A theoretical study based on the use of admittance loci method in the design of surface plasmon resonance (SPR) based structure using Ag-Au bimetallic alloy film of different alloy fractions and nanoparticle sizes has been reported along with some interesting performance related simulated results at 633 nm wavelength. The sensitivity and other performance parameter issues of the structure based on the choice of correct alloy fraction and nanoparticle size of Ag-Au bimetallic alloy film have also been discussed giving due importance to the dynamic range of the designed structure. 1. Introduction Surface plasmon resonance (SPR) occurs due to the interaction of the -polarized incident light with surface plasmon wave which propagates along metal-dielectric interface. The basic prism based configurations of SPR device were proposed earlier for observing surface plasmon resonance [1, 2]. SPR is a very useful technique for determining small change in refractive index (RI) of sensing sample at metal-sample interface. The sensing capability of SPR phenomenon was first reported for gas detection and biosensing [3]. A theoretical investigation on sensitivity comparison of prism and grating coupler based SPR sensors in angular and wavelength interrogation modes has been reported by Homola et al. [4]. Surface plasmon excitation in infrared region is very advantageous for sensing purposes. Surface plasmon excitation in infrared region involves the use of chalcogenide and silicon as coupling prism materials. Works on modeling of chalcogenide and silicon prism based surface plasmon resonance sensor for chemical sensing using infrared light have been reported earlier [5, 6]. An experimental work on surface plasmon resonance using various geometrical configurations of metal-dielectric interface has also been reported [7]. Admittance loci method has been used in thin film modeling [8] and design of SPR based devices [9–12]. Prism material dependency as well as sensing application of SPR based on admittance loci analysis has been reported earlier [13, 14]. Gupta and Kondoh have worked on tuning and sensitivity enhancement of SPR sensor [15]. Studies on the performance of SPR sensor using bimetallic alloy films have been reported earlier [16–18]. Some works on performance of fiber optic sensor using bimetallic alloy films have been reported [19, 20]. In the present work, admittance loci method has been used to design and analyze a plasmonic structure concerned with SPR based sensing with the main emphasis being given to the role played by alloy fraction and also the
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