A LEEM/μ-LEED investigation of phase transformations in TiOx/Pt(111) ultrathin films

Abstract

A combined use of low energy electron microscopy (LEEM) and microprobe LEED (μ-LEED) allows the in-situ observation of dynamical processes at the TiO_x/Pt(111) interface. The transformations between different surface-stabilized phases are investigated in the case of room temperature TiO_x reactive deposition with subsequent post-annealing. For a coverage of 0.6 MLeq, UHV annealing to 400 °C leads to the formation of the zigzag-like z-TiO_1.33 layer. At higher temperatures a rotated z-TiO_1.33 phase is observed, its lateral distribution being strongly influenced by surface morphology. Concurrently, the z-TiO_1.33 layer partially transforms into a kagomé-like TiO_1.5 structure. The resulting oxygen enrichment of the interface is interpreted by invoking Ti interdiffusion into the substrate. At a coverage of 0.45 MLeq, UHV annealing at 500 °C transforms the z-TiO_1.33 layer into a different zigzag-like z′-TiO_1.25 layer. Post-annealing in oxygen of the reduced phases or direct reactive deposition at high temperature both produce the rect-TiO₂ stoichiometric phase, showing characteristic needle-like domains aligned according to the rect-TiO₂ unit cell orientation.