M.A. Salim

An XPS study of iron sodium silicate glass surfaces

Abstract A series of (SiO2)0.7−x(Na2O)0.3(Fe2O3)x glasses (0.0 ≤ x ≤ 0.18) were prepared and investigated by means of X-ray photoelectron spectroscopy (XPS). The quantitative ratio [Fe2+]/[Fetotal], for each glass has been determined from an analysis of the Fe 3p spectra. For low Fe2O3 content both iron valencies are present, however, it was found that Fe3+ is the dominant species for high Fe2O3. From an analysis of the O 1s spectra, it was possible to discriminate between bridging and non-bridging oxygen atoms. It was found that the ratio of the non-bridging oxygen content to the total oxygen content increases with increasing iron concentration. It has also been shown that the non-bridging oxygen contribution to the O 1s spectra can be simulated by summing the contributions from the SiONa, SiOFe(II) and SiOFe(III) components present in the glass.

Structure of molybdenum-phosphate glasses by X-ray photoelectron spectroscopy (XPS)

Highly-concentrated molybdenum-phosphate glasses with analyzed compositions of Mo greater than 0.65 have been studied by X-ray photoelectron spectroscopy (XPS) and magnetization measurements. 1 eV shifts in the binding energies of P2p, P2s, Mo3d, and Mo3p from their respective values in P2O5 and MoO3 can be accounted for by changes in the next nearest neighbor environment of the P and Mo atoms upon the mixing of the two glass formers. The O1s spectrum is deconvoluted into two peaks with the lower-energy peak being associated with the oxygen atoms of the non-bridging PO structure as well as from various MO bonds and the higher-energy peak with the bridging oxygen atoms of the POP structure. From the amount of Mo6+ reduced to Mo5+, as determined from the magnetization results, the variations in the areas of these O1s peaks are discussed in terms of an existing structural model based on this binary glass being composed of a mixture of the structural groupings which occur in the crystalline phases of the MoO3:P2O5 system.

X-ray photoelectron and auger spectroscopy study of copper-sodium-germanate glasses☆

Abstract The role played by copper oxide in reducing the electrical conductivity of copper-sodium-germanate glasses has been investigated by X-ray photoelectron and X-ray excited Auger spectroscopy. Evidence for the presence of copper predominantly in the Cu + oxidation state has been obtained from the “shake up” satellite structure of the Cu 2p line. The observed Cu LVV Auger line shapes are significantly different in glasses and this indicates a different bonding environment of copper in the glass matrix. The reduction of electrical conductivity with the increase of copper content is explained in terms of cluster formation and to some extent due to the bonding of copper atoms with the glass matrix.

X-ray Photoelectron Spectroscopy (XPS) and Magnetization Studies of Iron–Vanadium Phosphate Glasses

Abstract Iron–sodium borate glasses with the chemical composition [(B2O3)0.70−x(Na2O)0.3(Fe2O3)x], where 0.00⩽x⩽0.15, have been prepared and investigated by X-ray photoelectron spectroscopy (XPS) and magnetization measurements. The core-level binding energies of O 1s, B 1s, and Fe 2p have been measured with both O 1s and B 1s peaks shifting by about 2 eV towards smaller binding energies in the Fe-containing borate glasses while the Fe 2p3/2 and 2p1/2 core levels for the glasses remain essentially unchanged from those of Fe2O3 powder. The O 1s spectrum is deconvoluted into two peaks and the variation in the ratio of the peak areas is discussed in terms of the local iron structure. We suggest that both X-ray photoelectron spectroscopy and magnetization measurements show that the Fe ions remain essentially in one oxidation state, probably Fe3+, for the Fe borate glasses. In addition, the appearance of a large hysteresis between the zero field-cooled and field-cooled magnetization data indicate that the Fe moments are clustered and that the predominant interaction is antiferromagnetic.

Composition-dependent loss of phosphorus in the formation of transition-metal phosphate glasses

Abstract Phosphate glasses containing MnO2, Co3O4 and CuO analyzed by Rutherford backscattering spectroscopy (RBS) have higher transition-metal (TM) concentrations in the glass than the initial batch composition. These compositional changes result from vaporization of phosphorus during the melt and are greater for the lower TM oxide batch composition glasses. X-ray photoelectron spectroscopy (XPS) shows that the copper ions exist as Cu+ and Cu2+, while cobalt ions exist as high-spin Co2+. The oxidation states for the Mn phosphate glasses could not be determined by XPS. The magnetization results, combined with RBS, indicate that more than 90% of the Cu ions occur as Cu2+, that all Co ions are in the high-spin Co2+ state and that more than half the manganese ions exist in the Mn2+ state. In addition to the measured phosphorus-to-metal atomic ratios, R, for the glasses being much less than those for the initial batch compositions, the R(glass) are essentially constant for R(batch) greater than ∼ 2.5, independent of the TM ion and the initial batch composition. This suggests that phosphate glasses containing relatively small quantities of cations probably exist as ultraphosphate networks.

X-ray photoelectron spectroscopic studies of zinc-tellurite glasses

Zinc–tellurite glasses with chemical composition [(ZnO)x(TeO2)100−x], where x=25, 30 and 35 have been prepared and investigated by X-ray photoelectron spectroscopy (XPS). Zn 2p peaks shift by about 0.25 eV towards higher binding energy in the zinc–tellurite glasses in comparison to its value in ZnO powder, while the Te 3p, Te 3d, and O 1s core levels for the glasses remain essentially unchanged from those of TeO2 powder. Each O 1s spectrum is deconvoluted into two peaks, in which the higher energy one is due to oxygen atoms in the hydroxides covering the sample surface. Although both bridging oxygen (BO) and non-bridging oxygen (NBO) atoms should certainly exist in these tellurite glasses, the electrons are delocalised in the NBO–Te–BO bonds which equalize the electronic density of the valence shell between BO and NBO atoms and make it difficult to distinguish.

XPS STUDY OF THE GROWTH KINETICS OF THIN FILMS OBTAINED BY THERMAL OXIDATION OF GERMANIUM SUBSTRATES

Abstract X-ray photoelectron spectroscopy (XPS) has been used to investigate the oxidation of (011) and (001)Ge surfaces. The sample surfaces were CP4 etched then pre-annealed under vacuum at T =600°C or Ar-sputtered before the oxidation. The oxidation treatments have been carried under pure dry oxygen atmosphere and for different durations. The results show that, at the early stages of the oxidation process, the oxide layer contains different oxidation states of germanium. As the oxidation duration increases, the proportions of the high oxidation states (Ge 4+ and Ge 3+ ) increase at the expense of those of Ge 1+ and Ge 2+ following first-order kinetics. Very small values of the oxide thickness that were calculated suggest the formation of islands of germanium oxide that cover part of the surface. The argon sputtering prior to the oxidation treatment enhances the growth rate of the oxide film during the first stage of the oxidation process.

X-Ray photoelectron spectroscopy (XPS) studies of copper–sodium tellurite glasses

Abstract Sodium tellurite glasses containing CuO with the nominal composition [(Na2O)0.3(TeO2)0.7−x (CuO)x], where x=0.00, 0.05, 0.15, and 0.20, have been prepared and investigated by X-ray photoelectron spectroscopy (XPS). The binding energies of Te 3p, Te 3d, O 1s, and Cu 2p core levels in these glasses have been measured and compared to the corresponding binding energies in TeO2 and CuO powders. The Te 3p and Te 3d core levels for the glasses were essentially unchanged from those of TeO2 powder and have little dependence upon the CuO content. Although the O 1s peak showed a small asymmetry on the higher energy side of the peak in the glasses, it was primarily the result of hydroxide contamination on the glass surface rather than the appearance of non-bridging oxygen atoms arising from a structural change in the TeO4. For glasses with x=0.05 and 0.15, the Cu 2p peaks were shifted by more than 1 eV towards lower binding energies in comparison to their values in CuO powder, which suggests the presence of Cu+ ions in these glasses. The appearance of satellite peaks in the Cu 2p spectra, however, provided definitive evidence for the presence of Cu2+ ions in these glass samples as well. The broadened Cu 2p3/2 peaks were correspondingly decomposed into two distinct peaks separated by approximately 1.25 eV, with the lower energy peak being associated with Cu+ and the higher one with Cu2+. The relative Cu2+ content estimated from the spectral analysis was found to vary from 15% for the x=0.05 glass sample to over 70% for the x=0.20 sample.

XPS study of transition metal doped silicate glasses

Abstract X-ray photoelectron spectroscopy (XPS) has been used to study the redox state of transition metal oxides in sodium silicate glasses with compositions 0.30Na 2 O–0.70SiO 2 and 0.3Na 2 O–0.6SiO 2 –0.1TMO, where TMO=Fe 2 O 3 , CuO and CoO. From the analysis of the core level spectra of the transition metals, it was found that both Fe 2+ and Fe 3+ exist simultaneously in the iron doped glass, while Cu + was the only species present in the copper doped glass. In the cobalt doped glass, Co 2+ was found to exist in both tetrahedral (tet) and octahedral (oct) co-ordinations. From the analysis of the O 1s spectra, it was possible to discriminate between bridging and non-bridging oxygen atoms in each glass sample. It was also shown that the non-bridging oxygen contribution to the O 1s spectra can be simulated by summing the contributions from SiONa, SiOFe 2+ and SiOFe 3+ for the iron doped glass, SiONa and SiOCu + for the copper doped glass and SiONa, SiOCo 2+ (tet) and SiOCo 2+ (oct) for the cobalt doped glass. The quantitative values for the [Fe 2+ ]/[Fe] and [Co 2+ (tet)]/[Co] concentrations ratios were found from the analysis of the Fe 3p and Co 3p core level spectra, respectively.

Study of the Lorentz-Lorenz law and the energy loss of 4He ions in titanium oxide films

The optical constants, thicknesses and densities of thin titanium oxide films, deposited by electron beam evaporation, were measured. The variation of the refractive index with the density, of titanium oxide samples in the form of thin films (present work) and bulk crystalline form (data from the literature), was observed to follow the Lorentz-Lorenz law. The molecular electronic polarizability deduced from the law was close (within the uncertainty in the measurement) to the value reported in the literature. Rutherford backscattering spectroscopy and X-ray photoelectron spectroscopy studies were carried out on the thin films.