Collapse of a mass-selected C 60ion beam collided on crystal surfaces

Abstract

Mass-selected C₆₀ ion beams were accelerated to different kinetic energies and deposited on the (0001) surface of highly oriented pyrolytic graphite and the (111) surface of a gold single-crystal. Scanning tunnelling microscopy (STM), Raman spectroscopy and laser desorption mass spectrometry were used to characterize the deposited species. The STM images showed that C₆₀ molecules colliding on the surface were not dissociated, but their cages collapsed and deformed to planar structures. The Raman spectra of the deposited species are different from the spectral feature of fullerene, and they were similar to that from the glassy carbon instead. The deposited species were desorbed and mass analysed. Both positive and negative C₆₀ ions were observed in the desorption mass spectra, confirming that the species collapsing on the solid surface were the C₆₀ clusters. It was also found that the collision energy resulting in the collapse of the cage structure of C₆₀ was around 400 eV, and that fragmentation of the collapsed species does not occur if the energy does not exceed 1 kV.