Growth of a quasicrystal-related structure and superstructure for ultrathin Ce–Ti–O films on Pt(111)

Abstract

Herein, oxide quasicrystal-related (OQC-R) structure and Ce–Ti–O-(3 × 3) superstructure ultrathin films were prepared on Pt(111) and characterized using scanning tunneling microscopy (STM) and low-energy electron diffraction. The OQC-R structure with dodecagonal clusters consisting of triangles, squares, and rhombuses was observed in STM images. The first discovery of the OQC-R structure with a magnetic rare earth metal expands the possibility of discovering new oxide quasicrystals with novel magnetism or superconductivity. By depositing Ti on an OQC-R ultrathin film and post-annealing, a honeycomb lattice of the Ce–Ti–O-(3 × 3) superstructure was prepared. From X-ray photoelectron spectroscopy (XPS) and resonant-photoelectron spectroscopy, the chemical states of the Ce and Ti atoms in the OQC-R structure corresponded to the Ce³⁺ and Ti²⁺ states, while those for the Ce–Ti–O-(3 × 3) superstructure corresponded to the Ce³⁺, Ti³⁺, and Ti²⁺ states. The phase transformation from the OQC-R structure to the Ce–Ti–O-(3 × 3) honeycomb superstructure likely occurred when the amount of Ti increased and was more oxidized. The elemental atomic density was also calibrated using XPS and Rutherford backscattering spectroscopy. These results propose tentative structural models of the OQC-R structure as Ce₁₈Ti₁₄O₄₁ and the Ce–Ti–O-(3 × 3) superstructure as CeTi₆O₉.