The surface‐enhanced Raman scattering (SERS) effect was discovered by Richard Van Duyne et al. in 1977. He and coworkers also first utilized an innovative strategy that used SERS to record spectra on such SERS‐inactive substrate surfaces as n‐gallium arsenide (100) surfaces, which were modified by silver nano‐islands. This nanostructure‐enhanced Raman spectroscopy on flat surfaces (NERSoFS) enabled such SERS applications to be expanded to a variety of materials by virtue of SERS‐active nanostructures such as Au or Ag nanoparticles and shell‐isolated nanoparticles. However, most of such systems, although yielding Raman spectra, produce rather low enhancements, especially when used to record spectra on flat surfaces of SERS‐inactive materials. In this work, along with the direction of Van Duyne's borrowing‐SERS strategy and on the basis of the strategy of cascading optical coupling, we consider a theoretically designed optical configuration, based on an attenuated total reflection‐cascading nanostructure to produce enhanced Raman spectroscopy (ATRc‐NERS) on flat surfaces. This system can effectively harvest the incident light, thereby boosting the local optical field of the incident light and also moderately increasing the radiation field of the Raman‐scattered signals. In this way, one can gain 1–2 additional orders of magnitude in Raman enhancement over present NERSoFS systems both on metallic and nonmetallic flat surfaces, which are otherwise SERS‐inactive. This ATRc‐NERS strategy can potentially be used to develop ultrasensitive and versatile tools for surface science, material science, catalysis, electrochemistry, and micro‐electronics and micro‐LED industries.

Plasmonic optical antennas (POAs), often constructed from gold or silver nanostructures, can enhance the radiation efficiency of emitters coupled to POAs and are applied in surface-enhanced Raman spectroscopy (SERS) and light-emitting devices. Over the past four decades, radiation enhancement factors (REFs) of POA−emitter systems were considered to be difficult to calculate directly and have been predicted indirectly and approximately, assuming POAs are illuminated by electromagnetic plane waves without emitters. The validity of this approximation remains a significant open problem in SERS theory. Herein, we develop a method based on the rigorous optical reciprocity theorem for accurately calculating the REFs of emitters in nanoparticle−substrate nanogaps for single-molecule SERS and scanning probe−substrate nanogaps for tip-enhanced Raman spectroscopy. We show that the validity of the plane wave approximation breaks down if high-order plasmonic modes are excited. The as-developed method paves the way toward designing high-REF POA nanostructures for luminescence-related devices.

To break through the bottleneck of SERS development in the surface analysis of a great variety of non-SERS active materials and atomically flat single-crystals, we invented shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) in 2010 [1]. The shell-isolated nanoparticleenhanced mode is capable of characterizing the surface water, reaction intermediate species in many important electrocatalytic or photo-electrocatalytic systems, and interfacial structures of the solid electrolyte film [2]. The strategy of using shell-isolated nanoparticles is grossly extendable to other surface spectroscopies, like surface-enhanced fluorescence spectroscopy [3], surface-enhanced second-harmonic generation [4], sum-frequency vibrational spectroscopy, and tip-enhanced spectroscopies [5], to improve the enhancement factor (up to 10 5 ) or spatial resolution (down to 10 nm). It will attract more attention if these techniques are applied to in-situ monitor the actual catalytic reaction systems, e.g., at single atoms or a single molecule. In the aspect of fundamental understanding of SHINERS, New plasmonic nanostructures and relevant instrumentation and theory for pushing sensitivity to the limit will be discussed in details [6]. Finally, we would like to explore on the radiation enhancement that cannot be easily predicted by the local field enhancement in the presence of plane-wave illumination at the Raman scattered wavelength in the case of nanoparticleon-mirror substrate. The mismatch could be understood by the radiation enhancement of the optical antenna in the reaction near-field region instead of the far-field region [7].