Preferred heteroepitaxial orientations of ZnO nanorods on Ag

Wurtzite ZnO nanorods were grown from solution onto coarse-grain bulk polycrystalline Ag substrates to explore the nature of preferred heteroepitaxial orientations. ZnO nanorods grow copiously on grains with <111> and <001> surface normals. Two epitaxial orientations were observed: 0001 ZnO ‖ 111 Ag with <21̄1̄0> ZnO ‖ <11̄0> Ag and 0001 ZnO ‖ 001 Ag with <21̄1̄0> ZnO ‖ <11̄0> Ag. Both feature ZnO basal plane growth, and the specific in-plane orientation relationships both feature alignment of close-packed directions in the interface. Nanorod growth was strongly suppressed on Ag grains in most other orientations. Although strain energy minimization is often invoked to explain the 0001 ZnO ‖ 111 Ag with <21̄1̄0> ZnO ‖ <11̄0> Ag orientation, associated with an almost ideal near-coincidence site lattice matching, our data suggests that strain may not be the sole, or even the most important, determinant of the preferred orientations during solution-based epitaxial growth in this system.