Charged clusters in thin film growth

A cauliflower structure is a granular film composed of spherical particles similar in size, each with numerous nanoscale nodules on its surface. The structure is produced during certain chemical vapour deposition (CVD) processes for diamond and silicon thin film growth. A classical account in terms of atomic unit deposition fails to explain the growth of such a cauliflower structure, as it requires a gas phase of much higher supersaturation than for onset of diffusion controlled growth. Another interesting and somewhat puzzling phenomenon encountered during a diamond CVD process is that while diamond is depositing on a graphite substrate, carbon atoms in the graphite itself are etched away into the vapour phase; that is, experience evaporation. Again, an elementary kinetic barrier mechanism fails to explain such CVD deposition of a less stable diamond phase combined with simultaneous evaporation of a stable graphite phase. In order to account for such puzzling CVD phenomena and others, a theory of charged clusters has been developed over the past decade as a new paradigm for thin film growth. The theory and its applications are reviewed in this work.