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 (similar to 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.