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

D. R. Jennison, O. Dulub, W. Hebenstreit, U. Diebold

Surface and Interface Sciences Department, Sandia National Laboratories, Albuquerque, NM 87185-1415, U. S. A.
Department of Physics, Tulane University, New Orleans, LA 70118, U.S.A.

Surf. Sci. 492 (2001) L677-L687

We use first-principles density functional theory to study ultrathin TiOx films on Pt(111). The preferred interface with Pt has Ti with O as an overlayer. 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, of TiOx bilayers encapsulating Pt(111) nanofacets: the energetics of stress relief is about ten times that of differences in the various possible O/Ti/Pt(111)-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 rows 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 fcc-site Ti, producing linear "canyons" (Ti/Pt dislocation cores occur between these stripes). Furthermore, alternating hcp- and fcc-site triangles, each with ten O-atoms, are separated by bridging O in an abrupt O/Ti misfit dislocation, thus producing a zigzag pattern. The above dislocations release strain along both the x- and y-directions in the surface plane. However, we have 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 images indicate the ends might indeed different than the line portions of the zigzag features.

Corresponding author: Ulrike Diebold (diebold at iap_tuwien_ac_at).

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