Adsorption and thermal stability of alkanethiol films on GaAs(110): A comparative study by TOF-DRS and TOF-SIMS

We present an ion beam study of the adsorption and the thermal stability of short alkanethiol molecules adsorbed on GaAs(110). Direct recoiling spectroscopy shows that the adsorption of ethanethiol and hexanethiol proceeds directly towards a dense standing up phase without passing through a stable phase of lying down molecules as is the case for Au(111). Measurements along specific azimuths suggest that both Ga and As rows are covered by the organic molecules. Short adsorption times from the vapor phase result in films having two desorption peaks near 300 and 500 K. On the other hand, leaving the sample in a thiol atmosphere for several hours produces more stable films, similar to those produced by immersion in the corresponding thiol-ethanol solution. TOF-SIMS results confirm the C–S scission mechanism during the thermal desorption.