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The sensitivities of localized surface plasmon resonant sensors can be improved by changing the shape, size, and arrangement of nanosized metal dots on a substrate. In this study, we fabricated nanosized gold structure arrays on a silica substrate by electron beam lithography combined with a liftoff process, and studied their performance as refractive index sensors. We found that the sensitivity of single gold square dot arrays increases with the pitch while the absorbance decreases. On the other hand, both the sensitivity and absorbance of twin gold square dot arrays increase as the gap distance decreases for a particular incident polarization. We discuss the sensitivity of these structures for practical sensor applications.

A resist pattern of half-pitch (hp) 50 nm, 120 nm deep was fabricated with near-field lithography (NFL) of i-line (l = 365 nm) using a positive-tone chemically amplified resist and a tri-layer resist process developed for NFL. The experimental results were in close agreement with the numerical results of electro-magnetic analysis using finite-difference time domain (FDTD) method. The possibility of fabricating sub-50 nm patterns was discussed over the numerical results.