Initial phase of C60 deposition on Si(100) and GaAs(100) studied in situ by Raman spectroscopy

C-60 was evaporated from a Knudsen cell onto the (100) surfaces of Si and GaAs at room temperature under ultra-high vacuum conditions. The deposition process was monitored in situ by Raman spectroscopy in the spectral region 1350-1600 cm(-1), where the most intense Raman features of C-60 are observed. In the initial stage of deposition on Si(100), the Raman spectra show a peak at 1469 cm(-1) which is soon replaced by another one at 1458 cm(-1). The same is observed for deposition on GaAs(100), where this effect is even more pronounced. The first peak is assigned to the intrinsic pentagonal pinch mode of pure C-60, while the second has been reported as the signature of the photoinduced polymerization of C-60 which is formed under light irradiation with sufficient intensity (similar to 10 W/cm(2)). Although the intensity in the monitoring experiment was as high as 60 W/cm(2), the deposited C-60 film appears not to be polymerized at sufficiently low coverages. From the Fabry-Perot interference modulation of the Raman scattering intensity, the growth rate of the C-60 film is calculated. The correlation with the evolution of Raman spectra reveals a critical thickness of about 15 nm for the onset of polymerization of the C-60 on both Si(100) and GaAs(100) under irradiation. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.