CPM Seminar

New Directions in Ultrahigh Vacuum Tip-Enhanced Raman Spectroscopy with Molecular-Resolution Scanning Tunneling Microscopy

Nan Jiang

Northwestern University

During the last few years, the study of ultrahigh vacuum tip-enhanced Raman spectroscopy (UHV-TERS) has been raised to an unprecedented level. By using ex-situ laser focusing and Raman collection optics without compromising UHV, multiple vibrational modes for molecular adsorbates on a solid surface have been resolved in TER spectra obtained concurrently with sub-nm resolution Scanning tunneling Microscopy (STM) imaging. In addition, the adsorbate-substrate interactions can be studied. With liquid helium cooling sample, molecules no longer diffuse on the surfaces. New vibrational characteristics of TER spectra can be obtained in R6G / Ag(111) system at 19K. Theoretical analysis of vibrational modes allowed interrogation of the interaction between rhodamine 6G and the Ag(111) surface. Further a substantial progress in TERS application is the integration of ultrafast spectroscopy with TERS. TERS using pulsed excitation in both atmosphere and UHV was demonstrated. And our results suggest that the UHV environment mediates signal decay. This approach provides the tools to understand the dynamical processes such as plasmon driven charge transfer with unprecedented temporal and spatial resolution.