Stability of polar oxide surfaces

The structures of the polar surfaces of ZnO are studied using nh initio cal culations and surface x-ray diffraction. The experimental and theoretical r elaxations are in good agreement. The polar surfaces are shown to be very s table, the cleavage energy for the (0001)-Zn and (000 (1) over bar)-O surfa ces is 4.0 J/m(2) comparable to 2.32 J/m(2) for the most stable nonpolar (1 010) surface. The surfaces are stabilized by an electronic mechanism involv ing the transfer of 0.17 electrons between them. This leads to 2D metallic surface states, which has implications for the use of the material in gas s ensing and catalytic applications.