A Multilayer Approach to the Design of Fine Dispersed Metallic two Component Materials
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1. INTRODUCTION The controlled fabrication of multicomponent materials with well defined compositional and structural properties has directed the technological development towards processes which influence the properties of interest during manufacturing. The deposition of a multilayered film is clearly such a process. This paper focuses on the possibility of constructing materials which consist of small particles dispersed in a mechanically different matrix by a multilayer deposition process. Although contradictory at first sight it will be shown that such materials can be manufactured by a sequential deposition approach. In Sec. 2 we present a thermodynamic model of the structural evolution of a material consisting of a sequence of a layer-forming and an island forming component. The model is based on to the minimization of the surface free energy of a three dimensional island on an arbitrarily shaped surface. It yields the phase distribution as well as the roughness evolution of the uppermost surface in the resulting system. In Sec. 3 we compare the theoretically obtained roughness values and phase distributions to the corresponding properties of Al-Pb-multilayers deposited on atomically flat Si(100) substrates. A short conclusion summarizes the theoretical results with a special focus on the connection between atomistic growth mechanisms and the thermodynamic model in respect to the formation of critical nuclei on arbitrarily shaped surfaces. 141
Mat. Res. Soc. Symp. Proc. Vol. 382 01995 Materials Research Society
2. THEORETICAL FORMULATION
The growth characteristics of metallic single component films with thicknesses in the region from several nm to some [im can roughly be divided into two groups: the formation of dense compact films at low substrate temperatures and the growth of three dimensional islands at high substrate temperatures. The film structure in the low substrate temperature regime is either determined by the ballistic aggregation mechanism [1,21 or columnar because of the movement of particles in the growth front due to surface diffusion [3]. In either case the surfaces of the deposited films are smooth and compact and the films continuously cover the substrate. The three dimensional island growth mode is well known from the literature[4 ] and characterized by the fact that no continuous layer is formed until the islands are large enough to overlap. We now wish to formulate a model which predicts the structural evolution of a multilayered system consisting of a layer-forming and an island-forming component. The input data shall be the average island size, the average island distance, and the thickness of the compact layer. Let us consider a metallic system consisting of the components A and B. A condenses as compact layer and B grows in the island mode. The average distance of the islands, D, is determined by the atomistic mechanism of surface diffusion, their average size by the amount of deposited material. These preliminaries can be achieved at a constant deposition temperature Ts if mater
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