Photoacoustic study of surface roughness on thin evaporated gold films

Photoacoustic (PA) techniques are employed to study surface roughness of thin gold films using the non-radiative decay of surface plasmon polariton (SPP) generated on the metal surface by an attenuated total reflection (ATR) method. The thin gold films are of the same thickness but of varying intrinsic surface roughness due to varying rates of evaporation. The Lorentzian curves obtained by angular PA-ATR scan are compared to the Lorentzian curves obtained by regular ATR, where the halfwidth is taken as a measure of the propagation length. The interaction of the SPP with surface roughness at the metal/air interface leads to surface thermalization of SPP that can only be measured by PA-ATR. This additional non-radiative channel results in an increase in the resonance curves halfwidth of the SPP. The results are compared with the case of silver films