In-situ microscopic investigations of the nucleation and growth of C$_{60}$ films on Bi(0001)/Si(111)

Growth of epitaxial C$_{60}$ films on Si is of particular interest for technological reasons. However, strong interaction between the C$_{60}$ molecules and the clean Si induces film growth in the Stransky-Krastanov mode with only local ordering in the first monolayer. Passivation of the Si dangling bonds -- for example with hydrogen -- leads to van der Waals bonding of adsorbates and thus higher degree of crystallinity in C$_{60}$ film, but the true relation between surface properties, and the crystallinity of the fullerene film is not yet fully understood. In this work, C$_{60}$ thin films were grown by UHV deposition on Si(111) substrate covered with thin Bi(0001) passivation layer. Real-time, dark-field low-energy electron microscope (LEEM) investigation of the growth revealed that C$_{60}$ film nucleates in fcc(111) phase, having an epitaxial relation with the Bi(0001) surface. At a growth temperature of $\sim $400K, preferential nucleation of C$_{60}$ at Bi twin boundaries has been detected. Low-energy electron diffraction (LEED) confirmed that film had a single orientation and an excellent crystallinity. The in-plane lattice parameter in the C$_{60}$ films with thickness up to 3ML has been measured to be 10.04 $\pm $ 0.02 A, which is very close to the bulk value of 10.01 A.