Numerical Study of Optical Behavior of Nano-Hole Array with Non-Vertical Sidewall Profile

Due to the limit of nanofabrication methods of the nano-hole array (i.e., focused ion beam, nanoimprint/electron beam lithography, and metal film evaporation on top of the free standing membrane), the nano-hole arrays patterned in a noble metal film always has a non-vertical sidewall profile. In this work, the optical transmittance of the non-vertical profile nano-hole array with different tapered angle (α) and structural periodicity (P) was numerically investigated. The optimum tapered angle in case of positive profile of the nano-hole arrays was found as 10° and 12° at structural period of 450 and 500 nm, respectively. However, in case of negative profile, the optimum tapered angle of the nano-hole array was obtained as 4° at both structural period of 450 and 500 nm. The first and the second resonance modes of the nano-hole arrays with negative profile were shown a blueshift of 16 and 9 nm on increasing the tapered angle from 0° to 16° at structural period of 450 and 500 nm, respectively. It was also found that nano-hole arrays with positive tapered profile result in higher transmission than the negative profile one.