| Surface plasmon means that the free electrons at the interface between the metal and the medium are co-oscillated under the electromagnetic field.This oscillating element excitation can be regarded as a quantized quasi-particle and has many novel optical properties.When free electrons in metal nanoparticles are subjected to an electromagnetic field,free electrons can only collectively oscillate on the surface due to the limitation of the size structure of the nanoparticles,and they are called localized surface plasmons(LSPs).The surface plasmon resonance can lead to the redistribution of electromagnetic field in the nanostructure.Surface enhanced Raman scattering(SERS)is the use of metal nanostructure electromagnetic field enhancement to enhance the weak Raman scattering signal,and the enhanced efficiency can be achieved to10~4-10~6or even higher.Surface plasmons can break through the diffraction limit,enabling nanoscale optical information transmission and processing.In addition,the unique characteristics of surface plasmons make it widely used in highly sensitive biological detection,sensing,and new light sources.The overall research direction in these aspects is to explore the local electric field enhancement effect in nanostructures.Surface-plasmon-based resonance sensors and surface-enhanced spectroscopic sensors have been widely used in life sciences.At present,the ultra-sensitive properties of surface plasmon resonance(SPR)based on metal nanostructures make label-free single-molecule detection possible.In this work,the particle heterodimer-gold film system was composed of different material particles(Ag-Au,Ag-Pd,Ag-Cu)and a particle heterodimer placed on the gold film.The distribution of hot spots affected by the material can be determined by the electric field distribution of the metal nanoparticle heterodimer-gold film system.The aggregation effect of gold nanoparticles and silver nanoparticles in the Au-Ag dimerization system is not obvious.However,for the Pd-Ag dimer-gold film system,the hot spot aggregation effect under Ag nanoparticles is slightly larger than that under Pd nanoparticles.Moreover,the non-uniform hot spots in the Ag-Cu dimer-gold film caused the light intensity under the Ag nanoparticles to be almost 100 times higher than that under the Cu nanoparticles.These results are further confirmed by surface charge distribution and wavelength dependence and analyzed by plasma hybridization theory.And the data of particle heterodimers on a dielectric Si film demonstrates the importance of the induced charge induced on the gold film surface in this focusing phenomenon.Our findings broaden the understanding of surface plasma coupling in different materials,which may have great applications in the field of surface plasmon related fields.Nanotechnology is responsible for discovering new materials with tunable electronic,optical,mechanical,and transmission properties to overcome many of today’s technical challenges.Over the past two decades,the synthesis of nanoparticles has been surprisingly remarkable and has made tremendous progress.Surface-enhanced Raman scattering(SERS)is a widely used chemical,biological,physical and material science because it enhances the inherently low-molecular Raman scattering cross section,even at the single-molecule level,its high surface sensitivity.And vibrational spectroscopy is widely used for qualitative and quantitative fingerprint analysis.Currently,there are two enhancement mechanisms that are widely accepted.The first of these mechanisms is electromagnetic(EM)enhancement,which is caused by the strong surface plasmon resonance of a curved metal surface coupled to incident light,which typically enhances Raman spectra over a large frequency range.The second of these mechanisms is chemical enhancement(CE),which can be thought of as a resonance Raman process between the terrestrial electron state of a molecule-metal complex and its new excitation level caused by charge transfer(CT).In recent years,metal surface and adsorbed molecules,by utilizing the hot spots generated by surface plasmon decay,plasma-induced chemical reactions have attracted more and more attention as it opens up a new way for studying chemical reactions to SERS active catalysts and controls the chemistry of metal catalysts. |
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