Adsorption of CO, CO 2 and NO molecules on a BaTiO 3 (0 0 1) surface

Abstract

Since the development of Scanning Tunnelling Microscopy (STM) technique, considerable attention has been devoted to various molecules adsorbed on various surfaces. Also, a new concept emerged with molecules on surfaces considered as nano machines by themselves. In this context, a thorough knowledge of surfaces and adsorbed molecules at an atomic scale are thus particularly invaluable. The present work describes the first Density Functional Theory (DFT) study of adsorption of CO, CO 2 and NO molecules on a BaTiO 3 surface following a first preliminary calculation of O and O 2 adsorption on the same surface. In the previously considered work, we found that a (0 0 1) surface with BaO termination is more stable than the one with TiO 2-termination. Consequently, we extended our study to CO, CO 2 and NO molecules adsorbed on a (0 0 1) surface with BaO termination. The present calculation was performed on a (1 × 1) cell with one monolayer of adsorbed molecules. Especially, a series of cases implying CO molecules adsorbed in various geometrical configurations has been examined. The corresponding adsorption energy varies in the range of −0.17 to −0.10 eV. The adsorption energy of a CO 2 molecule directly located above an O surface atom (called O s) is of the order of −0.18 eV. The O–C distance length is then 1.24 Å and the O–C–O and O–C–O s angles are 134.0° and 113.0°, respectively. For NO adsorption, the most important induced structural changes are the followings: (i) the N–O bond is broken when a NO molecule is absorbed on a Ba–O s bridge site. In that case, N and O atoms are located above an O and a Ba surface atom, respectively, whereas the O–Ba–O s and N–O s–Ba angles are 106.5° and 63.0°, respectively. The N–O distance is as large as 2.58 Å and the adsorption energy is as much as −2.28 eV. (ii) In the second stable position, the NO molecule has its N atom adsorbed above an O s atom, the N–O axis being tilted toward the Ba atom. The N–O s–Ba angle is then 41.1° while the adsorption energy is only −0.10 eV. At last, the local densities of states around C, O as well as N atoms of the considered adsorbed molecules have also been discussed.