nn7b06183_si_001.pdf (1.33 MB)
Tip-Enhanced Raman Spectromicroscopy of Co(II)-Tetraphenylporphyrin on Au(111): Toward the Chemists’ Microscope
journal contribution
posted on 2017-10-04, 00:00 authored by Joonhee Lee, Nicholas Tallarida, Xing Chen, Pengchong Liu, Lasse Jensen, Vartkess Ara ApkarianAtomically
terminated and nanoscopically smooth silver tips effectively
focus light on the angstrom scale, allowing tip-enhanced Raman spectromicroscopy
(TER-sm) with single molecule sensitivity and submolecular spatial
resolution. Through measurements carried out on cobalt-tetraphenylporphyrin
(CoTPP) adsorbed on Au(111), we highlight peculiarities of vibrational
spectromicroscopy with light confined on the angstrom scale. Field-gradient-driven
spectra, orientational fingerprinting, and sculpting of local fields
by atomic morphology of the junction are elucidated through measurements
that range from 2D arrays at room temperature to single molecule manipulations
at 5 K. Notably, vibrational Stark tuning within molecules, reflecting
intramolecular charge distributions, becomes accessible when light
is more localized than the interrogated normal modes. The Stark images
of CoTPP reveal that it is saddled, and the distortion is accompanied
by charge transfer to gold through the two anchoring pyrroles.