Figure 1
a Top and b side view of crystal structure of 3-ML X2N (X = Ca, Sr). It consists of three (X-N-X) unit layers with ABC-stacking. The symbols L1, L2 and G12 refer to the thicknesses of outermost layer, the next outermost layer and the interlayer gap between L1 and L2, respectively, as explained in the caption of Tabel 1.
