The surface plasmon erupted by bare metallic film has limitation of localizing high intensity field. Thus, nanostructures on the metallic film (such as nanowire, nanopost) have been used to enhance the Plasmon field by antenna effect. In the case of nanowire, field is highly localized at the sharpened edge of the nanowire. If there is an additional enhancing factor such as a gap between the edges of the nanostructures, area of highly localized field is formed. By adopting reversed trapezoidal structure, we expected to control area and intensity of highly localized plasmon field from both the nano-antenna effect and the gap plasmonic effect. So, we simulated trapezoidal nanowire structure changing the ratio of bottom length and top length of nanostructure. Then we can observe the variation of Plasmon field and intensity. In addition, we can obtain unusual result that the intensity of Plasmon field is highly reduced at specific ratio of bottom length and top length.
The effective confinement of light in a deep-subwavelength volume can be achieved in metallic nanostructures through the electronic resonance, surface plasmons (SPs). There are few ways to enhance the localization of the field such as adopting metallic nanopost or nanowire structures on the precious metallic film. The achieved highly enhanced field localization through SPs can be exploited for surface-enhanced spectroscopy, biosensor, enhancing energy emitter, and enhanced energy generator. Also, many researches have been tried with few-nanometer gap between the metals for achieving large field enhancements. In this paper, by comparing the scattering of gold nanoparticles, the effects of metallic film of substrates were investigated through simulation. In addition, as changing of the gap between gold nanoparticle and metallic surface, different resonance wavelengths were observed in scattering spectra from simulation and practical experiments. We confirmed that the gold film with gold nanoparticles shows the most distinctive scattering spectra. The numerical demonstration was matched with our experimental demonstration, also with the previously introduced papers as well.
This research is about surface-enhanced Raman spectroscopy based on the gap-plasmonic effects between the silver nanoisland (AgNI) substrate and gold nanoparticles (AuNPs). With calculation, we prove that plasmonic-coupling phenomena between AuNPs and AgNIs were formed, which eventually affect to the signal enhancements, and we simulate the field enhancement according to the AuNPs position on the AgNI substrates. Consequently, we experimentally confirm the Raman signal enhancement using target as AuNP attached DNA, which were distributed on the AgNIs substrate randomly. Raman spectra measured on the AgNI substrate exhibit approximately 20-fold signal enhancements compare to the signals measured on a uniform silver film, and the experimental spectra agreed well with the results of simulation. This method has merit in that significant Raman signal enhancements can be achieved for large areas without a complicated nano-lithographic process.
Surface enhanced Raman spectroscopy (SERS) based on plasmonic colocalization between DNA attached gold nanoparticles and silver nanoislands substrates. Raman spectra measured on a silver nanoislands substrate were observed 20 and 1.8 folds signal enhancements relative to them on a film substrate with high and low numerical apertures of lenses, respectively. By comparison between calculations and experiments results, we proved that distinct differences of the signal enhancements came from changing field of view on random nanoislands substrate. Consequently, we show that nanoislands substrates with a precise position control can be a good candidate for a SERS substrate which can achieve significant signal enhancements without a complicated lithographic process.