Site selection in single-molecule junction for highly reproducible molecular electronics

Adsorption sites of molecules critically determine the electric/photonic properties and its stability of heterogeneous molecule-metal interfaces. Then, selectivity of adsorption site is essential for development of the fields including organic electronics, catalysis, and biology. However, due to current technical limitations, site-selectivity remains a major challenge because of difficulty in precise selection of meaningful one among the sites. Here, we report the single site-selection at a single-molecule junction by performing newly developed hybrid technique: simultaneous characterization of surface enhanced Raman scattering (SERS) and current-voltage (I-V) measurements. The I-V response of 1,4-benzenedithiol junctions, reveals the existence of three meta-stable states arising from different adsorption sites. Notably, correlated SERS measurements show selectivity towards one of the adsorption sites, bridge sites. This site-selectivity represents an essential step towards the reliable integration of individual molecules on metallic surfaces. Furthermore, the hybrid spectro-electric technique reveals the dependence of the SERS intensity on the strength of the molecule-metal interaction, showing the interdependence between the optical and electronic properties in single-molecule junctions.