Finite-difference time-domain analysis of local electric field enhancement by nanoholes of varying shape and diameter in metal with different thicknesses

This work reports changes in surface plasmons according to the shape and diameter of nanoholes in thin metal films of varying thickness. Cylindrical and reversed trapezoidal nanoholes were simulated using the finite-difference time-domain (FDTD) method. Nanoholes of 10, 50, and 100 nm diameters were modelled in 40-, 60-, and 80-nm-thick metal films. The strongest local electric field enhancement occurred with a reversed trapezoidal hole of 10 nm size in a 100-nm-thick metal film. The resonance wavelength was red shifted by decreasing the hole size and/or increasing the metal film thickness.