Surface Plasmon Resonance of SnO2/Au Bi-layer Films for Gas Sensing Applications

Surface Plasmon resonance (SPR) sensor technology has great potential for detection and analysis of chemical and biochemical substances in many important areas including medicine, environmental monitoring, biotechnology, drug and food monitoring. Chemical sensing using SPR responses of semiconducting metal oxide films deposited on top of noble metal thin films could offer a simple, sensitive and reliable method for the detection of low concentration of gases. In this article, ultra-thin SnO2/Au bi-layer films of various thicknesses were deposited by pulsed laser deposition technique on BK7 glass substrates and their SPR responses were measured in the Kretschmann geometry of attenuated total reflection using a polarized light beam at 633 nm wavelength. The widths of the SPR dip and SPR angles were investigated as the function of the SnO2 and Au layer thickness and the wavelength of excited laser light in order to find the optimized structural parameters for SPR gas sensors based on SnO2/Au bi-layer films. The SPR responses of bi-layer films were also simulated with Macleod's general characteristic matrices method in order to compare with experimental data. The simulated results show the similar trend as the experimental date in term of the dependence of SPR angle and width with Au and SnO2 layer thickness, however, discrepancy between the simulated results and experimental data does existed, particularly, the shape of SPR response predicted by the theory is much broader than the experimental results. The SPR responses of the SnO2/Au bi-layer films upon 50 or 100 ppm NO gas exposure were measured and the primary results indicated that gas sensing using the SPR responses of the SnO2/Au bi-layer films is feasible.