Probing charge transfer under external bias at Cu/SrTiO₃ heterojunction

Supported metal-metal oxide heterojunctions are ubiquitous in designing highly efficient catalysts for energy conversion and storage devices. The interaction between metal and supports has attracted significant interest in developing novel catalysts. Especially, surface charge distribution and charge transfer between metallic particles and oxide supports are vital for understanding the catalytic reaction. Here, we investigate the effect of the external electric field and circumstances on the charge transfer within the Cu/SrTiO3 heterojunction. Based on the in-situ Kelvin probe force microscopy (in-situ KPFM) and density functional theory (DFT) calculations, we observe and analyze that the specific behavior of charge transfer could be switched by reversing the external electric field, indicating the role of Cu microparticles could be altered electrically between donor and acceptor. Moreover, the circumstances surrounding the Cu/SrTiO3 heterojunction influenced the transfer of charge as well. We also present a comprehensive model of the observed behavior based on work functions and electronic structure of Cu/SrTiO3 heterojunction. Our work provides insight into the charge transfer in metal -semiconductor heterojunction and is helpful to design highly active heterostructured catalysts.