Christiane Senemaud

Electronic distribution of SiO by x-ray spectroscopy

Abstract Si Kβ X-ray emission has been comparatively studied in Si, SiO and SiO 2 . Taking into account the chemical shift of the inner K level, the position of the valence band of SiO relative to those of SiO 2 and Si has been obtained. The existence of silicon monoxide is confirmed.

X-ray photoabsorption in metallic aluminium, polycristalline and amorphous Al2O3

Abstract The K photoabsorption spectrum of Al in pure Al, amorphous and γ Al 2 o 3 have been studied and compared with corresponding L spectra and with theoretical data. The results show that the Al photoabsorption curve is strongly influenced by the density of the empty allowed states on about 30 eV from the edge. For Al 2 O 3 , an interpretation of differences observed between K and L spectra is proposed.

Influence of disorder on the electronic distribution of InP by X-ray and photoelectron spectroscopies

Abstract Soft X-ray spectroscopy (SXS) and X-ray induced photoelectron spectroscopy (XPS) measurements have been performed on amorphous InP samples prepared by flash evaporation, comparatively to crystalline InP. SXS results reveal striking differences in the 3p states of the valence band distribution of a-InP as compared to c-InP. The presence of a partial chemical disorder in a-InP is deduced from XPS measurements.

Local electronic structure of Tl–Sn–Te compounds

Abstract We show that the combined application of Mossbauer spectroscopy and X-ray photoelectron spectroscopy (XPS) provides a consistent picture of the local electronic structure in Tl 5 Te 3 , TlTe, Tl 2 Te 3 , Tl 4 SnTe 3 and Tl 2 SnTe 5 . The results are discussed from a tight-binding calculation of the electronic populations. We show that values of the Tl 4f 7/2 core-level binding energy do not vary noticeably for the different compounds in agreement with the close values of the calculated Tl average charges. The results obtained by both the XPS and 125 Te Mossbauer spectroscopy are consistent with the existence of two types of Te atoms with very different atomic charges due to the differences in the number of Te 5p electrons. The variations of the Te charge are explained from changes in the nature of the Te nearest neighbors: Tl, Sn and Te as a function of the stoichiometry. Finally, we show that values of the 119 Sn Mossbauer isomer shift and the Sn 4d 5/2 core-level binding energy both increase from Tl 2 SnTe 5 to Tl 4 SnTe 3 in agreement with the increase of the calculated number of Sn 5s electrons and the decrease of the calculated number of Sn 5p electrons, respectively. These changes are related to the differences between the Sn local environments of the two ternary compounds.

2p Photoabsorption in amorphous, trigonal and monoclinic selenium

Abstract The 2p photoabsorption spectra of amorphous and polycrystalline trigonal and α-monoclinic selenium have been studied. Our experimental results, accounting for the transition probabilities and inner level broadening, are in qualitative agreement with Kramers pseudo-potential formalism calculations of the density of unoccupied states. The amorphous selenium spectrum seems intermediate between the two crystalline form spectra and we deduce that both trigonal chains and monoclinic rings are randomly distributed in the amorphous phase.

Electronic structure of Ge–As–Te glasses

Abstract The electronic structure of Ge 0.2 Te 0.8 and Ge 0.1 As x Te 0.9− x glasses with x =0.2, 0.46 and 0.54 has been experimentally determined by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The values of the Ge 3p 3/2 , As 3p 3/2 and Te 3d 5/2 core level binding energy do not vary significantly within this series of glasses in agreement with the covalent character of the bonds. The atomic contributions to the main observed peaks in the XPS valence bands and XAS spectra are obtained from a molecular calculation. This approach is first used for crystalline As 2 Te 3 and compared to a periodic tight-binding calculation in order to check its accuracy for the analysis of the experimental data in terms of local environments. The electronic structure of Ge 0.2 Te 0.8 is consistent with the existence of GeTe 4 units connected by Te–Te bonds but does not rule out the presence of Ge–Ge bonds. The XPS valence bands of the ternary glasses are formed by two broad bands which are due to the s- and p-type valence electrons of the different atoms, respectively. Increase of the As content mainly changes the p-type peak and the main XAS peaks at the As K and Ge K edges. These changes are due to the decrease in the number of As–Te bonds and the increase in the number of As–As bonds.

Band-structure and the average-gap model in a-Si1−xCx:H alloys

The dispersion of the subband refractive index in silicon-rich a-Si1−xCx:H is well described by “average gap” models. In these models, the average gap EM corresponds to a weighted average of the valence-to-conduction band transitions. In carbonated amorphous silicon (x < 20%) prepared under low-power-density conditions, EM is about twice the optical gap Eo4. A study of the structure by soft X-ray spectroscopy reveals a similar increase of the band-to-band energy with the carbon content.

Electronic structure of As2Te3-GeTe crystalline compounds

Abstract The electronic structures of As 2 Te 3 , GeTe and the layered compounds As 2 Ge n Te 3+ n with n =1–5 have been experimentally studied by means of X-ray photoemission spectroscopy (XPS). The XPS valence bands show changes as a function of n , which are explained by tight-binding calculations of the total and partial densities of states. The values of the binding energy of the Ge 3d 5/2 , As 3p 3/2 , and Te 3d 5/2 core-levels were measured and are related to the calculated atomic charges.

Electronic structure studies of amorphous and microcrystalline germanium

Abstract The ion bombardment of RF glow -discharge deposited Ge films induces an amorphous-microcrystalline transition which is revealed by in-situ ellipsometry and X-ray photoelectron spectroscopy. The influence of the ion bombardment on the amorphous and microcrystalline electronic structures, studied with both techniques, is discussed.

X-Ray Spectra of Amorphous and Crystalline GaP

The modification of the electronic density of states of tetra-hedrally bonded semiconductors on going from the crystalline to the amorphous form, have been related to the different elements of disorder: topological disorder (in particular odd-membered rings of bonds) and quantitative disorder (fluctuations in bond-length and bond-angle, and distribution of dihedral angles). In the case of compound, additional effects may arise from atoms of the same kind, ‘like-atom’ (maverik) bonds, which result from the chemical disorder or are introduced by the network topology. Extensive theoretical studies performed on GaAs (taken as the prototype of III-V compounds) have shown that the effects of like-atom bonds on the electronic density of states may depend appreciably on their clustering configuration2.