Estudo teórico de superfícies de nióbio

Abstract

We conducted an ab initio study of the adsorption of oxygen on surfaces Nb(110) and nitrogen in surfaces Nb(100) and Nb(110), for various monolayer coverages ranging from 1 to 0.5 monolayer. We find the energetically most stable structures and made an analysis of the geometry of these structures and their electronic structure through their band structures, their PDOS4 and simulated STM5 images. Our calculations were performed based on the density functional theory (DFT6) with the generalized gradient approximation implemented by Perdew, Burke and Enzerhof. The electron-ion interaction was described by Vanderbilt ultrasoft pseudopotentials and Kohm-Sham orbitals were expanded in a series of plane waves. The results show various structures N/Nb(100)-(n⇥1), N/Nb(110)-(n⇥1) and O/Nb (110)-(n⇥1) energetically stable. Our STM simulations indicate the formation of bright lines parallel to the lines of vacancy of adsorbed atoms, resulting in an anisotropy in the electronic structure of these surfaces. That is, the metallic character of the surface was enhanced in the direction parallel to the lines of vacancy. In N/Nb(100) and O/Nb(110) the surface structure of clean Nb (100) and Nb (110) is only slightly modified after the adsorption of nitrogen and oxygen, respectively. However in the structures N/Nb(110) we observed, in general, a strong clean surface reconstruction due to the adsorption of nitrogen.