Annealing Temperature Dependence of C60 on Silicon Surfaces: Bond Evolution and Fragmentation as Detected by NEXAFS

We report a near-edge X-ray absorption spectroscopy (NEXAFS) study of the C K-edge of C-60 molecules interacting with Si(100) and Si(111) surfaces. Annealing the C-60/Si systems at 1050K induces fullerene fragmentation and leads to SiC nucleation. Tuning the probing depth and studying polarization dependence, the NEXAFS results shed light on the evolution of the molecular states after thermal treatment, up to the fullerene fragmentation and SiC formation. The NEXAFS spectra of a single layer of C-60 deposited at 670K onto both surfaces show a strong C-60-substrate interaction. A polarization dependence of the spectra can be detected; this behaviour is similar to the results obtained on C60 covalently chemisorbed on A1 surfaces. We find, for both substrates, that fullerene fragmentation starts at the C-Si interfaces, involving the C atoms lying close to the Si substrate, implying an increase of the number of C-Si bonds at the fragmentation stage.