Raman Spectroscopic Nanoimaging of Optical Fields of Metal Nanostructures with a Chemically Modified Metallic Tip

Abstract

The confinement and the enhancement of optical fields near metallic nanostructures provide unique tools for versatile applications in nanoscale devices and spectroscopies. It is therefore of great importance to investigate plasmonic properties of metallic nanostructures, such as the distribution of optical fields and the wavelength dependence of localized surface plasmon resonance on the nanometer scale. In this article, we demonstrate nanoscale visualization of the distribution of optical fields and the wavelength dependence of localized surface plasmon resonance of gold nanostructures by means of a tip-enhanced Raman spectroscopy (TERS)-based technique, which is a novel application of TERS to visualize the plasmonic properties at the nanoscale. Owing to the capability of fetching frequency-resolved optical information in Raman spectroscopy and an innovative molecular-functionalized metallic probe that we previously developed, intrinsic features of both the field confinement and the wavelength dependence of localized surface plasmon resonance of gold nanostructures are successfully visualized with a spatial resolution as high as 11 nm. Our present results enable one to comprehensively understand inherent plasmonic properties of metallic nanostructures, which would help to study the nature of plasmonic nanostructures and develop a wide range of plasmonic applications, such as molecular sensing, energy transfer, or optical storage.

Optical Spectroscopy of Surfaces, Interfaces, and Thin Films

“…With the increased adoption of nanostructures in SERS applications, the visualization of optical fields and LSPRs is critical in optimizing development and implementation. Utilizing work first report by Bhattarai and El-Khoury and advancements in tip manufacturing, Verma and co-workers functionalized a single side of an atomic force microscopy (AFM) tip with a Raman reporter to image the optical field and LSPRs of nanostructures using TERS . By depositing Ag NPs onto a single side of a silicon AFM tip, these researchers developed a route for selective functionalization with the Raman reporter p -nitrobenzenethiol (4-NBT) for side-selective TERS.…”

“…Utilizing work first report by Bhattarai and El-Khoury 23 and advancements in tip manufacturing, Verma and co-workers functionalized a single side of an atomic force microscopy (AFM) tip with a Raman reporter to image the optical field and LSPRs of nanostructures using TERS. 24 By depositing Ag NPs onto a single side of a silicon AFM tip, these researchers developed a route for selective functionalization with the Raman reporter p-nitrobenzenethiol (4-NBT) for side-selective TERS. Imaging plasmonic Au nanotriangles by TERS at the Raman spectral modes for p-NBT, the ν(C−S) at 1080 cm −1 and the ν(CC) at 1580 cm −1 were used to visualize the local near-field by monitoring changes in the Raman intensity.…”

Label-free visualization of photosynthetic microbial biofilms using mid-infrared photothermal and autofluorescence imaging

“…6,7 However, the spatial resolution of FTIR spectroscopy is limited to several micrometers or more because of the diffraction limit of mid-IR light, which is not high enough to resolve single bacteria and their biofilm structures. Although AFM-based nanoscale vibrational imaging techniques are useful to study photosynthetic molecules, [8][9][10][11] these techniques have a limited field-of-view, typically in a few to ten micrometers scale and require mechanical contact between a metallic tip and a sample. They also require a long acquisition time for imaging while the sample can be mechanically damaged by the tip when high-speed imaging is performed.…”

Ultrastable tip-enhanced hyperspectral optical nanoimaging for defect analysis of large-sized WS 2 layers

“…A similar near-field technique for nanoscale optical imaging is the tip-enhanced photoluminescence (TEPL) (7)(8)(9). In both these techniques, a metallic nanotip is used to enhance and confine the light field within a nanometric volume in the vicinity of the tip apex through plasmon resonance, and the sample is probed through this confined light (10,11). This has opened the way for optical investigation of different samples at the spatial resolution of a few nanometers, far beyond the diffraction limit of the light (12)(13)(14).…”