Stepwise Growth of Ruthenium Terpyridine Complexes on Au Surfaces

Self-assembled monolayers (SAMs) of ruthenium-based molecular wires on solid surfaces are of great interest for optoelectronic and nanoelectronic applications. Here, we present a novel reactive Ru precursor, which enabled us to grow SAMs of Ru complex wires on Au surfaces even at room temperature. Thus, the Ru complex wire growth can be performed easily by sequential reaction of the reactive Ru precursor with terpyridine ligands without the harsh reaction conditions needed otherwise. Subsequently, we monitored the stepwise growth using infrared reflection absorption spectroscopy (IRRAS) and surface-enhanced Raman spectroscopy (SERS). A comparison of IRRAS and SERS data with theoretical spectra, derived from density functional theory calculations, enabled us to verify the formation of each individual growth step. Furthermore, we used these data to determine the orientation of the Ru-based molecular wires with respect to the Au surface. Growth step-dependent layer thicknesses obtained from variable angle spectroscopic ellipsometry verify the spectroscopic results. Thus, we provide a room-temperature method to realize Ru complex wire growth based on a reactive Ru precursor.