CNMS User Research
of Sub-stoichiometric Defects in the Formation of Nano-particles
T. Park (CNMS User), Baylor University; Minghu Pan, Vincent Meunier
and E. Ward Plummer (ORNL & University
The key step in the formation of face-sharing TiOx (x < 2) sub-oxides
on surfaces is the surface oxidation of Ti interstitials. Although
Ti is regarded as reactive, little is known concerning the reactivity
of Ti interstitials toward oxygen on the surface. In this work, a combination
of scanning tunneling microscopy and density functional theory allows
the accurate determination of the structure and stoichiometry of Ti
interstitial-based defects and their reactivity toward molecular oxygen
(attached Figure and Park et al. Phys. Rev. B, 2007). Ab
initio molecular dynamics calculations show that the
row of Ti interstitials, as a highly under-coordinated cationic site,
readily dissociates molecular
oxygen. The dissociated oxygen surrounds a Ti interstitial to form
an oxygen plane of a partial octahedron. On the other hand, the partially
oxidized Ti2O2 strand exhibits much subdued reactivity.
Although the line defect neither dissociates nor adsorbs molecular
oxygen, it serves
as a nucleation site for an oxidized Ti interstitial such as a TiO2
molecule and for further growth of the line defect.
The crucial role that Ti interstitials play in surface reconstructions
and formation of sub-stoichiometric defects has been recently elucidated
by our CNMS team (Park et al. Phys. Rev. Lett. 96, 226105, 2006).
As for the first case study, this work establishes the relationship
between distinct local structures and stoichiometry of these Ti interstitial-based,
surface defects and their chemical reactivity, exemplified in the
reaction with molecular oxygen. The results from this work should
be of broad interest as the interaction of oxygen with TiO2 is essential
in many photochemical and catalytic processes including the oxidation
of CO by gold nanoparticles supported on titania as well as other
reducible oxide supports.
Park, M. Pan, V. Meunier, and E.W. Plummer, “Re-oxidation of TiO2(110)
via Ti interstitials and Line Defects,” Phys.
Rev. B 75, 245415 (2007).
M. Pan, V. Meunier, and E.W. Plummer, “Surface Reconstructions
of TiO2(110) Driven by Sub-Oxides,” Phys.
Rev. Lett. 96, 226105 (2006).
The theoretical research used resources of the National Center for
Computational Sciences at ORNL. This research was conducted at the
Center for Nanophase Materials Sciences, which is sponsored at Oak
Ridge National Laboratory by the Division of Scientific User Facilities,
U.S. Department of Energy. KTP is supported by the Baylor University