Spreading of a mercury droplet on thin gold films

The spreading of a small mercury droplet (150 μm) on thin gold films is studied, using an optical microscope enhanced with a differential interference contrast system. The growing interfaces are analyzed in order to determine the roughness (α) and growth (β) exponents. For gold film thickness of 1500 Å we find that α = 0.88 ± 0.03 and β = 0.76 ± 0.03, while for gold thickness of 3000 Å, α = 0.96 ± 0.04 and β = 1.00 ± 0.04. Both sets of exponents satisfy the scaling relation α + α/β = 2. In both systems the roughness exponent α crosses over to a value close to 0.5 in the final stages of the experiment and for relatively long length scales (order of a few microns).