Stanislav A. Evlashin

Carbon nanowalls: the next step for physical manifestation of the black body coating

The optical properties of carbon nanowall (CNW) films in the visible range have been studied and reported for the first time. Depending on the film structure, ultra-low total reflectance up to 0.13% can be reached, which makes the CNW films a promising candidate for the black body-like coating, and thus for a wide range of applications as a light absorber. We have estimated important trends in the optical property variation from sample to sample, and identified the presence of edge states and domain boundaries in carbon nanowalls as well as the film mass density variation as the key factors. Also we demonstrated that at much lower film thickness and density than for a carbon nanotube forest the CNWs yield one order higher specific light absorption.

Influence of the growth temperature on structural and electron field emission properties of carbon nanowall/nanotube films synthesized by catalyst-free PECVD

Nanocrystalline graphite films composed of carbon nanowalls and cone-shaped carbon nanotubes have been synthesized without the use of any catalyst by means of plasma enhanced chemical vapor deposition in the plasma of direct current glow discharge. The effect of growth temperature on the structural and field emission properties of the nanocrystalline graphite films has been studied. It was demonstrated that variation of the surface temperature during plasma synthesis dramatically affects carbon nanowall and nanotube structural features. Moreover, higher growth temperature results in higher stability of the electron field emission properties of nanocrystalline graphite films.

Controllable Laser Reduction of Graphene Oxide Films for Photoelectronic Applications

This article presents a new simple method of creating light-absorbing carbon material for optical devices such as bolometers. A simple method of laser microstructuring of graphene oxide is used in order to create such material. The absorption values of more than 98% in the visible and more than 90% in the infrared range are achieved. Moreover thermal properties of the films, such as temperature dependence and the thermal response of the samples, are studied. The change in resistance with temperature is 13 Ohm K-1, temperature coefficient of resistance (TCR) is 0.3% K-1, and the sensitivity is 0.17 V W-1 at 300 K. Thermal conductivity is rather high at ∼104 W m-1 K-1 at 300 K. The designed bolometer operates at room temperature using incandescent lamp as a light source. This technique suggests a new inexpensive way to create a selective absorption coating and/or active layer for optical devices. Developed GO and rGO films have a large surface area and high conductivity. These properties make carbon coatings a perfect candidate for creating a new type of optoelectronic devices (gas sensors, detectors of biological objects, etc.).

Emission properties of carbon nanowalls on porous silicon

For the past two decades various methods of carbon nanostructures growth have been proposed. Special substrate pretreatment methods are generally used to grow carbon nanowalls on silicon substrates and among them are mechanical and catalytic methods and ion bombardment in an rf discharge with bias. This work describes the possibility of growing carbon structures on porous silicon in a dc discharge without any additional pretreatment of the substrate surface. Carbon structures were grown on n- and p-type (100) porous silicon substrates produced by using standard photoelectrochemical etching. The analysis of these carbon structures revealed nanocrystalline carbon with multilayer carbon nanotubes and fibers. All samples demonstrated low field emission thresholds (Etr < 3 V/μm) and high current densities, showing an achieved current density of more than 6 A/cm2 for an electric field of E ∼ 15 V/μm. The authors investigated various modifications of porous silicon samples and carbon structures and demonstrated ...

Ag on carbon nanowalls mesostructures for SERS

We have elaborated substrates for surface enhanced Raman scattering (SERS) based on carbon nanowalls (CNW) deposited with Ag nanoparticles and thin Ag films. For carbon nanowalls deposited with silver nanoparticles, the achieved analytical enhancement factor SERS was from 50 to 2500. Much higher analytical enhancement factor of SERS, up to 5×104, was obtained for carbon nanowalls deposited with thin Ag film. In this case the SERS signal is determined by fractal structure of carbon nanowalls covered by Ag films. Such fractal structure provides a strong inhomogeneous localization of light, formation of a large number of hot spots and leads as a result to significant enhancement of SERS signal.

Heteroepitaxy of Nickel and Copper on Diamond

Crystalline nickel and copper possess bcc lattices, the parameters of which are 1.2 and 1.35% smaller than that of diamond. Heteroepitaxial Ni and Cu films have been grown by magnetron sputtering on polished and then thermally annealed and etched {100} and {110} surfaces of natural diamond. The films exhibit island morphology and possess a highly perfect crystalline structure.

Heteroepitaxial Ir layers on diamond

Ir layers were deposited on single-crystal diamond using magnetron sputtering at substrate temperatures ranging from 830 to 1150 °C. The grown films have high adhesion to diamond and a low surface roughness Rq = 4–6 nm according to the AFM measurements. Crystalline perfection of Ir layers was investigated using x-ray diffraction and heteroepitaxial growth of Ir on diamond was confirmed. Because the lattice parameters of Ir and diamond are significantly different (7.65%) and because the deposition temperature of Ir is low in comparison with its melting point (2443 °C), diffraction reflections of the films are similar to analogous reflections of diamond, but wider. The films consist of elongated crystallites of length 10–100 nm. By broadening the reciprocal lattice points, we conclude that the level of microstresses in the Ir films increases as the substrate temperature during deposition of Ir films on the (0 0 1) diamond substrate increases, and that the level of microstresses decreases for the films on the (0 1 1) substrate. Simultaneously, the misorientation of Ir crystallites on the (0 1 1) substrate also decreases with increasing temperature.

Gaining cycling stability of Si- and Ge-based negative Li-ion high areal capacity electrodes by using carbon nanowall scaffolds

We report an approach to stabilize the electrochemical performance of silicon- and germanium-based thin film anodes by using carbon nanowall matrices. Silicon and germanium layers were deposited onto vertically oriented carbon nanowall scaffolds and this procedure has been repeated multiple times producing multilayered structures with increased silicon and germanium areal mass loading. It was demonstrated that the areal specific capacity of multilayered anodes achieves up to 2 mA h cm−2 without sacrificing cycling stability. Based on post-mortem SEM analysis of the electrodes we speculate that the reason for the improved cycling stability of multilayered highly loaded silicon/graphene composites is the ability to relax the mechanical stresses in the films.

A Comparative Analysis of Optical Methods for Detection and Prediction of Radionuclides Migration in the Geosphere

Here we report on a comparative analysis of laser techniques for detection and speciation of radionuclides and its complexes in the geosphere. The application of different methods is illustrated by the example of uranium(VI) speciation in aqueous environment and detection of trace elements on the ppm level in gases, which appear as a result of reprocessing of spent nuclear fuel.

Si wires growth by using of magnetron sputtering method

New method of Si wires synthesis by magnetron sputtering of solid target as a Si source is described. This method is simple, safe and cheaper in comparison with Chemical Vapor Deposition (CVD). Influence of silicon atom flow rates (target sputtering rate) and substrate temperature on the growth of different Si structures were studied. It was found that Si wires have different morphology, which depends on the Si flux and substrate temperature.