Home – Home – Jornals – Chemistry for Sustainable Development 2019 number 3

Temperature dependence of the formation of two-dimensional crystalline AlN phase on the (0001)Al2O3 surface under ammonia flow was investigated. Two regions were experimentally detected in the temperature dependence of the process rate. Within the region of relatively low temperatures (T < 940 °C), the rate of AlN formation is limited by chemical reactions. A kinetic scheme of the process was proposed, and effective kinetic constants of the main stages of the process were determined. At a higher temperature (T > 940 °C), the formation of the ordered AlN phase is determined by a continuous two-dimensional phase transition in the lattice gas formed on the surface of AlN cells. A three-parameter scheme is proposed to describe the process. A good agreement between theoretical and experimental isotherms was obtained for the following parameters of the lateral interaction between the filled AlN cells in the lattice gas: Ei = 0.725 eV - lateral repulsion of the neighbouring filled AlN cells; U = -0.725 eV - the energy of stabilisation arising during the formation of a filled cell; V = 0.09 eV - energy consumed for the formation of an intermediate metastable cell of the lattice gas. The critical temperature of phase transition is unambiguously determined by the established parameters of lateral interaction and is equal to 795 °C. The observed phase transition in AlN lattice gas is continuous because experiments were carried out at temperatures above the critical point.