Azobenzene derivatives formed a unique class of photoactive molecules that have the potential for nanoscale optical applications. The self-assembly behaviour of azobenzene molecules adsorbed on Au(111) was observed using scanning tunnelling microscopy. It was found that azobenzene created a surprising variety of surface structures whose commensurability with the underlying Au(111) herring-bone reconstruction was coverage-dependent. Two commensurate molecular chain phases exist in the low-coverage regime, and phase conversion between these structures could be induced using the scanning tunnelling microscopy tip. In the high-coverage regime, incommensurate molecular phases as well as commensurate molecular vacancy ordering were observed. These molecular structures reflected a coverage-dependent competition between molecule-molecule and molecule-substrate interactions.

Molecular Commensurability with a Surface Reconstruction - STM Study of Azobenzene on Au(111). A.Kirakosian, M.J.Comstock, J.Cho, M.F.Crommie: Physical Review B, 2005, 71[11], 113409 (4pp)