The process of oxidation of the Bi2Te3 surface was
investigated by x-ray photoelectron spectroscopy (XPS). The
oxidized surface layer was found to have a definite thickness, with
configurations where O is bonded with Bi and Te, and Bi and Te are
bonded with three and four oxygens, respectively. The oxidation time
dependence of the oxidized layer thickness d(t) estimated from the
XPS behaved as (t-t0)1/2 when d(t) was smaller than the
thickness of a single oxidized quintuple atomic layer in our
oxide model and behaved as t-t1 when it was larger than that.
Experimental data were compared to our oxidation process model for
the layered structure with the van der Waals gap and very good
agreement was found.
Tunnelling spectroscopy measurements were carried out on the mixed crystal TiSe 2−x S x (0 x 0.55) to investigate the change in the density of states in the CDW state. The temperature dependences of the CDW energy gap widths were obtained. Experiments showed that the flattening of the peak in the ρ-T curve with increasing x corresponds to the decrease in the CDW energy gap. A model was proposed in which the anomalous ρ-T characteristics in this system were explained in terms of the competition of the two conduction mechanisms associated with the metallic carriers and the 'excitonic' carriers.
The two-photon absorption coefficient β in InP has been measured in the wavelength range of 1640 to 1800 nm by the Z-scan technique in relatively thick materials. The values of β have been evaluated from the fit to the equation including the spatial and temporal profiles of the focused Gaussian beam. The polarization dependence of β has also been measured. The dependence has been expressed very well by the expression of β with the imaginary part of the third-order nonlinear susceptibility tensor χ (3) .
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