Analysis Of Peak Intensities Research Articles

Loss structures in the photoemission spectra of MnO: A careful analysis of peak intensities

A careful and rigorous analysis of the intensities of several features of the Mn $3s$ x-ray photoemission spectra of MnO, including the satellites at 20--30 eV below the main exchange split peaks is carried out. The previous interpretation of the 20--30 eV satellite is that they arose from electron correlation effects relative to the near degeneracy of the atomic levels. Our work shows that loss processes must also be taken into account. In particular, it is shown that only about 60% of the broad 20--30 eV satellite is due to near degeneracy correlation effects, while a contribution from the shakeup and plasmon loss structures constitutes the remaining 40% of the intensities of this feature.

Effects of ozone treatment of 4H–SiC(0001) surface

The effects of high-concentration ozone gas (~25%) exposure at atmospheric pressure with and without ultraviolet (UV) irradiation to a 4H–SiC(0001) surface has been investigated by X-ray photoelectron spectroscopy (XPS). The C 1s XPS spectrum for the 4H–SiC surface after standard RCA cleaning showed the appearance of a chemically shifted peak on the higher binding energy side of the SiC bulk peak. The chemically shifted peak was also observed even for the surface prepared by dipping a sample with sacrificed oxide film into 5% HF solution. Curve-fitting analysis using the Gaussian function revealed that the chemically shifted peak consisted of three components. The chemically shifted peak could be sufficiently eliminated using ozone exposure with UV irradiation. The cleaning mechanism of the 4H–SiC surface by ozone exposure is discussed, referring to the analysis of peak intensity for each component under different surface conditions corresponding to RCA cleaning and ozone exposure with and without UV irradiation.

Ion scattering and recoiling from liquid surfaces

We have shown that ion beams can be used to probe the surface composition and molecular orientation of liquid surfaces. Time-of-flight analysis of the kinetic energy of scattered inert gas ions and recoil atoms ejected from the surface reveals the identity of atoms in the topmost atomic surface layer of the liquid. In this report we describe the first scattering/recoil experiments on surfaces of a liquid siloxane and glycerol using helium, neon and argon ions in the 2–3 keV energy range. Analysis of peak intensities as a function of experimental parameters can be used to infer average molecular orientations in the surface. Spectra from the liquid siloxane are similar to that reported by Bertrand et al. [J. Phys. Chem. 97, 131 788 (1993)] for the long-chain hydrocarbon hexatriacontane deposited as oriented solid films on Si wafers. Our data indicates that the siloxane backbone is effectively shielded by the attached hydrocarbon groups, and for incoming ions the molecule effectively resembles a hydrocarbon. Recent sum-frequency generation spectroscopy experiments [J. Phys. Chem. B 101, 4607 (1997)] suggest that a glycerol molecule in the liquid is, on average, oriented with the carbon backbone normal to the surface. Our data is consistent with this result, but scattering/recoiling simulations are needed to definitively determine the orientation.

Raman spectroscopy for mineral identification and quantification for in situ planetary surface analysis: A point count method

Quantification of mineral proportions in rocks and soils by Raman spectroscopy on a planetary surface is best done by taking many narrow‐beam spectra from different locations on the rock or soil, with each spectrum yielding peaks from only one or two minerals. The proportion of each mineral in the rock or soil can then be determined from the fraction of the spectra that contain its peaks, in analogy with the standard petrographic technique of point counting. The method can also be used for nondestructive laboratory characterization of rock samples. Although Raman peaks for different minerals seldom overlap each other, it is impractical to obtain proportions of constituent minerals by Raman spectroscopy through analysis of peak intensities in a spectrum obtained by broad‐beam sensing of a representative area of the target material. That is because the Raman signal strength produced by a mineral in a rock or soil is not related in a simple way through the Raman scattering cross section of that mineral to its proportion in the rock, and the signal‐to‐noise ratio of a Raman spectrum is poor when a sample is stimulated by a low‐power laser beam of broad diameter. Results obtained by the Raman point‐count method are demonstrated for a lunar thin section (14161,7062) and a rock fragment (15273,7039). Major minerals (plagioclase and pyroxene), minor minerals (cristobalite and K‐feldspar), and accessory minerals (whitlockite, apatite, and baddeleyite) were easily identified. Identification of the rock types, KREEP basalt or melt rock, from the 100‐location spectra was straightforward.

Dissolution of Hectorite in Inorganic Acids

AbstractThe effect of acid type and concentration on the reaction rate and products of dissolution of hectorite in inorganic acids was investigated. The dissolution of hectorite in hydrochloric (HCl), nitric (HNO3) and sulphuric (H2SO4) acids was characterized using quantitative chemical analysis, infrared (IR) and multinuclear MAS NMR spectroscopies. The rate of dissolution increased with acid concentration and decreased in the order HCl ≥ HNO3 = H2SO4 at the same molar concentration. No differences were found in the reaction products of hectorite treated with the three acids. The rate of Li dissolution was slightly greater than that of Mg at lesser acid concentrations (0.25 M), indicating that protons preferentially attack Li octahedra. The gradual changes in the Si-O IR bands reflects the extent of hectorite dissolution. The analysis of 29Si MAS NMR spectra relative peak intensities with dissolution time and acid concentration provided direct dissolution rates for tetrahedral (Q3) Si. After acid dissolution, most Si was bound in a three dimensional framework site (Q4), but a substantial part also occurred in the Si(OSi)3OH (Q31OH) and Si(OSi)2(OH)2 (Q220H) environments. These three sites probably occur in a hydrous amorphous silica phase. Both AlJV and AlVt rapidly disappeared from 27Al MAS NMR spectra of the dissolution products with acid treatment. The changes in IR and MAS NMR spectra of hectorite due to acid dissolution are similar to those of montmorillonite.

Metal overlayers on organic functional groups of self-assembled monolayers. VI. X-ray photoelectron spectroscopy of Cr/COOH on 16-mercaptohexadecanoic acid

The interaction of Cr with the COOH groups of a self-assembled monolayer (SAM) of 16-mercaptohexadecanoic acid [HS(CH2)15COOH] on gold was studied by x-ray photoelectron spectroscopy (XPS). For each Cr overlayer thickness, a freshly prepared SAM was exposed to the evaporative deposition of Cr at ≤1×10−8 Torr and then transferred immediately in situ to a surface analysis chamber held at ≤5×10−10 Torr. Metallic Cr is deposited as evidenced by a Cr 2p3/2–2p1/2 splitting of 9.2 eV for 1 nm thick Cr films on Au. The C 1s and O 1s binding energies and intensities for the initial COOH-terminated SAM are consistent with the presence of the O=C—OH end group at the surface. For Cr overlayers of 0.04–1 nm average thickness, we identify Cr–COOH interactions primarily by changes in the O 1s level. For 0.04 nm Cr/COOH, the O 1s peak is narrowed and fitted by a single component at 532.9 eV that is between the O—C (533.9 eV) and O=C (532.5 eV) components of the bare SAM. The narrow width of this peak is evidence that the two oxygens of a single COOH end group interacting with Cr are indistinguishable by our instrument. For 0.07–1 nm average overlayer thickness, a low binding energy component (531.0–530.3 eV), assigned to a Cr(III) oxide, is of gradually increasing intensity. For coverages below 0.6 nm, analysis of XPS peak intensities indicates that adsorption of an adventitious oxygen-containing species has little effect on the results.

Room-temperature band-edge photoluminescence from cadmium telluride.

Room-temperature photoluminescence (PL) spectroscopy of II-VI semiconductor alloys has been proposed as a useful tool for determination of spatial variations in alloy concentration and impurity concentration. However, the nature of the PL recombination can affect the emission peak energy, as well as line shape. These effects in the band-edge emission of the compound II-VI semiconductor CdTe are reported here. PL measurements at 300 K were recorded from (1) highly doped n-type CdTe films grown by molecular-beam epitaxy, (2) undoped high-resistivity (\ensuremath{\rho}\ensuremath{\sim}${10}^{8}$--${10}^{9}$ \ensuremath{\Omega} cm) bulk CdTe, and (3) as-grown nominally p-type (\ensuremath{\rho}\ensuremath{\sim}${10}^{4}$--${10}^{5}$ \ensuremath{\Omega} cm) bulk CdTe. The dependence of PL emission intensity and line shape over a range of excitation from 0.003--70 W/${\mathrm{cm}}^{2}$ was studied. As the excitation power density was increased, a redshift in PL peak position was observed from all samples. PL peak position, intensity, and line-shape analysis show the highly excitonic nature of the radiative recombination in these materials, even though the free-exciton binding energy in CdTe is about 1/3 of kT at 300 K. In addition, the PL peak position can be more than 7 meV higher from n-type CdTe as compared to undoped CdTe.

Diffraction of Fe/Cr using Anomalous Dispersion Enhancement

ABSTRACTResults for a study using anomalous scattering to increase the X-ray contrast between Fe and Cr in metallic multilayers are reported. This increased contrast is sufficient to provide reliable values for actual bilayer distances and to begin semi-quantitative analysis of peak intensities even in the presence of orientational texture.

Fermi resonance in the infrared spectra of Nylon‐11

AbstractNylon‐11 is prepared by casting from the solvents trifluoroacetic acid and m‐cresol and by melt‐crystallization. Room‐temperature infrared spectra are compared in terms of possible crystal structures. The spectra are examined for the presence of Fermi resonance which occurs between the N‐H stretching fundamental mode and the overtone and combination modes of the amide I and II vibrations. An analysis of peak frequencies and intensities is used to provide support for the assignment of the amide II overtone and the amide I + II combination modes. A newly observed peak in the spectra is assigned to the amide I overtone. Symmetry considerations are discussed which predict the resonance of the overtone and combination modes with the N‐H stretching fundamental. © 1992 John Wiley & Sons, Inc.

CROSREL: Full relaxation matrix analysis for NOESY and ROESY NMR spectroscopy

A method is proposed for quantitative analysis of ROESY peak intensities, to which corrections are applied for their offset dependence and for direct HOHAHA effects. Additionally the effects of anisotropic and internal motion can be assessed. This method has been implemented for full relaxation matrix analysis in the CROSREL program. Although CROSREL is applicable to NOESY data, its use for ROESY peak intensities has been evaluated here, because of its innovative character in this respect. The agreement between calculated and experimental intensities is expressed by a weighted residual Rw factor, similar to X-ray crystallography. The merits of the program have been tested on methyl(d3) β-cellobioside, for which a ROESY buildup series has been acquired, and for which extensive MD simulations have been performed. It is concluded that correction for direct HOHAHA effects is obligatory for the analysis of ROESY data. Extension of the model for methyl β-cellobioside with internal and anisotropic motion, as was derived from MD data, did not improve the results obtained for assumed isotropic tumbling of a rigid model. It has been shown that ROESY peak intensities can be analysed successfully by the CROSREL program.

Structure determination of [d(ATATATAUAT)]2 via two‐dimensional NOE spectroscopy and molecular dynamics calculations

Proton homonuclear two-dimensional (2D) NOE spectra were obtained for the decamer [d(ATATATAUAT)]2 as a function of mixing time, and proton resonance assignments were made. Quantitative assessment of the 2D NOE cross-peak intensities was used in conjunction with the program MARDIGRAS, which entails a complete relaxation matrix analysis of the 2D NOE peak intensities, to obtain a set of upper and lower bound interproton distance constraints. The analysis with MARDIGRAS was carried out using three initial models: A-DNA, B-DNA and Z-DNA. The distance constraints determined were essentially the same regardless of initial structure. These experimental structural constraints were used with restrained molecular dynamics calculations to determine the solution structure of the decamer. The molecular dynamics program AMBER was run using A-DNA or B-DNA as starting model. The root-mean-square (rms) difference between these two starting models is 0.504 nm. The two starting models were subjected to 22.5 ps of restrained molecular dynamics calculations. The coordinates of the last 10.5 ps of the molecular dynamics runs were averaged to give two final structures. MDA and MDB. The rms difference between these two structures is 0.09 nm, implying convergence of the two molecular dynamics runs. The 2D NOE spectral intensities calculated for the derived structures are in good agreement with experimental spectra, based on sixth-root residual index analysis of intensities. A detailed examination of the structural features suggests that while the decamer is in the B-family of DNA structures, many torsion angle and helical parameters alternate from purine to pyrimidine, with kinks occurring at the U-A steps.

Analysis of vibronic mode coupling in pentacene by fully resonant coherent four-wave mixing

This paper develops the theoretical framework for the analysis of relative peak intensities in fully resonant, three laser, coherent four-wave mixing spectra of molecular vibrational and vibronic levels. For a Franck–Condon system, the relative vibronic peak intensities are shown to scale as the square of the absorption spectrum for all resonances not associated with the normal mode selected by the fixed vibrational resonance. A large enhancement of vibronic resonances involving the selected mode is predicted for typical potential well offsets. Higher order mode coupling causes deviations from these predictions by allowing other coupled resonances to be enhanced as well. Vibrational peak intensities are similarly related to the emission spectrum. Pentacene in benzoic acid mixed crystals at 2 K are used to experimentally study the mode mixing effects. It is shown that important coupling occurs between the 747.7 and 790.8 cm−1 vibronic modes of the pentacene S1 electronic state. Two possible mechanisms for this coupling are suggested. This work shows that the relative intensities of vibrational and vibronic resonances in fully resonant four-wave mixing spectra can serve as a useful probe of mode coupling.

Epitaxial metastable (GaSb) 1- x(Ge( 2- y)Sn 2y) x quarternary alloys on GaAs(100): 1085 Crystal growth, structure, and raman scattering

Epitaxial metastable (GaSb) 1- x )(Ge 2(1- y) Sn 2y x quaternary alloys have been grown with 0 ≤ x ≤ 1 and 1085 y ≤ 0.27 by RF multitarget sputter deposition on GaAs(100) substrates. Films, ≈1 μm thick, deposited under the same growth conditions on Corning 7059 glass substrates were polycrystalline with a very strong (220) preferred orientation. A growth phase map, plotted as a function of x, y, and deposition temperature T s, showed that the maximum growth temperature decreased rapidly with increasing Sn concentration, ranging from ≥ 500°C for 0 ≤ x ≤ 1 with y = 0 to ⩾ 150°C for x = 0.6 with y = 0.27. The lattice parameter a 0 of the alloys decreased linearly with increasing x for a given y and increased linearly with y for a given value of x. a 0 ranged from 0.6094 nm for GaSb to 0.5775 nm for (GaSb) 0.2(Ge 1.86Sn 0.14) 0.8. Form an analysis of fundamental and superstructure diffraction peak intensities, the zincblende-to-diamond structural phase transition was found to occur near x ≈ 0.3. Raman scattering results showed a two-peak behavior over the composition range investigated. The GaSb-like longitudinal-optical peak near 234 cm -1 softened and broadened with increasing x for all y values. A weak “Ge-like” mode increased in frequency from 265 cm -1 at x = 0.05 with y = 0.07−0.27 to 280 cm -1 at x = 0.6 and y = 0.07. The reaction path for phase decomposition in these alloys was found using hot-stage transmission electron microscopy to proceed through a series of intermediate metastable phases. Alloys with low Sn concentrations were stable for 2 h anneals at temperatures ⩾ 475°C. However, thermal stability decreased with increasing Sn concentrations to ⩾ 225°C for a 2 h anneal of alloys with low x and high y values.

Oxygen defect in YBa2Cu

A combined x-ray photoemission and diamagnetic-susceptibility study of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathrm{x}}$ with x\ensuremath{\simeq}6 and 7 has been performed, with emphasis on the oxygen defect and the effect of heating in vacuum. By comparing spectra taken at these two oxygen contents, the core levels observed in the O 1s and Ba 4d spectral range are identified. Peak-intensity analysis indicates (1) that the oxygen released during the in situ heating is derived from or near the Cu-O-Cu-O chains of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ and (2) that there is a random distribution of oxygen defects in or near these chains leading to two chemically dissimilar barium atoms even in single-orthorhombic-phase samples.

X-ray photoelectron spectroscopy and Auger spectroscopy studies of thin silicon nitride films thermally grown on silicon

The composition of silicon nitride films obtained by rapid thermal nitridation of silicon in NH3 at 1000–1250 °C for 10–20 s was analyzed using x-ray photoelectron spectroscopy (XPS) and Auger spectroscopy. The films were 10–25 Å thick. The depth resolution of Auger sputter profiling was not sufficient to analyze these films. Instead, depth profiles were obtained by chemical etching techniques. XPS peak intensity profiles and analysis of XPS peak shapes indicated that oxygen contamination was incorporated within the film in a silicon oxynitride state. The concentration of oxygen was peaked at both the surface of the film and the substrate–film interface. Observed XPS peak shifts within the film are explained by the variation in oxygen content. A 10%–20% decrease in Dλ (product of density and electron escape depth) was detected near the interface. Despite the extreme thinness of these films, they were found to be resistant to room-temperature oxidation and to degradation from chemical cleaning techniques.

A spectroscopic study of electron and ion beam reduction of SnO 2(110)

The reduction of SnO2(110) by 160 eV electron bombardment has been studied by XPS. Oxygen desorption is characterised by an initial cross section of 2.8 × 10−20 cm2. Growth of core peaks due to Sn(0) accompany oxygen loss; this contrasts with reduction under Ar ion bombardment, where only Sn(II) is formed. Plasmon loss satellites 14 eV below the new core peaks identify the Sn(0) as metallic tin. Careful analysis of peak intensities shows that electron beam reduction does produce some Sn(II) in addition to the Sn(0) species.

Reliability of low-energy electron diffraction for studies of surface order-disorder phenomena.

It is shown that a determination of critical exponents in surface phase transformations based on a kinematic analysis of LEED peak intensities is subject to errors caused by multiple scattering that are large enough to prevent a clear assignment to a known universality class. The multiple-scattering contribution arises from short-range flucutations and has its maximum value at the transition temperature. The specific-heat exponent of the surface phase can be measured directly from the variation of the integral-order-beam intensity with temperature that is caused by the multiple scattering.

An analysis of angular dependent XPS peak intensities

Angle resolved X-ray photoelectron (XPS) studies of clean Ni(100) and of exitaxial Cu and Co films on Ni(100) have been interpreted with the aid of single scattering cluster calculations. It is found that for atoms in the top few atomic layers, photoelectron forward scattering by overlying atoms in the lattice causes XPS peak intensities to be enhanced at angles corresponding to nearest neighbor and next-nearest neighbor internuclear axes. Angle resolved XPS should thus be an excellent approach for gaining structural information on, for example, epitaxial overlayers or surface reconstructions.

Structure of alumina-supported Mo/Co hydrodesulfurization catalysts via EXAFS

Electrochemical properties of Li2O-V2O5-P2O5-Fe2O3 quaternary-glass and crystallized-glass cathodes were compared in terms of the local structural changes of vanadium and iron ions with increasing discharge capacity by in-situ X-ray absorption fine structure (XAFS) measurements. 10.3Li2O-69.2V2O5-10.2P2O5-10.3Fe2O3 glass was prepared by the melt-quenching method. The crystallized glass was produced by heat treatment of the glass at 375 °C in air. The crystal phase of the crystallized glass was found to be a single phase of β-vanadium bronze. The glass exhibited a discharge capacity of around 300 mAh g− 1 and a capacity retention of 66% after 100 cycles. On the other hand, the crystallized glass exhibited a capacity of around 340 mAh g− 1 and a capacity retention of 68% after 100 cycles. In the cases of glass and crystallized glass, in-situ X-ray absorption near-edge spectroscopy (XANES) spectra revealed that a redox reaction of vanadium and iron ions occurs as a compensation reaction for lithium-ion insertion. In addition, the absorption-energy shift of the vanadium and iron K-edges in the case of glass was larger than that in the case of crystallized glass despite the same discharge capacity. The analysis of pre-edge peak intensities and extended X-ray absorption fine structure (EXAFS) analysis revealed that the vanadium and iron coordination symmetry of the glass can transform more easily than that of the crystallized glass under lithium-ion insertion. These results imply that the origin of good cycleability differs in the cases of glass and crystal-phase cathodes.

An XPS investigation of alumina thin films utilized in inelastic electron tunneling spectroscopy

X-ray photoelectron spectroscopy (XPS) has been applied to characterize a number of different aluminum oxide (alumina) thin films utilized in inelastic electron tunneling spectroscopy (IETS). Since IETS has been found to be an effective means for obtaining vibrational information on catalytic systems, reliable means of clarifying the exact relationship between the IET thin film “model” catalysts and high surface area commercial aluminas are of considerable importance. XPS data might profitably provide such a means of comparison, although sufficiently reliable XPS data for commercial samples are not currently available. The various thin film aluminas are characterized as to their chemical nature, chemical state distributions, and relative oxygen-to- alumina concentration ratios by analysis of peak positions, peak widths and peak intensities, respectively. Moreover, effects due to heating and halogenating the surface have been investigated independently, since these are commonly utilized to enhance the catalytic behavior of commercial aluminas.