"Tailor-Made" inhibitors in crystal growth: a Monte Carlo simulation study
   
Author(s): van Enckevort WJP (van Enckevort, Willem J. P.), Los JH (Los, Jan H.)  
JOURNAL OF PHYSICAL CHEMISTRY C    Volume: 112    Issue: 16    Pages: 6380-6389    
   
Abstract:
The impact of tailor-made inhibitors, that is, additives with horizontal and downward bonds similar to the growth units but with weaker or repelling bonds upward, on the growth and etching of crystals is studied. Kinetic Monte Carlo simulations applied to the {001} face of the solid-on-solid Kossel crystal are used. For thermally roughened faces, the measured reduction of growth rate as a function of inhibitor concentration and bond strength is described by a simple analytical model, considering an averaged blocking efficiency for each inhibitor molecule adsorbed on the crystal surface. In contrast to the rough faces, for flat faces, growth kinetics is no longer linear, and a dead supersaturation zone develops, where growth is almost blocked. The width of the dead zone as a function of step free energy and inhibitor concentration in the mother phase largely follows Cabrera and Vermilyea's theory of step pinning by adsorbed impurities. Concentration measurements show that the fraction of inhibitor molecules incorporated into the crystal lattice increases for increasing supersaturation up to a maximum value at the end of the dead zone, after which it diminishes again. Etching of flat faces again reveals nonlinear kinetics and the presence of a dead undersaturation zone, where etching is prohibited. This observation is explained using a one-dimensional model, in which the process of etching is considered as a stripping off of surface steps by kink propagation in the presence of inhibitor molecules.