Exclusion of PCBM molecules from C60 domain on Au (111)

To investigate the influence of asymmetric intermolecular interactions of phenyl-C-61-butyric acid methyl ester (PCBM), the behaviors of C-60 and PCBM molecules deposited on the same Au (111) surface were observed by scanning tunneling microscopy under ultra-high vacuum conditions. After annealing, the system formed polygonal islands, the peripheries of which were occupied by PCBM molecules having their functional groups directed outside of the island, whereas the inside was composed of hexagonally packed C-60 molecules. Such exclusion of PCBM from the C-60 domain is attributed to asymmetric intermolecular interactions of PCBM: namely, the cage of PCBM has an affinity for C-60 and the cages of other PCBM owing to van der Waals interactions. However, the functional groups of PCBM prevented C-60 from attaching. The PCBM molecules at the periphery pinned the island's edges along the stripes of a herringbone reconstruction region owing to the weak affinity of the tail for the fcc region to determine the shape of the islands. (C) 2020 The Japan Society of Applied Physics