▎ 摘　　要

Based on first-principles calculations, we study the electronic structures of 2D alkaline-earth metal hydroxide X(OH)(2)/graphene (X = Ca, Mg) heterostructures. The results show that the characteristics of the band gap size of X(OH)(2) and Dirac cone of graphene are preserved well, and p-type Schottky barriers with a small Schottky barrier height (SBH) are formed in the hetero-multilayers. Moreover, double Dirac cones are also found in the X(OH)(2)/bilayer graphene (X(OH)(2)/BLG) cases. Interestingly, negative electric fields can easily induce the transition from p-type Schottky to Ohmic contact, while the p-type to n-type Schottky transition can be realized by positive electric fields. In addition, the electric field-modulations of the Schottky barrier are more sensitive in the X(OH)(2)/BLG systems. These studies may open the possibility of using X(OH)(2)/graphene as building blocks in the fabrication of Schottky devices.