Imaging Defective Electronic States in Ultrathin CeO₂ Nanostructures Grown on Graphene by Pulsed Laser Deposition

We report here the growth of ultrathin films of ceria by pulsed laser deposition on HOPG/graphene substrates. The controlled growth of CeO₂(111) nanoislands on graphene via pulsed laser deposition (PLD) demonstrates a strong dependence on the substrate defect density, where defects serve as preferential nucleation sites. Higher oxygen partial pressure during deposition enhances surface diffusion, promoting the formation of triangular dendritic nanostructures. Scanning tunneling spectroscopy (STS) reveals mutual electronic interactions between the ceria nanoislands and the graphene substrate, while high-resolution STM imaging identifies ordered oxygen vacancy arrays within the CeO₂ surface. Bias-dependent STM mapping further highlights the complex electronic configuration of the islands. The presence of these ordered defects suggests the potential for precise spatial control, enabling tailored electronic properties through doping or optimized graphene interactions. These findings advance defect-engineered oxide nanostructures, offering promising applications in catalysis, sensing, and optoelectronics via vacancy manipulation in ultrathin films.