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).