Abstract
Recently, freestanding atomically thick Fe metal patches up to 10 atoms wide have been fabricated experimentally in tiny pores in graphene. This concept can be extended conceptually to extended freestanding monolayers. We have therefore performed ab initio molecular dynamics simulations to evaluate the early melting stages of platinum, silver, gold, and copper freestanding metal monolayers. Our calculations show that all four freestanding monolayers will form quasi-2D liquid layers with significant out-of-plane motion and diffusion in the plane. Remarkably, we observe a 4% reduction in the Pt most likely bond length as the system enters the liquid state at 2400 K (and a lower effective spring constant), compared to the system at 1200 and 1800 K. We attribute this to the reduced average number of bonds per atom in the Pt liquid state. We used the highly accurate and reliable Density Functional Theory (DFT-D) method that includes dispersion corrections. These liquid states are found at temperatures of 2400 K, 1050 K, 1600 K, and 1400 K for platinum, silver, gold, and copper respectively. The pair correlation function drops in the liquid state, while the bond orientation order parameter is reduced to a lesser degree. Movies of the simulations can be viewed online (see Supplementary Material).
Highlights
It has been difficult to fabricate freestanding monolayer metal films experimentally
The pair correlation function drops in the liquid state, while orientational order is reduced to a lesser degree
The use of high quality density functional theory (DFT)-D theory provides a substantial temperature correction of 20% compared to the previous calculations
Summary
It has been difficult to fabricate freestanding monolayer metal films experimentally. Freestanding atomically thick iron membranes suspended in and supported by tiny graphene pores have been fabricated [1]. These iron layers were only up to 10 atoms wide. This is an exciting development, but due to the presence of the pores around the periphery, the iron patches differed structurally from the predictions for an extended freestanding 2D monolayer. We will be studying freestanding systems of quasi-2D metal atoms with significant out-of-plane motions, using highly accurate Density Functional Theory with dispersion corrections (DFT-D)
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