Probing the inner workings of single molecules with atomically terminated, nanoscopically smooth metallic tips via tip-enhanced Raman Spectroscopy*

In the past two decades, tip-enhanced Raman spectroscopy has emerged as a powerful technique for nanoscale chemical analysis.  Central to this technique is the fabrication of metallic tips as mediators between the incident light and the chemical response of the sample.  In this regard, we employ a process of electrochemical polishing and field-directed ion sputtering to develop atomically sharp and nanoscopically smooth tips capable of achieving subatomic spatial resolution.  These tip characteristics are believed to be necessary for their function as minimum-loss antennas that channel incident light into localized surface plasmons at the tip apex. The confinement leads to electromagnetic field enhancement in excess of 10⁸, sufficient to detect the Raman scattering signal from single molecules.  The design and batch production of these tips will be discussed, and their utility illustrated via studies of adsorbed benzene on an atomically flat copper surface, within an ultra-high vacuum scanning tunneling microscope.  The studies underscore the potential of this method to probe the inner workings of individual molecules – a new frontier in chemical science.