Modeling of large cluster synthesis

Abstract

The original idea of the ionized cluster beam thin film deposition technique was based upon producing, ionizing and accelerating beams of atoms clusters from vaporized material onto a substrate in a vacuum environment using a supersonic jet source. However, the conditions and nozzles for this cluster synthesis found so far require rather high stagnation pressures (more than 1 atm) which is impractical for many materials with lower vapor pressures than, for example, zinc. Simulation of this process using classical nucleation theory and one-dimensional gas flow equations is described here. This approach is an extension of previous methods used for simulation of condensation of water vapor during supersonic expansion in nozzles and the simulation mechanism of large clusters from vaporized solid materials. Zinc cluster sizes predicted by the model are in qualitative and quantitative agreement with our experimental results. Simulation results are discussed in terms of the best nozzle geometry which will result in larger clusters at a lower stagnation pressure. Novel nozzle designs simulated in this work show that clusters may be formed at lower pressures which would extend the method to a much wider range of materials. Thus development of such new nozzles for use at lower pressure and temperature would significantly impact this method.