Table 2.

Plasma frequency (${\mathsf{\omega }}_p$) and onset of the interband transitions (${\omega }_{Inter}$) for some common metals used in SERS. The former values are taken from West et al. [157]; the latter are taken from Cottancin et al. [160] (gold, silver and copper) and from Ehrenreich et al. [161] (aluminum).

Metal	${\mathit{\omega }}_{\mathit{p}}$	${\mathit{\omega }}_{\mathit{I}\mathit{n}\mathit{t}\mathit{e}\mathit{r}}$
Gold	8.9 eV (139 nm)	2 eV (620 nm)
Silver	9.2 eV (135 nm)	4 eV (310 nm)
Aluminum	12.7 eV (98 nm)	1.4 eV (886 nm)
Copper	8.7 eV (142 nm)	2 eV (620 nm)