Surface-induced ordering of alkanes on graphite: scanning tunneling microscopy and molecular dynamics studies

Abstract

_We have conducted an investigation of the interaction of a series of n-alkanes with the surface of highly ordered pyrolytic graphite (HOPG) using scanning tunneling microscopy (STM) and molecular dynamics (MD) computer simulation. The alkanes studied in this work (CnH2n+2 with n=16, 17, 20, 28, and 32) yield STM images which are highly suggestive of an ordered quasi-two-dimensional phase on the graphite surface. Individual molecules on the graphite surface adopt a rod-like conformation and are arranged in a 'rank-and-file' structure. Analysis of the STM height profiles indicates the presence of two dominant spatial frequency components. The high-frequency component has a period of about 0.30 nm and is independent of the carbon number of the alkane. The low frequency components have periods ranging from 3 nm to 5.5 nm. These values correlate closely with those obtained from estimates of the length of fully extended alkanes and from molecular dynamics computer simulations of surface-adsorbed alkanes. These...