Dynamics of vacancies in two-dimensional Lennard-Jones crystals

Yao, Zhenwei; Cruz, Mónica Olvera de la

doi:10.1103/physreve.90.062318

Cited by 8 publications

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References 35 publications

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“…On the other hand, the ridged structure of black phosphorus monolayers and other materials with a similar atomistic structure leads to their celebrated anisotropic electron and optical properties . At the same time, such unique atomic arrangement has striking consequences for crystalline order − that remain unexplored up to date.…”

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Two-Dimensional Disorder in Black Phosphorus and Monochalcogenide Monolayers

et al. 2016

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Ridged, orthorhombic two-dimensional atomic crystals with a bulk Pnma structure such as black phosphorus and monochalcogenide monolayers are an exciting and novel material platform for a host of applications. Key to their crystallinity, monolayers of these materials have a four-fold degenerate structural ground state, and a single energy scale E C (representing the * To whom correspondence should be addressed † Department of Physics. elastic energy required to switch the longer lattice vector along the x− or y−direction) determines how disordered these monolayers are at finite temperature. Disorder arises when nearest neighboring atoms become gently reassigned as the system is thermally excited beyond a critical temperature T c that is proportional to E C /k B . E C is tunable by chemical composition and it leads to a classification of these materials into two categories: (i) Those for which E C ≥ k B T m , and (ii) those having k B T m > E C ≥ 0, where T m is a given material's melting temperature. Black phosphorus and SiS monolayers belong to category (i): these materials do not display an intermediate order-disorder transition and melt directly. All other monochalcogenide monolayers with E C > 0 belonging to class (ii) will undergo a two-dimensional transition prior to melting. E C /k B is slightly larger than room temperature for GeS and GeSe, and smaller than 300 K for SnS and SnSe monolayers, so that these materials transition near room temperature. The onset of this generic atomistic phenomena is captured by a planar Potts model up to the orderdisorder transition. The order-disorder phase transition in two dimensions described here is at the origin of the Cmcm phase being discussed within the context of bulk layered SnSe.

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