Annealing temperature dependence of C60 on silicon surfaces: bond evolution and fragmentation as detected by NEXAFS

Abstract

We report a near-edge x-ray absorption spectroscopy (NEXAFS) study of the C K-edge of C60 molecules interacting with Si(100) and Si(111) surfaces. Annealing the C60/Si systems at 1050 K 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 C60 deposited at 670 K onto both surfaces show a strong C60-substrate interaction. A polarization dependence of the spectra can be detected; this behaviour is similar to the results obtained on C60 covalently chemisorbed on Al 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.