Abstract
We have studied the scattering of neutral C 60 molecules from surfaces at the impact energy range of 10–50 eV. The reactive interaction of hyperthermal C 60 with a clean polycrystalline nickel surface was found to be strongly dependent upon surface temperature and C 60 beam dose. Following adsorption and decomposition of C 60 on the substrate, two different types of carbon overlayer phases were identified. The high temperature (passivated) phase gave rise to direct inelastic scattering in the form of sharply-peaked angular and energy distributions. The scattering dynamics of C 60 molecular beams from this surface was probed by high resolution angular and energy distributions and vibrational energy measurements at various impact energies, surface temperatures and scattering and incidence angles. The scattered energy scales linearly with impact energy and kinetic energy losses vary with scattering angle from ∼85% to ∼40% (peak values). We have developed an improved method for measuring average vibrational energy of large polyatomic molecule or cluster and applied it to the surface scattered C 60. Vibrational excitation was found to be below 2% of impact energy, showing that C 60 is nearly non-deformable at these collision energies. This value is much lower than estimated before for higher energies C 60 + ion surface scattering. Analyzing the results we find nearly complete decoupling between normal and tangential energy losses. The agreement obtained between model prediction and experiment provides evidence in favor of spherical potential barrier geometry. The tangential losses are described in terms of various models of rotational excitation, and the involvement of translational slip during the scattering process is concluded. The C 60 surface interaction well depth was determined from the scattering results and compared with the measured desorption energy. Our detailed results describe the first real “bouncing” regime for C 60 scattering off surfaces, in agreement with recent molecular dynamics calculation.
Published Version
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