Robust electronic and mechanical properties to layer number in 2D wide-gap X(OH)₂ (X  =  Mg, Ca)

Motivated by the recent synthesis of 2D alkaline-earth-metal hydroxide nanosheets, through first-principles calculations, we study the layer number and electric field modulations of the structural, electronic and mechanical properties of 2D X(OH)₂ (X  =  Ca, Mg) multilayers. Increasing the layer number from one to ten, the Young's modulus (Poisson's ratio) slightly increases (decreases) and then remains saturated when the thickness is larger than four layers; while the characteristics of direct wide-gaps and work functions are robust to the layer number. In addition, the large elastic deformation (∼20% biaxial stretch strain) indicates that 2D X(OH)₂ possesses excellent mechanical flexibility. In particular, unlike conventional 2D materials, the electric field modulations of the band gap are very remarkable, especially for the X(OH)₂ monolayer. (paper)