Visualizing Electric Fields at Au(111) Step Edges via Tip-Enhanced Raman Scattering

Abstract

Tip-enhanced Raman scattering (TERS) can be used to image plasmon-enhanced local electric fields on the nanoscale. This is illustrated through ambient TERS measurements recorded using silver atomic force microscope tips coated with 4-mercaptobenzonitrile molecules and used to image step edges on an Au(111) surface. The observed two-dimensional TERS images uniquely map electric fields localized at Au(111) step edges following 671 nm excitation. We establish that our measurements are not only sensitive to spatial variations in the enhanced electric fields but also to their vector components. We also experimentally demonstrate that (i) few nanometer precision is attainable in TERS nanoscopy using corrugated tips with nominal radii on the order of 100-200 nm, and (ii) TERS signals do not necessarily exhibit the expected E dependence. Overall, we illustrate the concept of electric field imaging via TERS and establish the connections between our observations and conventional TERS chemical imaging measurements.

Nanoscale Chemical Reaction Imaging at the Solid–Liquid Interface via TERS

“…We tentatively assign the product spectrum to cis-DMAB on this basis. Difference in the relative intensities of the observable states can otherwise be rationalized on the basis of modified TERS selection rules 38 and/or the removal of orientational averaging in our case of Raman scattering from a nanoscopic probing volume. 47…”

“…Our AFM/TERS setup is described elsewhere. 10,37,38 For the purpose of this work, initial topographic AFM measurements were performed in tapping mode feedback using a silicon tip (Opus, 160AC-NN) coated with 100 nm of Au by arc-discharge physical vapor deposition (target:…”

Taking the Plunge: Nanoscale Chemical Imaging of Functionalized Gold Triangles in H2O via TERS

“…20 Note that unlike our present report, our previous work probed a solid-air interface and utilized a side-illumination geometry. 20 More generally, it is possible to image the nature, 21,22 magnitude, 1,23 and vector components 24 comparison between the recorded and simulated local field profiles allows us to preclude the inplane (X and Y) components, even though the incident polarization is along X (see the inset of Figure 2B). On the basis of this simple side-to-side comparison, it appears that our TERS images broadcast either the total enhanced local optical field or its z-component.…”

“…The frequencydependent images otherwise only reflect the relative intensities of the vibrational lines, which is expected in our case of ensemble-averaged TERS spectral imaging. 20,24…”

Low cost tips for tip-enhanced Raman spectroscopy fabricated by two-step electrochemical etching of 125 µm diameter gold wires

“…9 displays a strongly enhanced signal from the two trenches. This could in principle be due to a higher concentration of molecules in the channels, in combination with the presence of enhanced electric fields [ 72 ], caused by molecular diffusion into SERS-active sites [ 62 ]. Whatever the origin of the signal, we are able to map this effect with a spatial resolution equivalent to the scan step (10 nm).…”