Plasmonic metal nanostructures can concentrate incident optical fields in nanometer-sized volumes, called hot spots. This leads to enhanced optical responses of molecules in such a hot spot but also to chemical transformations, driven by plasmon-induced hot carriers. Here, we employ tip-enhanced Raman spectroscopy (TERS) to study the mechanism of these reactions in situ at the level of a single hot spot. Direct spectroscopic measurements reveal the energy distribution of hot electrons, as well as the temperature changes due to plasmonic heating. Therefore, charge-driven reactions can be distinguished from thermal reaction pathways. The products of the hot-carrier-driven reactions are strikingly similar to the ones known from X-ray or e-beam-induced surface chemistry despite the >100-fold energy difference between visible and X-ray photons. Understanding the analogies between those two scenarios implies new strategies for rational design of plasmonic photocatalytic reactions and for the elimination of photoinduced damage in plasmon-enhanced spectroscopy.
Keywords: Hot electrons; desorption induced by electronic transitions; photoinduced damage; plasmon-driven photocatalysis; tip-enhanced Raman spectroscopy.