Controllable Fabrication And Enhanced Optical Sensing Of Noble-Metal Two-Dimensional Nanoarrays

Noble metal(Au,Ag etc.)nanoparticles possess intrinsic localized surface plasmon resonance(LSPR)effect.When these noble metal nanoparticles are arranged into twodimensional(2D)periodic nanoarrays,new near-or far-field coupling interactions will appear under the excitation of light.These intriguing properties offer the promise of enabling important applications in many fields,including optical sensing,information storage,nanolasers,etc.The traditional lithography preparation of noble-metal nanoarrays usually involves expensive instruments and complex processes,which limits their further applications.Colloidal crystal templating is expected to realize the construction of noble-metal nanoarrays with large-area due to its low-cost,simple process,and flexible periodicity,promoting the 2D noble-metal nanoarrays to further apply in the optical sensing.Based on the non-close-packed Au nanosphere array obtained by colloidal crystal templating,this dissertation aims to develop the noblemetal nanoarrays with unique engineered units by physical strategy or chemical growth method for optical coupling characteristics and further applications in optical sensing.This dissertation mainly includes the following studies:(1)A unique Au@Ag periodic nanoparticle array with controllable thickness of Ag film is fabricated by using magnetron sputtering deposition strategy.The optical sensing performance based on diffraction peak towards H2S is systematically studied.The mechanism of high selectivity to H2S has been revealed:the specific chemical reaction between Ag and H2S.We deeply explore the synergistic effect of Ag film thickness and controllable array periodicity on the sensing performance.Compared to the traditional LSPR optical sensor,the unique sensor based on diffraction peak of the array exhibits high sensitivity to H2S and successfully detect H2S in blood plasma.This study provides a new mean for highly sensitive and selective detection towards H2S.(2)The controllable fabrication of 2D Au polyhedron array is developed by using seed-mediated growth method.The role of polyvinylpyrrolidone(PVP)as stabilizer and capping agent in the growth of structural units are explored.It is revealed that the slow kinetic growth and the competitive adsorption between PVP and N,Ndimethylformamide(DMF)on Au {110} are the key factors to realize the controllable preparation of structural units.Finite-difference time-domain(FDTD)calculation and experimental data confirm that the surface enhanced Raman scattering(SERS)activities of Au polyhedron array originate from the electric field enhancement of sharp vertexes near Au {110}.The Au polyhedron array can detect 10-9 M 4-aminothiophenol(4-ATP)and exhibit excellent stability and signal repeatability.This study would contribute to the structural diversity of 2D nanoarrays.(3)The Au nanostar arrays with tunable gaps are developed based on the solvothermal synthesis.By tailoring the experimental factors,we can realize the controllable preparation strategies of 2D close-and non-close-packed structures.The growth mechanism of Au nanostar array dominated by kinetic regulation is revealed:PVP with the low molecular weight can accelerate the deposition rate of atoms on the{111} facets.These results show that the co-enhancement of tip electric field and coupling electric field are decisive for the excellent SERS performance of 2D closepacked Au nanostar arrays towards 4-ATP.This work provides the feasible theoretical basis for the SERS detection due to the multi-modal electric field enhancement.(4)A unique hetero-Au nanosphere/Ag nanoplate 2D nanoarray is developed by using the gas/water interface self-assembly method.The influence of Ag nanoplate thickness and the array periodicity on the reflection of incident light are studied.FDTD calculation and experimental data confirm the mechanism of Ag nanoplate reflection enhancing SERS activities.The highly sensitive detection to 4-ATP and thiram are realized.The enhance factor(EF)towards 4-ATP can achieve～1.3 × 107.This work can provide technical guideline for the SERS substrates with efficient optical capture.