A. B. Pevtsov

Phase transition-governed opal–VO2 photonic crystal

Three-dimensional opal–VO2 photonic crystals were prepared by the chemical bath deposition technique. The x-ray diffraction and Raman spectroscopic data confirm the crystalline perfection of VO2 impregnated into synthetic opal pores. It is shown from the optical reflectivity measurements that the photonic bandgap of the opal–VO2 composite is governed by the phase transition in VO2.

Subpicosecond shifting of the photonic band gap in a three-dimensional photonic crystal

We demonstrate spectral shifting of the photonic band gap in a three-dimensional photonic crystal within a time of less than 350fs. Single 120fs high-power optical pulses are capable to induce the transition from the semiconductor to the metallic phase of VO2 in the pores of our artificial silica opal. The phase transition produces a substantial decrease of the real part of the effective refractive index of the photonic crystal and shifts the spectral position of the photonic band gap.

Three-dimensional ordered silicon-based nanostructures in opal matrix: preparation and photonic properties

Abstract Three-dimensional ordered opal–Si nanocomposites with direct (opal voids are infilled with silicon) and inverted (opal skeleton is removed from the initial composite) structures have been synthesized. The thermal chemical vapor deposition technique is used to incorporate silicon into the voids. An electron microscopy analysis reveals a uniformly thick silicon layer on the inner surface of opal voids. Maxima in the reflection spectra from the (1 1 1) surface of the composites are shown to arise due to the Bragg diffraction of light. These maxima are interpreted as a manifestation of photonic band gap that is tunable in position and width by varying the fill factor of the opal voids.

Raman scattering spectra and electrical conductivity of thin silicon films with a mixed amorphous-nanocrystalline phase composition: Determination of the nanocrystalline volume fraction

Raman spectra and electrical conductivity of thin films of hydrogenated silicon with mixed amorphous-nanocrystalline phase composition have been studied. It is shown that interpretation of experimental data in terms of percolation theory permits one to determine the integrated Raman-scattering cross-section ratio of the nanocrystalline to amorphous phase and to obtain a quantitative estimate of the volume fraction of each phase.

Optical properties of a Fabry–Pérot microcavity with Er-doped hydrogenated amorphous silicon active layer

Fabry–Perot hydrogenated amorphous silicon (a-Si:H)/amorphous-SiOx:H microcavities with an erbium-doped a-Si:H active region are fabricated by a plasma-enhanced chemical-vapor deposition technique in a single technological cycle without exposure to air between the intermediate operations. A metalorganic compound is used to incorporate erbium in the active a-Si:H layer. Transmission, reflection, and photoluminescence spectra of the microcavities are measured. The experimental data are compared to theoretical calculations performed in terms of field amplitudes generated by stochastic excitation sources.

Filtering of elastic waves by opal-based hypersonic crystal.

We report experiments in which high quality silica opal films are used as three-dimensional hypersonic crystals in the 10 GHz range. Controlled sintering of these structures leads to well-defined elastic bonding between the submicrometer-sized silica spheres, due to which a band structure for elastic waves is formed. The sonic crystal properties are studied by injection of a broadband elastic wave packet with a femtosecond laser. Depending on the elastic bonding strength, the band structure separates long-living surface acoustic waves with frequencies in the complete band gap from bulk waves with band frequencies that propagate into the crystal leading to a fast decay.

Hysteresis of the photonic band gap in VO2 photonic crystal in the semiconductor-metal phase transition

VO2 photonic crystals exhibiting a semiconductor-metal phase transition at 55–75°C have been synthesized by the infiltration of vanadium dioxide (VO2) into opal crystals and the subsequent removal of SiO2 by etching. A study of the optical reflection spectra of such crystals demonstrated that they are characterized by a wide photonic band gap (in the [111] direction of light propagation) in the visible spectral range. The energy position of this band gap changes abruptly upon a phase transition. The temperature shift and hysteresis of the position of the photonic band gap were measured. Quantitative calculations of the reflection spectra of photonic crystals of opal and VO2 were performed in terms of the model of a layered periodic medium, and numerical values of the geometric parameters and optical constants of the studied three-dimensional periodic structures were obtained.

Photonic Crystals with Tunable Band Gap Based on Infilled and Inverted Opal-Silicon Composites

Abstract : Three-dimensional opal-Si composites with both direct (a variable extent of filling of opal voids with Si) and inverted structures have been synthesized. A structural analysis of these fabricated systems is performed. Reflectance spectra from the surface (III) of the composites are measured. Observed spectral features are interpreted as a manifestation of the direction III photonic band gap that is tunable in position and width in the visible and near-infrared spectral ranges.

Three-dimensional array of silicon nanoscale elements in artificial SiO2 opal host

Abstract Regular systems of silicon nanoclusters containing up to 1014 cm−3 elements have been fabricated in a sublattice of voids of artificial opal. Structural studies of samples by transmission electron microscopy (TEM), high resolution electron microscopy (HREM) and Raman measurements were carried out. The regular lattices of Pt–Si junctions were obtained and the current as a function of voltage properties were measured.

Fabrication of regular three-dimensional lattices of submicron silicon clusters in an SiO2 opal matrix

Silicon is now the most important material in modern solid-state electronics. Regular systems of silicon nanoclusters containing up to 1014 cm−3 elements were obtained in a sublattice of opal (SiO2) voids. By using three-dimensional dielectric matrix-carriers similar to opal, it may be possible to obtain three-dimensional ensembles of semiconductor nanodevices. Various parameters of these “opal-silicon” nanocomposites were measured.