Molecular Electronics on Silicon: An Ultrahigh Vacuum Scanning Tunneling Microscopy Study

An ultrahigh vacuum scanning tunneling microscope (STM) was employed as a tool to characterize two distinct molecular electronic strategies on the Si(100) surface. Initially, the self-directed growth of one-dimensional styrene molecular chains on hydrogen-passivated Si(100) was investigated. High-resolution empty states imaging of these styrene nanostructures confirms alignment of phenyl groups along the chain. However, attempts at STM charge transport measurements were limited by tip induced desorption of styrene molecules. Consequently, an alternative oxygen radical chemistry was also investigated. In particular, the chemical adsorption of 2,2,6,6-tetramethyl-1- piperidinyloxy (TEMPO) onto clean Si(100) leads to the formation of an exceptionally stable silicon-oxygen bond that can withstand high bias charge transport measurements up to ±5 volts. Direct charge transport measurements through individual TEMPO molecules on degenerately n-type doped Si(100) reveal room temperature negative differential resistance behavior for negative sample biases exceeding -3 volts.