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-energy electron diffraction. It was found that the Pd island grew epitaxially on the TiO2 surface with the following orientation relationship; Pd(111)//TiO2(110) and Pd[12̄1]//TiO2[001]. This orientation relationship was observed in the temperature range from room temperature to 1170 K and in the Pd thickness range from 5 to 40 Å, where Pd formed islands on the substrate in this temperature and thickness range. The simultaneous appearance of a TiO2-2×1 superstructure and the encapsulation of the Pd islands by the underlying TiO2 surface was found after annealing at 1170 K in 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 O2 atmosphere of 5×10−5 Torr partial pressure did not remove the encapsulating material.