L. M. Sorokin

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.

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.

Structural and photonic properties of opal-GaN nanocomposites

Electron microscopic methods have been applied to demonstrate that gallium nitride synthesized in opal voids has perfect crystal structure. Studies of optical reflection spectra revealed that the obtained opal-〈gallium nitride〉 nanocomposites retain the photonic-crystal properties of the ordered host matrix at any (0–100%) degree of opal void filling with gallium nitride.

Specific properties of the PZT-based thin-film capacitor structures with excess lead oxide

The effect of excess lead oxide on the microstructure and ferroelectric properties of lead zirconate titanate (PZT) films was studied in PZT-based thin-film capacitor structures. It is shown that excess lead in the form of lead oxide is localized at the grain boundaries and film-platinum electrode interfaces, which can result in the appearance of internal electric fields and the self-polarization of PZT films. It is suggested that the selfpolarization effect is related to the formation of a built-in electric charge with different densities at the bottom and top metal electrode-ferroelectric film interfaces.

A comparative TEM study of the 3D lattice of tellurium nanoclusters fabricated by different techniques in an opal host

An electron-microscope study of synthetic opals containing tellurium introduced into the regular void array either by melt injection or by evaporation from solution is reported. In the first case, a three-dimensional array of tellurium clusters interconnected by bridges was revealed. The clusters retain the same crystallographic orientation as one moves from one cluster to another. This suggests that cooling after inserting tellurium results in its directional crystallization, which is possibly controlled by the interconnecting channels. The second technique of tellurium introduction produces a nonuniform cluster array, with three-dimensional clusters growing not in all voids. The surface of most of the silica spheres is coated by a thin discontinuous layer of tellurium. This structure of the cluster array accounts for the nonlinear current-voltage characteristic of the object as a whole. A possibility of engineering cluster lattices differing in structural parameters has been demonstrated.

TEM and HREM study of the 3D superlattices consisting of nanoclusters in synthetic opal matrix

Abstract Results of TEM and HREM study of synthetic opals containing different guest materials embedded in their regularly distributed voids either by melt injection or by chemical route are discussed. It was established that in a number of cases (besides HgSe and In as guest materials) one can fabricate rather uniform 3D cluster lattices. Clusters in voids of opal have a single-crystal structure. Structural details of In cluster lattice are shown to result in specific feature of superconducting parameter (critical magnetic field) of In- particle array in the opal matrix.

Structural, photonic band-gap, and luminescence properties of the opal-erbium composite

Erbium oxide and silicates were embedded in the pores of synthetic opal by using the chemical bath deposition technique. Electron-microscopic images showed the synthesized compounds to be deposited predominantly in a thin uniform layer on the inner surface of the pores. An analysis of the transmittance spectra suggested that the opal-erbium composite thus obtained retained the photonic band-gap properties of the original ordered opal matrix. The Er3+ ions in the composite emitted light at several wavelengths in the visible and near-IR regions (550, 860, 980, 1240, 1530 nm) at 80 K.

Current-voltage characteristics of Si/Si1 − xGex heterodiodes fabricated by direct bonding

We have studied the current-voltage (I–U) characteristics of Si/Si1 − xGex (0.02 < x < 0.15) heterodiodes fabricated by direct bonding of (111)-oriented n-type single crystal silicon wafers with p-type Si1 − xGex wafers of the same orientation containing 2–15 at % Ge. An increase in the germanium concentration NGe in Si1 − xGex crystals is accompanied by a growth in the density of crystal lattice defects, which leads to a decrease in the minority carrier lifetime in the base of the heterodiode and an increase in the recombination component of the forward current and in the differential resistance (slope) of the I–U curve. However, for all samples with NGe ≤ 15 at %, the I–U curves of Si/Si1 − xGex heterodiodes are satisfactory in the entire range of current densities (1 mA/cm2–200 A/cm2). This result shows good prospects for using direct bonding technology in the fabrication of Si/Si1 − xGex heterostructures.

Studying 3C-SiC epilayers grown on the (0001)C face of 6H-SiC substrates

Epitaxial 3C-SiC films grown on the (0001)C face of 6H-SiC substrates by sublimation epitaxy in vacuum have been studied. The results of x-ray diffraction measurements show evidence of a rather high structural perfection of silicon carbide epilayers. The Raman spectroscopy data confirm that the 3C-SiC layer grows immediately on the 6H-SiC substrate without any transition layers. It is concluded that the structures under consideration are well suited for the investigation of a two-dimensional electron gas at the 3C-SiC/6C-SiC heterojunction

Thermal conductivity of HgSe loaded in the pore lattice of a synthetic opal single crystal

Samples of the opal + HgSe nanocomposite with 100% filling of the first-order opal pores by mercury selenide were prepared. The effective thermal conductivity κeff and electrical resistivity ρeff were measured in the temperature range T=5–200 K, and the thermopower coefficient α was measured in the interval 80–300 K. The coefficient α of HgSe in opal was shown to remain the same as that in bulk mercury selenide samples with similar carrier concentrations. The mechanism of carrier scattering in the HgSe loaded in opal also did not change. The total thermal conductivity κtot0 and electrical resistivity ρ0 were isolated from κeff and ρeff, and the electronic (κe0) and lattice (κph0) components of thermal conductivity of HgSe in opal were determined. The magnitude of κph0 was found to be considerably smaller than κph of bulk HgSe with the same carrier concentration throughout the temperature interval studied (5–200 K). For T>20 K, this behavior of κph0(T) is accounted for by the presence of specific impurities and defects forming in HgSe, and for T<20 K, by the onset of boundary scattering of phonons in the bottlenecks of the horn-shaped channels connecting first-order octahedral and tetrahedral opal pores loaded by mercury selenide.