Single crystal-like two-dimensional layers form in ZnO produced by r.f. sputter deposition in the presence of a bias field. The films were c-axis orientated with a bulk lattice constant (a) modulated by a superlattice where the superlattice constant as = 3a. The structure was metastable for films less than 20nm thick but stable for thicker films. The superlattice was considered to arise from a wurtzite-sphalerite phase transformation between grain boundaries. This transformed the short-range order of c-axis orientated microcrystalline grains into a long-range ordered layer structure.

Superlattice Formation and Faulted Structures in RF-Sputtered ZnO. Belmekki, B., Raven, M.S.: Philosophical Magazine A, 1985, 52[1], 19-27