Two-Dimensional Disorder in Black Phosphorus and Monochalcogenide Monolayers
Two-Dimensional Disorder in Black Phosphorus and Monochalcogenide Monolayers
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DOI：
10.1021/acs.nanolett.5b04613
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发表时间：
2016-03-01
期刊：
影响因子：
10.8
通讯作者：
Barraza-Lopez, Salvador
中科院分区：
文献类型：
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作者：
Mehboudi, Mehrshad;Dorio, Alex M.;Barraza-Lopez, Salvador
具有块状Pnma结构的脊状、正交形二维原子晶体，如黑磷和单硫化物单分子膜，是一种令人兴奋的新材料平台，可用于许多应用。结晶性的关键是，这些材料的单分子膜具有4倍简并的结构基态，并且单一的能量标度E-c(代表沿x或y方向切换较长晶格矢量所需的弹性能量)决定了这些单分子膜在有限温度下的无序程度。当系统被热激发超过与E-c/k(B)成正比的临界温度T-c时，最近的邻近原子被轻轻地重新分配，就会出现无序。E-C可通过化学成分进行调节，这导致将这些材料分为两类：(I)E-c>；=k(B)T(M)的材料；以及(Ii)k(B)T(M)>；E-c>；=0的材料，其中T-m是给定材料的熔化温度。黑磷和SIS单分子膜属于(I)类：这些材料不表现出中间有序的无序转变和直接熔化。所有其他E-c和gt；0属于(II)类的单硫族化合物单分子膜在熔化前将经历二维转变。GeS和GeSE的Ec/kB略大于室温，而SnS和SnSe单层的Ec/kB小于300K，因此这些材料在室温附近发生转变。这种普遍的原子现象的开始被一个平面的Potts模型捕捉到有序-无序的转变。这里描述的二维有序-无序相变是在体层状SnSe的背景下讨论的CMCM相的起源。
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 4-fold degenerate structural ground state, and a single energy scale E-c (representing the 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. Ec/kB 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 order-disorder 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.