Desorption of Physisorbed Molecules from the Sapphire Surface by Yttrium–Aluminum Garnet Laser Second-Harmonic Radiation

Energy fluence dependences for the laser-enhanced desorption of physisorbed NO, SO₂, CO₂, NH₃, and C₆H₆molecules from the sapphire surface by second-harmonic radiation of a pulse neodymium-doped yttrium–aluminum garnet (YAG) laser were experimentally studied. It was shown that the one-photon absorption of radiation at the second-harmonic wavelength ( = 532 nm) by adsorbed NO molecules was so low that their desorption was accomplished via two-photon absorption. Nonlinear energy fluence dependence with a nonlinearity index of greater than 4 was observed for polyatomic molecules. The desorption of these molecules did not occur at the YAG laser emission wavelength ( =1064 nm), thus suggesting that the long-wavelength edge of their one-photon absorption lies within the range 1064–532 nm.     

Cubical equations of state for predicting the phase equilibria of poorly studied substances

A new procedure for determining the coefficients of the Peng-Robinson equation of state is proposed, for which a minimum of information is required. It is shown that using the Morachevskii complexity factor of molecular interaction in the algorithm for calculating the saturation vapor pressure of substances enables us to study the parameters of the vapor-liquid equilibria of substances with various polarities. Based on our validation of the procedure for determining the coefficients of the Ping-Robinson equation, it is concluded that the values for the saturation vapor pressure of halide derivatives of hydrocarbons calculated from tabular reference data agree satisfactorily in practice.     

Growth kinetics of epitaxial layers of gallium phosphide by temperature-gradient zone recrystallization

A study is made of the dependence of the growth rate of epitaxial layers of gallium phosphide under conditions of temperature-gradient zone recrystallizatton on the thickness of the zone and the temperature. The coefficient of diffusion of phosphorus into gallium is calculated, and also the rate of change of the phosphorus concentration in the zone due to vaporization, the activation energies of the diffusion and vaporization processes, and also the atomickinetic coefficients of the crystallization process.     

Consistency of crystal-lattice parameters and thermalexpansion coefficients in five-component heterostructures based on compounds AIIIBV

The possibility of expansion of the limits of variation in the width of the forbidden band in five component solid solutions of compounds A^IIIB^V with consistency of crystallattice parameters and thermal-expansion parameters of the binary substrate and epitaxial layer is analyzed. Possible regions, and the corresponding character, of variation in composition in five-component solid solutions of compounds A_IIIB^V with simultaneous consistency of the crystal-lattice parameters and thermal-expansion coefficients with the binary substrates are identified.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 59–64, January, 1989.     

Breakdown voltage of p-n-junctions obtained by zone melting with a temperature gradient using linear zones

The breakdown voltage of planar p-n-junctions produced in plates of n-type silicon by zone melting with a temperature gradient using linear aluminum zones have been investigated. It is shown that a general the breakdown voltage of such p-n-junctions varies in the direction of motion of the zone, due to the variable conditions under which the p-n-junction is formed. A method of calculating the breakdown voltage along the p-n-junction perpendicular to the semiconductor plate is described. This method enables the necessary conditions for producing p-n-junctions with the same breakdown voltage to be chosen. The theoretical results are confirmed experimentally.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, Vol. 12, No. 1, pp. 91–95, January, 1969.     

Water treatment to remove acid and basic dyes by biosorption on polysaccharide composites

A composite material based on cross-linked cationic starch and sodium alginate was synthesized and studied. The composite is an effective biosorbent for removing various types of synthetic dyes from water. The influence exerted on adsorption of a basic dye (Methylene Blue) and an acid dye (Methyl Orange) by temperature, pH, solution ionic strength, and biosorbent amount was examined, and the dye adsorption kinetics was studied. The adsorption isotherms were analyzed using various models of sorption equilibrium.     

Possibility of surface plasmon-polaritons amplification by direct current in two-interface systems with 2D Bragg structure on the surface

The method for calculation of the local field factor that describes electrodynamical properties of three-layered systems with 2D photonic crystal is proposed. Analytical calculations are performed in the frame of Green function method on the base of the effective susceptibility concept. The possibility of surface waves amplification by direct electrical current in the systems under consideration is studied. Numerical analysis clearly proves the presence of convective instability. It means that three-layered systems can be considered as a surface waves’ amplifier. Because of periodical structure the phase synchronism domain lies in the range of entirely accessible in practice values of wave vector and frequency. The experimental setup and real systems parameters for observation of surface waves amplification effect are discussed.     

Effect of growth conditions on formation of grain boundaries in epitaxial silicon layers

The formation of grain boundaries of the general type, along with small-and large-angle symmetric grain boundaries with the 〈 〉 axis in the epitaxial layers grown onto bicrystal substrates by the method of thermal migration has been studied. The solvent was aluminum. It is shown that if the grain boundaries in the epitaxial layer are tilted to the crystallization front or if there is a temperature gradient tangential to this front, their orientation differs from their orientation in the substrate. The large-angle symmetric boundaries are more stable than the boundaries of the general type. The grain-boundary energy and rotation moment of large-angle symmetric boundaries are evaluated.