Surface characterisation by surface plasmon resonance technique

Metallic gold (Au) film of approximately 45 nm thick was deposited on the glass slide by vacuum evaporation method under the vacuum 10(-6) Torr. Surface plasmon resonance(SPR) curve was taken in the form of reflected intensity R-p variation as a function of the angle of incidence theta for the three layered (glass-Au-air)system and the resulting SPR curve was well fitted by Fresnel's theory to find thickness and optical constants of Au film. The organic overlayers of tetra-undecyl-tetra p- nitrophenylazocalix(4) resorcinarene (Azo 1) compound was deposited by spin coating method. SPR measurements were taken in air as well as in pure water, for an overlayer containing Azo 1 spun on Au coated slides. The large change in the refractive index of water 1.33 as compared to that of air 1.00 causes large shifts in the SPR resonance angle theta (SPR) The exact determination of the optical parameters of a organic film can be possible by varying the dielectric medium interfacing the overlayer. SPR data for both media used throughout this work were fitted to Fresnel reflection theory for a four layerd (glass-Au-Azo1-air or water) system. By varying the Azo 1 film thickness during the fitting procedure different solutions have been obtained for the film dielectrric constant and hence its refractive index. The refractive index versus thickness for both media were plotted and from the intersecting point of the two curves an exact solution has been found which gives film optical parameters of organic(Azo 1)overlayers.