Atomistic Mechanisms for the Nucleation of Aluminum Oxide Nanoparticles

A predictive
model for nanoparticle nucleation has not yet been successfully achieved.
Classical nucleation theory fails because the atomistic nature of
the seed has to be considered. Indeed, geometrical structure as well
as stoichiometry do not always match the bulk values. We present a
fully microscopic approach based on a first-principle study of aluminum
oxide clusters. We calculated stable structures of AlxOy and their associated
thermodynamic properties. From these data, the chemical composition
of a gas composed of aluminum and oxygen atoms can be calculated as
a function of temperature, pressure, and aluminum to oxygen ratio.
We demonstrate the accuracy of this approach in reproducing experimental
results obtained with time-resolved spectroscopy of a laser-induced
plasma from an Al2O3 target. We thus extended
the calculation to lower temperatures, i.e., longer time scales, to
propose a scenario of composition gas evolution leading to the first
alumina seeds.