Spreading of a mercury droplet on thin gold films

The spreading of a small mercury droplet (150 gm) 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 (alpha) and growth (beta) exponents. For gold film thickness of 1500 Angstrom we find that alpha = 0.88 +/- 0.03 and beta = 0.76 +/- 0.03, while for gold thickness of 3000 Angstrom, alpha = 0.96 +/- 0.04 and beta = 1.00 +/- 0.04. Both sets of exponents satisfy the scaling relation alpha + alpha/beta = 2. In both systems the roughness exponent alpha 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). (C) 2002 Elsevier Science B.V. All rights reserved.