Nucleation, growth and transformation of amorphous and crystalline solids condensing from the gas phase

Abstract

The condensation of solids was investigated from the initial nucleation stage through continuous film growth, using evaporation and high-energy ion-beam sputtering. At all stages the kinetics of the nucleation process and the structural characteristics of the condensed phase (glassy, polycrystalline and monocrystalline) were defined. Although many condensates were explored, the specific system discussed is germanium condensing on a variety of amorphous and crystalline substrates.

The kinetic behavior observed in crystalline deposits was found consistent with the accepted atomistic model for nucleation. This allowed determination of such nucleation parameters as: the activation energies of surface diffusion,Q _d and adsorption,Q _ad ,the critical nucleus size,n ^*, and others. Values of such parameters were found to be systematic functions of the kinetic energy and flux of incident particles and of the type and temperature of the substrate.

Two flux and temperature dependent structural order transitions were observed in the very initial nucleation stages and found to coincide with corresponding transitions inn ^*. Correlation was also established between these transitions and two structural transitions occurring during continuous film growth. This was aided by the occurrence of all four transitions in intermediate condensation stages, i.e. prior to coalescence of nucleation clusters into continuous film.

All results were very distinctly affected by the vapor state of the adsorbates, implying considerable correlation between condensation on solid surfaces and in a vapor.