S. G. Romanov

Anisotropy of light propagation in thin opal films

Thin opal films are prepared by crystallization in a moving meniscus, and their optical transmission spectra are recorded in polarized light and studied. It is shown that the anisotropy of light propagation in the films is unambiguously related to the photonic band structure of opal and depends on the angle of incidence, the orientation of the incidence plane with respect to the opal lattice, and the wavelength and polarization of the incident light. Azimuthal diagrams of transmitted polarized light are constructed in the range of photonic band gaps of three orders for oblique incidence of a light beam. The anisotropy is found to vary with the light wave-length independently in perpendicular polarizations. A model of the band structure of opal wherein opal is represented as an fcc lattice of close-packed spheres adequately describes the optical transmission of opal films only in the range of the first-order photonic band gap.

Electrical conductivity and superconductivity of ordered indium-opal nanocomposites

The electrical conductivity is measured experimentally and the parameters of the superconducting transition are determined in a regular spatial network of multiply connected submicron-sized indium grains embedded in voids of an ordered opal dielectric matrix. The In-opal nanocomposite was prepared by pressure injection of the molten metal into voids of opal samples. Arrays of In grains of different sizes were produced by properly varying the characteristic geometric sizes of the opal voids, which offered the possibility of observing quantitative and qualitative changes in the temperature dependence of electrical resistance and studying the size effects on the critical temperature and critical magnetic field in the In-opal nanocomposites. It was found that, as the coherence length becomes comparable to the size of the superconducting grains, the parameters of the superconducting transition in the nanocomposite increase sharply.

Interface phenomena and optical properties of structurally confined InP quantum wire ensembles

Three-dimensional regular ensembles of InP quantum wires have been produced in channels of porous dielectric matrices by metal-organic chemical vapor deposition. These matrices differ both in the diameter of the channels (0.7, 3, and 8 nm) and in their spatial arrangement. The InP layer thickness does not exceed two-three monolayers. A comparative study of Raman, optical absorption, and photoluminescence spectra revealed the dependence of the optical properties of these quantum wires on interface effects, namely, atomic interaction in the wires, wire-matrix, and wire-wire interactions. It is shown that the wire-matrix interaction distorts the InP lattice, broadens the wire electronic density-of-states spectrum in the vicinity of the fundamental gap, and redistributes the relaxation of photoinduced excitations among states belonging to the wire itself and to defects in the matrix bound to the wire.

Specific features of polarization anisotropy in optical reflection and transmission of colloidal photonic crystals

This paper reports on the measurements (in linearly polarized light) of the transmission and reflection spectra of colloidal photonic crystals with three-dimensional and one-two-dimensional photonic band structure, i.e., opal films and Langmuir-Blodgett crystals with a refractive index contrast of ∼1.5: 1.0. It has been shown that the polarization anisotropy is enhanced considerably in the diffraction resonance range both in transmitted and reflected light, and that the anisotropy in the resonance range can be as high as 99%. The interaction of photonic crystal eigenmodes has been found to affect the polarization anisotropy. The assumption has been made that the coincidence of the maxima in polarization anisotropy of the resonant and nonresonant light reflection in colloidal crystals originates from the disorder in their lattices. The generality of the results obtained is confirmed by the fact that the polarization anisotropy manifests itself in the same way in colloidal crystals with different lattice symmetries.

Polarization anisotropy of optical transmission in opals and Langmuir-Blodgett crystals

The transmission spectra of thin-film colloidal photonic crystals with three-dimensional and one-dimensional-two-dimensional photonic energy band structures, i.e., opals and Langmuir-Blodgett crystals with a refractive index contrast of ∼1.5: 1.0, have been measured in linearly polarized light. It has been demonstrated that the polarization anisotropy in the light transmitted through the crystal is uniquely related to the diffraction resonance and that the degree of polarization can exceed 90%. A higher degree of polarization is provided by lattices that are characterized by a smaller attenuation of light polarized in the plane of incidence. It has been revealed that the diffraction resonances from the crystal planes for which the dispersions are in anticrossing with the dispersion of the growth planes acquire the same anisotropy. The general character of the results obtained has been confirmed by the fact that the polarization anisotropy identically manifests itself in colloidal crystals that have different symmetries and lattice orderings.

Effect of dimensionality on the spectra of hybrid plasmonic-photonic crystals

Based on colloidal crystals of various dimensionality, hybrid metal-dielectric plasmonic-photonic heterocrystals have been prepared. It has been shown that the spectra of optical transmission of heterocrystals are mostly controlled by the sum of contributions of composing plasmonic and photonic crystals. At the same time, there are a number of phenomena caused by the mutual effect of heterostructure components, which lead to a deviation of observed optical properties from the linear superposition of responses of these crystals. In particular, it has been found that the anomalous transmission controlled by the plasmonic crystal decreases with increasing the dimensionality of the photonic crystal attached to it. At the same time, light reflection on a metallized surface changes light diffraction in photonic crystals and leads to Fabry-Perot oscillation amplification. It has been assumed that an intermediate layer is formed, in which Bloch modes of the photonic crystal and surface plasmon-polaritons of the plasmonic crystal are hybridized.

Opals with a thin-film metallic defect-hybrid colloidal plasmonic photonic crystals

Hybrid photonic crystals consisting of a thin-film opal and a thin profiled gold film situated on the surface or inside the opal have been prepared. The optical transmittance spectra of hybrid crystals have been studied. It has been found that the spectra exhibit minima due to diffraction resonances in the photonic crystal and bands of enhanced transmission due to transfer of radiation through the metal film surface by plasmon polaritons. It has been shown that the transmittance spectra of hybrid crystals with a metal film on the surface are subjected to a stronger modification than the hybrids having a metal film inside the crystal.

Variation of spontaneous emission in the opal stop-band with an enhanced refractive-index contrast

Photoluminescence spectra of an opal with an anatase layer grown on its inner surface were studied. Measurements were carried out with a high angular resolution at various pump power levels and detection angles. The intensity and probability of emission were found to acquire an anisotropy corresponding to the frequency and angular dispersion of the first opal photonic band gap. As the pump power increases, the suppression of spontaneous emission in the photonic band gap is shown to be replaced by its amplification. The amplification of spontaneous emission is tentatively assigned to the existence of localized defect optical modes in the photonic band gap.

Light diffraction features in an ordered monolayer of spheres

The structure and optical diffraction properties of monolayers of monodisperse spheres crystallized on transparent dielectric substrates are studied. Two types of diffraction phenomena are considered: surface light diffraction on the lattice of spheres and waveguide resonances in the monolayer plane. For experimental study of these phenomena, optical retroreflection and transmission spectra are measured as functions of the light incidence angle and azimuthal orientation of the incidence plane. The monolayer structures determined by scanning electron microscopy and light diffraction methods are in quantitative agreement. It is concluded that one-dimensional Fraunhofer diffraction is applicable to describe surface diffraction in the hexagonal lattice of spheres. In the case of oblique light incidence, anisotropy of diffraction and transmission spectra depending on the light incidence plane orientation with respect to the sphere lattice and linear polarization of incident light is detected. Waveguide resonances of the planar two-dimensional photonic crystal are approximated within the light diffraction model in the “empty” hexagonal lattice. The best approximation of the waveguide resonance dispersion is achieved using the effective refractive index, depending on the wavelength. Surface diffraction suppression by waveguide resonances of the photonic crystal is demonstrated. Surface diffraction orders are identified as diffraction at singular points of the Brillouin zone of the planar twodimensional photonic crystal.

Optical properties of metal nanoparticles in chrysotile channels

Chrysotile samples with macroscopically ordered channels filled by gold and silver have been studied using optical transmission spectroscopy. The channels had inner diameters below 5 nm and lengths up to about 1 cm. The transmission spectra of samples strongly depend on the polarization of probing light. The observed spectral properties are probably related to plasmon resonances of metal particles and to surface plasmon polaritons.