Heteroepitaxial Growth of Epitaxial C 60 -Thin Films on Mica(001)
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S. Henke, KI H. Thilrer, S. Geier, B. Rauschenbach, B. Stritzker, Institut fIr Physik, Universitlt Augsburg, D-86135 Augsburg ABSTRACT On mica(001) thin C6o-films are deposited by thermal evaporation at substrate temperatures from room temperature up to 2250C. The dependence of the structure and the epitaxial alignment of the thin CQo-films on mica(001) on the substrate temperature and the film thickness up to 1.3 jim at a well-defined deposition rate (0.008 nm/s) is investigated by atomic force microscopy and X-ray diffraction. The shape and the size of the CQ 0 -islands, which have an influence on the film quality at larger film thicknesses, are sensitively dependent on the substrate temperature. At a film thickness of 200 rum the increase of the substrate temperature up to 225°C leads to smooth, completely coalesced epitaxial C6o-thin films characterized by a roughness smaller than 1.5 nrm, a mosaic spread Ao) of 0.10 and an azimuthal alignment AA of 0.45'. INTRODUCTION
There is a considerable scientific and technical interest in the growth and structure of epitaxial fullerene thin films. The mechanisms of the growth of the well-known fullerene C6o should be representative for other fullerenes as C70 or C84 and applicable to the growth of well-oriented doped fullerene films via coevaporation and the growth of fullerene precursors for diamond films. The growth of (11l)-oriented epitaxial Co-thin films has been observed previously using mica(001) as a substrate [1,2]. Atomic force microscopy studies [3] have demonstrated that film growth starts with isolated islands. Once the surface has been completely covered, a subsequent layer-by-layer growth has been observed. The quality of the epitaxial alignment of the thin Co-films on mica(001) is sensitively dependent on the sublimation method using different deposition rates (hot-wall-method [4], effusion cell [5], thermal evaporation [6]) and strongly falls off by an increase of the film thickness up to
some Am. It is the purpose of this paper to illustrate the dependence of the structure and the epitaxial alignment of the thin Cw-films on mica(001) on the substrate temperature and the film thickness at a well-defined deposition rate. The deposition rate of 0.008 nm/s has been kept constant, which results in a good epitaxial alignment of the C6o-crystals on mica(001) [7]. Furthermore, the influence of the substrate temperature and the film thickness on the structure and topography of the C2o-films is investigated. EXPERIMENTAL
For sublimation CQ-microcrystalline powders synthesized with a purity of 99.9% and a resistive Ta-crucible were used. Under sublimation conditions the base pressure was in the range of 10-6 Torr. The distance between the Ta-heater and the substrate holder was about 8 cm. The film thickness was measured by a water cooled quartz microbalance thickness monitor placed directly beside the substrate holder. The substrate temperature was varied from room temperature (RT) up to 225TC and the thickness of the films from 10 nm up to 1300 nm. The mica (0
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