The encapsulation of Pd by the supporting TiO2(110) surface induced by strong metal-support interactions

Thin films of Pd deposited on the TiO2(110) surface were investigated using coaxial impact-collision ion scattering spectroscopy and reflection high-e nergy electron diffraction. It was found that the Pd island grew epitaxiall y on the TiO2 surface with the following orientation relationship; Pd(111)/ /TiO2(110) and Pd[1 (2) over bar 1]//TiO2[001]. This orientation relationsh ip was observed in the temperature range from room temperature to 1170 K an d in the Pd thickness range from 5 to 40 Angstrom, where Pd formed islands on the substrate in this temperature and thickness range. The simultaneous appearance of a TiO2-2 x 1 superstructure and the encapsulation of the Pd i slands by the underlying TiO2 surface was found after annealing at 1170 K i n ultra-high vacuum. In the process of encapsulation, the crystal structure of the Pd islands remained unchanged. This suggests that the encapsulating material is transported by the surface migration on the Pd particles. The heat treatment in the O-2 atmosphere of 5 x 10(-5) Torr partial pressure di d not remove the encapsulating material. (C) 2000 Elsevier Science B.V. All rights reserved.