Microscopic Approach of the Metal Insulator Adhesion

Abstract

As a first step in the calculation of the adhesion energy and wetting angle of non-reactive liquid metal-insulator systems, we have performed an analytical study of the electronic structure of such an interface, with special emphasis on the Metal Induced Gap States (MIGS). It includes three steps: i) a tight-binding approach of the dispersion relation and Green’s function of insulators of NaCl rocksalt or ZnS zincblende structure; ii) a matching with free electron-like wave functions at the NaCl (100) or ZnS (110) surfaces, which yields the density and penetration depth of the MIGS as a function of the ionocovalent characteristics of the insulator and of the metal Fermi level; iii) a selfconsistent determination of the Fermi level position in a Thomas-Fermi approximation. The Schottky barrier height is derived under a simple analytical form and its dependence upon the metal work function is found in good agreement with experimental results. We stress why the MIGS are expected to play an important role in the understanding of the observed tendencies of adhesion and wetting as a function of the electronic nature of the metal (Fermi level density of states and work function) and of the insulator (ionocovalent character).