OpticalAbsorption on Submonolayer Silver and Gold Films
Keisuke Shinosaki
February，1982
Opticalabsorption of submonolayer Ag and Au films deposited onafusedquartzATR prism were measured．The observed spectra wereinterpreted wellby the model of two−
dimensionally distributed ellipsoids of rotation providing that the dielectric constants of island particles vary with their size．The free electron part of the dielectricconstants ef，。e WaS COnfirmed to obey the theory of classicalsize effect．The bound electron part eb。。nd
WaS aSSumed to be modified frbm the bulk value by the following equation
− 70 −
eb。。nd（hw）＝k認慧（hw−hw。）
Where k and hw。are adjusting parameters．It was found that hw。increases with decrease
in particle size．Theincreasein hd′。meanS that the opticalband gap，i・e・，tranSitionfrom
d−bands to the Fermisurface，becomes widerthanthatofthebulk．Thisresultisconsistent with the XPS valence band observations of Ag and Au particles where the top of the d−
bands was found to shift to thelower energy direction with decreasein particlesize．The resultis also consistent with the energy band structure calculation where the position and the width ofthe d−bands are very sensitive to the crystallinelatticefield，becausethelattice field of smallparticleis consideredto be modifiedfrom the bulk one・Thevalueofkwas
around1．0for Ag andO．5〜0．8for Au．Theisland structure parameters deduced from
the observedabsorption spectrabythe use ofthe modified eb。。nd Werefoundto be reaso−
nable．
