IMPURITY BLOCKING OF CRYSTAL-GROWTH - A MONTE-CARLO STUDY

The well-known phenomenon of the blocking of crystal growth at low sup ersaturations by a low density of immobile impurities adsorbed on the crystal surface has been investigated by the Monte Carlo technique. Th e computer simulations were carried out for [100] steps on the (OO1) f ace of a solid-on-solid Kossel crystal covered by a square array of im mobile impurities. Above and slightly below the roughening temperature , blocking of crystal growth was found to be due to the creation of an extra internal surface free energy as a result of the incorporation o f impurities. Here the width of the dead supersaturation zone is inver sely proportional to the squared distance between the impurities. At l ower temperatures growth is blocked by pinning of the growth steps at the impurity centres as proposed in an early paper by Cabrera and Verm ilyea (1958), in which the width of the ''dead zone'' is inversely pro portional to the impurity separation. Further issues addressed to in t his paper are a kinetic impurity blocking for rough faces and the bloc king of step propagation by randomly deposited impurities as well as b y the smallest possible impurities of one growth unit in size. (C) 199 8 Elsevier Science B.V. All rights reserved.