Three-dimensional structures formed with C60 and amorphous silicon -: a feasibility study on the formation of a composite material

The co-deposition of silicon and C-60 leads to the formation of a composite material, where the concentration of the components can be controlled via the respective particle fluxes. Information on the composition and electronic properties of the thin layers is obtained by photoelectron spectroscopy in the ultraviolet (UPS) and X-ray regime (XPS), while transmission electron microscopy (TEM) was employed for selected samples. The C-60 cages remain intact upon deposition and are embedded in an amorphous silicon (a-Si) matrix. The interaction between the Si and C-60 leads to a shift of all C-60-related spectral features and pinning of the Fermi level at the internal C-60-a-Si heterojunction and the valence band offset (the energy difference between the valence band maxima of the two components) is about 1.0 eV. The electronic properties at the internal C-60-a-Si interface are equivalent to a 2D layer system and independent of the thin film composition. The composite material is highly stable LIP to a temperature of 700 degreesC, when the fullerenes break down and react completely with the a-Si matrix to form SiC. The presence of small SiC crystallites embedded in ail a-Si matrix is confirmed with TEM. (C) 2002 Elsevier Science B.V. All rights reserved.