Figure 1

Schematic diagrams of studied structures. (a) the DERS structure and (b) the structure with concentric rings. The upper subfigure is the top view and the lower subfigure is the cross-section view. The dipole antenna in the center of the upper subfigure is 130-nm long, 45-nm wide, and 50-nm high with a 20-nm gap. The corrugated structure is placed on TiO₂ spacer over the gold ground with a glass substrate. The diameter of the center groove is fixed at 500 nm in the DERS structure, and it is indicted as D in the structure-added concentric rings. The periodicity and width of the grating rings in (b) are denoted as P and W. The thickness of TiO₂ spacer is 40 nm in the DERS structure in (a), and it is indicated as H in the structure with concentric rings in (b). The thickness of the gold layer atop the glass is 150 nm.