Determining molecular orientation via single molecule SERS in a plasmonic nano-gapElectronic supplementary information (ESI) available. See DOI: 10.1039/c7nr05107g

In this work, plasmonic nano-gaps consisting of a silver nanoparticle coupled to an extended silver film have been fully optimized for single molecule Surface-Enhanced Raman Scattering (SERS) spectroscopy. The SERS signal was found to be strongly dependent on the particle size and the molecule orientation with respect to the field inside the nano-gap. Using Finite Difference Time Domain (FDTD) simulations to complement the experimental measurements, the complex interplay between the excitation enhancement and the emission enhancement of the system as a function of particle size were highlighted. Additionally, in conjunction with Density Functional Theory (DFT), the well-defined field direction in the nano-gap enables to recover the orientation of individual molecules. Through combining single molecule SERS measurements, DFT and FDTD calculations, the molecular orientation within the plasmonic nano-gap is recovered.