Probing the interfacial interactions of N719 with MoS2 using intrinsic surface enhanced Raman scattering

Unravelling the interaction of organic molecules bound to semiconductor surfaces is key to tune the optical and electronic properties of molecule-based functional devices. Here, we investigated the chemisorption of (Bu4N)2[Ru(dcbpyH)2-(NCS)2] (N719) ruthenium dye onto the semiconductor molybdenum disulfide (MoS2) using surface-enhanced Raman spectroscopy (SERS). Atomically thin bilayer (2L) MoS2 films were grown on the c-plane sapphire substrate using gas-phase chemical vapor deposition (CVD). The formation and number of layers of MoS2 were confirmed by Raman spectroscopy and atomic force microscopy. Under 785 nm laser excitation, bilayer MoS2 showed SERS activity based on chemical mechanism (CM) for N719 molecules adsorbed onto its surface at various concentrations. The selective enhancement of Raman modes of the bipyridyl ring and the functional group represents a sulfur-carbon bond through sharing of delocalised electrons in the ring with sulfur in MoS2. The SERS limit-of-detection for N719 dye was found to be 1x10-9 M at a laser power of 0.5 mW. Decarboxylation of the side-chain functional group was observed in conjugated samples after a storage of three weeks. MoS2@N719 proved to be an useful study-case for binding related environmental changes in two-dimensional semiconductor-organic systems apart from proving to be an excellent SERS substrate.