Schematic Structural Analysis of Honeycomb Structure Ultrathin Ce–Ti–O Films on Pt(111) Using Photoelectron Holography and Ab Initio Calculation

(√3 × √3)R30 honeycomb superstructure ultrathin Ce–Ti–O film was prepared and confirmed using scanning tunneling microscopy (STM) and low-energy electron diffraction. The structural model of (√3 × √3)R30 honeycomb superstructure ultrathin film is determined using ab initio calculation and photoelectron holography. In the density functional theory (DFT) calculations, the (√3 × √3)R30 honeycomb superstructural model was calculated in two different conditions. The photoelectron holograms of Ti2+ and Ti3+ were separated from Ti 2p photoelectron spectra of (√3 × √3)R30 honeycomb superstructure, using a display-type retarding field analyzer. From the different forward-focusing peaks on the photoelectron holograms of Ti2+ and Ti3+, the vertical height between Ti divalent atoms and O atoms is higher than that between Ti trivalent atoms and O atoms. Also, the distance and direction of O and Ce atoms above Ti could be found. As a result, the simulated photoelectron holograms and the simulated STM image of the calculated Ce–Ti–O honeycomb superstructural model agree with the experimental photoelectron holograms and the experimental STM images.