Temperature dependence of anomalous structure in the derivative absorption spectra of Si:P

Temperature dependence of wavelength-derivative absorption spectra of Si:P has been measured, with emphasis on temperature behaviors of anomalous exciton-absorption structure previously observed nearly at the free-exciton absorption thresholds. Such anomalous structure has been observed even at high temperatures where the principal bound-exciton component almost disappears. This result confirms our previous identification that the structure is related to free-exciton absorption rather than bound-exciton absorption.     

Efficiency of Si L 2,3 x-ray generation in the SiO2/Si system by electron impact

The paper reports a study of the depth profile of the generation efficiency and escape of the ultrasoft silicon L _2,3 x-ray radiation excited by electrons of various energies. The generation function describing the excitation efficiency is the kernel of an integral equation determining the dependence of x-ray emission intensity on primary-electron energy. To determine the form of this function, a study was made of the dependence of the Si L _2,3 x-ray spectral intensity and of its silicon L _2,3 component bands, from crystalline silicon and amorphous dioxide SiO₂, on primary-electron energy in samples made from dioxide layers of various thicknesses grown on crystalline silicon. These experiments permitted investigation of the generation-function cross sections at the depth of the Si-SiO₂ interface. The theoretical simulation of the generation function made use of the simplest laws governing electron interaction with solids and of the cross section of the inner-level ionization by electron impact in its most general form. A comparison of the experimentally obtained relative contributions of the Si and SiO₂ emissions with the calculations shows them to be in good agreement up to primary-electron energies of 2–3 keV. Fiz. Tverd. Tela (St. Petersburg) 40, 1932–1936 (October 1998)     

Fully relativistic calculations of the L2,3-edge XANES spectra for vanadium oxides

Fully relativistic multielectron method based on the numerical solution of the Dirac equation was used to calculate the L_2,3-edge X-ray absorption near edge structure (XANES) spectra of VO₂, V₂O₃, and V₂O₅ crystals. The key-points of the method are: i) usage of the molecular orbitals (MO); ii) absence of any fitting parameters; iii) wide area of application: to any ion in any symmetry; iv) possibility of numerical analysis of the MO composition. The calculated spectra are in a satisfactory agreement with experimental data available in the literature, including the absolute values of the transitions energy, the shape of the absorption bands, and polarization dependence. The assignment of the absorption bands in terms of the electronic configurations was done. The structure of the absorption bands is attributed to the splitting of the vanadium p- and d-orbitals; the magnitude of this splitting is estimated from the spectra. Covalency effects were considered for all hosts; it was shown that the contribution of the oxygen wave functions increases with increasing the vanadium oxidation state. Dependence of the relative positions of the vanadium 3d and oxygen 2p levels and energies of the “ligand–metal” charge transfer transitions on the vanadium oxidation state was analysed.     

Temperature dependence of many-body effects in Si accumulation layers: An experimental observation

We have studied the temperature dependence of inter-subband transitions in the accumulation layer of (111) and (110) Si planes, and have found evidence for a reduction in the strength of exchange and correlation effects with an increase in temperature.     

Temperature dependence of infrared spectra

A simple form of cell for the study of infrared absorption spectra at low and high temperatures is described. Preliminary results of a study of the temperature-phase dependence of fluorobenzene and m-toluic acid spectra are reported.     

Doping dependence of the electronic Raman spectra in cuprates

We report electronic Raman scattering measurements on Bi₂Sr₂(Y_1−xCa_x)Cu₂O_8+δ single crystals at different doping levels. The dependence of the spectra on doping and on incoming photon energy is analyzed for different polarization geometries, in the superconducting and in the normal state. We find the scaling behavior of the superconductivity pair-breaking peak with the carrier concentration to be very different in B_1g and B_2g geometries. Also, we do not find evidence of any significant variation in the lineshape of the spectra in the overdoped region in both symmetries, while we observe a reduction of the intensity in B_2g upon decreasing photon energies. The normal state data are analyzed in terms of the memory-function approach. The quasiparticle relaxation rates in the two symmetries display a dependence on energy and temperature which varies with the doping level.