Atomic mechanism of the phase transition in monolayer bismuthene on copper oxide

Problems associated with large-scale growth of high-quality single-layer bismuthene constitute one of the main obstacles to the applications of bismuthene in electronic devices. Here we report the direct synthesis of high-quality bismuthene using molecular-beam epitaxy on dielectric copper oxide thin films. Scanning tunneling microscopy (STM) reveals the generation of dimer pair arrays and black-phosphorus-like bismuthene (BKP-Bi, alpha phase) at the initial stage on Cu3O2/Cu(111) surface. A phase transition from BKP-Bi to blue-phosphorus-like bismuthene (BLP-Bi, beta phase) is characterized by high-resolution STM, complemented with first-principles calculations based on density-functional theory (DFT) showing a bond-breaking path. Employing the phase transition, we also demonstrate the construction of an atomically sharp in-plane homojunction along the phase boundary. DFT calculations reveal a one-dimensional edge state along the homojunction.