First-Principles Study of the Surface Energy and the Atom Cohesion of Wurtzite ZnO and ZnS - Implications for Nanostructure Formation

The surface energies of eight oblique surfaces of wurtzite ZnO and ZnS, (10 (1) over bar1) (10 (1) over bar2): (11 (2) over bar1); and (11 (2) over bar2), are estimated by using first-principles calculations. Calculations for simple cases of atom addition are performed to understand the fast growth of wurtzite ZnO and ZnS in the [0001] direction. The slow growth of wurtzite ZnO and ZnS in the [000 (1) over bar] direction is ascribed to the relatively weak cohesion of zinc atoms to the (000 (1) over bar)-O or S surface. The average electric fields inside ZnO and ZnS are estimated.