Temperature-dependent interaction of C60 with Ge(1 1 1)-c(2 × 8)

We report photoemission and low energy electron diffraction (LEED) data of a C-60 multilayer adsorbed on Ge(111)-c(2 X 8) surface, as a function of annealing temperature. Remarkable changes take place in the valence band (VB) as the temperature is increased. Three phases are revealed, with different LEED patterns, coverages and molecular distance, including a 'bulk-like' C-60 hexagonal single layer, not observed so far, the 3root3 x 3root3R30degrees and root13 x root13R14degrees phases already known from literature. The ultra-violet VB spectra show strong similarities with C-60 adsorbed on Si surfaces, with the splitting of the C-60 highest occupied molecular orbital (HOMO) derived bands into two peaks, due to the C-60 bonding with the substrate. The bond is activated by the temperature and implies molecular deformation. At similar to700 degreesC the C-60 features disappear and, core level photoemission spectra indicate carbon desorption or interdiffusion into the substrate.