The roughness and growth of a silver–mercury reaction interface

The spreading of small droplets (50–200 μm) of Hg on thin Ag films has been studied, using optical microscope, scanning electron microscope (SEM) and atomic force microscope (AFM). The growing rough surfaces have been analyzed in order to determine the roughness (α) and growth (β) exponents. For Ag thickness of 500–2000 Å we have found that α=0.66±0.03 and β=0.46±0.02, while for Ag thickness of 0.1 mm, α=0.77±0.04 and β=0.60±0.02. Both sets of exponents satisfy the scaling relation α+α/β=2. In both systems the roughness exponent α crosses over to 0.5 in the final stages of the experiment and for relatively long length scales (order of a few μm).