Au, Ag, and Cu, while for SiO 2 films of 300 nm and thicker, the resonance linewidth shows the same tendency as for Pt and Pd. The resonance linewidths of Pt and Pd are up to twice as large as those of Au, Ag, and Cu, whereas those of HEA are only 1.5 times larger than Au, Ag, and Cu, which is expected to reduce the absorption loss of Pd and Pt. To discuss the optical behavior of these metals in detail, their permittivities were determined over a wide range of wavelengths from UV-visible to mid-infrared by spectroscopic ellipsometry (Table ).