Preparation And Characterization Of SERS Substrates Based On The Surface Piasmon Resonances

Surface-enhanced Raman scattering SERS technique has presented great application potential in medical diagnosis,environment monitoring and food detection because it is high-sensitivity,label free,loss less,fast and efficiency.Many efforts have been concentrated on all kinds of strategies to produce efficient SERS platforms.However,how to prepare large-area,reproducible,stable,cheap SERS substrates is one of the hot topics both at home and abroad,and it is also a problem to be solved urgently at present.In this paper,we mainly design and prepare SERS substrates with good properties based on the surface plasmonic resonances,and reveal the relevant physical mechanism by investigating the structural geometries,optical properties and SERS properties of the samples and their internal relation,and further explore the application in Raman detection.Firstly,we report a simple and controllable method to produce large-area efficient SERS platforms with spatially-stacked plasmonic hotspots.The SERS platforms consist of double layer metal porous films and are easily fabricated by magnetron sputtering,annealing,etching of hydrofluoric acid vapor,and transfer of the metal porous film.The stacked dual-layer metal porous films show prominent Raman enhancement effect under the detection of different target molecules.The detection limit is demonstrated down to 10^-13 M by detecting rhodamine 6G?R6G?molecules.These superior Raman properties can be mainly ascribed to the highly-dense spatially-stacked plasmonics hotspots formed in the dual-layer metal porous films.The simple,controllable,and scalable fabrication strategy and superior Raman performance make these platforms promising candidates for the development of inexpensive,efficient and mass-produced SERS substrates.Secondly,the composite structure of colloidal crystal and plasmonic structure is proposed to enhance the Raman scattering of analytes.The colloidal crystal-plasmonic composite structure is fabricated by the combination of magnetron sputtering,annealing process and self-assembly method.At first,a layer of gold film was sputtered and annealed on the glass slide to form a layer Au nano-net film.Then a layer of silica dioxide microsphere array was self-assembled on the Au nano-net film.Lastly,a layer of gold film with controllable thickness was sputtered on the silica dioxide microsphere array.The final samples can extremely enhance the Raman signal of analytes and can be used in the biomedicine,diagnose,food security detection and environment monitoring,etc.Thirdly,we present a feasible way to strongly enhance Raman signal via introducing an ultra-thin dielectric film with high index to form the metal-dielectric-metal triple layer structure based on the above mentioned researches.The metal-dielectric-metal triple layer structure is with quasi-three-dimensional plasmonic hotspots.The Raman intensity is obtained with an enhancement factor of735%for the dual-layer metal structure buffered with an ultra-thin silicon film as compared to that of the similar structure but with an ultra-thin silica film.Moreover,it is observed that the silicon layer based surface-enhanced Raman scattering substrate can provide the Raman signal as 2⁵ times larger as that of the silica buffered substrate.These distinct responses confirm the ultra-thin high-index semiconductor film is with the capability to additionally enhance Raman scattering.Otherwise,the upper and lower metal clusters can support multiple kinds of plasmonic resonances,which produce remarkable physical enhancement for Raman signals.Besides these impressive optical properties,the substrates are with prominent advantages on the structural feature since the fabrication process can be fulfilled simply,suggesting a feasible way for large-area and low-cost SERS platform.The findings can pave an avenue to achieve insights on the high index dielectric enhanced Raman scattering and hold potential applications in the optoelectronics.