Coverage-Dependent Adsorption of Bifunctional Molecules: Detailed Insights into Interactions between Adsorbates

Adsorption of bifunctional molecules is important for chemical modification of semiconductor surfaces, since such molecules can be used to alter the terminal functionality. In this work, the effect of coverage in the reaction of catechol (1,2-benzenediol) and resorcinol (1,3-benzenediol) with the (100) surface of germanium is investigated by surface spectroscopy experiments and theoretical methods. The benzenediols are site-specifically adsorbed on the Ge surface dimers through dissociative adsorption of either one or two of the −OH groups. Infrared spectroscopy and density functional theory results suggest that the dually tethered products selectively assume certain geometrical configurations at the surface. Infrared and X-ray photoelectron spectroscopies reveal that singly tethered species become increasingly prevalent as the coverage approaches saturation. Monte Carlo simulations that account for specific binding configurations and interadsorbate interactions, identified through density functional theory calculations, quantitatively reproduce the experimentally observed coverage-dependence of singly and dually tethered adsorbates for both benzenediols. Our results indicate that the singly bound adsorbates with unreacted hydroxyls appear on the reactive pristine Ge surface due to a limitation of available adjacent reaction sites, and show that interadsorbate interactions play a major role in determining reaction product distributions.