Nucleation and initial growth of In deposited on Si3N4 using low-energy (≤300 eV) accelerated beams in ultrahigh vacuum

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Abstract
Transmission electron microscopy has been used to investigate the nucleation and initial stages of growth of In deposited on Si3N4 from accelerated partially ionized beams in ultrahigh vacuum (UHV). The substrates were thin, electron transparent windows and the number density as well as the size and spatial distributions of the islands were determined as a function of ion energy and nominal film thicknesses t between 1.5 and 12 nm. A UHV-compatible ion source provided In beams in which, for these experiments, the ionized fraction was either 0%, 36%, or 42% and the acceleration energy E ranged from 150 to 300 eV. A quartz-crystal microbalance was used to estimate the amount of material lost by sputtering and to determine the net deposition rate. Comparing results obtained at nearly constant values of t, the use of accelerated beams was shown to alter the film nucleation kinetics leading to a progressive shift towards larger average island diameters with increasing E. The rate of secondary nucleation also decreased giving rise to much more uniform island size distributions in films grown from accelerated beams. These results are discussed in terms of ion-irradiation-induced dissociation of small clusters and enhanced adatom surface diffusion.

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