The new dimension of silver
Although significant progress in the fabrication and applications of graphene-like materials has been made, free-standing metal monolayers are extremely rare due to the challenges in fabrication. Furthermore, such structures are often unstable versus 3D close-packed forms. Silver is an important noble metal with many unique properties, and has a wide range of applications in daily life and industry. Here, we display a new dimension of silver, i.e., a 2D Ag monolayer, with reduced dimensionality and quantum confinement. We observe that the Ag monolayer is stable in ab initio molecular dynamics simulations up to 800 K for 10 ps. The bond strength per atom actually increases from 0.21 eV for the bulk with twelve bonds to 0.33 eV for the 2D layer with six bonds. This increase in bond strength contributes to the stability of the free-standing 2D layer. Detailed density functional theory calculations are used to predict the properties of this material. The 2D Ag monolayer is the global minimum structure. One electron is delocalized into the whole sheet and is donated to a nearly free 2D electron gas.