Nanopatterning on H-Terminated Si(111) Explained as Dynamic Equilibrium of the Chemical Reaction with Methanol

Abstract

Here the microscopic mechanism that leads to the surprising formation of a nanopattern upon methanol reacting with a H-terminated Si(111) surface [Michalak et al., Nat. Mater. 2010, 9, 266–271] is reinvestigated from both theory and experiment. First-principles calculations determine the fully OCH3-terminated Si(111) surface as the thermodynamic ground state in the presence of methanol, seemingly in contrast to the experimentally found nanopattern. At 65 °C the presence of H2 initiates desorption of the methoxy groups and thereby leads to a dynamic equilibrium of the reaction of methanol with the H-terminated Si(111) surface, which is a 1/3 OCH3-terminated and 2/3 H-terminated Si(111) surface, with all OCH3 groups standing as NNNs, corresponding to the nanopattern observed earlier. Investigating fluorine group termination of Si(111) as a test system the present study demonstrates that the combination of theoretical and experimental techniques used here is in fact sufficiently sensitive to resolve complex molecular systems even with lateral resolution.