The well-known herringbone reconstruction of the Au (111) surface consists of a regular array of line dislocations, which may act as nucleation sites for metals or organic materials [1, 2]. In this study, we reveal for the first time the selective adsorption of C60 molecules at the elbow sites on Au(111). Deposition of submonolayer of C60 molecules onto a Au(111) surface at room temperature usually leads to the co-existence of three structures [3]. In recent experiments we observed site-selective adsorption of individual C60 molecules, which show an obvious preference for nucleating at the elbows of the x type dislocation lines. As coverage increases, compact C60 islands are observed to form on the FCC regions between two neighboring C60 molecules. Interestingly, only about 50% of the elbow sites are active in mediating the formation of these nanometre sized C60 islands. The observed site-specific adsorption and nucleation is interpreted based on findings from high resolution STM imaging which reveals the atomic scale structure of the surface defects around the elbow sites.

 

Another site-selective adsorption phenomenon was observed after depositing C60 moleules onto parallal gold stripes (gold-fingers) [4], which were fabricated from monoatomic gold steps by high tunnelling current STM scanning. These gold-fingers have different kinds of microfacet ({111} and {100}) on their two parallal steps. The C60 moleules prefer to adsorb on the less stable {100} steps and form close packed islands, while the {111} steps only have their FCC regions been occupied by the molecules. Besides the energy difference, the different underlying herringbone patterns of the two steps may also be a key factor leading to site-selective adsorption to the gold fingers.

 

References:

1. I. Chado et al., Appl. Phys. Lett. 226 (2004) 178.

2. T. Yokoyama et al., Nature 413 (2001) 619.

3. X. Zhang, R.E. Palmer and Q. Guo, Surf. Sci. 602 (2008) 885.

4. Q. Guo, F. Yin and R.E. Palmer, Small 1 (2005) 76-79.