The dynamics and geometry of solid-liquid reaction interface

The spreading of small droplets (50-200 mu m) of Hg on thin Ag films has be en studied. The Hg front formation mechanism has been determined using opti cal microscope, Scanning Electron Microscope (SEM) and Atomic Force Microsc ope (AFM) analyses. The dynamics and geometry of the growing rough surfaces observed in our experiment, have been analyzed using the concepts of dynam ic scaling and self-affine fractal geometry, in order to determine the corr esponding roughness (alpha) and growth (beta) exponents. We have studied tw o systems, one in which the silver thickness was 500-2000 Angstrom and the other where the silver thickness was 0.1 mm. We have found that alpha = 0.6 6 +/- 0.03 and beta = 0.46 +/- 0.02 in the first system, and alpha = 0.77 /- 0.04 and beta = 0.6 +/- 0.02 in the second one. Each of these pairs sati sfies the scaling law alpha+alpha/beta = 2 within the experimental error. I n addition, it was found, in both systems, that for final stages of the exp eriment, the roughness exponent alpha crosses over to alpha approximate to 0.5 for relatively long length scales (order of a few microns). These findi ngs indicate that different mechanisms govern the process in various time a nd length regimes: diffusion and wetting at early stages, and chemical reac tion at final stages and short-length scales. (C) 2000 Elsevier Science B.V . All rights reserved.