OPTICAL-PROPERTIES OF NANOSIZED GOLD PARTICLES

Gold particles smaller than 2 nm in diameter were grown in glass. Thei r optical absorption spectrum did not show the usual plasma absorption band for gold particles; this band was spread by the small particle s ize. The absorption spectrum was calculated from the bulk optical prop erties of gold, modified for the small particle size; there was good a greement between calculated and measured spectra. The smallest particl es containing from 20 to 40 gold atoms showed a lambda(-4) dependence of absorption on wavelength h. This result implies that the absorption in these particles was entirely from free electrons at wavelengths ab ove 0.3 mu m.