Purely site-specific chemisorption and conformation of trimethylamine on Si(100)c(4 x 2)

One of the fundamental points of interest on the Si(100) surface is how the spatial localization of electron density on the buckled silicon dimer controls the site-specific reaction toward different Lewis acid and Lewis base molecules. We have investigated the adsorption of trimethylamine (TMA) on Si(100)c(4x2) using scanning tunneling microscopy (STM) at 80 K. The adsorbed TMA appears as a triangle-shaped bright protrusion in the occupied-state STM image. The triangle-shaped protrusion is ascribed to three methyl groups in the adsorbed TMA. The center of the protrusion is located on the down atom site, which indicates that the adsorption of TMA occurs only on the down dimer atom. Thus, TMA adsorption on Si(100)c(4x2) is found to be purely site-specific on the down dimer atom and can be categorized in Lewis acid-base reaction.