Abstract
A method for quantitative investigation of kinetics of nucleation and growth from the vapour on microseeds suspended in a inert gas flow has been developed. If the supersaturation is small, this method enables one to study the formation of single nuclei. The rates of naphthalene crystal nucleation on anthracene in certain temperature and vapour supersaturation ranges have been determined. Qualitative analysis of the experimental results has evidenced naphthalene crystal nucleation at steps and kinks on the anthracene crystal surface; these nuclei are formed from a polymolecular adsorption layer. The nuclei-substrate and nuclei-polymolecular adsorption layer interface energies as well as the activation energy for admolecule transition through the nuclei-polymolecular adsorption layer interface in the naphthalene-anthracene system have been estimated. The effect of UV radiation of the semiconductor substrate (anthracene) on nucleation of certain molecular crystals on them has been investigated. It has been found that under action of UV irradiation the nucleation rate increases as compared to crystallization in the dark. This holds true for substances whose molecules are electron acceptors with respect to the substrate crystal. In this case the neutral donor-acceptor complexes formed by the admolecules of the condensed substance can, prior to nucleation, capture the free carriers arising from dissociation of excitons formed by light absorption. Therefore, local charges appear on the substrate surface, and the presence of charges results in the increase in the nucleation rate. Experimental data according to theory [14] have shown that charges giving rise to the nucleation have a value of the ordr of an electron charge.
Published Version
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