Abstract
The strong focusing and field enhancement effects of a metal nanofinger surrounded by multiple concentric rings are investigated through both COMSOL Multiphysics and finite-difference time-domain (FDTD) simulations. The aspect ratio of the nanofinger is the main parameter determining the full width at half maximum (FWHM) and the strong local field enhancement. The optimal values of the aspect ratio for the maximal enhancement and minimal FWHM are close to 1.8 and 3.0, respectively. Furthermore, the optimal aspect ratio of maximal field enhancement intensity decreases linearly with the incident wavelength, and the optimal aspect ratio of minimal FWHM increases linearly with the metal film thickness. The nanofinger fabricated with the focused ion beam method has a small conical angle, which results in a higher field enhancement and smaller focal spot size than straight sidewall finger. However, the shorter finger defect deteriorates FWHM and field enhancement because of the bias from the optimal aspect ratio value.
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