Abstract
Many of the established processes in the fabrication of thin films use plasma or ion beam assisted techniques to control film composition and structure. To improve the understanding of the role of low energy ions we investigate the influence of temperature (273-873 K) on the growth of Au clusters, which are deposited on amorphous carbon substrates. The use of a mass selected ion beam facility ...
Abstract
Many of the established processes in the fabrication of thin films use plasma or ion beam assisted techniques to control film composition and structure. To improve the understanding of the role of low energy ions we investigate the influence of temperature (273-873 K) on the growth of Au clusters, which are deposited on amorphous carbon substrates. The use of a mass selected ion beam facility allowed to control the ion energies and afforded a narrow energy distribution. The Au+ energy was adjusted between 320 and 20 eV, a substantial structural modification of the carbon layer surface due to irradiation or annealing can be excluded. The films were characterized with transmission electron microscopy (TEM), and photoelectron spectroscopy (PES) and subjected to equivalent annealing cycles in situ. In the core level PES a dynamic final state effect which leads to a cluster size dependent peak shift was exploited to determine cluster sizes in the subnanometer regime. TEM and PES are established successfully as complementary methods and allow to access the complete size range and implantation depth of the Au ions. Annealing leads to a substantial increase in the number of small clusters, a cluster ripening is only observed towards the end of the annealing cycle. At the highest ion energies of 200 and 320 eV, the initial distribution contains only very small clusters (a few atoms) and the growth proceeds faster for 200 eV. A qualitative model, which considers the particle fluxes within the system, is used to analyze these results and confirms the critical role of the subsurface Au reservoir. The initial ion energy determines the Au implantation depth and controls the Au concentration in the reservoir. The Au concentration then determines the diffusive flux of atoms to the surface and thus drives the nucleation of new, small clusters and controls the growth rate. Only the presence of such a reservoir allows the nucleation of new Au clusters as the annealing temperature is increased. These results indicate pathways to the control of cluster size and impact on the interpretation and control of thin film deposition. (c) 2006 American Institute of Physics.
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