Abstract
N-Heterocyclic olefins (NHOs), possessing highly polarizable electron-rich double bonds, have recently received increased attention as promising ligands to modify the properties of various surfaces such as Cu, Au, and Si. This work demonstrates the precise "writing" of molecules on a Cu(111) surface by using the electric field of a scanning tunneling microscope (STM) tip. This selectively switches the molecules from a mobile, physisorbed state to a chemisorbed state with molecular, nanoscale spatial resolution under ultrahigh vacuum conditions. We utilize STM and high-resolution electron energy-loss spectroscopy supported by density-functional theory to investigate adsorption and orientation of the molecules on the Cu(111) surface. We find that IPr-NHO adopts two distinct adsorption states on Cu(111): a mobile, physisorbed state and a chemisorbed state. We can distinguish between the two states using X-ray photoelectron spectroscopy and show that the mobile species can be transformed into the immobile species via interaction with the STM tip with molecular precision. This enables "writing" of IPr-NHO on Cu(111) as the molecules can be chemisorbed in a predefined assembly in intentionally designed shapes, opening new possibilities for nanofabrication, molecular electronics, and tunable surface chemistry.