| AVS 61st International Symposium & Exhibition | |
| Surface Science | Wednesday Sessions |
| Session SS+AS+EN-WeM |
| Session: | Dynamic Processes of Single Atoms and Molecules at Surfaces |
| Presenter: | Mitsunori Kurahashi, National Institute for Materials Science (NIMS), Japan |
| Authors: | M. Kurahashi, National Institute for Materials Science (NIMS), Japan Y. Yamauchi, National Institute for Materials Science (NIMS), Japan |
| Correspondent: | Click to Email |
O2 adsorption on Al(111) has been investigated intensively as the most representative system of surface oxidation. The dynamical process happening on the surface, however, remained unclear. An STM study by Brune et al.[1] has proposed that adsorbed O-atoms are atomic and are well separated each other. Initially, this has been ascribed to the transient mobility driven by the O2 chemisorption energy ("hot-atom" mechanism)[1], but this mechanism has been found to be unlikely. The abstraction mechanism, in which one O-atom is bound to the surface while the other is ejected, has been proposed alternatively based on the resonance enhanced multi-photon ionization measurement.[2] It is however not evident whether or not the abstraction process is the dominant event at low translational energies (E0). In addition, the STM study by Schmid et al.[3] has suggested that the adsorbates consist of two O-atoms locating at nearby sites. This cannot be explained by the abstraction mechanism.
In this study, we focused attention to the alignment dependence in the O2 sticking to clarify the reaction mechanism. A single spin-rotational state-selected [(J,M)=(2,2)] O2 beam, for which we can specify both the molecular alignment and spin direction relative to the magnetic field, was adsorbed on an Al(111) surface. The results show that O2 molecules parallel to the surface have much higher sticking probabilities than those perpendicular to the surface at E0 < 0.2 eV. The E0 dependence of the sticking probability indicates that the dissociation barrier at the perpendicular geometry is about 0.1 eV higher than at the parallel geometry. The present results reveal that the abstraction process, which occurs at the perpendicular geometry, is a minor event at low E0.[4]
[1] Brune et al., Phys. Rev. Lett., 68, 624 (1992). [2] Komrowski et al., Phys. Rev. Lett., 87, 246103 (2001).[3] Schmid et al.,Surf. Sci., 478, L355 (2001). [4] Kurahashi et al., Phys. Rev. Lett., 110, 246102 (2013)