Three-dimensional structures formed with C 60 and amorphous silicon––a feasibility study on the formation of a composite material P. Reinke a, * , P. Oelhafen b , S. Christiansen c a II. Physikalisches Institut, Universit€ atG€ ottingen, 37073 G€ ottingen, Germany b Institut f€ ur Physik, Universit€ at Basel, Klingelbergstr. 82, CH-4056 Basel, Switzerland c Institut f€ ur Werkstoffwissenschaften, Universit€ at Erlangen-N€ urnberg, 91058 Erlangen, Germany Abstract 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 up to a temperature of 700 °C, when the fullerenes break down and react completely with the a-Si matrix to form SiC. The presence of small SiC crystallites embedded in an a-Si matrix is confirmed with TEM. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: Fullerenes; Silicon; Amorphous surfaces; Photoelectron spectroscopy; Surface structure, morphology, roughness, and topography 1. Introduction The present activities in the development of novel materials are dominated by the investiga- tion of smallscale structures and the exploitation of their special properties. The aim of the present study is to establish the feasibility of fullerene in- corporation in a semiconducting matrix (amor- phous silicon) and to investigate the electronic properties of this composite material with photo- electron spectroscopy. While the interaction of fullerenes with different substrates and atoms has been studied intensely [1–12], the incorporation of C 60 in a semiconductor or metal matrix [13–15] is rarely attempted and therefore our knowledge about the synthesis and properties of the com- posite materials is indeed limited. One advantage in the use of fullerenes as em- bedded clusters stems from the fact that the elec- tronic structure of C 60 remains nearly unchanged when progressing from an isolated molecule to the Surface Science 507–510 (2002) 630–635 www.elsevier.com/locate/susc * Corresponding author. Tel.: +49-551-3976; fax: +49-551- 394493. E-mail address: petra.reinke@phys.uni-goettingen.de (P. Reinke). 0039-6028/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S0039-6028(02)01327-4