Simulação da cinetica do crescimento de pontos quanticos semicondutores em vidros

AUTOR(ES)
DATA DE PUBLICAÇÃO

2000

RESUMO

The growth kinetics of pontos quânticos (QD) in a vitreous matrix is important because its linear and non linear optical properties depends on their sizes and dispersion. QD s are fabricated by melting the semiconductors elements together with the vitreous matrix. After melting, the glass is submitted to a thermal treatment to lower temperatures, (500- 600°C) in which the semiconductors elements acquire enough mobility for rearrange themselves in the form of a QD. Because the absorption and emission of atoms in the surface of the QD s are much faster than their diffusion in the matrix, there is an equilibrium concentration in its surface, which depends on the QD s radius. Growth will happen when this concentration is smaller than the dispersed elements concentration in the matrix and dissolution in the opposite case. While there is no overlap of the concentration field of two neighbor QD s, the growth of each one of them is independent of the presence of the other ones. When the overlap begins starts a competition for the dispersed atoms in the matrix with advantage for the larger QD s, a process known as coalescence. In coalescence stage the size distribution increases, because the smaller QD s redissolve, decreasing in size and liberating atoms to the glass matrix that will feed the growth of the largest ones. Once our objective is to obtain the narrowest size distribution we should stop the growth at this point. In this work we solved the diffusion equation subject to certain conditions at a boundary that changes with time. Using a mathematical technique called Green s double potencials, instead of the conventional Green s function for a fixed boundary, the problem was transformed in a problem of an integro-differential equation for the boundary. Once we find the time evolution of the boundary we obtain the diffusion field around the QD

ASSUNTO(S)

reatores nucleares - cinetica vidros de spin crescimento poços quanticos

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