Chemical Shifts Of Core Levels Research Articles

Electron density redistribution in Sn-doped Bi2Te3

X-ray photoelectron spectroscopy is used to investigate the redistribution of the density of electronic states in the valence band, and of the binding energies and chemical shifts of core levels in bismuth telluride caused by introduction of impurity tin atoms. A substantial increase in the density of electronic states below the valence-band top at energies μ≈15–30 meV has been revealed. This feature in the energy spectrum accounts for the unusual behavior of the kinetic coefficients in p-Bi2Te3:Sn crystals.

First-principles calculations of SiC(001) surface core level shifts

We have computed chemical shifts of core levels at clean and defected Si-terminated SiC(001) surfaces, by carrying out total energy calculations within the local density approximation of density functional theory. Our results allow one to interpret measured Si 2p core level spectra and in particular to identify the nature of the different peaks observed experimentally. Furthermore, our findings point at ad-dimers as common defects on the Si-terminated SiC(001) surface.

Quasiparticle calculations of surface core-level shifts

We report quasiparticle calculations of chemical shifts of core levels at clean and adsorbate-covered Si surfaces. Core-state excitation energies are given as poles of the electronic one-particle Green's function of the many-electron system. To calculate the Green's function, we employ the $\mathrm{GW}$ approximation for evaluating the necessary electronic self-energy operator. The core states whose shifts are addressed in this work are explicitly included in the valence shell. We present results for three different surfaces. For the As:Si(111)-(1$\ifmmode\times\else\texttimes\fi{}$1) and H:Si(111)-(1$\ifmmode\times\else\texttimes\fi{}$1) surfaces, we obtain core-level shifts in good agreement with experimental data. For the clean Si(001) surface a high sensitivity of the chemical shifts on the actual dimer structure of the surface is observed.

Applications of the Xia Scanning Photoemission Spectromicroscope for Element Identification on Material Surfaces

AbstractThe Second Generation Scanning Photoemission Microscope at the beamline X1A of the National Synchrotron Light Source (NSLS), X1A SPEM II, is designed for spatially resolved elemental and chemical analysis by X-ray Photoelectron Spectroscopy (XPS) on material surfaces. Based on Fresnel Zone Plate (ZP) microfocusing techniques with the use of a bright and coherent photon source, this microscope is capable of acquiring XPS spectra from a small area irradiated by the focused beam and taking element-specific (using photopeaks) or chemical-state-specific (by detecting the chemical core level shifts) images with a spatial resolution defined by the focused spot size.

Photoelectron spectroscopic studies on interfacial reactions in Zr/2×1(100)Si and Zr/SiO2/(100)Si systems

Interfacial reactions in Zr/clean-2×1(100)Si and Zr/SiO2/(100)Si systems have been studied by x-ray and ultraviolet photoelectron spectroscopy. It has been found that no silicidation reaction occurs at the Zr/2×1(100)Si interface at temperatures below 400 °C and, however, the existence of a thin SiO2 layer at the interface causes interfacial reactions even at as low as 80 °C. The silicidation in the latter system is thought to be initiated by Si atoms produced by the reduction of SiO2 due to chemically active Zr. Chemical shifts of core levels of Zr 3d5/2 and Si 2p electrons due to the silicidation are found to be +0.3 and −0.6 eV, respectively

Strong metal-support interaction: The role of electronic and geometric factors in real [formula omitted] catalysts

XPS, X-ray-induced AES (XAES), AES, SIMS, and ISS studies of metals (Pt, Rh) supported on TiO 2 powder catalysts combine to give new evidence in favor of electronic nature of SMSI. When reduced at high temperatures (HTR), the XPS spectra, of Me TiO 2 , corrected for extra-atomic relaxation, exhibit negative chemical shifts of core levels along with a gain in intensity of the density of states near the Fermi edge, indicating an increase of electron density on metal clusters. Tauster's model of SMSI is further confirmed by the appearance of mixed RhTi + and RhTiO + clusters in SIMS spectra of Rh TiO 2 (HTR), which reflect direct interaction between metal atoms and Ti 3+ cations. The latter were detected by Ti L 3M 23V Auger peaks. The Rh + Ti + depth profile and the ISS Rh Ti ratio reveal some migration of TiO x entities onto metal surface, but no strong encapsulation of metallic particles is observed in real TiO 2-supported catalysts reduced at temperatures as high as 500 °C. Thus, the observed decrease in the activities of Me TiO 2 in the C 2H 6 hydrogenolysis and C 6H 6 hydrogenation reactions seems to be accounted for by both geometric and electronic factors. The kinetics of 16O 18O homomolecular isotopic exchange measured for the first time on these catalysts is in accordance with the proposed SMSI model and explains its degradation during catalyst exposure to O 2 at low or elevated temperatures.

Structural properties of a-SiC:H- and a-SiN:H-Alloys from XPS-analyses and IR-absorption

XPS-analyses and IR-absorption in a-Si 1−xC x:H and a-Si 1−xN x:H versus alloy composition for a-SiC:H show a kink in chemical shifts of core levels which indicates an alternating S C network structure and a strong increase in H content. For a-SiN:H the results point towards a statistical distribution of Si and N and a noticeable decrease in hydrogen content.

Photoelectron Spectroscopy of Solids

This paper is concerned with information about electronic structure and bonding in solids which can be derived from valence band and core level photoelectron spectroscopy. The role, in research of this kind, of the excitation processes discussed elsewhere in this symposium is of concern. A number of factors contribute to the apparent chemical shifts of core levels and valence bands in solids. These factors are considered and then results for gold alloys are taken as an example of the bonding information which can be derived. Angle resolved photoelectron spectroscopy provides information about wave function symmetry as well as energy. This is reviewed and one-electron energy vs. k results for Ni metal are inspected. Such results provide the best experimental test yet devised of energy band theory and of the potentials employed.

Electronic structure of aluminum and aluminum-noble-metal alloys studied by soft-x-ray and x-ray photoelectron spectroscopies

X-ray photoelectron spectra (XPS) and $\mathrm{Al} K$ and $\mathrm{Al} {L}_{2,3}$ soft-x-ray spectra (SXS) of valence bands for aluminum-noble-metal alloys are rationalized on the basis that SXS spectra are dominated by dipole selection rules while XPS spectra chiefly reflect the noble-metal $d$ bands. We find, in agreement with theory, that the main peaks in the $\mathrm{Al} 3s$ partial densities of states are at higher binding energy than those for the noble metal $d$ states. Peaks in the $\mathrm{Al} 3p$ partial densities of states approximately coincide with the higher-energy peaks in the partial densities of noble-metal $d$ states. The remarkable large chemical shifts of core levels in these alloys are noted and the $\mathrm{Au} {N}_{6,7}$ SXS emission from aluminum-noble-metal alloys also discussed. The Auger spectra from Al-Ag and Al-Cu alloys provide strong additional evidence that single-atom effects dominate in the Auger processes for these alloys.