X-ray Photoelectron Valence-band Spectra Research Articles

Discrete Variational (DV)-X? Calculations of Incomplete Cubane-Type Molybdenum Clusters [Mo3X4(H2O)9]4+ (X= O,S)1

Electronic structures of two incomplete cubane-type clusters [Mo3X4(H2O)9]4+ (X =O, S) have been calculated by the discrete-variational (DV)-Xα method. The calculations explain the experimental results of valence-band X-ray photoelectron spectra, electronic spectra, and reactivity difference toward acetylene. The net charge of Mo in [Mo3S4(H2O)9]4+(S) is more negative than that of Mo in [MO3O4H2O)4+] (O), and the bridging sulfur atoms are the main negative charge-source for the molybdenum atoms in the cluster S. As for S,levels of HOMO (45e) and LUMO (46e) consist mainly of Mo 4d andμ-S 3p atomic orbitals, and contribution ofμ3-S 3p to the orbitals is not large. The existence of Mo-Mo, Mo-μ-S, and Mo-μ3-S bounds is clear from the contour maps of the orbitals. As for O levels of HOMO (40e) and LUMO (41c) consist mainly of Mo 4d andμ-O 2p atomic orbitals. Contribution ofμ3-O 2p to the orbitals is not large except in the orbital 30a1,. The existence of Mo-Mo, Mo-μ-O, and MO-μ3-O bonds also is appreciable from the contour maps of the orbitals.

Gamma-Alumina (γ-Al2O3) by XPS

This article presents the main core lines and the valence band x-ray photoelectron (XPS) spectra obtained for a commercial gamma-alumina (γ-Al2O3) powder. The electronic record includes the Al 2p, Al 2s, O 1s, O 2s, C 1s, and valence band spectra. Although it is usually difficult to distinguish among the various forms of aluminum oxide [Al2O3], oxyhydroxide [AlO(OH)] and hydroxide [Al(OH)3] based on the core XPS binding energies, the valence band spectra for many of these materials are unique. The valence band spectrum for γ-Al2O3 shows two broad distinct peaks that are separated by about 3.3 eV.

Electronic structure of rutile (TiO 2)

The energy band, band gap and density-of-states (DOS) have been calculated for rutile (TiO 2) using the embedded-cluster numerical discrete variational method. The chemically complete cluster TiO 4O 2 is embedded in the periodic crystal lattice of rutile and the entire system is treated iteratively by one-electron local-density theory. The interaction of the cluster with the crystal environment is represented by an effective potential with boundary conditions which contain cluster-host Coulomb and exchange interactions as well as intracluster interactions. A comparison with rutile valence-band X-ray photoelectron spectra (XPS) and optical absorption data shows that the results are generally in reasonable agreement with the experiment; the agreement being particularly good for the band gap. We also plot the map of charge-density distribution of valence-electrons, from which the interaction between Ti and O atoms and the degree of Ti 3 d  O 2 p covalency are indicated.

X-Ray Spectra and Electronic Structures of Rh and (NH4)3RhCl6

With a two-crystal vacuum spectrometer, the Rh L β 2,15 emission spectrum in fluorescence from (NH 4 ) 3 RhCl 6 has been measured together with that from rhodium metal. The metal spectrum consists of a single broad band, while the (NH 4 ) 3 RhCl 6 spectrum is composed of a prominent peak and its low-energy shoulder. The measured L β 2,15 emission spectrum of Rh metal is compared with available X-ray photoelectron valence-band spectra and theoretical X-ray L β 2,15 emission spectra. It is shown that there is good agreement between them. The Rh L β 2,15 emission spectrum of (NH 4 ) 3 RhCl 6 is presented along with the Rh L III absorption, Cl K β emission and Cl K absorption spectra of this compound, reported previously. These spectra are interpreted in terms of the molecular orbitals of octahedral complex [RhCl 6 ] 3- .

Angular dependence of X-ray-excited valence-band photoelectron spectra of diamond

Angle-resolved valence-band X-ray photoelectron spectra from (110) single-crystal diamond surfaces are reported and discussed. Comparison of the spectra from polished, oxidatively eroded and heated (ca. 1070 K) surfaces enabled the O 2s and O 2p contributions to the spectra to be positively identified. The marked angular dependence of the relative intensities and energies of the major intrinsic valence-band components is attributed to the sampling of different portions of the Brillouin zone at different angles of photoelectron emission, as a result of wavevector-conserving direct transitions, in accordance with theoretical expectations. The angle-integrated valance-band profile obtained by summation is compared with previous experimental work and with calculated densities-of-states.

The ferromagnetic to paramagnetic phase transition of Fe studied by x-ray photoelectron spectroscopy

Valence band x-ray photoelectron spectra from Fe(100) have been measured as a function of temperature to above the Curie temperature, T c . The room temperature data can be reconciled with the theoretical one-particle density of states (DOS). At T = 1.034 T c , the data do not resemble the paramgnetic DOS of Fe as calculated in the disordered-local-moment limit.

Electron spectroscopic studies of tantalum carbide

Carbon-K characteristic loss, carbon-KVV Auger, and valence-band X-ray photoelectron spectra were measured for a well-ordered, nearly stoichiometric (100) surface of tantalum carbide. These spectra compare well with curves that were generated by using a calculated total density of states.

Electron spectroscopic studies of tantalum carbide

Carbon-K characteristic loss, carbon-KVV Auger, and valence-band X-ray photoelectron spectra were measured for a well-ordered, nearly stoichiometric (100) surface of tantalum carbide. These spectra compare well with curves that were generated by using a calculated total density of states.

Interpretation of ESCA spectra for non-stoichiometric titanium carbides on the basis of MO—LCAO calculations

The results of electron structure calculations for the single clusters TiC 6 20−, TiC 5□ 16−, TiC 4□ 2 12−, TiC3□ 3 8−, TiC 5□ 16.64−, TiC 4□ 2 13.32−; and double clusters Ti 2C 10 32−, Ti 2C 8□ 2 24−, Ti 2C 10□ 32.72− and Ti 2C 8□ 2 24.80− by the semi-empirical Mulliken—Wolfsberg—Helmholtz method with self-consistency of charges and configurations are given. The data obtained are compared with measurements of the Ti 2 p-level binding energies and X-ray photoelectron valence band spectra for TiC x ( x = 0.86–0.97). The variation of the metal atom charge in the limits of the homogeneity region for TiC and the appearance of this effect as a chemical shift of the Ti 2 p-level are discussed. A special set of cluster calculations was performed to check the possibility of Ti valency variation in the homogeneity region of TiC x .

Electronic structure of molybdenum disulphide

X-ray emission spectra (S, Kβ1,3 and L2,3M; Mo, Lβ2,15 and 5p→ 3d) and valence band X-ray photoelectron (X.p.) spectra from molybdenum disulphide were aligned on a common energy scale using X.p. core data. These spectra show that Mo 4d character is extensively present in the so-called “sulphur p band” and that sulphur 3p character is also present in the least tightly bound “Mo 4dz2” orbital. Mo 5p and S 3s orbitals are also shown to play a part in covalent bond formation in the “p band”. The general picture that emerges is one of extensive covalent bonding between molybdenum and sulphur. The structure of the spectra can be adequately rationalised using a simple molecular orbital model based upon a MoS6(D3h) unit.

Electronic Structure of Rutile Oxides TiO2, RuO2 and IrO2 Studied by X-ray Photoelectron Spectroscopy

Valence band X-ray photoelectron spectra of the rutile oxides TiO2, RuO2, and IrO2 show a distinct evolution as a function of the increasing number of metal d-electrons. The observations are found to be in excellent agreement with recent theoretical models. Intensity analysis and photo-ionization cross sections are used to confirm the nature of the band responsible for conducting properties. The result is in accordance with a crystal field model proposed earlier. The deduced number of "free electrons" in the valence band is used to correlate the asymmetry recorded for the core level lines.

Electronic Structure and Catalytic Behavior of Tungsten Carbide

Tungsten carbide has been shown to be an effective catalyst for a number of reactions that are readily catalyzed by platinum, but not at all by tungsten, and it was speculated that this behavior is due to changes in the electron distribution when carbon is added to tungsten. A test of this hypothesis, made by measuring the valence band x-ray photoelectron spectrum of tungsten carbide and comparing it with the spectra of tungsten and platinum, shows that, near the Fermi level, the electronic density of states of tungsten carbide more nearly resembles that of platinum than that of tungsten.

Valence band photoelectron spectra of platinum cyanides

Valence band X-ray photoelectron spectra of K 2[Pt(CN) 4]·3H 2O (1), K 2[Pt(CN) 4]Cl 0.3· xH 2O ( 2), and K 2[Pt(CN) 4Cl 2]·3H 2O ( 3), and the ultraviolet photoelectron spectrum of ( 2) have been recorded. These spectra imply that the binding energy of the highest occupied molecular orbital (HOMO) in ( 1) is greater than in ( 2). A band-like character for the HOMO of ( 2) with finite electron density at the Fermi level is consistent with this observation. The photoelectron spectra are correlated with the solid state electronic absorption spectra. Shifts in the K 3 binding energies are attributed to considerable differences in lattice site potentials between ( 1) and ( 2).