Chain-length dependence of metastable striped structures of alkanethiols on Au111

The chain-length dependence of metastable striped phases of alkanethiols films partially covering the gold surface has been determined by means of atomic force microscopy. These structures are obtained from solution and consist of molecules adsorbed with their carbon chains flat on the surface. The stripes run parallel to the next-nearest-neighbor direction of Au(111) and have been found to always coexist with islands of upright molecules. The stripe spacing changes linearly with molecular length differently than twice the chain length. This dependence is discussed in terms of both interdigitation and herringbone-like lamella models. With time and under ambient conditions, these phases transform, without increasing coverage, by aggregation of the lying flat molecules to the preexisting islands with upright configuration.