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 metal island films have an imaginary part of the effective dielectric constant larger than the real part at the wavelength 632.8 nm, which is distinctly different from those of the bulk metals. This indicates that the surface mode supported by these metal island films is not the free-electron surface-plasmon mode but another type of long-range surface mode. This type of surface mode can exist in any metal island film as long as the film has the proper thickness and appropriate boundary layers.