A Simple Approach to the Energetics of Surface Defects in Transition Metals

A SIMPLE APPROACH TO THE ENERGETICS OF SURFACE DEFECTS IN TRANSITION METALS 

IPhysique des Solides Universite Paris-Sud F91405 Orsay, France 2CEA/DSM/DRECAM/ SRSIM CE de Saclay 

The last twenty years have seen a rapid development of surface physics. In particular, the properties of clean perfect surfaces (with two-dimensional periodicity) are henceforth well known and understood. In recent years, the focus has been put onto surfaces with defects (adatoms, steps, vacancies, impurities...) which can now be investigated experimentally due either to the progress of old techniques (field ion microscopy or He diffraction, for instance) or to the rapid development of new methods (STM, AFM, SEXAFS...). 

we will first briefly recall the principles of this method in the case of transition metals. Then we will apply it to two illustrative examples the surface segregation energy of an impurity is a pure host and the growth of adislands on FCC(lll) surfaces of the same chemical species. 

TOTAL ENERGY CALCULATIONS IN THE TIGHT-BINDING APPROXIMATION 

We will limit ourselves here to transition metals. It is well known that in these metals, the cohesive properties are largely dominated by the valence d electrons, and consequently, sp electrons can be neglected save for the elements with an almost empty or filled d valence shell. Since the valence d atomic orbitals are rather localized, the d electronic states in the solid are well described in the tight-binding approximation. In this approximation, the cohesive energy of a bulk crystal is usually written as  

Ed is the center of gravity of the d band, A ]E) the total density of states and Ep the Fermi energy. 

---