Metal-to-insulator transition in silver nanolayers grown on silver oxide nanoparticles

Abstract

Silver nanometre thick layers were grown on Ag₂O particles of size ~21 nm by subjecting the latter to a heat treatment at temperatures ranging from 500 to 543 K. Optical-absorption measurements on particles of core-shell structure and dispersed in ethyl alcohol were carried out over a temperature range from 290 to 340 K. The results were analysed using size-dependent dielectric permittivity incorporating a free-path effect. The analyses showed the existence of a metal-to-insulator transition in silver nanoshells with a thickness equal to or less than ~2 nm. The extracted values of electrical conductivity over this temperature range showed a semiconducting behaviour with an activation energy of 0.05 ± 0.01 eV. Direct electrical resistivity measurements substantiated these results obtained from optical absorption data. The activation energies determined from both the above measurements were in satisfactory agreement.