Electronic properties of small silver particles: the optical constants and their temperature dependence

Specimen size dependences of the dielectric constant and of its variations with temperature have been investigated by measuring the optical plasma resonance absorption of small silver particles embedded in glass. The following relations hold at the wavelength 405 nm: epsilon 2 (imaginary part at 300K)=0.23+2.64/R, and epsilon 2 (300K)- epsilon 2 (1.5K) approximately=0.07-0.08/R where R is the particle radius in nm. Agreement has been found with the free path effect but not with the quantum size effect theories of Kawabata and Kubo (1966) and of Glauberman and Adamyan (1969). The behaviour of the temperature dependence can partly be explained by thermal lattice contraction. The ratio of electron density to the optical effective mass shows no distinct changes as R varies from 10.5 nm to 1.1 nm. It may hence be concluded that normal metallic properties are present in silver particles embedded in glass which contain more than about 400 atoms.