Laser dewetting behaviors of Ag and Au thin films on glass and Si substrates: Experiments and theoretical considerations

This article studies the effects of film and substrate on the laser-induced dewetting of metal thin films. Ag and Au films, both 10 nm in thickness, were deposited onto glass and Si substrates and dewetted using a single pulse from a nanosecond-pulsed Nd:YAG laser at lambda = 1,064 nm. The Ag film was completely dewetted into nano-particles at a pulse energy density of about 70 mJ/cm(2) on the glass substrate while an energy density over 390 mJ/cm(2) was needed for the Si substrate. This is attributed to the fact that Si has a much higher thermal conductivity than glass and that the laser energy absorbed by the film significantly dissipated into the Si substrate rather than being solely used to heat the film. The Au film required slightly more laser energy in comparison to the Ag film. The energy densities of a laser pulse required to dewet the Ag and Au films were theoretically derived using one-dimensional heat conduction equations and thermodynamic data. The difference between the experimental and calculated pulse energies was more significant for the Si substrate. This indicates that lateral thermal diffusion occurred considerably on the Si substrate even with a nanosecond pulse duration. We demonstrate both experimentally and theoretically that as the thermal conductivity of the substrate increases, the film area dewettable by a laser pulse is decreased.