UNUSUAL EXTINCTION SPECTRA OF NANOMETER-SIZED SILVER PARTICLES ARRANGED IN 2-DIMENSIONAL ARRAYS

Two-dimensional arrays of 1000 Angstrom silver particles were prepared by adsorption from colloidal suspensions onto glass slides derivatize d with (3-mercaptopropyl)trimethoxysilane. By variation of the concent ration of the colloidal suspensions, slides with different interpartic le distances were obtained, and their extinction spectra were measured in water. A blue shift (up to 90 nm) and sharpening of the peak corre sponding to the plasmon resonance was observed as the distance between particles decreased to a value comparable to, or less than, their dia meter. The angular dependence of the extinction spectra was studied fo r s- and p-polarized light. The data are interpreted to result from co herent coupling of the plasmon resonances in closely spaced silver par ticles upon irradiation with light.