Self-excited oscillatory regimes in the growth of thin films from a multicomponent vapor: Dynamics and control

Abstract

A model system describing the nucleation of films from a multicomponent vapor with allowance for chemical reactions between different components in the initial phase is investigated in detail. It is shown that the condensation of thin films can proceed by different avenues, depending on the values of external parameters such as the temperature or the precipitation rate of particles of the component that limits the chemical reaction. In particular, low precipitation rates are characterized by a stable condensation regime, in which any deviations from equilibrium die out. At medium precipitation rates the phase transition takes place in a self-excited oscillatory regime corresponding to a stable limit cycle. Finally, at high precipitation rates the stable limit cycle breaks up, and the new phase usually condenses in a sawtooth (accretion) regime. A procedure is developed for controlling the given oscillatory processing by judicious time variation of the external parameters. The investigated system is found to have a special kind of memory in that for external parameters with identical values but different histories the films condense differently; even a slight difference in the past behavior of the external parameters can lead to different precipitation regimes. It is concluded that these memory effects are in fact responsible for the poor reproducibility encountered in some cases of experiments on film growth utilizing chemical reactions.