Phenyl attachment to Si(001) via STM manipulation of acetophenone

The attachment of organic molecules to semiconductor surfaces and their measurement using scanning tunneling microscopy and spectroscopy (STM/STS) is considered to be a potential route toward conductance measurements of single molecules with known structural and electronic configuration. Here, we investigate a model system—acetophenone on Si(001)—and demonstrate that this adsorbate can be manipulated using the STM such that it adopts a configuration where it stands upright with a free-standing phenyl ring and strong Si–O linkage to the substrate. For the structural identification we combine STM imaging with density functional theory (DFT) calculations to describe the adsorbate structures that were observed in our experiments and the reaction pathways that link them; of these the upright configuration is the most thermodynamically stable. The chemical structure of the upright configuration suggests that π-conjugation within the adsorbate extends to the silicon surface resulting in strong hybridization of the molecular states with the substrate. This is supported by the absence of any significant features in STS curves recorded over the adsorbate. The structure of this adsorbate and its robust attachment to silicon makes it attractive for future STM/semiconductor-based molecular conductance measurements