Abstract
A novel tip-enhanced Raman spectroscopy setup with longitudinal field excitation generated by a plasmonic lens is investigated. A symmetry-breaking structure plasmonic lens that is expected to realize a strong longitudinal electric field focus has been designed to generate suitable excitation for enhancement in a tip antenna. The focusing performance of the plasmonic lens is theoretically simulated by the finite-difference time-domain method and experimentally verified by the detection of optical near-field distribution. A plasmonic lens assisted tip-enhanced Raman spectroscopy setup has been constructed and used to investigate specimens of carbon nanotubes. Tip-enhanced Raman spectra with distinct excitation wavelengths show similar Raman shifts but different intensities. Experimental results presented in this paper demonstrate that the Raman signal is considerably enhanced. It indicates that the novel tip-enhanced Raman spectroscopy configuration is feasible and is a promising technique for tip-enhanced Raman spectroscopy measurements and characterizations.
Highlights
The optical antenna properties of metallic nanostructures attract considerable interest for a wide range of applications [1,2,3,4], in particular, due to such antennae featuring high confinement and strong enhancement of the local light-matter interaction [5,6]
The tip-enhanced Raman spectra of the Single-walled carbon nanotube (SWCNT) were respectively detected under each wavelength excitation
In conclusion, a novel tip-enhanced Raman spectroscopy (TERS) setup based on plasmonic lens (PL) excitation was built up
Summary
The optical antenna properties of metallic nanostructures attract considerable interest for a wide range of applications [1,2,3,4], in particular, due to such antennae featuring high confinement and strong enhancement of the local light-matter interaction [5,6]. The strong local field enhancement on the metallic tip antenna is known to be responsible for tip-enhanced Raman spectroscopy (TERS) or related photochemical effects [7,8,9,10]. In the TERS technique, the signal enhancement near the antenna is due to the excitation of localized surface plasmons (LSPs) and the lightning-rod effect [11-13]. Both effects are highly sensitive to the polarization of the excitation optical field corresponding with the axis of the tip.
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