Surface-enhanced and STM tip-enhanced Raman spectroscopy of CN− ions at gold surfaces

Combined surface- and tip-enhanced Raman spectroscopy (SERS and TERS, respectively) experiments for CN− adsorbed at Au-surfaces are presented. STM tip-induced frequency shifts for the CN-stretch vibration are observed. This effect is attributed to a distinct weighting of the individual contributions to TERS, depending on the particular field distribution, which peaks underneath the tip apex and drops quickly beyond this region.