Intrinsically patterned corrals in monolayer Ag₅Se₂ and selective molecular co-adsorption

Functionalized two-dimensional (2D) materials play an important role in both fundamental sciences and practical applications. The construction and precise control of patterns at the atomic-scale are necessary for selective and multiple functionalization. Here we report the fabrication of monolayer pentasilver diselenide (Ag₅Se₂), a new type of intrinsically patterned 2D material, by direct selenization of a Ag(111) surface. The atomic arrangement is determined by a combination of scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and density-functional-theory (DFT) calculations. Large-scale STM images exhibit a quasi-periodic pattern of stoichiometric triangular domains with a side length of ~ 15 nm and apical offsets. The boundaries between triangular domains are sub-stoichiometric. Deposition of different molecules on the patterned Ag₅Se₂ exhibits selective adsorption behavior. Pentacene molecules preferentially adsorb on the boundaries, while tetracyanoquinodimethane (TCNQ) molecules adsorb both on the boundaries and the triangular domains. By co-depositing pentacene and TCNQ molecules, we successfully construct molecular corrals with pentacene on the boundaries encircling TCNQ molecules on the triangular domains. The realization of epitaxial large-scale and high-quality, monolayer Ag₅Se₂ extends the family of intrinsically patterned 2D materials and provides a paradigm for dual functionalization of 2D materials.