The Role of the Structural and Chemical Effects in Metallic Surfaces: A Theoretical Approach

G.F. CABEZA; N.J. CASTELLANI; P. LEGARÉ

Santa Fe

Congreso; ENPROMER 2001: 3rd MERCOSUR Congress on Process Systems Engineering – 1st MERCOSUR Congress on Chemical Engineering; 2001

The idea of designing a surface in order to obtain well-defined catalytic properties is one of the most interesting objectives in some recent surface science studies on metals. The reason is that they reveal electronic and chemical original properties. It is important to track the fundamental origin of this, as it would open the possibility to built tailored materials for highly directed applications. A first goal is to understand the role played by structural and chemical effects in these systems. Here we examine the case of Pt overlayers deposited on single crystal faces of Ni and Co, with a mismatch of nearly 10 % in their lattice parameters. In this way, electronic changes could be induced on Pt due to structural constrains. Firstly, we present and analyze the local electronic structure of surface atoms in terms of the local density of electronic states. They were obtained from a density functional theory method applied to a semi-infinite solid. Then, we characterize the chemical properties by the adsorption of small atoms or molecules such as H or CO, using a molecular orbital method with cluster models. We show how the chemical behavior of the bimetallic system can be related to the electronic changes. A fictitious Pt surface, with a contracted lattice parameter, helps to visualize the influence of structural effects on the Pt electronic structure.