Plana density O o S CO Ə to There A= الدا Ⓒ 3 ex b 9 ooo B 19 10 bord of b 3 atoms 2D repeat Planow density BE unit

as 2 ah EX area 2D repeat unit 20 D T R 2 6 a - (111) Все ре F 15 1 atom in plane / unit surface 3 3 √29 I 16√3 3 * @A ra 2 a O XXX A (1 9 2 R 31 @ x A O Q 1 A above plane x under plane cell 4√3 3 17 -R 7 atoms 2 OM 2