Nanoscale Probing of Adsorbed Species by Tip-Enhanced Raman Spectroscopy

Tip-enhanced Raman spectroscopy (TERS) is based on the optical excitation of localized surface plasmons in the tip-substrate cavity, which provides a large but local field enhancement near the tip apex. We report on TERS with smooth single crystalline surfaces as substrates. The adsorbates were CN^- ions at Au(111) and malachite green isothiocyanate (MGITC) molecules at Au(111) and Pt(110) using either Au or Ir tips. The data analysis yields Raman enhancements of about 4×10⁵ for CN^- and up to 10⁶ for MGITC at Au(111) with a Au tip, probing an area of less than 100 nm radius.