Comparative photoacoustic study of surface roughness on silver and gold thin films

Photoacoustic Spectroscopy (PAS) of surface plasmon SP on evaporated films of the two nobel metals Ag and Au of dielectric ε˜
_m
(=ε'+iε) was employed to study the difference in intrinsic surface roughness (as evaporated) of the two metals. The SP were generated in the visible on the metal films Attenuated Total Reflection method. The halfwidth Γ of the resulting resonances is taken as the sum of the inverse of the attenuation lengths in the propagation of SP. Our measurements for various Ag and Au films of the same thickness and evaporated under similar conditions indicate that the bulk decay mechanism plays the dominant role in attenuation for SP in Au while surface decay via surface roughness plays the dominant role in the case of Ag. These results are explained in terms of the band structure of the two metals""