Alla A. Sitnikova

Detonation Nanodiamonds as Catalyst Supports

The article reports on experimental study of catalytic properties of a new system: Pt on detonation nanodiamond (Pt/DND) for the carbon monoxide oxidation reaction. The catalytic activity of Pt/DND structures as a function of platinum content in the catalyst within the 7–80 wt % intervals was studied and the structure of the Pt/DND catalyst was investigated by X-ray diffraction and HRTEM. The Pt/DND catalysts developed demonstrate a high degree of conversion of CO to CO2 at room temperature, a feature making them attractive for commercial applications as catalytic systems for purification of air from carbon monoxide in houses and industrial areas. The new catalysts were incorporated in solid-state electrochemical CO gas sensors. A statement on efficiency of the detonation nanodiamonds as a support for catalytic metals of platinum groups has been done.

Structure of Nanodiamonds Prepared by Laser Synthesis

A study is reported of nanodiamonds obtained by a new method—pulsed laser ablation of a specially prepared carbon target. In the mechanism employed to produce a diamond phase, this method is similar to that of detonation synthesis of nanodiamonds. The main structural characteristics of the material have been determined and compared with the corresponding characteristics of detonation nanodiamonds.

Modification of Silicon Oxide by High Energy Electron Beam

During interaction between thin film SiO2 and electron beam with high power density, amorphous silicon dioxide modifies. Silicon nanoclusters are formed in radiated area. Result of this interaction is formation of Si/SiO2 nanocomposite. We studied modified SiO2 by TEM, microdiffraction and cathodoluminescence.

One-step synthesis of a suspended ultrathin graphene oxide film: application in transmission electron microscopy.

Ultrathin graphene films find their use as advantageous support for nano- and biomaterials investigations. Thin film causes a very slight deterioration to measured signals, thus providing more details of the objects structure at nanoscale. The ultimate thinness of graphene works in the best way for this purpose. However, obtaining suspended thin film of a large-area, which is convenient for applications, is often a relatively complicated and time-consuming task. Here we present a one-step 1-min technique for synthesis of an extremely thin (about 1-2 nm) continuous film suspended over cells of a conventional copper grid (50-400 μm mesh). This technique enables us to acquire a large-area film which is water-resistant, stable in organic solvents and can act as a support when studying nanoparticles or biomaterials. Moreover, the very mechanism of the film formation can be interesting from the point of view of other applications of ultrathin graphene oxide papers.

Spontaneous and stimulated emission in the mid-ultraviolet range of quantum-well heterostructures based on AlGaN compounds grown by molecular beam epitaxy on c-sapphire substrates

This paper reports on the results of investigations of the spontaneous and stimulated luminescence in AlGaN heterostructures with a single quantum well and a high Al content (up to ∼80 mol % in barrier layers), which were grown by plasma assisted molecular beam epitaxy (PAMBE) on c-sapphire substrates. It has been demonstrated that the stimulated emission occurs in the mid-ultraviolet range of the spectrum at wavelengths of 259, 270, and 289 nm with threshold excitation power densities of 1500, 900, and 700 kW/cm2, respectively. It has been shown that there exists a possibility of TE polarization (E ⊥ c) of both stimulated and spontaneous luminescence down to wavelengths of 259 nm.

Investigation of Subcontact Layers in SiC after Diffusion Welding

In our early analytic reports [1,2] has been made the supposition that during the diffusion welding (DW) in subcontact area of SiC is formed the intermediate amorphous layer. In the present work are given the first results of transmission electron microscopy (TEM) and electron diffraction investigations of subcontact layers in n0-n- 4H-SiC. TEM examinations show that the boundary between aluminium and silicon carbide looks like stripy interface layer of ~ 25 nm thickness. This is the evidence that during diffusion welding in subcontact surface layer of SiC the shear micro deformations have been taking place and due to this process the plane inclusions of small-grained phase have been appeared. The image of contact area obtained in diffracted SiC rays (dark field) apparently confirms that stripy zone belongs to silicon carbide because the aluminium (black zone) fell out of contrast. Diffraction picture obtained from bulk zone of silicon carbide looks like monocrystallin, but the micro diffraction pattern obtained from the subcontact (stripy zone) gives a lot of concentric rings, that makes evidential the fact of existence of small-grained inclusions. Deciphering of this electron-diffraction pattern reveals the presence of such elements as residue SiC, Al, Si, as well as inclusions of graphite.

Low-Temperature Transport Properties of Graphene and Multilayer Graphene on 6H-SiC

Transport properties of multigraphene layers on 6H-SiC substrates was studied. It was found that the curves of magnetoresistance and Shubnikov- de Haas oscillations shown the features, typical for single-layred graphene. The low temperature resistance demonstrated an increase with temperature increase, which also corresponds to a behavior typical for single-layered graphene (antilocalization). However at higher temperatures the resistance decreased with an increase of temperature, which corresponds to a weak localization. We believe that the observed behavior can be explained by a parallel combination of contributions to the conductivity of single-layered graphene and of multigraphene.

Heteroepitaxial Growth of 3C-SiC on Polar Faces of 6H-SiC Substrates, TEM Investigations

Abstract Results of an epitaxial growth of 3C-SiC epilayers on Si (0001) and C(000¯1) faces of hexagonal 6H-SiC substrates are described. TEM study of grown layers as well as interface between cubic and hexagonal polytypes is presented. Difference between the layers on the Si and C faces are discussed.

Integrated characterization of multilayer periodic systems with nanosized layers as applied to Mo/Si structures

The potential inherent in integrated characterization of multilayer periodic systems employed in development of extreme-ultraviolet mirrors was demonstrated using the example of Mo/Si structures grown by magnetron sputtering in different technological regimes. An integrated study provided mutually consistent data on the thicknesses and crystal structure of the layers, as well as on the quality of the interfaces. Measurements by atomic force microscopy permitted a comparison of surface roughness of the substrates and the multilayer systems grown on them. An analysis of the power spectral density functions revealed that low-frequency roughness is replicated from the substrate, whereas the high-frequency one can become smoothed out in the course of growth. X-ray diffractometry performed in the thin film mode showed that the Mo layers in the samples studied have different crystal structures, from the amorphous and polycrystalline to the [110]-textured one. An analysis of the transmission electron microscopy data confirmed that there is a difference in the degrees of crystallinity of Mo layers. The thicknesses of individual layers, the period, and the irreproducibility of the thicknesses and the period were determined using X-ray reflectometry. The root-mean-square roughness amplitude of the interfaces was estimated, and the existence of transition layers originating primarily from the Si layer was demonstrated. The study was used to formulate a proper strategy for the analysis of multilayer periodic systems with nanosized layers.

Photocurrent and Photoluminescence of Amorphous Silicon Nanoclusters Embedded in Silicon Suboxide Matrix

We have presented a technique, based on magnetron sputtering of silicon target in the mixture of argon, silane, and oxygen. Addition of oxygen gas was shown to cause formation of silicon suboxide layers with amorphous silicon nanoclusters without subsequent annealing. The layers exhibit significant photoluminescence at room temperature. Their photoluminescence spectra reveal special features predicted in the preceding well-known theoretical works. Heterostructures, fabricated with such layers, show high photocurrent efficiency in short-wavelength spectral region. Our results demonstrate that the investigated structures are promising for photoelectric and photovoltaic applications.