Fig. 14

a Absorbing spectrum of the NPA structure varying with nanoparticle size. b Absorbing spectrum of the NPA structure for nanoparticles with different shapes. S sphere, E ellipsoid, a the major axis semidiameter of the ellipsoid, b is the minor axis semidiameter of the ellipsoid. For E1 and E2, the electric filed is along the major-axis direction. For E3, the electric field is along the minor-axis direction