Low-dimensional materials with high stabilities and outstanding mechanical properties are essential for next generation microelectromechanical systems (MEMS). The successful synthesis of two-dimensional (2D) tungsten nitride makes it a promising candidate for the MEMS application. Here, we have confirmed the existence of experimentally synthesized W₂N₃ and predicted three additional new 2D monolayer tungsten nitrides: WN₂, WN₄, and W₃N based on extensively structural searches by CALYPSO method and first-principle calculations. The calculations indicate that the nitrogen-rich WN₄ monolayer possesses large in-plane negative Poisson ratios attributed to the 4-fold-coordinated WN₄ ν_x = −0.103 and ν_y = −0.113, which are tetrahedron combined with the strong coupling between the 2p orbitals of N and 5d orbitals of W. Our findings not only enrich the family of 2D transition metal nitrides with excellent mechanical properties but also open avenues for design and synthesis of other novel 2D layered materials.

中文翻译：

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二维氮化钨中的负泊松比：电子和结构性质的协同效应

具有高稳定性和出色机械性能的低尺寸材料对于下一代微机电系统（MEMS）至关重要。二维（2D）氮化钨的成功合成使其成为MEMS应用的有希望的候选者。在这里，我们已经确定了实验合成的W ₂ N ₃的存在，并基于CALYPSO方法的广泛结构搜索和第一性原理计算，预测了另外三个新的2D单层氮化钨：WN ₂，WN ₄和W ₃ N。计算表明，富氮的WN ₄单层具有大的面内负泊松比，这归因于4倍配位的WN₄ ν _X = -0.103和ν _ÿ = -0.113，其与N的2p轨道和W.我们的研究结果的5d轨道之间的强耦合的四面体结合不仅具有优良的机械性能丰富的2D过渡金属氮化物的家庭，但还为其他新颖的2D分层材料的设计和合成开辟了道路。