Exploring Azobenzenethiol Adsorption on the Ag/Ge(111) Surface with Surface Raman Spectroscopy

Self-assembled monolayers (SAMs) formed with thiols on surfaces represent the most representative system of such kind. Their detailed adsorption orientation and kinetics are however rarely elucidated completely, making the development of the SAM systems mostly based on try-and-error approach. We have studied the adsorption of azobenzenethiol (azoSH) on the Ag/Ge(111)-(root 3 x root 3)R30 degrees surface, as an archetype of SAMs on compound surfaces, with in situ surface Raman spectroscopy. Two different adsorbates have been identified with their vibrational signatures and orientations. They respectively correspond to the two adsorption sites of this compound surface system, owing to distinct molecule-surface interactions, and both exhibit Langmuir adsorption behavior. These traits are compared with that on the Ge(111) surface, bearing homogeneous adsorption propensity, where one precursor of adsorption has been identified. The revelation of the detailed adsorption traits of azoSH has demonstrated that surface Raman spectroscopy is expedient in revealing complex adsorption behaviors of the SAM systems.