Study on growth of C₆₀ molecules on GaAs(001) substrate by scanning tunneling microscopy

We have studied the growth of C₆₀ film on GaAs(001) 2 × 4-β phase surface epitaxially grown by MBE. Due to the delicate equilibrium between the interaction of C₆₀ molecules and the interaction of C₆₀ molecule with the substrate, the toplayer of C₆₀ film, unlike that on the metal and silicon substrate, shows a non-close packed structure. The facet structure of C₆₀ film exhibits that the top-two layers are hcp but the others are fee, which implies an existence of the phase-transition from hcp to fee structure in the film growth. The measurement results that the lattice constant of fee is 1.13 nm, larger of 13% than that of C₆₀ crystal, and hcp is not ideal which is compressed along c-axis. The strain in C₆₀ film and the minimum of the total energy should be responsible for the existence of the phase-transition. On GaAs(001)-c(4 × 4) surface, the structure of C₆₀ film shows fcc(111) surface and the film grows in three-dimensional mode which is quite different from that on other substrates.