Dimerization of Nitrosobenzene Derivatives on an Au(111) Surface

Abstract

In this study, we have investigated the ability of C-nitrosobenzenes to dimerize on an Au(111) surface and form ordered self-assembled bilayers (SABs). Use of scanning tunneling microscopy (STM) revealed that nitrosobenzene derivatives are able to form both well-ordered monolayers (SAMs) and bilayers (SABs). High-resolution STM images showed that within SAM regions molecules are arranged into hexagonal structures. Moiré-type superstructure with a periodicity of 1.5 nm was observed, indicating a 3√3 × 3√3 molecular arrangement. Molecularly resolved STM images showed that within bilayers molecules are also arranged into hexagonally ordered structures at intermolecular spacing of ∼0.4 nm. Furthermore, it was observed that the second layer is better ordered than the first one, probably because of the softer background. Use of atomic force microscopy (AFM), through measured height differences between monolayers and bilayers, further confirmed the formation of SABs. The results of the present study demonstrate that nitrosobenzenes represent convenient molecular models that can be used for systematic design and study of bilayers on metal surfaces. Besides the previously known properties of C-nitroso compounds to form dimers in crystals, here we have found a new situation under which these molecules dimerize, which is, in principle, a 2D crystallization.