STUDY ON GROWTH OF C 60 MOLECULES ON GaAs(001) SUBSTRATE BY SCANNING TUNNELING MICROSCOPY

We have studied the growth of C 60 film on GaAs(001) 2×4-β phase surface epitaxially grown by MBE.Due to the delicate equilibrium between the interaction of C 60 molecules and the interaction of C 60 molecule with the substrate,the toplayer of C 60 film,unlike that on the metal and silicon substrate,shows a non-close packed structure.The facet structure of C 60 film exhibits that the top-two layers are hcp but the others are fcc,which implies an existence of the phase-transition from hcp to fcc structure in the film growth.The measurement results that the lattice constant of fcc is 1.13 nm,larger of 13% than that of C 60 crystal,and hcp is not ideal which is compressed along c-axis.The strain in C 60 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 C 60 film shows fcc(111) surface and the film grows in three-dimensional mode which is quite different from that on other substrates.