Growth and electronic structure of the nodal line semimetal in monolayer Cu2Si on Cu(111)

Cu₂Si, a single-layer two-dimensional material with a honeycomb structure, has been proposed to have Dirac nodal line fermions. In this study, the synchrotron radiation X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and angle-resolved photoemission spectroscopy (SR-XPS, SR-UPS, and SR-ARPES) techniques were used to investigate the dynamic process of in situ deposition of single-layer Cu₂Si on a Cu(111) crystal surface via molecular beam epitaxy (MBE). Cu₂Si existed as a monolayer (ML) alloy, and there were competing mechanisms of distinct chemical states of silicon in different growth periods, according to a detailed examination of the experimental SR-XPS and SR-UPS spectra. Additionally, a weak interaction between the Cu₂Si ML and Cu(111) was demonstrated via SR-ARPES and first-principles computations. The unique electronic structure of the Cu₂Si ML was not destroyed by either this weak interaction or the disordered silicon produced on the surface during the growth process. The study of the Cu₂Si growth kinetics provides a guarantee and a basis for the future exploration of the exotic properties of Cu₂Si.