Compared to their parent materials, oxygen vacancy (VO)–ordered phases of complex oxides exhibit distinct physical properties and show great potential in multifunctional devices. With the expected unique behaviors, however, most of the VO‐ordered oxide films are extremely difficult to synthesize due to their thermodynamic instabilities. Herein, using LaCoOx as an example, the synthesis of large‐scale monophased VO‐ordered LaCoO2.67 and LaCoO2.5 films is realized by annealing as‐grown perovskite LaCoO3 films in vacuum with a special heating method. Their macroscopic properties, including the magnetic and electric transport and optical properties, are measured. It is demonstrated that the functionalities of LaCoOx films can be manipulated by tuning the concentration and ordering of the VO. The method in this work can be applied to fabricate a wide range of VO‐ordered oxide films.

The stability of the (4 × 4) reconstruction is studied on SrTiO3(111) and LaTiO3(111) surfaces by scanning tunneling microscopy. While the reconstruction may effectively compensate the surface polarity, the associated large lattice distortion on SrTiO3 with relatively strong polarity has to be relaxed by extra adsorbates. Alternatively, substituting Sr by La can reduce the polarity and stabilize the clean reconstructed surface. This provides the driving force for La segregating towards the surface during the heteroepitaxy of SrTiO3 on LaTiO3-covered SrTiO3(111), and thus, the interface sharpness will be deteriorated. To improve the quality of heterointerfaces where the surface polarity of substrates tends to be increased by the epitaxial films, the growth kinetics must be optimized to play the major role.