profiles are presented which demonstrate that this detection capability is attained with micron thick layers. Confirmatory evidence of profile shapes and impurity concentrations has been obtained from independent electrical data.
The development of surface shape during sputter‐depth profiling in Auger electron spectroscopy
Authors: Makh S. S. , Smith R. , Walls J. M. 
Published: December 2004

AbstractIon bombardment is an important process in surface analysis, not only for surface cleaning, but also for obtaining composition‐depth profiles through thin films and interfaces. Although the use of depth profiling is well established for initially flat surfaces and the problems associated with ion‐induced artefacts such as surface topography, preferential sputtering and redeposition are well recognized, the additional problems which occur when non‐flat surfaces are bombarded have been neglected. For example, depth profile analysis of rods, wires, fibres, etc., using Auger electron spectroscopy is now of interest for many commercial purposes. However, the erosion of such geometries is non‐uniform since different angles of incidence are presented to the incoming ion beam. In this paper, computer simulations are presented which illustrate the erosion of such geometries and a quantitative analysis is given for the resulting degradation in depth resolution as a function of sample and electron beam diameter.
A correlation of the average sample mass and the sputtering yield in SIMS
Authors: Katz William , Williams Peter , Evans C. A. 
Published: December 2004

AbstractPrevious work has shown that the sputtering yield of a matrix strongly affects the secondary ion yield of a material bombarded by reactive primary ions. Examining several homologous series of compounds, we have determined a linear correlation between sputtering yield and average substrate mass. This relationship enables quantitative predictions of the substrate sputtering yield and stoichiometry prior to SIMS analysis. This approach should be generally applicable to any sputtering technique.
Surface structural investigations by photoemission spectroscopy
Authors: Margaritondo G. 
Published: December 2004

AbstractPhotoemission techniques are currently being used by several authors for surface geometry investigations. In particular great emphasis is being placed on photoelectron diffraction effects in the final state which are a direct source of structural information. Other surface structure investigations involve more conventional initial‐state photoemission experiments. We briefly discuss some of the above appraches and their advantages with respect to the ‘traditional’ structural probes.
Defect structures at solid surfaces
Authors: Lagally M. G. , Welkie D. G. 
Published: December 2004

AbstractThe analysis of surface structural defects at the atomic level using low energy electron diffraction (LEED) is briefly considered. The angular distribution of the diffracted intensity contains information on the defect structure. A number of defects can be distinguished and quantified by studying the behavior of the angular width of diffracted beams with changes in diffraction parameters.
ESCA studies of Ni‐25 At% Fe alloy. 1—surface preparation treatments and oxidation
Authors: Olefjord I. , Marcus P. 
Published: December 2004

AbstractThe surface compositions of Ni‐25 at% Fe single crystals ((100) and (110)) were analysed by ESCA. The spectra were interpreted by comparison with reference spectra obtained from Ni, Fe, NiO, Fe2O3 prepared in situ. Various surface pretreatments were investigated. The appropriate treatment to obtain a surface composition identical to the matrix composition is electropolishing and subsequent ion etching; the etching time is critical because the electropolished surface is enriched with nickel. Annealing at 800 °C can also be used to obtain the correct surface composition, but ion etching is then required to remove sulphur segregated to the surface during annealing. Oxidation at 25 °C and 500 °C (PO2 = 10−4Torr) gives an iron enriched oxide. At 500 °C, nucleation and lateral growth of oxide islands were observed. Both the islands formed in the early stage and the final oxide covering the whole surface have the composition of the spinel NiFe2O4.
ESCA studies of metals and alloys: Oxidation, migration and dealloying of cu‐based system
Authors: Barr Tery L. 
Published: December 2004

AbstractA short, critical review is provided on the utilization of surface techniques, particularly ESCA, for the study of metal and alloy corrosion problems. Some of the attributes and difficulties of these techniques are considered. An interrelated series of Cu systems are chosen as representative examples of the use of ESCA in this type of study. Included are: (1) the oxidation in air (natural passivation) of polycrystalline Cu, (2) the thermal degradation of a Cu98Be2 alloy. This process readily exhibits preferential surface migration. (3) An ESCA study of the air oxidation of α‐brass (Cu75Zn25). This produces a clear example of preferential oxidation. (4) The ESCA analysis of this same air passivated α‐brass following progressive exposures to simulated seawater. This provides a dramatic example of ion‐field induced dealloying; i.e., dezincification.
Low energy electron loss studies of cuInSe2 surfaces
Authors: Jamjoum O. , Kazmerski L. L. , Lichtman D. L. , Bachmann K. J. 
Published: December 2004

AbstractThe low energy loss spectra (LELS) of clean and oxygen contaminated (111) p‐type CuInSe 2 single crystals are reported. Losses due to interband transitions and plasmon excitations are observed. By varying the primary electron energy (100–500 eV) both surface and bulk features of the conduction bands are probed. As oxygen is adsorbed on the surface of the CuInSe 2 (at room temperature), the In and Se atoms seem to associate with themselves and with oxygen, whereas the Cu atoms do not seem to play a direct role in the oxidation process. LELS Spectra are presented as a function of primary beam energy and oxygen absorption.
Surface structure and NiO dispersion for NiO/γ‐Al2O3 catalysts
Authors: Gambaro L. A. , Fierro J. L. G. , Tejuca L. González , Agudo A. López 
Published: December 2004

AbstractChemisorption of CO at temperatures below 100°C has been used to evaluate the dispersion of NiO in a series of NiO/γ‐Al2O3 catalysts. CO adsorption measurements were supplemented by i.r. spectroscopy to establish the CO/NiO stoichiometry. From monolayer coverage data derived from Freundlich's equation, the percentage of NiO dispersion and the average NiO crystallite size were calculated. The crystallite size of supported NiO was found to be practically constant for NiO loadings from 1 to 8 wt%, experimenting an abrupt increase for higher NiO contents. These results were consistent with additional information on the surface structure of the catalysts obtained by IR spectroscopy, X‐ray diffraction, magnetic susceptibility, and reduction with H2.
Transmission electron microscopy of ultramicrotomed barrier anodic films on aluminium
Authors: McCune R. C. , Plummer H. K. 
Published: December 2004

AbstractUltramicrotomy was utilized to produce thin section specimens of anodized aluminium to permit a measurement of the film thickness in cross section by transmission electron microscopy. This direct approach to film thickness measurement has an inherent precision of ±0.5 nm, and may be utilized to measure films as thin as 5.0 nm. Two types of film growth procedures were studied using this technique: one utilizing an aqueous ammonium tartrate solution as the electrolyte, and a second using a nonaqueous electrolyte of ammonium pentaborate in ethylene glycol. While both electrolytes yielded barrier values of approximately 1.5 nm V−1, in agreement with literature values, the aqueous electrolyte tended to show a zero‐potential offset of nearly 10 nm greater than the nonaqueous electrolyte. Furthermore, films grown in aqueous solutions tended to have a less dense surface morphology, which was distinguishable in transmission electron microscopy.
Analysis of diffusion mechanisms in thin polycrystalline Au–Ag films using auger electron spectroscopy
Authors: Bukaluk Antoni 
Published: December 2004

AbstractThe diffusion process of silver through gold polycrystalline films 1000 Å thick for different heating times and different temperatures was studied. Auger electron spectroscopy (AES) with simultaneous argon ion sputtering was used to obtain the composition profiles of silver diffusing through gold thin films. The interdiffusion coefficients were extracted from the diffusion profiles using the rate of decrease of the concentration gradient at the Au–Ag film interface (the ‘centre gradient’ method) and the rate of rise of Ag concentration plateau in the Au film (the ‘plateau rise’ method). The grain boundary diffusion coefficients have been evaluated by means of the depth profile analysis, based on the Whipple model. The activation energies of each mechanism have been determined from the Arrhenius plots.
X‐ray photoelectron diffraction studies of zinc selenide
Authors: Sian Crawford E. , Evans Stephen , Raftery Elizabeth , Scott Michael D. 
Published: December 2004

AbstractPolar and azimuthal angle‐resolved XPS studies of ZnSe layers grown epitaxially on {100} GaAs by H2 transport of the elements are described. Comparison of the polar X‐ray photoelectron diffraction (XPD) patterns obtained for rotation about [110] and [110] axes confirms the dominant influence of structural factors in determining the shape of the patterns. Azimuthal XPD patterns are shown to reflect symmetry properties directly related to the emitting sites, and their use to determine the symmetry of an exposed single‐crystal surface is demonstrated. The outermost ∼100 Å of all the ‘as‐grown’ ZnSe layers were ∼20–35% Zn rich. Ar ion bombardment (800 eV, ∼5 μA) rapidly restored the surface stoichiometry to within 10% of 1:1. The disorder concurrently introduced resulted in XPS peak broadening without impairment of the polar XPD pattern. Annealing at 300°C in high vacuum removed the disorder without affecting either the stoichiometry or the XPD pattern. It is inferred that split‐<100> interstitials are the preferred sites both for atoms displaced by ion bombardment and for the excess Zn initially present.
SIMS study of the SiO2/Si interface and of the Si+O2 system
Authors: Degreve F. , Ged Ph. 
Published: December 2004

AbstractDepth profiles of mono and polyatomic ions (Si+, SiO+, Si, Si++) have been determined by SIMS under Ar+ ion bombardment on 100 Å to 700 Å thick thermal SiO2 layers. The main experimental results are: (1) The best depth resolution is obtained with Si+ (49 ± 6 Å); (2) The ion intensity profiles plotted against the sputtering time are systematically shifted from one species to another; (3) The sputtering time needed to obtain a 50% signal variation in the interface region varies linearly with the oxide thickness for all the above species; (4) The slope of the corresponding straight lines are identical but the intercepts differ from 1 ± 6 Å for Si up to 36 ± 6 Å for SiO+. Furthermore, similar intensity shifts are seen for the above ions when a silicon substrate is argon bombarded under various oxygen pressure conditions. The experimental data shows that the shifts of the secondary ion profiles and the non zero intercepts are not necessarily due to cascade mixing and may involve sputter yield or ionization probability variations in the interfacial region.
GaAs oxides formed at room temperature in air: Comparison of X‐ray photoelectron spectroscopic and ion microprobe mass analyses
Authors: Demanet C. M. , Rawsthorne E. D. , Stander C. M. 
Published: December 2004

AbstractAn ion microprobe mass analysis (IMMA) study of the oxides formed on GaAs at ambient temperature and in ambient atmosphere is compared with a similar study carried out using XPS. The distribution of the various oxides identified from their unequivocal fragment ions is analysed. The multilayer model proposed on the basis of XPS results is largely confirmed with the exception of gallium hydroxide which, from the IMMA results, appears to be distributed across the whole oxide thickness.
Correlation between CdS photoanodic behaviour and electrode chemical modifications: An X‐ray photoelectron spectroscopic study
Authors: Riga J. , Verbist J. J. , Josseaux P. , Kirsch‐de Mesmaeker A. 
Published: December 2004

AbstractThe photosensitivity increase of CdS films as a function of the illumination time, is correlated to chemical changes of the electrode surface, analysed by XPS. It is shown that the formation of Cd(OH)2 or CdO is responsible for the photosensitivity change of the illuminated electrode in contact with H2O/NaOH alone. When thiocresol or p‐mercaptobenzoic acid is added as reductant, a layer of organic compounds is formed on the electrode during the photoelectrochemical process. However, the XPS and photocurrent spectra indicate that this layer does not prevent the occurrence of Cd(OH)2 or CdO responsible for the photosensitivity changes of the CdS film.
The shape of the background in AES: Nonlinear features in log N(E) v. Log E
Authors: Peacock D. C. , Duraud J. P. 
Published: December 2004

AbstractBy replotting emitted electron spectra, N(E), as log N(E) v. log E, parts of the background which obey a power law can be identified as linear segments. The importance of this linearity for Auger electron spectroscopy (AES), and the conditions under which it can be observed, are discussed. A simple expression is presented which describes the essential shape of the spectral background for analysis energies in the range 50–2000 eV and primary energies between 3 and 20 keV. It has been suggested elsewhere that such simple expressions are inadequate because ionization of inner shells by backscattered and secondary electrons can introduce broad low intensity features which disrupt the linearity of log N(E) v. log E. In the present work numerically calculated spectral shapes are compared with experimental AES spectra from various specimens including Al and Si. It is shown that some broad features which are often observed in EN(E) (constant spectrometer resolving power) spectra arise solely as a consequence of replotting power law backgrounds in this form and cannot be adduced as evidence of the ionization mechanism. Furthermore, subsurface electron sources can cause nonlinearities in logarithmic spectra which should not be ascribed to the ionization mechanism. It is concluded from a comparison of calculated spectra with those observed experimentally that the ionization mechanism causes only small deviations from linear behaviour which should not prevent the fitting of power law backgrounds to experimental AES data.
Quantifying data from Auger spectra and images
Authors: Walker C. G. H. , Peacock D. C. , Prutton M. , El Gomati M. M. 
Published: December 2004

AbstractA method for quantifying Auger spectra and including matrix effects is described. This method corrects iteratively for the effects of electron back‐scattering, the inelastic mean free path and atomic density in the sample using established methods. New algorithms have been developed to assist the user interactively with the analysis of spectra collected from surfaces covered by thin films of unknown composition or thickness, or by coverage of another material. Error analysis has been included for both homogeneous and thin film cases. A ‘figure of merit’, used to inform the user if a thin film model of the surface is accurate, is introduced. The algorithms can be implemented on a small microcomputer. Their application to quantitative Auger analysis by multi‐spectral imaging is also described. Each point in a set of images has been corrected for the factors that influence the Auger current to arrive at surface compositions at each pixel for each element. Some of the advantages and problems of quantifying Auger images will be outlined. The use of multi‐spectral Auger images is seen as a powerful means of identifying surface phases of materials and is given the acronym MULSAM—MULti‐Spectral‐Auger Mapping.
Effect of analytical method on thickness measurements of thin oxide films
Authors: Tapping R. L. , Davidson R. D. , Jackman T. E. , Davies J. A. 
Published: December 2004

AbstractThe thickness of thin natural oxide films formed on silicon, nickel, aluminium, iron, tantalum and zirconium has been measured using nuclear reaction analysis (NRA) and Auger electron spectroscopy (AES) in combination with ion beam sputtering. It is shown that ion beam effects severely limit the use of AES and ion beam sputtering in measuring thin oxide thicknesses. Relatively non‐destructive techniques such as NRA or angle‐resolved x‐ray photoelectron spectroscopy (XPS) provide more reliable information.
Esca and reels characterization of electrically conductive polyimide obtained by ion bombardment in the keV range
Authors: Marletta Giovanni , Oliveri Carmelo , Ferla Giuseppe , Pignataro Salvatore 
Published: December 2004

AbstractPolymide films were bombarded with Ar+ at 150 keV at various doses from 5 × 1012 to 2 × 1017 ions cm−2. Ion bombardment was found to produce a drastic decrease of the electrical resistivity of the polymide from about 1016 to 3 × 10−3 Ω cm, the effect being dependent on the ion dose. The chemical structure of the conductive films obtained was characterized by means of ESCA and REELS techniques. The modification of the original polymer seems to proceed at low ion doses (up to 5 × 1014 ions cm−2) by means of the progressive elimination of the carbonyl groups and the related destruction of the imidic rings, while at high doses (from 5 × 1015 ions cm−2) the carbonization of the polyimide occurs with the production of an amorphous carbon still containing significant amount of residual N and O atoms.