Abstract
An existence proof for single-molecule tip-enhanced Raman spectroscopy (SMTERS) is given using the frequency domain approach involving the two isotopologues of Rhodamine 6G (R6G) that were previously employed for single-molecule surface-enhanced Raman spectroscopy (SMSERS). A combination of experimental and theoretical studies provides a detailed view of the isotopic response of R6G–d0 and R6G–d4 in the 600 – 800 cm–1 region. The single-molecule nature of the TERS experiment is confirmed through two lines of evidence. First, the vibrational signature of only one isotopologue at a time was observed from multiple TER spectra. Second, the spectral wandering of the 610 cm–1 mode of R6G–d0 was less than ±4 cm–1, which in turn is less than the 10 cm–1 isotopic shift so that no confusion in assignment resulted. As a consequence, the total TERS enhancement factor can now be accurately established as EFTERS = 1.0 × 1013 because only one molecule at a time is measured. Furthermore, EFTERS can be partitioned into an...
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