Molecular Imaging with the Scanning Tunneling Microscope

Abstract

Two classes of molecular materials can be directly investigated by scanning tunneling microscopy (STM), namely (1) organic conductors and (2) ultrathin organic layers on conducting substrates. Since STM itself does not require ultrahigh vacuum conditions, both the free surfaces as well as interfaces with fluid ambients are accessible. Unique is the ability of STM to investigate molecular defects on the atomic length scale. Moreover, it allows, for the first time, to directly observe molecular dynamics on the time scale of milliseconds and longer. After the description of some experimental aspects of fast STM imaging of molecular materials, a number of examples will be discussed in some detail. They include a radical cation salt, β-(BEDT-TTF)₂ I₃, under ambient conditions and monolayers of an alkane and an alkyl-derivative (didodecylbenzene) adsorbed at the interface between an organic solution and the basal plane of graphite.