Study On A New Method Of Surface Enhanced Raman Scattering

Rough surface of noble metal has an extraordinary enhancement for electric field,which means a lot to Raman detection. This essay discusses the optical properties ofthe gold, and have deeply researched electric field enhancement of severalgold-structures. This essay comes up with the conclusion that enhancement factor isgreatly affected by the size and form of the structure and makes us betterunderstanding of the enhancement theory. It is composed of four parts:Firstly, the extinction properties of nano-scale gold sphere are studied using theDDA method, which have a regular change with the variation of size and form of thenano-structure. The model of the gold is determined with Drude-Lorentz model.When the size of nano-sphere is determined, absorbance increases firstly and thendecreases and the scattering is rising generally, the latter becomes the dominant factorlater. When the lambda of incident light is determined, the extinction coefficientincreases to a peak and then decreases generally.Secondly, a thorough study is made about electric enhancement of differentstructures. Given the free path of electrons, constant of material, frequency ofPlasmon, the enhancement factors of sphere, triangle, two spheres, two triangles underdifferent sizes and intervals have been calculated by finite element method. Theresults show that the enhancement factors decrease in the sequence of two triangles,two spheres, triangle and sphere. Another interesting point is that when orientation oftwo spheres is the same as polarization, there appears to be a ‘hot spot’ at the intervalof two spheres. When interval varies from1nanometer to10nanometers, enhancement factor is larger as interval is smaller. While the top angels of twotriangles range from90degrees to30degrees, enhancement factor falls down.In this part electric and magnetic field of sub-wavelength slits is theoreticallystudied by RCWA. The theory indicates that when the period of slits approachingwavelength of incident light, the transmission shows a sharp change. How severalfactors such as slits period, depth of slits, incident angel affect are studied byMATLAB. The theory shows that it can be used as substrates if parameters areproperly adjusted, and calculation shows it to be a104Raman enhancement factor.The last part aims at strengthening the electric field between two gold nano-wiresby putting them into periodical sub-wavelength slits,which combines the effect ofamplifying electric field from the near-field coupled effect and the quasi-F-Presonance. The study indicates that the electric field between the gold nano-wiresshows periodical variation when depth of slits changes, while it turns out a sharp peakwhen the period is close to the wavelength of incident light, and it decreases rapidlyas the interval of wires increases. According to the result that is calculated by finiteelement method, it gets a200electric field enhancement which means a109Ramanenhanced factor in hot spot between the two gold nano-wire sin sub-wavelength slitsby reasonably adjusting the period and depth of the slit, which is three orders ofmagnitude than two lonely wires.