On the short-time compositional stability of periodic multilayers

The short-time stability of concentration profiles in coherent periodic mul tilayers consisting of two components with large miscibility gap is investi gated by analysing stationary solutions of the Cahn-Hilliard diffusion equa tion. The limits of the existence and stability of periodic concentration p rofiles are discussed as a function of the average composition for given mu ltilayer period length. The minimal average composition and the correspondi ng layer thickness below which artificially prepared layers dissolve at ele vated temperatures are calculated as a function of the multilayer period le ngth for a special model of the composition dependence of the Gibbs free en ergy. Far period lengths exceeding a critical value, layered structures can exist as metastable states in a certain region of the average composition. The phase composition in very thin individual layers, comparable with the interphase boundary width, deviates from that of the corresponding bulk pha se. (C) 1999 Elsevier Science S.A. All rights reserved.