Directional Raman scattering from single molecules in the feed gaps of optical antennas.

Controlling light from single emitters is an overarching theme of nano-optics. Antennas are routinely used to modify the angular emission patterns of radio wave sources. "Optical antennas" translate these principles to visible and infrared wavelengths and have been recently used to modify fluorescence from single quantum dots and single molecules. Understanding the properties of single molecules, however, would be advanced were one able to observe their vibrational spectra through Raman scattering in a very reproducible manner but it is a hugely challenging task, as Raman scattering cross sections are very weak. Here we measure for the first time the highly directional emission patterns of Raman scattering from single molecules in the feed gaps of optical antennas fabricated on a chip. More than a thousand single molecule events are observed, revealing that an unprecedented near-unity fraction of optical antennas have single molecule sensitivity.