STRUCTURAL-PROPERTIES OF HETEROEPITAXIAL C-60 FILMS ON CAF2(111)

Epitaxially grown C60 films on CaF2(111) substrates have been studied by reflection high-energy electron diffraction at deposition temperatu res of 30-300-degrees-C and average thicknesses of 1-50 nm. At these t emperatures and thicknesses, C60 forms an incommensurate overgrowth of fcc-stacked hexagonal layers with a characteristic nearest-neighbor s pacing of 0.99 nm. Deposition temperatures below 150-degrees-C result in unidirectional growth in accordance with the crystallographic direc tions of the substrate. Higher deposition temperatures, however, resul t in two equivalent, rotated domain orientations characterized by a si gnificantly lower degree of lattice mismatch (3% versus 16% for the un idirectional arrangement). The C60 films grown at high temperature pro duce brilliant reflection patterns indicating a high degree of long-ra nge order, uniformity and flatness.