Stepwise Growth of Ruthenium Terpyridine Complexes on Au Surfaces

Abstract

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.

Impact of device design on the electronic and optoelectronic properties of integrated Ru-terpyridine complexes

“…4'-Mercaptophenyl-2,2':6',2"-terpyridine (MPTP), 4'- [4-(acetylthio)phenyl]-2,2':6',2"-terpyridine (MPTP-SAc), 1,4-bis(2,2':6',2"-terpyridine-4-yl)benzene (BTP), the complex RuCl2(DMSO)MPTP-SAc, and the precursor [Ru(acetone)6](PF6)3 (Ru-PF6) were prepared according to procedures previously described [15,19,[25][26][27]. The analysis of the prepared substances, including 1 H-NMR, UV/vis, and mass spectroscopy, display a high purity [15].…”

“…Ru(TP)2-complex wires were grown between electron beam lithographically fabricated nanoelectrodes according to the recently developed routine which enables the assembly of the molecular building blocks on solid surfaces at room-temperature under mild conditions and thus, represents an on-chip preparation method [19]. In parallel, the first steps of the consecutive wire growth on Au substrates were monitored by XPS measurements.…”

“…The wire growth was completed by incubation of samples (iii) in Ru-PF6 solution for a second time, thereby forming samples (iv) (Figure 1). Recently, we showed by evaluation of the IRRAS and Raman spectra of the individual wire growth steps (i) -(iii) and comparison of these spectra to the spectra of bulk model substances that the formation of the Ru(TP)2-complexes was largely successful [19]. However, a detailed investigation of the oxidation state of the Ru ions bound to the respective molecular compounds is not feasible by these methods.…”

“…Using TP-based ligands and a reactive Ru precursor, we recently succeeded to establish a roomtemperature method to grow Ru-TP supramolecular wires by sequential reaction [19]. The stepwise wire growth was verified by infrared reflection absorption spectroscopy and surface-enhanced Raman spectroscopy in combination with density functional theory calculations, as well as variable angle spectroscopic ellipsometry.…”

“…They are fabricated by electron beam lithography (EBL) in a lift-off process and the use of a self-aligned Al2O3 hard mask to define the nanogap size [20,21]. The resulting nanoelectrode pairs are used for the on-chip preparation of Ru(TP)2-complex wires according to the wire-growth protocol developed recently and thus, to assemble Ru(TP)2-complex wire nanodevices [19].…”