TY - JOUR
T1 - Two-Dimensional Disorder in Black Phosphorus and Monochalcogenide Monolayers
AU - Mehboudi, Mehrshad
AU - Dorio, Alex M.
AU - Zhu, Wenjuan
AU - Van Der Zande, Arend
AU - Churchill, Hugh O.H.
AU - Pacheco-Sanjuan, Alejandro A.
AU - Harriss, Edmund O.
AU - Kumar, Pradeep
AU - Barraza-Lopez, Salvador
N1 - Funding Information:
Conversations with Y. Yang, L. Bellaiche, B.M. Fregoso, L. Shulenburger, and F. de Juan are acknowledged. A.M.D. acknowledges support from NSF through REU grant DMR- 1460754. Molecular dynamics calculations were performed at Arkansas'' Trestles and at TACC''s Stampede (Grant XSEDE TG-PHY090002), and S.B.-L. thanks J. Pummill, D. Chaffin, and P. Wolinski at Arkansas'' High-performance computing center for their support.
PY - 2016/3/9
Y1 - 2016/3/9
N2 - 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 EC (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 Tc that is proportional to EC/kB. EC is tunable by chemical composition and it leads to a classification of these materials into two categories: (i) Those for which EC ≥ kBTm, and (ii) those having kBTm > EC ≥ 0, where Tm 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 EC > 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.
AB - 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 EC (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 Tc that is proportional to EC/kB. EC is tunable by chemical composition and it leads to a classification of these materials into two categories: (i) Those for which EC ≥ kBTm, and (ii) those having kBTm > EC ≥ 0, where Tm 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 EC > 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.
KW - 2D atomic materials
KW - black phosphorus
KW - layered monochalcogenides
KW - molecular dynamics
KW - phase transitions
KW - structural degeneracies
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U2 - 10.1021/acs.nanolett.5b04613
DO - 10.1021/acs.nanolett.5b04613
M3 - Article
C2 - 26866878
AN - SCOPUS:84960533183
VL - 16
SP - 1704
EP - 1712
JO - Nano Letters
JF - Nano Letters
SN - 1530-6984
IS - 3
ER -