Structural properties of heteroepitaxial C 60 films on CaF 2(111)

Abstract

Epitaxially grown C 60 films on CaF 2(111) substrates have been studied by reflection high-energy electron diffraction at deposition temperatures of 30–300°C and average thicknesses of 1–50 nm. At these temperatures and thicknesses, C 60 forms an incommensurate overgrowth of fcc-stacked hexagonal layers with a characteristic nearest-neighbor spacing of 0.99 nm. Deposition temperatures below 150°C result in unidirectional growth in accordance with the crystallographic directions of the substrate. Higher deposition temperatures, however, result in two equivalent, rotated domain orientations characterized by a significantly lower degree of lattice mismatch (3% versus 16% for the unidirectional arrangement). The C 60 films grown at high temperature produce brilliant reflection patterns indicating a high degree of long-range order, uniformity and flatness.