Leonid Mochalov

PECVD synthesis of As–S glasses

Chalcogenide glasses of the As–S system were first obtained by melting of solid products of interaction between As and S in low-temperature argon plasma. The plasma-chemical synthesis was performed at a reactor wall temperature not exceeding 250°C. The content of S in the As–S glasses is 54 to 72 mol %. The elemental, phase, and impurity composition of the glasses and their glass-transition point and optical properties were studied.

Influence of the preparation technique on the optical properties and content of heterophase inclusions of AS 2 S 3 chalcogenide glasses

Bulk samples of As-S chalcogenide glasses were prepared by an interaction of vapors of volatile precursors in low-temperature non-equilibrium plasma discharge (plasma enhanced chemical vapor deposition (PECVD process)). Elemental arsenic and sulfur (As + S), and arsenic monosulfide and sulfur (As4S4 + S) were used as initial substances. In parallel, the As-S bulk samples were synthesized by “traditional” melting of the initial substances in the evacuated quartz ampoule from the same precursors. The optical properties of the bulk samples were compared. The exhausted gas mixtures were analyzed to clarify the difference in carbon impurities content. 3D laser ultra microscopy was used to determine the content of heterophase inclusions in the samples.

Comparison of optical properties and impurities content of Ge-Sb-S-I glasses prepared by different methods

Bulk samples of Ge-Sb-S-I chalcoiodide glasses of different compositions were prepared by plasma enhanced chemical vapor deposition (PECVD). GeI4, SbI3 and elemental sulfur were the initial substances. Impurities content, optical, and structural properties of the samples were studied. The data obtained were analyzed and compared with the properties of the bulk samples prepared by interaction of the same initial substances into reactive-distillation column at 650°C. The dependence of optical properties of the glasses on preparation technique was discussed.

A study of silicon tetrafluoride reduction with hydrogen in radiofrequency discharge

The process of plasma-chemical conversion of silicon tetrafluoride in a radiofrequency (13.56 MHz) discharge has been studied. The dependence of the yield of silicon on the specific energy input and the H2/SiF4 molar ratio has been examined in the pressure range of 0.1–0.3 Tort. The maximum yield of silicon is 60%, and the optimal specific energy consumption is 44.6 MJ per mole of Si. A mechanism has been proposed for the plasma-assisted reduction of silicon tetrafluoride under the given experimental conditions.

Investigation of the composition-structure-property relationship of As x Te 100 − x films prepared by plasma deposition

AsxTe100-x amorphous films of different chemical content were prepared by Plasma-Enhanced Chemical Vapor Deposition (PECVD). For the first time the optical properties of As-Te chalcogenide materials have been measured in UV-VIS-IR ranges (from 0.2 to 25μm) for a very wide range of chemical compositions (20-80at.% As). As-Te films have been tuned from 0.80 to 1.10eV. The IR results obtained have been juxtaposed with the Raman spectroscopy findings to establish the correlation between optical and structural properties of the materials developed. Reversible and irreversible changes in the phase composition of the As-Te films under annealing of the surface by laser irradiation have been demonstrated and studied. In order to determine the potential areas of application of the prepared As-Te films the thermal and photo sensitivity has been also investigated.

Catalytic effects of electrode material on the silicon tetrachloride hydrogenation in RF-arc-discharge

A silicon tetrachloride reduction in RF-arc-discharge (40.86 MHz) has been experimentally studied. The electrode material significantly affects the composition of the chlorosilanes in the gas phase at the outlet of the reactor which may be attributed to high and at the same time different catalytic activity of Cu, Ni, Nb, and Zr metals belonging to the transition of d-elements and W f-elements of the periodic table. The corrosion has been observed on the electrodes with the formation of chlorides of Cu, Ni, Nb, Zr, and W metals. In the system formed by two electrodes and plasma there are three main reactive regions in which the recovery of silicon tetrachloride by hydrogen at different flows is conducted independently from each other. The analysis of exhaust gases, chemically active plasma and condensed phase by emission-spectroscopy and GCMS spectrometry made it possible to propose the mechanism of formation of observed intermediate species and final products. On the basis of the obtained results we can conclude that this type of RF-plasma discharge includes two mechanisms of plasma chemical reactions: one with the participation of active particles formed in plasma and one initiated by the catalytically-active surface of the electrode.

A new reverse mode light shutter from silica-dispersed liquid crystals

ABSTRACT Nanoparticle dispersions in liquid crystalline materials at low concentrations allow both investigating the formation of defects in liquid crystal (LC) and enhancing the light-scattering properties of LC optical devices. Reverse mode LC dispersions are LC devices, which look like transparent in their OFF state, when no electric field is applied, and opaque in their ON state. In this paper, a new reverse mode device, formed by a dispersion of a LC mixture in a silica nanoparticle crosslinked network, is presented. The morphology and the electro-optical properties of these silica nanoparticle/LC composites were investigated for two different LC mixtures with a negative dielectric anisotropy. The observed transmittances and relaxation times were found to depend strongly on the silica amount and chemical–physical properties of LC used in the sample preparation. GRAPHICAL ABSTRACT

Structure and optical properties of PECVD-prepared As-Se-Te chalcogenide films designed for the IR optical applications

For the first time films of the As-Se-Te (15≤As≤40, 30≤Se≤65, 5≤Te≤30) chalcogenide system have been prepared by Plasma-Enhanced Chemical Vapor Deposition (PECVD) at low pressure (0.1 Torr). RF (40 MHz) inductively coupled non-equilibrium plasma discharge has been chosen as the initiator of chemical interaction between precursors. Elemental As, Se, and Te of high-purity were used as the initial substances. High-pure argon was utilized as career gas as plasma feed gas. The obtained chalcogenide planar materials have been studied in terms their physical-chemical properties. The films were modified by continuous and femtosecond laser irradiation.

Thin phase tailoring of As-Te phase change materials

The possibility of usage of Plasma-Enhanced Chemical Vapor Deposition (PECVD) has been demonstrated in terms of its effectiveness for preparation of As-Te chalcogenide films of different chemical and phase composition. The samples were synthesized via direct interaction of arsenic and tellurium vapors into low-temperature non-equilibrium RF (40 MHz) plasma discharge at reduced pressure. Phase and structural evolution of AsxTe100−x films, (where x = 31, 35, 38, and 49), based on equilibrium coexistence of two phases (AsTe and As2Te3) and implemented by gradual change of deposition parameters has been carried out. The variable parameters were as the ratio of the initial substances in the gas phase as the temperature and the electron density in the plasma discharge. The films obtained have been also modified by laser irradiation with the wavelength of 632.8 nm. A possible mechanism of phase modification has been proposed and discussed.

2D-layered As-S chalcogenide material with strong structural luminescence

The novel physical properties of two-dimensional and layered “beyond graphene” chalcogenide materials suggest a strong base to study new fundamentals underlying condensed matter physics. Among these materials layered arsenic monosulfide is a key to advancing 2-D photosensitive devices such and quantum computer. Here we demonstrated the synthesis of two dimensional arsenic monosulfide (As4S4) via interaction of elemental arsenic and sulfur in low-temperature non-equilibrium plasma discharge at low pressure. Moreover, we assume that plasma chemical vapor deposition is the one is the most promising method of tailoring of 2-D materials due to ceteris paribus the existence of two additional implements - temperature and concentration of electrons in plasma discharge. The optical and structural properties of the films were investigated. The data were analyzed and compared with the same obtained for thin films, prepared by different techniques. The strong structural luminescence phenomenon is observed. The possible mechanism formation of thin film structure was suggested.