Interband absorption of Pb-island films, consisting of Pb particles larger than about 50 A in diameter, has been measured in the photon energy range of 0.5-6.5 eV. The interband absorption located from 4.23±0.07 to 4.44±0.06 eV, the initial state for which is positioned at the bottom of the conduction bands, disappeared below about 300 A in diameter. The interband absorption located from 3.68±0.04 to 3.78±0.04 eV was shifted to higher energies with decreasing particle size below about 300 A in diameter, and became weaker with shift. The shift causes the initial state to be present in the lower portion of the conduction bands. The disappearance and the weakening are due to the decrease in the density of states (DOS) at the lower portion of the conduction bands. Such a decrease can be attributed to the effect of the reduced coordination number of surface atoms on the DOS of the conduction bands.
