Photocrystallization of amorphous selenium (a-Se) films under illumination by polarized light with 632.8 or 647.1 nm wavelength has been studied by Raman spectroscopy. Preferential orientation of trigonal crystalline, selenium (t-Se) obtained as a result of photocrystallization has been observed, threefold c axis of t-Se being oriented perpendicular to the direction of the polarization of the illuminating light. Although the mechanism of polarization-dependent photocrystallization seems to be optical in origin, an alternative, essentially thermal, mechanism of the polarization-dependent photocrystallization of a-Se is discussed.

We report on a photoinduced phenomenon in solids, namely, photomelting at low temperature. We have found that both trigonal and amorphous selenium can be molten by illumination with light at a temperature of ∼77 K. This phenomenon is pure optical (athermal) and it is associated with light-induced breaking of the interchain (intermolecular) bonds in selenium. The photomelting is important for basic science (as an example of photoinduced phase transition in condensed matter and as a key photoinduced phenomenon in selenium and related materials) and for applications (as a tool for fine manipulation with shape of solids by light at low temperatures).

The temperature dependence of the dielectric constant of opal containing dispersed sodium nitrate was measured in the temperature interval from 370 to 600 K. Features associated with the ferroelectric and melting - freezing phase transitions in sodium nitrite particles were observed. A low-temperature shift of the Curie point of compared to that of the bulk was found on cooling, and significant broadening (up to K) of the melting - freezing phase transition was observed. A giant enhancement of the dielectric constant (up to at 100 Hz) of was found at high temperatures, when the sodium nitrite particles melt, transforming to electrolytic drops.

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Using high numerical aperture lenses, we detected doublet optical phonon, forbidden by selection rules, in Raman spectra of Si strained in the (001) plane (bulk Si as well as strained Si device structure grown on SiGe). This allowed us to quantitatively determine stress and its distribution in strained Si with the ∼10% accuracy, assuming symmetric biaxial stress. At the same time, we demonstrate some deviations of the real stress from the assumed model. For better accuracy, one has to consider these deviations as well as a possibility of improvement of available Si phonon deformation potential values.

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Reflection and transmission characterization of a hexagonal photonic crystal in the mid infrared

The temperature dependence of the Raman spectrum of single helical Se chains in nanochannels of AlPO 4 -5 was studied. Dramatic changes in the spectra due to structure transformations in this one-dimensional system are observed. The chains are found to be ordered at 77 K. Reversible weak disordering of the chains (mainly due to the large-amplitude torsional vibrations) occurs with increasing temperature. At temperatures above ϳ340 K, a phase transition accompanied with a structural relaxation of the chains to the strongly disordered state with unfixed dihedral angles ("torsional melting") is observed. [S0031-9007(99)08571-3]