Evidence of new 2D material: Cu₂Te

The number of two-dimensional (2D) materials has grown steadily since the discovery of graphene. Each new 2D material demonstrated unusual physical properties offering a large flexibility in their tailoring for high-tech applications. Here, we report on the formation and characterization of an uncharted 2D material: 'Cu₂Te alloy monolayer on Cu(111) surface'. We have successfully grown a 2D binary Te-Cu alloy using a straightforward approach based on chemical deposition method. Low electron energy diffraction (LEED) and scanning tunneling microscopy (STM) results reveal the existence of a well-ordered alloy monolayer characterized by (√3 × √3)R30° superstructure, while the X-ray photoemission spectroscopy (XPS) measurements indicate the presence of single chemical environment of the Te atoms associated with the Te-Cu bonding. Analysis of the valence band properties by angle resolved photoemission spectroscopy (ARPES); in particular the electronic states close to the Fermi level suggests a strong hybridization between Te and Cu electronic states leading to an appearance of new dispersive bands localized at the surface alloy, which is confirmed by first-principles calculations. These bands are strongly influenced by the surface reconstruction and undergo a back-folding at the boundaries of the reduced surface Brillouin zone (SBZ). More interesting, a band gap of about 0.91 eV and a Rashba splitting in the conduction band are obtained. These findings taken together clearly prove the presence of 2D-type electron system within the Cu₂Te alloy layer, which is promising for spintronic application.