Abstract
We investigate field enhancement inside metal-insulator-metal gaps with asymmetric thicknesses and tapered shapes in the terahertz regime. Finite-difference time-domain simulations were conducted for calculation of field enhancement factor. The calculation indicates that for asymmetric sample, field enhancement increases proportionally with the decrease of the thinner of the two metal film thicknesses surrounding the gap. Concomitantly, angle variation has little effect on the field enhancement if the thickness of the narrowest gap region is fixed. A model based on the capacitor concept is proposed for intuitive understanding of the phenomena.
Highlights
Electric field can be enhanced near the edge of a metal structure due to free charge accumulation at the apex
Field enhancement in asymmetric and tapered gaps between two metals with 5 nm width was examined at THz regime by numerical studies
finite-difference time-domain (FDTD) results show that the thickness of the smallest gap region is the most important factor in field enhancement
Summary
Electric field can be enhanced near the edge of a metal structure due to free charge accumulation at the apex. By calculating field enhancement of the gap with changing tapered angle and thickness symmetrically and asymmetrically, the effects of the gap shape and the symmetry on field concentration between metals are examined. FDTD results for each type of the structure are plotted in Fig. 3 when the gap thickness tgap is 50 nm and θ is set at 60° for all the said four structures: x-component of the electric field distributions [Fig. 3(a)] and x component of the current density distributions [Fig. 3(b)].
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