Effect of an oxide layer on the far-infrared absorption of small silver particles

We measure the far-infrared absorption of silver smoke, with volume-averaged radii 600 Å̊, inside a Teflon host. The size distribution and the oxide-layer thickness of silver smoke were included in analyzing the measured absorption coefficient. The high resistivity of the oxide layer introduces a large electric dipole absorption coefficient well characterized by α=C${\omega }^2$ for 20 ${\mathrm{cm}}^{\mathrm{-}1}$${\mathrm{cm}}^{\mathrm{-}1}$, where C is proportional to the thickness of the oxide layer. Because of the oxide layer, the absorption coefficient due to the electric dipole becomes comparable to that of the magnetic dipole for 50 ${\mathrm{cm}}^{\mathrm{-}1}$${\rho }_c$=0.08±0.03 Ω cm.