Infrared spectroscopy enables us to investigate the vibrational modes of (bio-)molecules and, thus, their composition, state and environment. To increase the sensitivity of this technique down to monolayers or even single molecules we employ metallic nano-structures. These exhibit plasmonically induced near-fields which are locally confined (tens of nm) to the structures surface. Via the near-field the vibrational signature of close by molecules is enhanced by orders of magnitude.
We exploit this effect in two ways: either we use a structured surface to sense monolayers of molecules at a surface (Surface-Enhanced Infra-Red Absorption Spectroscopy, SEIRAS) or we use a metallic Atomic Force Microscope (AFM) tip as a local antenna for spatially resolved infrared spectroscopy (scattering-type Scanning Near-field Optical Microscopy, sSNOM).