Optical absorption edge of a new GaSe polytype

The optical energy gap of the δ modification of GaSe is reported. The energy shift of the exciton in this polytype is explained in terms of interlayer separation by comparison with the ? structure under high pressure.     

Spectroscopic characterization of lithium doped borate glasses

B₂O₃-xLi₂O₃ (x=0, 0.1, 0.5) glasses have been prepared by the Sol-Gel method. The evolution of the composition and the structure of the materials upon thermal treatments are analyzed. Raman spectroscopy measurements reveal that the structure transforms from crystalline to amorphous. After a thermal treatment at 400°C, the materials exhibit a strong luminescence band which disappears upon further heating. In the case of no dopant (x=0) heating at 1150°C results in a Raman spectrum which is almost identical to the one corresponding to bulk B₂O₃ glass obtained by melting and quenching.     

Raman detection of phonon-phonon coupling in GaxIn1−xP

The coupling between the zone center phonons and continua has been observed and interpreted from the changes in the line shape of the TO Raman spectra and the existence of a side band on the low energy side of the LO phonon in mixed Ga_xIn_1?xP.     

Raman study of squaric acid

Raman spectra of squaric acid have been measured at various temperatures below and above the transition temperature. Six low frequency bands below 300 cm^?1 are assigned to translational and librational modes of the squaric molecule on the basis of the recent crystal determination by X-ray diffraction. A discussion is given of the striking temperature dependence of these external modes in the ordered phase in connection with the phase transition.     

Structure dependent oxidation of clean Si(111) surfaces

The initial process of oxygen adsorption is investigated by high resolution photoemission yield spectroscopy on (2 × 1) and (7 × 7)Si(111) surfaces. The corresponding changes in work function, ionization energy and surface state distribution, within and close to the gap, depend strongly on the initial structure. It is shown for the first time that, after completion of a “monolayer” of oxygen, the dangling bond states completely disappear on the (7 × 7) structure while a few percents remain unaffected on the (2 × 1).     

Resonant Raman scattering near the 1S exciton level in cuprous oxide

Raman scattering experiments on the Γ₁₅⁻ LO₁ mode in Cu₂O crystals were performed using incident light near the resonance with the 1S exciton level of the ‘yellow serie’. The enhancement of the Raman efficiency observed in this experiment is attributed to the activation of the normally forbidden transition by stoechiometric defects in the Cu₂O crystals.     

Ultra-high vacuum deposition of sodium on indium monoselenide: intercalation or chemical reaction?

A X-ray photoelectron spectroscopy (XPS) study of the behaviour of sodium films deposited in ultra-high vacuum on InSe single-crystal or thin epitaxial films at room temperature and upon moderate annealings (up to 475 K) is reported. Major changes affect the substrate spectra, in particular indium, and clearly show the influence of the substrate morphology. For the InSe single-crystal substrate, annealing tends to restore the initial InSe surface as shown by XPS and RHEED, while for InSe films, no restoration occurs. In both cases, sodium has a partial ionic character and two phases are evidenced: one, [NaIn⁰Se_β], where indium is close to metal or covalent indium, and the other, Na_'[InSe], where indium is more ionic close to InSe. The results emphasize that interdiffusion and fast chemical reaction predominate for the thin film substrate; for the bulk substrate, interfacial reaction and surface diffusion are competitive.     

Band crossing in Pb1−xSnxSe under hydrostatic pressure

Laser emission from Pb_1−xSn_x Se diodes for x = 0.115 at 78.5°K is observed under hydrostatic pressure up to 14.7kbar. Direct evidence for an inversion of valence and conduction bands is obtained from the pressure coefficient measured on the same diode over the whole experimental range. We discuss briefly the nature of the band structure after the cross over point and suggest an explanation for an abrupt increase of the threshold current for laser action in these diodes at small gaps.