Elastic theory of surface deformation in C60 adsorption

• Published in: Surface science 2007-03, Vol.601 (6), p.1494-1500
• Main Authors: LEVI, Andrea C, CALVINI, Piero
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Physics
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/j.susc.2007.01.008

In molecular physisorption, beyond attractive and repulsive forces, a third contribution arises from the elastic deformation of the surface. In this paper the dimple appearing on a gold surface upon physisorption of a C60 molecule is studied and its effect on the adsorption energy is evaluated. The depth and shape of the dimple are studied on the basis of the theory of elasticity. The equilibrium equation is solved in the presence of the body forces originating from a suitable Au-C60 interaction potential and the solution for the deformation field is obtained by means of a two-step procedure. In the first step a curl-free deformation field is obtained, which takes the effects of the body forces into account, but generates mismatch of the boundary conditions. In the second step the solution of the equilibrium problem in the absence of body force is generated, which compensates the previous boundary condition violation. Thanks to linearity, the final solution is obtained as the sum of the results of the two steps. An (approximate) iterative scheme is applied for taking the surface deformation into account in imposing that no forces act on the Au surface. When the distance z0 of the centre of the C60 cage from the surface is rather large, the dimple is represented by a bulging surface, but, as the C60 approaches the Au surface, the surface recedes and a well formed dimple appears. The corresponding depth at the mechanical equilibrium position (z0=4.8A) turns out to be 36.3pm.