bluuebunny/crossref_metadata_2025 huggingface dataset:
Recurrent αβ loop structures in TIM barrel motifs show a distinct pattern of conserved structural features
Authors: Scheerlinck Jean‐Pierre Y. , Lasters Ignace , Claessens Michel , De Maeyer Marc , Pio Frederic , Delhaise Philippe , Wodak Shoshana J.
Published: May 2005

A systematic survey of seven parallel α/β barrel protein domains, based on exhaustive structural comparisons, reveals that a sizable proportion of the αβ loops in these proteins—20 out of a total of 49—belong to either one of two loop types previously described by Thornton and co‐workers. Six loops are of the αβ1 type, with one residue between the α‐helix and β‐strand, and 13 are of the αβ3 type, with three residues between the helix and the strand. Protein fragments embedding the identified loops, and termed αβ connections since they contain parts of the flanking helix and strand, have been analyzed in detail revealing that each type of connection has a distinct set of conserved structural features. The orientation of the β‐strand relative to the helix and loop portions is different owing to a very localized difference in backbone conformation. In αβ1 connections, the chain enters the β‐strand via a residue adopting an extended conformation, while in αβ3 it does so via a residue in a near α‐helical conformation. Other conserved structural features include distinct patterns of side chain orientation relative to the β‐sheet surface and of main chain H‐bonds in the loop and the β‐strand moieties. Significant differences also occur in packing interactions of conserved hydrophobic residues situated in the last turn of the helix. Yet the α‐helix surface of both types of connections adopts similar orientations relative to the barrel sheet surface. Our results suggest furthermore that conserved hydrophobic residues along the sequence of the connections, may be correlated more with specific patterns of interactions made with neighboring helices and sheet strands than with helix/strand packing within the connection itself. A number of intriguing observations are also made on the distribution of the identified αβ1 and αβ3 loops within the α/β‐barrel motifs. They often occur adjacent to each other; αβ3 loops invariably involve even numbered β‐strands, while αβ1 loops involve preferentially odd β‐strands; all the analyzed proteins contain at least one αβ3 loop in the first half of the eightfold α/β barrel. Possible origins of all these observations, and their relevance to the stability and folding of parallel α/β barrel. Possible origins of all these observations, and their relevance to the stability and folding of parallel α/β barrel motifs are discussed.
Conformational deformation in deoxymyoglobin by hydrostatic pressure
Authors: Yamato Takahisa , Higo Jun'ichi , Seno Yasunobu , Gō Nobuhiro
Published: May 2005

Pressure effect on the equilibrium conformation in sperm whale deoxymyoglobin and its volume fluctuation are studied by the normal mode analysis and strain tensor analysis. The pressure‐induced deformation of interhelix regions are found to be remarkably more compressed than the other parts of the molecule. The intrahelix compressibility is shown to be relatively small. We also calculate the compressibility of the three hydrophobic clusters, located at the bottom, distal, and proximal side of the heme. Its value is found to decrease in the indicated order. The average compressibility of these hydrophobic clusters is less than the average interhelix compressibility, even though there are large cavities in these clusters. In order to study overall deformation, we define a linear compressibility and calculate it for all pairs of Cαatoms. The pressure‐induced deformation is observed to be heterogeneous also in this analysis. The calculated root‐mean‐square displacement of the constituent atoms in the equilibrium conformation at 1,000 atm from those at 0 atm is 0.12 Å, which is much smaller in magnitude than the average value of the atomic fluctuations at room temperature. In the water solvent, the volume excluded by the protein molecule in the equilibrium conformation is reduced by 0.9%, when the pressure is raised from 0 to 1,000 atm. The calculated magnitude of the root‐mean‐square volume fluctuation is 0.3% of the excluded volume at room temperature. The square of the volume fluctuation is given as a sum of contributions from individual normal modes. Contributions from low frequency normal modes are found to dominate over those from higher frequency normal modes. The estimated value of the isothermal compressibility of deoxymyoglobin is 9.37 × 10−12 cm2/dyn. © 1993 Wiley‐Liss, Inc.
Crystal structure of Escherichia coli TEM1 β‐lactamase at 1.8 Å resolution
Authors: Jelsch Christian , Mourey Lionel , Masson Jean‐Michel , Samama Jean‐Pierre
Published: May 2005

The X‐ray structure of Escherichia coli TEM1β‐lactamase has been refined to a crystallorgphic R‐factor of 16.4% for 22,510 reflections between 5.0 and 1.8 Å resolution; 199 water molecules and 1 sulphate ion were included in refinement. Except for the tips of a few solvent‐exposed side chains, all protein atoms have clear electron density and refined to an average atomic temperature factor of 11 Å2. The estimated coordinates error is 0.17 Å. The substrate binding site is located at the interface of the two domains of the protein and contains 4 water molecules and the sulphate anion. One of these solvent molecules is found at hydrogen bond distance from S70 and E166. S70 and S130 are hydrogen bonded to K73 and K234, respectively. It was found that the E. coli TEM1 and Staphylococcus aureus PC1 β‐lactamases crystal structures differ in the relative orientations of the two domains composing the enzymes, which result in a narrowed substrate binding cavity in the TEM1 enzyme. Local but significant differences in the vicinity of this site may explain the occurrence of TEM1 natural mutants with extended substrate specificities. © 1993 Wiley‐Liss, Inc.
Continuous measurement of water in organic solution by membrane‐inlet mass spectrometry
Authors: Bohátka Sándor , Degn Hans
Published: May 2005

With a membrane made of a relatively polar material, membrane‐inlet mass spectrometry can be used to measure the water activity in organic liquids of low dielectric constant. The detection limit for water depends on the solubility of water in the organic liquid. In butanol, hexanol, octanol and octane the detection limits at 45°C are 7, 4, 3 and 0.3 ppm, respectively. The half‐time of the water reponse at 45°C is 20 s. The method can be used for continuous monitoring of water in reaction systems in organic solvents. Examples given are the condensation of 2,4‐dimethyl‐3‐pentanone with phenylhydrazine in hexanol solution and the hydrolysis of acetylchloride in octane solution.
Specific reactivity of the ‘magic bullet’ matrix in the negative‐ion fast‐atom bombardment mass spectra of organic anions
Authors: Aubagnac Jean‐Louis , Man Michel Wong Chi , Elguero José
Published: May 2005

The magic bullet matrix shows a noticeable and specific reactivity towards two organometallic anions (borate and silicate). Thus, before selecting this matrix to study organic salts by fast‐atom bombardment mass spectrometry, it is necessary to check for this specific reactivity.
Negative‐ion mass spectra of methylated diuretics
Authors: Ehrhardt J. D.
Published: May 2005

The negative‐ion mass spectra of 19 methylated diuretics are presented and correlations between these spectra and the chemical structures of the compounds are indicated. The spectra are of interest as the basis of an anylytical method for the identification of small quantities of diuretics in the urine of hypokalemic patients.
Study of water–cryoprotector mixtures by low temperature fast‐atom bombardment mass spectrometry
Authors: Boryak Oleg A. , Kosevich Marina V. , Shelkovsky Vadim S. , Blagoy Yurii P.
Published: May 2005

Frozen solutions of a cryoprotector, glycerol, in water were studied by low temperature fast‐atom bombardment mass spectrometry in the temperature range from − 196° to 0°C. Strong dependence of the mass spectral pattern on the water‐glycerol ratio and temperature of the sample was observed. The evolution of mass spectra of the frozen 2000:1 water‐glycerol mixture with increase of the sample temperature is reproducible: in the lower portion of the temperature range (−196° to −120°C) the spectra contain a set of cluster ions, (H2O)nH+, (n = 1–15), characteristic of pure water; then the spectra show a superposition of peaks due to water clusters and glycerol itself, the latter with characteristic changes with temperature rise: degraded ‘peak at every mass’ pattern in the −120° to −80°C range followed by a build‐up of glycerol clusters, GnH+, (n = 1–3) in the −80°C to −55°C range. At approximately −55°C to −50°C a sublimation of water component occurs, detected by [H2O]+· ion, and the remainder of the spectral pattern coincides with that of pure glycerol up to ambient temperature. Mixed water‐glycerol clusters were never observed. An explanation of such spectral behavior is proposed based on ideas about the morphology of the frozen solutions, characterized by water microcrystallites separated by eutectic channels containing cryoprotector. The independent sputtering of the two substances from different domains of the frozen sample surface is discussed.
‘On‐line’ liquid chromatography/nuclear magnetic resonance mass spectrometry—a powerful spectroscopic tool for the analysis of mixtures of pharmaceutical interest
Authors: Pullen Frank S. , Swanson Alistair G. , Newman Michael J. , Richards Don S.
Published: May 2005

Liquid chromatography (LC), simultaneously coupled with both nuclear magnetic resonance (NMR) and mass spectrometry (MS) ‘on‐line’ is a powerful structural tool and has a potentially vast range of uses within the pharmaceutical industry. Data from a mixture of fluconazole and related triazoles have been obtained from an LC/NMR‐MS system developed ‘in‐house’, demonstrating the power of this novel analytical approach.
Multiresidue determination of quinolone antibiotics using liquid chromatography coupled to atmospheric‐pressure chemical ionization mass spectrometry and tandem mass spectrometry
Authors: Doerge Daniel R. , Bajic Steve
Published: May 2005

Liquid chromatography coupled to atmospheric‐pressure chemical ionization mass spectrometry and tandem mass spectrometry (MS/MS) methods for the determination and quantification of four quinolone antibiotics were adapted from a published procedure for liquid‐liquid extraction from catfish muscle and high‐performance liquid chromatographic analysis. In‐source collision‐induced dissociation was used to optimize fragmentation to produce mass spectra consisting of the protonated molecule and two characteristic fragment ions of nearly equal intensity. Selected ion monitoring of three ions per quinolone yielded sensitive detection in catfish muscle extracts (estimated instrumental detection limits 0.8‐1.7 ppb). The intensity ratios were used to confirm the presence of three of the quinolones based on the accurate agreement (⩽10% deviation) between ratios derived from fortified catfish extracts and those from standard quinolones. MS/MS was used to increase the specificity and sensitivity of analysis. Scans using constant neural loss (CNL) of 18 mass units gave a sensitive response for the quinolones suggesting that CNL scans may be applicable to multiresidue screening for unknown quinolones. MS/MS with multiple reaction monitoring of the [MH18]+ transition for each quinolone yielded the highest sensitivity analysis in catfish extracts (estimated instrumental detection limits 0.08–0.16 ppb).
Reverse isotope dilution analysis of 13CO2 using gas chromatography/isotope ratio mass spectrometry: Application to the quantitative determination of 13CO2 released by human polymorphonuclear leukocytes
Authors: Lamrini Rachid , Lacan Philippe , Francina Alain , Guilluy Roger , Brazier Jean Louis
Published: May 2005

We propose a new method for the quantitative determination of carbon dioxide released by a biological microgenerator: a suspension of human polymorphonuclear leukocytes (PMNL). This method is based on the reverse isotope dilution analysis by gas chromatography/isotope ratio mass spectrometry of 13CO2 released by PMNL in a controlled isotope abundance atmosphere containing 3% CO2.13CO2 release is effective after PMNL stimulation in the presence of [13C]glucose, labeled on positions 1, 2 or 6. The validation of this method is carried out by the measurement of the isotope ratio 13CO2/12CO2 using known amounts of [13C]sodium hydrogen carbonate and the comparison with theoretical isotope abundances derived from various CO2 equilibria. Complete release of CO2 is achieved by the acidification of the medium. This method requires only few cells, displays high sensitivity and specificity and can be applied to the analysis of large series of samples using an automatic sample injector. In addition, this method can also be applied to other types of biological microgenerators of carbon dioxide.
Electrospray mass spectrometric characterization of fluoroquinolone antibiotics: Norfloxacin, enoxacin, ciprofloxacin and ofloxacin
Authors: D'Agostino Paul A. , Hancock James R. , Provost Lionel R.
Published: May 2005

We report the electrospray (ESI) mass spectra of four fluoroquinolones, enoxacin, norfloxacin, ofloxacin and ciprofloxacin, a group of highly potent antibiotics that have not been previously characterized by this ionization technique. At low sampling cone voltage settings, 50 and 100 V, the electrospray mass spectra contained primarily molecular adduct ions. At a sampling cone voltage setting of 150 V, collisionally activated dissociation mass spectra containing structurally significant product ions were produced and accurately mass measured at a magnetic sector resolution of 3000. Gradient separation and characterization of these compounds was demonstrated by analysis using packed capillary column liquid chromatography with UV and ESI‐MS detection. UV detection limits in the 1 to 2 ng range ((signal‐to‐noise ratio S/N) = 10:1) were estimated and interpretable mass spectra with S/N ratios in excess of 100:1 were observed for 1.5 ng of analyte during electrospray mass spectrometric analysis.
Sequencing electroblotted proteins by tandem mass spectrometry
Authors: Fabris D. , Vestling M. M. , Fenselau C. , Cordero M. M. , Doroshenko V. M. , Cotter R. J.
Published: May 2005

Electroblotting proteins separated by gel electrophoresis provides a suitable support for further manipulations and analysis of small amounts of relatively pure samples. On‐membrane digestion, peptide mapping by mass spectrometry, and database searching offer sensitive and fast tools to identify the analyte. By providing sequence information, tandem mass spectrometry can go a step further, confirming the database identification, solving problems connected with post‐translational modifications and sequence variations, or supplying the stretches of internal sequence necessary to synthesize an oligonucleotide probe for gene isolation. The viability of this approach was successfully evaluated using different tandem mass spectrometric techniques: metastable decomposition in a matrix‐assisted laser desorption/ionization (MALDI) time‐of‐flight instrument with a curved‐field reflectron; low energy collision‐induced dissociation in a MALDI quadrupole ion trap mass spectrometer; and high energy collision‐induced dissociation in a high‐performance four‐sector mass spectrometer with massive cluster‐impact ionization.
Error‐tolerant protein database searching using peptide product‐ion spectra
Authors: Bonner Ron , Shushan Bori
Published: May 2005

A method for matching proteins in databases with unknown samples using data derived from peptide production masses is described. The power of the method is due to the speed of analysis and to the ability to locate proteins in a database even when the experimental data show anomalies due to derivatization or post‐translational modification.
Characterization of fresh and spent HDS catalysts by Auger and X‐ray photoelectron spectroscopies
Authors: Brinen J. S. , Graham S. W. , Hammond J. S. , Paul D. F.
Published: May 2005

High resolution scanning Auger measurements have been made of HDS catalysts recovered from a heavy oil refining operation. Element maps and Auger spectra point out spectral inhomogeneities existing on the used catalyst which hitherto have not been reported. Once charging has been controlled, the information obtained sheds a new dimension for the study of catalysts on insulating support materials.
Affinity of lead for noble metals on different supports
Authors: Gandhi H. S. , Williamson W. B. , Logothetis E. M. , Tabock J. , Peters C. , Hurley M. D. , Shelef M.
Published: May 2005

Direct association of lead compounds with Pt, Pd and Rh sputtered onto ZrO2, TiO2 and Al2O3 wafer supports was observed. The samples were exposed to combustion products of iso‐octane containing 1.5 g Pb gal−1 as Motor Mix, 0.8 mg P gal−1 and 0.03 wt% S at 700°C in an overall lean exhaust; however, the samples experienced alternating rich and lean exhaust pulses. A semi‐quantitative electron microprobe study showed that the association of lead compounds to the surface of Pt, Pd and Rh was at least 2 or 3 orders of magnitude higher compared to the amount found on the supports. On Pt lead was present predominantly as PbSO4, on Rh as PbO or Pb metal, and as solid solution in Pd. These large differences in the form of Pb compounds could explain the known fact that Pd and Rh are more sensitive to Pb poisoning than Pt. The higher activity of Pt in catalyzing the oxidation of SO2 to SO3 results in the formation of stable but inert PbSO4 on Pt. On the other hand, Rh and Pd are poor catalysts for SO2 oxidation and therefore Pb remains as PbO or Pb on Rh and forms PdPb solid solutions with Pd. In both cases (Pd and Rh) the active sites for catalytic reactions are poisoned. Halide‐containing lead species were more specific than volatile PbO in poisoning noble metals as indicated by various independent experimental observations.
Application of X‐ray‐induced Auger electron spectroscopy to state analyses of hydrogen implanted in Y, Zr and Nb metals
Authors: Baba Yuji , Sasaki Teikichi A.
Published: May 2005

X‐ray‐induced Auger electron spectroscopy (XAES) was used to examine the surface chemical states of hydrogen implanted metals. The chemical shifts of the M4,5N2,3V Auger peaks from their metallic states were 1.0 eV, 3.3 eV and 2.2 eV, respectively, for ion‐implanted Y, Zr and Nb. The separation energies were found to be much larger than those of the corresponding 3d5/2 lines in the XPS spectra.
Comparative study of ion implantation profiles in metals
Authors: Takadoum J. , Pivin J. C. , Pons‐Corbeau J. , Berneron R. , Charbonnier J. C.
Published: May 2005

Secondary ion mass spectrometry and glow discharge optical spectrometry are used to determine the depth profiles of Ni and Fe matrices implanted with B and P. These measurements enable the emission yields of secondary ions (for SIMS) or photons (for GDOS) emitted under ion bombardment to be quantified and consequently the implanted samples can be used as standards. The profiles obtained by both methods are in good agreement and independant of the surface roughness. They are compared to real distributions determined by Rutherford backscattering (RBS) and to theoretical ones predicted by the model of Winterbon, Sigmund and Sanders; the concentrations measured at the maximum of the distribution are smaller then the theoretical ones and the experimental profiles are wider than those given by the theory. The causes of the alterations in the profiles are discussed and the surface contamination of the samples is studied by mean of GDOS profiles.
Analysis of polymer surfaces by SIMS. 4—A study of some acrylic homo‐ and co‐polymers
Authors: Briggs D. , Hearn M. J. , Ratner B. D.
Published: May 2005

Static SIMS spectra from essentially undamaged acrylic polymers have been obtained for total ions doses of 2 × 1012 ions cm−2. For a series of polymethacrylates the spectra can be interpreted in terms of a constant contribution from the polymer backbone plus dominant fragments from the ester side chain. Isomeric butyl methacrylate polymers can be distinguished. Negative ion spectra reflect the O:C atomic ratio of the bulk polymer. Positive ion relative intensities from ethyl methacrylate: hydroxyethyl methacrylate random copolymers correlate with polymer composition. Previous SIMS data from polymethacrylates have been shown to represent highly damaged surfaces.
Quantitative XPS: The calibration of spectrometer intensity—energy response functions. 2—Results of interlaboratory measurements for commercial instruments
Authors: Seah M. P. , Jones M. E. , Anthony M. T.
Published: May 2005

An interlaboratory experiment to establish X‐ray photoelectron spectrometer intensity–energy response functions has been completed. The measurements made by fifteen participants give results for seven instrument models from four manufacturers. Two methods of determining the response function are tested: (i) by peak area measurement and (ii) using the background data from wide scan spectra from reference foils of Cu, Ag and Au. The peak area data show excellent reproducibility, and area ratios, when corrected for instrument response functions, are consistent to a standard deviation of 4% for Ag and Au between all instruments and conditions. The response functions relative to the VG Scientific ESCA 3 Mk II are proportional to En where, in the constant ΔE mode, n = −;0.20±0.03 for the Leybold LHS10, −0.15±0.10 for the Perkin–Elmer PHI 550, 0.00±0.03 for the VG Scientific ESCA 3, and 0.20±0.02 for the VG Scientific ESCALAB I and II. The AEI/Kratos ES 200B/300 gives a complex, but defined, function. In the constant ΔE/E mode the latter instrument gives n in the range 1.3 to 2.0 and the VG Scientific ESCALAB II 1.79±0.05.
Investigating cyanide electrodes by surface analytical methods with different depths of information
Authors: Ebel Maria F. , Wernisch J. , Pungor E.
Published: May 2005

Three surface analytical techniques with different depths of information (XRFA, SEM and XPS) have been employed to prove experimentally a theoretical model which describes the function of a secondary electrode.
SIMS study of the penetration of metallic secondary impurities in screen‐printed silicon solar cells
Authors: Van Craen M. , Frisson L. , Adams F. C.
Published: May 2005

The penetration of metallic B, Ti, Fe, Cu and Ag in silicon solar cells was studied. They were prepared using the screen printing process for metallization. The level and depth of penetration were determined using secondary ion mass spectrometry (SIMS). Quantitative SIMS depth profile analysis was performed using ion implanted substrates as standard materials. The influence of different production parameters, such as silicon crystal orientation, metallization temperature, composition of the Ag‐paste and the presence of an anti‐reflective TiOx coating on the silicon cells were determined. The penetration of some metallic species has considerable influence on the solar cell characteristics and its efficiency. The penetration levels can not be explained by diffusion but are probably related to more reactive interactions.
Quantitative ISS/XPS measurements on HDS catalysts
Authors: Brinen J. S. , D'Avignon D. A. , Meyers E. A. , Deng P. T. , Behnken D. W.
Published: May 2005

ISS and XPS spectra were obtained for hydrodesulfurization (HDS) catalysts made by two different preparative methods. Quantitative XPS measurements were used with ISS depth profiles to demonstrate that quantitative ISS data could be obtained despite the irregular structure of catalyst surfaces. Atomic compositions as a function of depth were then obtained by (1) use of ISS data directly or (2) by XPS formalism using a non‐constant depth distribution.
Absolute background determination in XPS
Authors: Tougaard S. , Jørgensen B.
Published: May 2005

A recent method, which contains no adjustable parameters, is used to deconvolute the background intensity of inelastically scattered electrons from the XPS spectrum of silver in the 200–900 eV kinetic energy range. The inelastic background signal is found to match the measured spectrum in the energy regions between peaks. In the deconvoluted spectrum the behaviour on the low energy side of each peak is similar, with a tail of primary electrons extending ∼50 eV below the peak. The range of validity of the deconvolution procedure is discussed.
Electron and ion beam degradation effects in AES analysis of silicon nitride thin films
Authors: Fransen F. , Berghe R. Vanden , Vlaeminck R. , Hinoul M. , Remmerie J. , Maes H. E.
Published: May 2005

Silicon nitride films are currently investigated by AES combined with ion profiling techniques for their stoichiometry and oxygen content. During this analysis, ion beam and primary electron effects were observed. The effect of argon ion bombardment is the preferential sputtering of nitrogen, forming “covalent” silicon at the surface layer (AES peak at 91 eV). The electron beam irradiation results in a decrease of the covalent silicon peak, either by an electron beam annealing effect in the bulk of the silicon nitride film, or by an ionization enhanced surface diffusion process of the silicon (electromigration). By the electron beam annealing, nitrogen species are liberated in the bulk of the silicon nitride film and migrate towards the surface where they react with the covalent silicon. The ionization enhanced diffusion originates from local charging of the surface, induced by the electron beam.
Calculations of electron inelastic mean free paths from experimental optical data
Authors: Powell C. J.
Published: May 2005

Calculations are reported of inelastic mean free paths (IMFPs) for 100–2000 eV electrons in C, Mg, Al, Al2O3, Cu, Ag, Au, and Bi from experimental optical data. These calculations require knowledge of the momentum‐transfer dependence of the differential scattering cross section; this information was taken from Penn's calculations. The calculated IMFPs agree reasonably with direct calculations and with measured electron attenuation lengths (ALs). Since accurate measurements of ALs are difficult, it is suggested that calculations of the present type are useful if the needed optical data are available. The present approach is also useful for materials (such as the transition and noble metals) for which it is not possible to make a meaningful distinction between valence‐electron and core‐electron excitations as required in current IMFP calculations. The dependence of the calculated IMFPs on electron energy varied with material and was associated with different spectral distributions of the electron energy‐loss function. The trend in the dependence of IMFP on energy was similar to that found in analysis of AL data.
XPS study of ion‐induced changes on the surface of an organosilicon model polymer
Authors: Tóth A. , Bertóti I. , Székely T. , Mohai M.
Published: May 2005

Changes in composition and bonding induced by bombardment with argon or nitrogen ions in a commercial poly‐methyl‐phenyl‐cyanopropyl‐siloxane fluid were examined by XPS. The actual surface composition depended on the ion energy, the etch time and the nature of the gas applied. It was found that phenyl groups were damaged seriously, reaction of the cyano groups took place with the formation of CN type bonds and the polymer degraded with elimination of fragments containing mostly C at the first stage and mainly O and Si at advanced stages. In addition nitrogen was found to build into the polymer surface when bombarding by nitrogen ions. Irreversible changes in the spectra of the fluid polymer were regarded as a sign of crosslinking.
An experimental investigation of backscatter factors in Auger spectroscopy
Authors: Underhill P. R.
Published: May 2005

A systematic experimental investigation of relative backscatter factors as a function of primary beam energy and substrate atomic number using the carbon KLL and copper LMM Auger peaks is described. The results are compared to the Monte Carlo calculations of Ichimura et al. (1981). Good agreement between experiment and theory is found in the case of large overpotentials but the theorietical calculations are found to overestimate the backscatter contribution with increasing Z as the overpotential decreases.
Study of interfaces in oxidized Fe/Si system by XPS and XAES: Use of the Auger parameter
Authors: Rivière J. C. , Crossley J. A. A.
Published: May 2005

Auger Parameters for a variety of silicon compounds have been measured by a combination of XPS using both AIKα ZrLα characteristic x‐radiation, and of XAES using Bremsstrahlung radiation. The Parameters so derived have then been used to study the chemical states of silicon at and near interfaces in the oxide film formed by air‐and CO2‐oxidation of Fe/Si alloys. Supportive evidence for the interpretations is provided by the widths and shapes of the silicon KL2,3 L2,3 Auger peaks.
The characterization of heterogeneous catalysts by XPS based on geometrical probability 1: Monometallic catalysts
Authors: Kuipers H. P. C. E. , Van Leuven H. C. E. , Visser W. M.
Published: May 2005

Geometrical probability can be used as a basis for the quantification of XPS‐signals stemming from random samples such as, for instance, supported heterogeneous catalysts. From a study of three ideal cases, namely extended layers of constant thickness, equally sized spheres and hemispheres on a randomly oriented support, it has been established that the effects of angular and layer thickness averaging are interconnected in such a way that a general model can be derived. It has been found that signal ratios as measured by XPS for convex particles are determined by the surface/volume ratios of the supported phases, nearly independent of particle shape.
Mechanism of silicon surface roughening by reactive ion etching
Authors: Oehrlein Gottlieb S. , Schad Robert G. , Jaso Mark A.
Published: May 2005

Rough silicon surfaces resulting from CF4 reactive ion etching have been studied by scanning electron microscopy/scanning Auger microscopy and x‐ray photoemission spectroscopy. The experimental data demonstrate a roughening mechanism based on laterally non‐uniform etch rates due to the existence of involatile surface residues.
Probing polymer surface and interface dynamics
Authors: Andrade J. D. , Chen W.‐Y.
Published: May 2005

Polymeric materials generally exhibit various molecular motions and relaxations. Such relaxation processes, which include the glass transition temperature, have significant effects on physical and mechanical behavior. Polymer molecules and segments at surfaces and interfaces also exhibit motions and relaxations. In air or vacuum, such motions ‘permit’ the surface to restructure to minimize the surface free energy. In aqueous solution, the polymer surface restructures and reorients to optimally interact with the aqueous solvent, thereby minimizing the interfacial free energy. XPS and related high vacuum techniques probe the vacuum‐equilibrated surface. The best way to probe the polymer‐liquid interface is via dynamic contact angle or wetting methods. A number of issues and concerns are discussed: (1) the size or hierarchy of structures: (2) the time course of surface dynamic processes; (3) theory, modeling, and simulation of surface dynamics; and (4) experimental methods.
Data compilations: their use to improve measurement certainty in surface analysis by aes and xps
Authors: Seah M. P.
Published: May 2005

Data compliations are an integral and vital part of the development of the measurement scheme for surface analysis. They have three main functions that will be considered in this survey: (i) the provision of numerical values for use in calculations of quantitative surface analysis, (ii) the provision of unbiased data for the development of theory, and (iii) the establishment of a benchmark to judge the value of current research. A brief review will be made of practical data relating to AES and XPS instruments; electron guns, x‐ray sources, spectrometers and detectors. Next, data compilations of experimental measurements of relative sensitivity factors, attenuation lengths and backscattering factors will be contrasted. Finally, theoretically derived data banks of cross sections, inelastic mean free paths, asymmetry parameters, etc will be considered and conclusions drawn of the need for further work.
Characterization of the imaging properties of a double‐pass cylindrical‐mirror analyzer
Authors: Erickson N. E. , Powell C. J.
Published: May 2005

The imaging properties of a double‐pass cylindrical‐mirror analyzer have been investigated using extensions of the technique recently described by Seah and Mathieu. Elastic‐peak intensity data obtained as an electron beam was rastered across a test specimen, was recorded in digital form and later used to generate ‘three‐dimensional’ images. Images have been obtained for a range of operating conditions and for displacements of the specimen from its optimum position. Measured image widths were in semi‐quantitative agreement with those expected from a simple analysis although deviations attributed to instrument imperfections were found. Elastic‐peak images provide a convenient and quantitative means of assessing instrument performance and defining the specimen area being analyzed for the selected conditions.
Measurement of the sputtering yield with a 3d stylus surface mapping system: application to copper and α‐brass
Authors: Quantin J. C. , Darque‐Ceretti E. , Combarieu R. , Delamare F.
Published: May 2005

This paper present a method for determing the sputtering yield of a material bombarded by an ion beam, using a 3D stylus surface mapping system. Data obtained of copper are discussed. The influences on the sputtering yield of progressive addition of zinc is observed. The results are in good agreement with previous theoretical results.
Grazing incidence x‐ray diffraction of an aisi 1006 nitrogen implanted steel
Authors: Moncoffre N. , Brunel M. , Deydier P. , Tousset J.
Published: May 2005

Nitrogen implantations were performed on a very low alloyed steel XC06, AISI 1006 at various doses (1017, 2 × 1017, 4 × 1017 ions cm−2) and various temperatures (20, 100, 150, 200°C). A study of the nitride phase evolution as a function of the two parameters (dose and temperature) is performed. The nitrogen distribution profiles are obtained using the 15N(p, αγ)12C nuclear reaction whereas the iron nitride phases are followed by means of glancing angle RX diffraction. (N)‐martensite, ε‐nitride and ε‐carbonitride phases of different nitrogen and carbon composition are identified. These results are correlated with Mössbauer results that put in evidence a carbonitride formation depending on implantation temperature and with recent Rutherford backscattering results that quantify the carbon contamination depending on implantation conditions. Moreover a preferential orientation of these phases depending on temperature is noticed.
XPS and AEM studies of carbon‐supported HDS catalysts
Authors: Brinen J. S. , Allard L. F. , Daly F. P.
Published: May 2005

A series of carbon‐supported HDS catalysts has been characterized by XPS and high resolution analytical electron microscopy. the size, distribution and composition of clusters or particles of Co and Mo oxides on the support materials is shown to be related to variations in processing treatments. These results are discussed in terms of catalyst activity measurements and surface analytical information (XPS data).
Electronic state and catalytic activity of SiO2 doped γ–Al2O3
Authors: Bertóti I. , Mink G. , Székely T. , Varsányi G. , Réti F.
Published: May 2005

Silica‐alumina catalysts have been applied for a long time in cracking and reforming reactions. Lewis type surface sites are generally accepted to serve as active centers. In this respect, surface properties of these materials are of main concern. In the present work SiO2 doped γ‐Al2O3 with less than a monolayer coverage were prepared by the reaction of SiCl4 (g) with γ‐Al2O3 at 820‐1120 K. Catalytic activity of the samples was tested by a model reaction of n‐hexane cracking. Surface composition and electronic state were evaluated by XPS investigations performed on a KRATOS XSAM 800 instrument. Catalytic activity (conversion) varies remarkably with increasing Si content showing a sharp maximum at low Si coverage. The observed shift of Al 2p lines with increasing Si content is interpreted as an enhancement of the acceptor or acidic character of the surface Al atoms. The Auger parameter for Si(α'Si), (composed by addition of Si 2p BE and Si (KLL) KE values) passes also through a maximum at the same Si‐content, as does the conversion curve. A close correlation of the Auger parameter and the catalytic activity is established for samples with (Si/Al)≲7%. This leads to a conclusion, that the rise in extra‐atomic relaxation energy may serve as an additional indication of enhanced catalytic activity.
Study of near‐surface disorder and surface residues after reactive Ion etching of Silicon
Authors: Oehrlein G. S. , Coyle G. J. , Clabes J. G. , Lee Y. H.
Published: May 2005

Helium ion channelling, nuclear reaction profiling and x‐ray photoemission measurements of CF4/X%H2 (0≤X≤40) and CCIF3/50%H2 dry etched Si surfaces are reported. It is shown that plasma exposure of a clean Si surface leads to the deposition of a thin (∼30∼50) Å thick C,F‐containing film (or C,F, C1‐containing in the case of CC1F3/H2 etching). A subsurface Si carbide layer is formed during reactive ion etching. The near‐surface region (∼30∼50 Å) of the Si substrate is heavily disordered as found by ion channeling. A modified, less damaged layer containing a high concentration of hydrogen is formed in the case of the H2 containing gases (as shown by nuclear reaction profillin) and extends more than 250 Å from the surface. It is found that heating the plasma exposed substrates to 400°C in dry O2 for 30 min is efficient in recovering good quality Si surfaces.
Applications of SIMS, SAES and XPS to problems in the semiconductor industry
Authors: Alnot P. , Huber A. M. , Olivier J.
Published: May 2005

Electronic devices based on III‐V compounds can be significantly affected in their behaviour by surface and interface properties. This paper will show the usefulness of surface and interface analytical tools such as SIMS, SAES and XPS in overcoming such problems. Case studies in relation with some of the main problems of III‐V compounds technologies will be described.
The role of electron spectroscopy in corrosion science
Authors: Castle J. E.
Published: May 2005

The two principal electronspectroscopies – photoelectron and Auger electron – now represent the mature methods of surface analysis and both have been used to further the study of corrosion almost since their inception. This review will examine those areas in which significant developments have been made by their use and will highlight their continuing role in post‐corrosion failure analysis.

Specific topics which will be covered include: (1) aqueous corrosion: the formation and composition of passive layers, their interaction with surrounding solutions, and their failure by pitting and stress corrosion; (2) coated surfaces: pretreatment for coating, locus of failure and disbonding under chemical or electrochemical attack; and (3) high temperature oxidation: segregation to the surface, the formation of stable layers and interlayer reaction, and the composition of barrier layers and of spalling interfaces.
XPS study of sizing removal from carbon fibers
Authors: Santiago F. , Mansour A. N. , Lee R. N.
Published: May 2005

X‐ray photoelectron spectroscopy (XPS) was used to investigate the effectiveness of the techniques commonly used to remove polyvinyl alcohol (PVA) sizing from graphitized carbon fibers. Unsized samples of P55 and P100 mesophase‐pitch fibers were used as standards for comparison and the oxygen‐to‐carbon ratio on the fiber surfaces was the primary criterion for judging the degree of sizing removal. No significant change in fiber sizing was found to result from either ‘burn‐off’ in air or soaking in boiling water. Characterization of as‐received sized fiber revealed that the PVA surface undergoes major changes in composition as a result of normal ageing processes. The unsized fibers were found to have extremely low levels of adsorbed oxygen and no detectable hydrocarbons after extended exposure to air. Direct comparison with cleavage surfaces of Ticonderoga graphite showed that unsized pitch fiber surfaces are chemically indistinguishable from the basal plane of graphite, with a very low defect density which decreases with increasing fiber modulus. The implications for carbon‐fiber‐reinforced composite technology are discussed.
Deconvolution as a correction for photoelectron inelastic energy losses in the core level XPS spectra of iron oxides
Authors: Hawn David D. , DeKoven Benjamin M.
Published: May 2005

In this paper core level XPS spectra of polycrystalline Fe metal and several oxides are corrected by deconvolution using the ratio method for energy loss effects and spectral broadening due to both an achromatic x‐ray source and finite analyzer resolution. These ideas are applied to the XPS spectra of Fe, FeO, Fe2O3, and Fe3O4 in order to obtain the intrinsic lineshape. The backscattered electron energy loss spectra are effective in distinguishing Fe and its oxides. For Fe metal and its oxides, the electron energy loss deconvolved spectra have a flat baseline and enhanced resolution. This background removal method is found to be more reliable than either linear or sigmodial background approximations. This allows for a determination of the relative sensitivity factor for the Fe 2p and O 1s core levels.
Applications of factor analysis to electron and ion beam surface techniques
Authors: Solomon J. S.
Published: May 2005

Factor analysis, a mathematical technique for extracting chemical information from matrices of data, is used to enhance Auger electron spectroscopy (AES), core level electron energy loss spectroscopy (EELS), ion scattering spectroscopy (ISS), and secondary ion mass spectroscopy (SIMS) in studies of interfaces, thin films, and surfaces. Several examples of factor analysis enhancement of chemical bonding variations in thin films and at interfaces studied with AES and SIMS are presented. Factor analysis is also shown to be of great benefit in quantifying electron and ion beam doses required to induce surface damage. Finally, examples are presented of the use of factor analysis to reconstruct elemental profiles when peaks of interest overlap each other during the course of depth profile analysis.
Chemical state depth profiles from SIMS ion energy distributions using factor analysis
Authors: Solomon J. S.
Published: May 2005

The energy distribution curves of secondary ions are affected by the chemical state of surface atoms. Variations in these distributions due to changing chemistry were used to construct chemical state profiles of surface layers. Factor analysis of Ta+ energy distribution curves, recorded while sputter profiling anodized tantalum, is shown to provide quantitative profiles of the two chemical states of tantalum present in the oxide/metal structure.
XPS study of reduction effects in Nb‐doped PZT ceramics
Authors: Rajopadhye N. R. , Bhoraskar S. V. , Badrinarayan S.
Published: May 2005

Electrical conductivity in lead zirconate titanate ceramic containing niobium oxide as impurity showed a marked increase when it was reduced in hydrogen atmosphere. X‐ray photoelectron spectra were used to investigate the chemical behaviour of the reduction products. Depth profiling for reduced Nb‐doped PZT indicated the presence of metallic Pb, whereas Zr, Ti and Nb did not exhibit any change in the valency. The amount of PbO showed a marked increase on the surface compared to that of inner layers in the samples. On the basis of the observed results the increase in the electrical conductivity is correlated to the oxygen vacancies produced because of the reduction in hydrogen.
Surface modification of a contact lens co‐polymer by plasma‐discharge treatments
Authors: Fakes D. W. , Newton J. M. , Watts J. F. , Edgell M. J.
Published: May 2005

XPS and contact angle measurements have been used to investigate the surface modification of an alkyl‐acrylate/polysiloxane co‐polymer by plasma‐discharge treatments. The improved wettability brought about by the plasma treatments is shown to result from the oxygenation of the surface layers and the conversion of the polysiloxane component to a silica‐like phase. By analysis with MgKα, AlKα, and AgLα induced XPS this oxygenation is shown to decrease with depth. The total thickness of this altered zone has been estimated by comparing these results with data from argon ion bombardment studies.
From SEXAFS to SEELFS
Authors: Woodruff D. P.
Published: May 2005

Surface extended x‐ray absorption fine structure (SEXAFS) is now becoming an established method of surface structural analysis. The basic method is described and examples of its application are given with particular emphasis on the potential of the method to investigate structural problems in applied surface science. Developments in the application of the same physical effects in electron ionization are reviewed, particularly in surface electron energy loss fine structure (SEELFS), and some of the relative merits of the methods, at their present states of development, are discussed.
Simultaneous AES and SIMS depth profiling of standard Ta2O5 films
Authors: Mathieu H. J. , Landolt D.
Published: May 2005

Standard Ta2O5 30 nm films have been applied for simultaneous Auger electron analysis (AES) and secondary ion mass spectroscopy (SIMS) to characterize and calibrate depth porifles. A combined SIMS/AES‐system (Atomika Kit 3000–30/Perkin Elmer PHI 545) was used applying 2–12 keV Ar+ primary beam energy with/without Wien filter at almost normal incidence (2° off normal to avoid neutral particles). The investigated parameters were ion‐beam energy, raster frequency, Wien filter and influence of simultaneous electron beam. Optimum depth resolution at almost normal incidence was found to be 1.7 nm for O–AES and O+ (16)‐SIMS peak.
SIMS analysis, under caesium bombardment, of Si in GaAs/(Al, Ga) as superlattices: Detection limit and depth resolution
Authors: Gauneau M. , Chaplain R. , Regreny A. , Salvi M. , Guillemot C. , Azoulay R. , Duhamel N.
Published: May 2005

Silicon is widely used for n‐doping of GaAs/(Al, Ga)As layered structures grown by molecular beam epitaxy or metallo‐organic chemical vapour phase deposition for high speed and opto‐electronic devices, so the determination of Si doping levels in these structures is of primary importance. The secondary ion mass spectrometry technique has been revealed as a very powerful method for such a determination. But, in this particular case, some difficulties are encountered at low doping levels because of the presence of ions interfering with the main silicon isotope at mass 28. This paper deals with the search for satisfactory experimental conditions for such a silicon analysis under caesium primary ion bombardment, the main requirements being the detection limit and the depth resolution. It will be shown that AIH molecular ions are the interfering species and two approaches have been explored to avoid this interference: use of high mass resolving power facilities of a double focusing mass spectrometer, or experimentation at low vacuum conditions. A compromise is ineviatable between maximum sensitivity in the 1–2 1015 cm−3 range by detecting negative secondary ions and good depth resolution, equal to about, 40 Å, by using positive secondary ion collection. The ultimate performances of the technique are limited by the silicon surface segregation process and factors like the initial surface morphology of the samples, the flatness, and parallelism with the surface, of the crater bottoms and the beam induced roughness.