Basic Information

Abstract Number: 2590 - 3
Author Name: Andreas P Ruediger - INRS-EMT
Session Title: Biological TERS: Instrumentation Development and Applications
Event Type: Symposia
Event Title: Refractive Index Monitoring at the Nanoscale

Presider Name:Igor LednevCo-Author:Mischa Nicklaus, Julien Plathier
Affiliation:University at Albany, SUNYAffiliation:INRS-EMT

Date: Thursday, March 12, 2015
Start Time: 02:10 PM (Slot #3)
Location: 239

Abstract Content

The near field enhancement in tip-enhanced Raman spectroscopy (TERS) implicitly relies on the tip-sample interaction as part of the tip’s surface plasmon resonance. While this resonance can be considered to be spectrally large as compared to the Raman signature, the exact peak position does significantly depend on the dielectric permittivity of the surrounding media and in particular the local refractive index of the sample environment as part of this media.

Our initial experiments were meant to demonstrate the chemical and structural integrity of ferroelectric nanostructures and while we were indeed able to achieve a spatial resolution below 5 nm, the back-scattered light contained a strong tip signature that was superimposed to a relatively weak Raman signal from the sample. Approximating the surface plasmon resonance by a Lorentzian line shape paved the way to discriminating tip again sample contributions.

We thus demonstrate for the initial case of inorganic nanostructures how residual fluorescence from the apex of the gold tip can be used to determine the relative shift of the surface plasmon resonance which has three immediate implications: first, the quality factor of TERS tips depends strongly on the sample so there is no ‘perfect’ TERS tip to cater for all samples and second, the peak intensities of the Raman spectrum become a function of the envelope of the enhancing surface plasmon, which depends again on the position on the sample. Last but not least, we demonstrate how to extract local refractive index variations of the sample with a sensitivity of better than 10 percent relative change, which enables detection schemes for local phase transformations, variations of oxidation states or at least a direct optical signature from the tip, which is modulated through the sample in cases where the Raman signature might be otherwise undetectable.