Optoplasmonic probe to realize scanning near-field Raman microscopy.

Abstract

Tip-enhanced Raman spectroscopy (TERS) is a powerful scanning probe technique for Raman detections in nanotechnology to date. However, limited by the physical principles of a nanosize tapered metal (or metal-coated) probe used in a TERS device, only far-field without near-field Raman signal can be collected by the TERS with the metal probe. This makes conventional TERS lower in efficiency and cannot be a real near-field Raman microscopy. In this paper, we propose a simple and realizable optoplasmonic probe model, which is composed of a dielectric microsphere and a metal nanobowtie, to realize an ideal scanning near-field Raman microscopy (SNRM). Using finite-difference time-domain (FDTD) method, calculation results of electric field distributions of the proposed probe demonstrate that the probe provides three outstanding characteristics, including strong enhancement of local electric field, nanoscale distributions of the produced electric filed, and collection enhancement of emitted energy with wide wavelength range in near field. These characteristics of the probe resolve the detecting restrictions of metal probes and provide a real near-field scanning method. Therefore, a potentially novel SNRM can be expected to extend Raman application range greatly.