•The strong SERS polarization dependence of Ag nanorice dimer on metal or dielectric film has been demonstrated.•The induced image charge on metal film pays a great contribution to the enhancement of SERS intensity.•The small nanorice of heterodimer owns a perfect ability to gather energy.The polarization dependence plays a great impact on the SERS intensities for the surface plasmon coupling between nanoparticle aggregating. In this work, the SERS intensities collected from nanorice heterogeneous dimer or homogeneous dimer on Au, ITO and glass substrates exhibit strong polarization dependence. This result is further analyzed by the simulated surface charge distribution and electromagnetic enhancement distribution. Our data illustrate that SERS polarization dependence exhibits in all gaps in whole system, not only the gaps between nanorices but also gaps between nanorices and film, which could be important for the application of SERS as an ultrasensitive sensing technique.Download high-res image (117KB)Download full-size image

The influence of polarization dependence is an unavoidable problem in surface-enhanced Raman spectroscopy (SERS) applications, especially for anisotropically-enhanced structures with strong surface plasmon coupling. In this work, the polarization dependence of SERS in crossed nanowires (NWs) on metal or dielectric films was investigated both experimentally and theoretically. The measured SERS spectra indicated that the strong polarization dependence of the crossed NWs was greatly influenced by the substrate, which was determined by only the direction of the bottom NWs for a metal film or the top NWs for a dielectric film. The studies further demonstrated that this polarization dependence was not related to the diameter ratio or intersecting angle of the NWs. The present work not only improves the applications of SERS but also increases our understanding of surface plasmon excitation in complicated metal nanostructures.

The electromagnetic field redistribution in metal nanostructure–film systems exhibits great capability of confining light on plain film, which has great significance in surface-enhanced Raman scattering (SERS) of a molecule on plain film or 2D material. In this work, the SERS spectra of a monolayer molecule on metal or dielectric film were investigated with the help of a metal nanoparticle–nanowire structure. The results indicated that SERS intensity from an adjacent nanoparticle was much greater than that from an individual nanowire, which was confirmed by the simulated electric field distribution through finite method. The polarization dependence of both experimental and simulated data pointed out the importance of electromagnetic field redistribution in this phenomenon. Furthermore, the shape independence of a nanoparticle found in this work greatly improved the application prospect of this nanoparticle–nanowire assisted SERS on film.

•More than one trapping site was generated in the Au polygon tetramers array.•The trapping performance was largely influenced by the number of sides.•The influence of side number on trapping became weaker while the nanoparticle got bigger.•The trapping site and performance were influenced not only by structure configuration but also by wavelength of light.Highly bounding light at metal surface by localized surface plasmon resonance (LSPR) improves the optical trapping of nanoparticles, which is called plasmonic trapping. Since LSPR is high related to the geometry of metal structures, the construction of metal nanostructure is extremely significant in the nano-trapping. In this work, the plasmonic trapping of dielectric nanoparticles in periodic gold polygon tetramers is investigated through finite-difference time-domain (FDTD) method. The simulation results of electric field distribution and the corresponding optical force indicate the number of side is quite important to the trapping efficiency that the square tetramers is obviously superior to other ones with more sides. However, this efficiency difference is also related to the size of nanoparticle that it is more sensitive to the smaller nanoparticles. Furthermore, the results also figure out not only trapping efficiency but also the trapping position is greatly influenced by the wavelength of trapping light in the same gold polygon tetramers. All our results open a way to selectively trap nanoparticles with required size at appointed positions, which has extensive application prospects in manipulation of nanoparticles in solution.

The influence of polarization dependence is an unavoidable problem in surface-enhanced Raman spectroscopy (SERS) applications, especially for anisotropically-enhanced structures with strong surface plasmon coupling. In this work, the polarization dependence of SERS in crossed nanowires (NWs) on metal or dielectric films was investigated both experimentally and theoretically. The measured SERS spectra indicated that the strong polarization dependence of the crossed NWs was greatly influenced by the substrate, which was determined by only the direction of the bottom NWs for a metal film or the top NWs for a dielectric film. The studies further demonstrated that this polarization dependence was not related to the diameter ratio or intersecting angle of the NWs. The present work not only improves the applications of SERS but also increases our understanding of surface plasmon excitation in complicated metal nanostructures.