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      Spinodal decomposition ranges of In x Ga1-x Ny P1-y and GaAs x Ny P1-x-y alloys

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          Abstract

          We have described spinodal decomposition ranges of GaP-rich GaAs x NyP1-x-y and In x Ga1-x NyP1-y alloy lattices matched to the GaP (001) substrate up to temperatures of 600°C. Transformation of bonds, strain and coherency strain energies at the phase separation are taken into account. The alloys are considered to be strictly regular solutions. The strain energies of the alloys were calculated with the interaction parameters estimated by the valence force field model. It is shown that GaAs xNyP1-x-y, having one mixed sublattice, are more promising from the spinodal decomposition standpoint than In xGa1-xNyP1-y, with two mixed sublattices.

          Translated abstract

          Describimos las regiones de descomposición espinodal de las aleaciones GaAs xNyP1-x-y y In xGa1-xNyP1-y crecidas sobre el substrato GaP (001) hasta una temperatura de 600°C. Se tomó en cuenta la transformación de los enlaces, las energías de deformación y de deformación de coherencia en la separación de fase. Las aleaciones se consideran como soluciones estrictamente regulares. Las energías de deformación de las aleaciones se calculan con los parámetros de interacción estimados por el modelo de campo de fuerza de valencia. Se muestra que las aleaciones que tienen una subred de mezclado GaAs xNyP1-x-y, son más prometedoras desde el punto de vista de la descomposición espinodal que las aleaciones con dos subredes de mezclado In xGa1-xNyP1-y.

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          Photo-induced charge transfer across the interface between organic molecular crystals and polymers

          Photo-induced charge transfer of positive and negative charges across the interface between an ordered organic semiconductor and a polymeric insulator is observed in the field-effect experiments. Immobilization of the transferred charge in the polymer results in a shift of the field-effect threshold of polaronic conduction along the interface in the semiconductor, which allows for direct measurements of the charge transfer rate. The transfer occurs when the photon energy exceeds the absorption edge of the semiconductor. The direction of the transverse electric field at the interface determines the sign of the transferred charge; the transfer rate is controlled by the field magnitude and light intensity.
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            Why do ultrasoft repulsive particles cluster and crystallize? Analytical results from density functional theory

            We demonstrate the accuracy of the hypernetted chain closure and of the mean-field approximation for the calculation of the fluid-state properties of systems interacting by means of bounded and positive-definite pair potentials with oscillating Fourier transforms. Subsequently, we prove the validity of a bilinear, random-phase density functional for arbitrary inhomogeneous phases of the same systems. On the basis of this functional, we calculate analytically the freezing parameters of the latter. We demonstrate explicitly that the stable crystals feature a lattice constant that is independent of density and whose value is dictated by the position of the negative minimum of the Fourier transform of the pair potential. This property is equivalent with the existence of clusters, whose population scales proportionally to the density. We establish that regardless of the form of the interaction potential and of the location on the freezing line, all cluster crystals have a universal Lindemann ratio L = 0.189 at freezing. We further make an explicit link between the aforementioned density functional and the harmonic theory of crystals. This allows us to establish an equivalence between the emergence of clusters and the existence of negative Fourier components of the interaction potential. Finally, we make a connection between the class of models at hand and the system of infinite-dimensional hard spheres, when the limits of interaction steepness and space dimension are both taken to infinity in a particularly described fashion.
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              Caustic activation of rain showers

              We show quantitatively how the collision rate of droplets of visible moisture in turbulent air increases very abruptly as the intensity of the turbulence passes a threshold, due to the formation of fold caustics in their velocity field. The formation of caustics is an activated process, in which a measure of the intensity of the turbulence, termed the Stokes number St, is analogous to temperature in a chemical reaction: the rate of collision contains a factor exp(-C/St). Our results are relevant to the long-standing problem of explaining the rapid onset of rainfall from convecting clouds. Our theory does not involve spatial clustering of particles.
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                Author and article information

                Journal
                rmf
                Revista mexicana de física
                Rev. mex. fis.
                Sociedad Mexicana de Física (México, DF, Mexico )
                0035-001X
                April 2007
                : 53
                : 2
                : 114-119
                Affiliations
                [01] México D. F. orgnameIPN orgdiv1Escuela Superior de Ingeniería Mecánica y Eléctrica México
                [02] México D. F. orgnameIPN orgdiv1CINVESTAV orgdiv2Departamento de Ingeniería Eléctrica México
                Article
                S0035-001X2007000200005 S0035-001X(07)05300200005
                f661ef5a-8844-4610-93d8-998612353741

                This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

                History
                : 28 September 2006
                : 16 March 2007
                Page count
                Figures: 0, Tables: 0, Equations: 0, References: 33, Pages: 6
                Product

                SciELO Mexico

                Categories
                Research

                descomposición espinodal,Aleaciones cuaternarias,spinodal decomposition,Quaternary alloys

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