SCANNING-TUNNELING-MICROSCOPY AND SPECTROSCOPY STUDIES OF C-70 THIN-FILMS ON GOLD SUBSTRATES

Thin films of high-purity C70 were deposited on polycrystalline gold surfaces and studied by scanning tunneling microscopy (STM) in ultrahigh vaccum. Topographic images reveal initial-stage growth patterns ranging from close packing with a twofold symmetry to random stacking. C70 molecules appear oval-shaped, in agreement with the proposed D5h structure Of C70. Static orientational disorder is observed in both close-packed and random-stacked regions. The adsorbed C70 molecules show the highest STM contrast at bias voltages well below the HOMO-LUMO gap voltage. These and scanning-tunneling-spectroscopy results are discussed and compared with those obtained previously on similarly prepared C60 thin films.