Interaction of C60with Clean and Hydrogenated SiC-(3×3) Probed Through the Unoccupied Electronic States

The effect of hydrogenation on the conduction bands of the Si-rich 6H-SiC(0001)-(3x3) reconstruction is studied using inverse photoemission spectroscopy in order to distinguish surface from bulk states. These results are exploited for the comparative study of the interaction of C-60 adsorbed on (3x3) and on hydrogen-terminated (3x3). For the latter, as in the case of hydrogen-terminated Si, C-60 is electronically decoupled from the substrate. Upon annealing a C-60 thick film deposited on hydrogenated (3x3) up to 670 K, there is a hint for a possible hydrogen transfer to the C-60 molecules. The initially physisorbed molecules then adopt covalent bonding with Si, forming the contact layer. Part of the substrate is already found uncovered at this temperature. By further annealing up to 860 K all H atoms have desorbed. Finally, at 1100 K the remaining covalently bound C-60 have desorbed. Unexpectedly, the structural damages caused by H and C-60 deposition and by the successive annealing steps do not prevent a final restoration of the initial (3x3) reconstruction at about 1100 K.