Binary molecular layers of C-60 and copper phthalocyanine on Au(111): Self-organized nanostructuring

The binary molecular system of C-60 and copper phthalocyanine(CuPc) molecules has been investigated by scanning tunneling microscopy (STM) at room temperature and at 50 K. As substrate Au(111) was chosen. When C-60 and CuPc molecules are sequentially deposited, it is found that well-ordered domains of both molecules may coexist simultaneously Hence hexagonal ordering of C-60 and quadratic ordering of CuPc is observed side by side but no ordered mixed layer of both molecules or heteroepitaxy from one molecule on the other is found. Instead the boundaries of the CuPc domains are often decorated by C-60 molecules and for a particular choice of parameters, with regard to the film preparation, individual CuPc molecules may adsorb on top of a C-60 layer. The interaction with the underlying C-60 layer permits the molecules to perform a localized, hindered rotation. At room temperature the hopping frequency is so high that only the time average of the rotation is seen by STM while at 50 K the rotation is frozen and the CuPc molecule is trapped in one definite position.