Polarity-Dependent Growth Rates of Selective Area Grown ZnO Nanorods by Chemical Bath Deposition.

Polarity is known to affect the growth and properties of ZnO single crystals and epitaxial films, but its effects are mostly unknown in ZnO nanorods. To leave polarity as the only varying parameter, ZnO nanorods are grown by chemical bath deposition under identical conditions and during the same run on O- and Zn-polar ZnO single crystals patterned by electron beam lithography with the same pattern consisting of 15 different domains. The resulting well-ordered O- and Zn-polar ZnO nanorod arrays with high structural uniformity are formed on all the domains. The comparison of their typical dimensions unambiguously reveals that Zn-polar ZnO nanorods have much higher growth rates than O-polar ZnO nanorods for all the hole diameter and period combinations. The distinct growth rates are explained in the framework of the surface reaction-/diffusive transport-limited elongation regime analysis, which yields a much larger surface reaction rate constant for Zn-polar ZnO nanorods. The origin of the difference is attributed to polarity-dependent dangling bond configurations at the top polar c-faces of ZnO nanorods, which may further be affected by polarity-dependent interactions with the ionic species in aqueous solution. These findings show the relevance of considering polarity as an important quantity in ZnO nanorods.