Alfred C. Miller

Role of S/Se ratio in chemical bonding of As-S-Se glasses investigated by raman, x-ray photoelectron, and extended x-ray absorption fine structure spectroscopies

Chalcogenide glasses have attracted considerable attention and found various applications due to their infrared transparency and other optical properties. The As–S–Se chalcogenide glass, with its large glass-formation domain and favorable nonlinear property, is a promising candidate system for tailoring important optical properties through modification of glass composition. In this context, a systematic study on ternary As–S–Se glass, chalcogen-rich versus well-studied stochiometric compositions, has been carried out using three different techniques: Raman spectroscopy, x-ray photoelectron spectroscopy, and extended x-ray absorption fine structure spectroscopy. These complementary techniques lead to a consistent understanding of the role of S∕Se ratio in chalcogen-rich As–S–Se glasses, as compared to stochiometric composition, and to provide insight into the structural units (such as the mixed pyramidal units) and evidence for the existence of homopolar bonds (such as Se–Se, S–S, and Se–S), which are the ...

X-ray photoelectron spectroscopy of Al- and B-substituted sodium trisilicate glasses

X-ray photoelectron spectroscopy (XPS) has revealed physical and chemical structure differences between aluminum and boron substituted sodium silicate glasses, Na2O · xR2O3 · (3 − 2x)SiO2, prepared by a melt quench method, where R = Al or B, and x = 0, 0.2, 0.4, 0.6, 0.8, 1. The structure of sodium aluminosilicate (SAS) glasses deduced from the analysis of XPS data is found to agree with the four-coordinated aluminum structure model with Na balancing the local charge. The structure of sodium borosilicate (SBS) glasses is mostly consistent with Brays model with the need to consider a ‘contending factor’ for Na. Sodium is not fully ionized as often assumed. Its ionicity increases in both SAS and SBS glasses with increasing Al/B substitution. Net charge on atoms according to Paulings model has been calculated as a guidance in analyzing the XPS spectra.

Structural paradigm of Se-rich Ge–Se glasses by high-resolution x-ray photoelectron spectroscopy

The structure of binary GexSe100−x chalcogenide glass family (0≤x≤30) is determined by high-resolution x-ray photoelectron spectroscopy (XPS). On the basis of compositional dependences of fitting parameters for Ge and Se core level XPS spectra, the ratio between edge- and corner-shared tetrahedra is determined. We find that this ratio for glasses with 20≤x≤30 is almost constant with a value same as for the high-temperature crystalline form of GeSe2.

In situ high-resolution X-ray photoelectron spectroscopy of light-induced changes in As–Se glasses ☆

Abstract To establish the mechanism of reversible photoinduced changes such as in the recently discovered opto-mechanical effect in chalcogenide glasses, we have measured the effect of He–Ne laser light on the electronic structure of As–Se glasses using high-resolution X-ray photoelectron spectroscopy (XPS). We present the first results during in situ irradiation of As–Se bulk glass and amorphous films in the spectrometer, as well as after ex situ exposure in air. The non-reversible light-induced changes are due to the segregation of Se on the surface, increased homogeneity for As, and a greater heterogeneity in the chemical environment of Se. In addition, there are reversible changes in the valence band (VB), indicating transfer of lone-pair states of Se to a new kind of bonding state deeper in the band, which have a smaller population in the absence of light.

XPS Study of the Oxidation Behavior of the Cu3Sn Intermetallic Compound at Low Temperatures

The oxidation of Cu-Sn intermetallic compounds is of significant technological interest in relation to the wetting behavior of Sn-base solders to Cu and Cu alloys. However, there are very few studies on this subject in the literature. In this present study, oxide films formed on the intermetallic compound Cu 3 Sn in pure O 2 at temperatures <350°C have been analyzed using XPS. Single-phase samples of different Cu-Sn intermetallic compounds, made by hot isostatic pressing of rapidly solidified powders, were provided by NIST. The sample surfaces were mechanically cleaned, and oxidized in situ in the XPS chamber. Results obtained so far indicate that the oxidation behavior of e-Cu 3 Sn, in terms of both microchemistry and growth kinetics, is strongly temperature dependent. A tin oxide film was observed at 150-200°C, while a mixed copper and tin oxide film was noted at 350°C. Results for oxidation of e-Cu 3 Sn are interpreted in terms of available phase equilibria and growth kinetics data.

A model for analysis and quantification of ion scattering spectroscopy data

Abstract An improved model has been developed for numerically fitting experimental ion scattering spectroscopy data. This model is a combination of the models described previously by Nelson [J. Vac. Sci. Technol. A 4 (1986) 1567] and Young and Hoflund [Anal. Chem. 60 (1988) 269]. It allows for quantification of the neutralization decay rate, accurate fitting of the different elemental peak shapes, extracting information which is usually difficult to obtain due to poor mass resolution, subtraction of the inelastic background and providing a measure of the composition of the outermost atomic layer. The model has been used to analyze ISS spectra obtained from isotopically pure 24 Mg and Mg of natural abundance (79% 24 Mg, 10% 25 Mg and 11% 26 Mg). The factors which influence spectral (mass) resolution have been examined using the model, and calculated results show that both the width of the scattering angle and the energy spread of the primary ion beam significantly affect resolution.

Structure of Se-rich As-Se glasses by high-resolution x-ray photoelectron spectroscopy

To establish the validity of various proposed structural models, we have investigated the structure of the binary As{sub x}Se{sub 100-x} chalcogenide glass family (x{<=}40) by high-resolution x-ray photoelectron spectroscopy. From the composition dependence of the valence band, the contributions to the density of states from the 4p lone pair electrons of Se and the 4p bonding states and 4s electrons of Se and As are identified in the top part of the band. The analysis of Se 3d and As 3d core-level spectra supports the so-called chain crossing model for the atomic structure of Se-rich As{sub x}Se{sub 100-x} bulk glasses. The results also indicate small deviations ({approx}3-8%) from this model, especially for glass compositions with short Se chains (25<x{<=}40). For example, the presence of As-As homopolar defect bonds in the stoichiometric As{sub 40}Se{sub 60} and of Se-Se-Se fragments in a glass with composition x=30 is established.

X-ray photoelectron spectroscopy analysis of bulk Pd-Ni-P metallic glasses

Abstract The core-level and valence-band spectra were obtained from high-resolution X-ray photoelectron spectroscopy of the bulk glassy and crystalline Pd x Ni80- x P20 ( x = 20–70) alloys. Upon crystallization of glassy Pd40Ni40P20, which exhibits the highest glass stability, a small change in chemical bonding is observed. This appears as a charge transfer from P atoms to Ni and Pd atoms. The level of chemical bonding between P and the metals seems to increase linearly as a function of x throughout the composition range. The density D ( E F) of states at the Fermi level is significantly lower for the alloys with respect to those of the d-band metals, in agreement with the Nagel-Tauc criterion for glass stability. However, its value is not the lowest for the x = 40 composition which is most resistant to crystallization. The existing electronic models are not fully adequate for explaining the high glass stability of the Pd40Ni40P20 alloy.

Influence of modifier oxides on the structural and optical properties of binary TeO2 glasses

Five different glass compositions with equal TeO2 molar concentration and various intermediate constituents were prepared to examine the influence of such intermediate species on the tellurite network. A correlation between the glasses’ structural network and optical properties is presented. Peak Raman gain coefficients, on the order of 40 times the gain of SiO2, are reported in this paper.

Photoinduced changes in the electronic structure of As4Se3 glass

In situ irradiation experiments were performed on the oxygen-free surface of bulk As2Se3 glass that was fractured in the UHV environment of the X-ray photoelectron spectroscopy (XPS) chamber. The results are in agreement with theoretical simulations, which predict a large concentration of valence alternation pairs in this glass. Compared to previous experiments conducted in air, we find relatively small photoinduced changes in the XPS spectra. The analysis of high-resolution experimental data describes the nature of the light-induced permanent changes in the structural units of the Se atoms and reversible changes in the structural units of the As atoms. The valence band spectra do not appear affected significantly by laser irradiation. 2003 Elsevier B.V. All rights reserved. PACS: 79.60.)I; 31.15.Qg; 71.55.)i