LSPR Modulation And SERS Enhancement Mechanism In Periodic Nanoarrays

As we all know,in addition to molecular vibration scattering,surface plasma resonance(SPR)was considered as one of the important sources for surface-enhanced Raman scattering(SERS)signal to be greatly enhanced.With the deepening of people’s understanding of the mechanism of local surface plasmon resonance in metal,the application and understanding of SERS spectrum also became broader and deeper.At present,various variations of Raman scattering based on surface plasmon resonance enhancement have been developed,such as Tip-Enhanced Raman Spectroscopy(TERS),shell-isolated nanoparticle-enhanced Raman spectroscopy(SHINERS),anti-stokes Raman spectroscopy(SE-CARS),femtosecond stimulated Raman spectroscopy(SE-FSRS),and Surface Enhanced Hyper Raman Spectroscopy(SEHRS).Although SERS enhanced system developed rapidly and changed in various forms,since SERS had some contributions of chemical enhancement besides physical enhancement.Therefore,currently SERS has not formed a set of unified and complete theories.Based on the above SERS development status,this paper constructed a nano-array structure with special morphology to study the SERS enhanced mechanism under complex photoelectric environment and achieved a series of innovative research results in the construction of special plasma electrical environment and the study on SERS enhanced theory.The main research content includes the following three parts.1.Hexagonal close-packed tilted Ag nanorod arrays that exhibit excellent uniformity and reproducibility were prepared.The tilt angle was easily controlled by regulating the sputtering angle,accompanied by a reduction and constancy in the gap size of adjacent nanorods,which is 30° and 90° relative to the sputtering direction.The surface enhanced Raman spectroscopy(SERS)technique was used to characterize the interaction of tilted Ag nanorod arrays with polarized laser excitation.Interestingly,the SERS polarization-dependence increased with increasing tilt angle of the Ag nanorods.To elucidate the essential factors responsible for this SERS result,three-dimensional(3D)electromagnetic enhancement distribution for the proposed system was numerically simulated based on p-and s-polarization excitation.Most importantly,the fundamental reasons for the polarization dependence of SERS were obtained by a quantitative 3D numerical simulation of hotspot distribution for adjacent nanorods.2.To establish the interference mechanism of carrier concentration with PERS signals on SERS without the additional influence of electric field,a simulation of the constant distribution of electric field and the different current densities were carried out using Lumercial finite difference time domain(FDTD)software.By scanning the incident light excitation condition through the numerical FDTD simulation,a special electrical environment was created in the horizontal nanocavity architecture arrays,where the current density was varied while the electric field intensity was maintained at a consistent level.According to the FDTD simulation results,the angle dependent sputtering was applied to produce horizontal nanocavity architecture arrays.At last,the horizontal nanocavity architecture arrays were fabricated by the angle dependent sputtering and Raman measurement was performed in accordance with the optical incident excitation conditions ascertained from FDTD simulation calculation.The measurement results revealed that the peak positioned at 1075 cm-1 was redshifted substantially,which was due to the electron cloud redistribution in the molecule caused by the change in the ratio of electric field strength to current density with constant electric field.3.The FDTD method has been used to simulate rectangular nanocolumn array with thickness varying.The extraordinary optical transmission in the rectangular nanocolumn array results from the resonant electric field in the structure.The number of resonance points in the structure has no impact on the extraordinary optical transmission.A subsequent quantitative optical analysis is performed for the nanocolumn arrays of different heights,which shows the number of resonance points in the structure depend on the wavelength of exciting light.This indicates that a higher nanocolumn array is capable of more diversity in the distribution of resonance points.The present study increases our understanding of surface plasmon excitation in rectangular nanocolumn array with variable thickness,which has strong potential for applications in surface-enhanced spectroscopy,nanosensors,and other surface plasmon related fields.