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Effects of in-plane stiffness and charge transfer on thermal expansion of monolayer transition metal dichalcogenide
Authors:Wang Zhan-Yu  Zhou Yan-Li  Wang Xue-Qing  Wang Fei  Sun Qiang  Guo Zheng-Xiao  Jia Yu
Institution:a International Joint Research Laboratory for Quantum Functional Materials of Henan, Zhengzhou University, Zhengzhou 450001, China;b School of Physics and Engineering, Zhengzhou University, Zhengzhou 450001, China;c Department of Mechanical and Electrical Engineering, Henan Industry and Trade Vocational College, Zhengzhou 451191, China;d Department of Chemistry, University College London, London WC1H 0AJ, U.K.
Abstract:The temperature dependence of lattice constants is studied by using first-principles calculations to determine the effects of in-plane stiffness and charge transfer on the thermal expansions of monolayer semiconducting transition metal dichalcogenides.Unlike the corresponding bulk material,our simulations show that monolayer MX_2(M = Mo and W;X = S,Se,and Te) exhibits a negative thermal expansion at low temperatures,induced by the bending modes.The transition from contraction to expansion at higher temperatures is observed.Interestingly,the thermal expansion can be tailored regularly by alteration of the M or X atom.Detailed analysis shows that the positive thermal expansion coefficient is determined mainly by the in-plane stiffness,which can be expressed by a simple relationship.Essentially the regularity of this change can be attributed to the difference in charge transfer between the different elements.These findings should be applicable to other two-dimensional systems.
Keywords:transition metal dichalcogenide  thermal expansion  phonon
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