Structure of an ultrathin TiOx film, formed by the strong metal support interaction (SMSI), on Pt nanocrystals on TiO2(110)

We use first-principles density functional theory to study ultrathin TiOx f ilms on Pt(1 1 1). The preferred interface with Pt has Ti with O as an over layer. However, this ordering, preferred over Ti/O/Pt by 2.9 eV/Ti-O unit, produces > 10% stress. This explains a complex structure, seen using STM, o f TiOx bilayers encapsulating Pt(1 1 1) nanofacets: the energetics of stres s relief is about ten times that of differences in the various possible O/T i/Pt(1 1 1)-layer site occupations, thus favoring dislocation formation. A structure is found that is stable. It consists of a series of linear misfit dislocations at the relatively weak Ti/Pt interface that are 6/7 Ti/Pt row s wide. In addition, strong interactions at the O/Ti interface and O-layer strain also cause the Ti/Pt interface to abruptly change from hcp- to fee-s ite Ti, producing linear "canyons" (Ti/Pt dislocation cores occur between t hese stripes). Furthermore, alternating hcp- and fcc-site triangles, each w ith ten O-atoms, are separated by bridging O in an abrupt O/Ti misfit dislo cation, thus producing a zigzag pattern. The above dislocations release str ain along both the x- and y-directions in the surface plane. However, we ha ve been unable to find a stable structure if the zigzag ends consist of O, but stability is found if they consist of Ti. Finally, reverse bias STM ima ges indicate the ends might indeed different than the line portions of the zigzag features. (C) 2001 Published by Elsevier Science B.V.