EXPERIMENTAL-OBSERVATIONS OF A LONG-RANGE SURFACE-MODE IN METAL ISLAND FILMS

The excitation of a long-range surface mode supported by gold, copper. aluminum, and iron metal island films has been investigated. These me tal island films have an imaginary part of the effective dielectric co nstant larger than the real part at the wavelength 632.8 nm, which is distinctly different from those of the bulk metals. This indicates tha t the surface mode supported by these metal island films is not the fr ee-electron surface-plasmon mode but another type of long-range surfac e mode. This type of surface mode can exist in any metal island film a s long as the film has the proper thickness and appropriate boundary l ayers.