Density control of ZnO nanorod arrays on mixed self-assembled monolayers

We demonstrate the feasibility of controlling the density of ZnO nanorod arrays by using mixed self-assembled monolayers (SAMs) composed of molecules with hydrophobic methyl end groups and hydrophilic amine end groups. As the concentration of amine groups in the mixed SAMs increased, the density of ZnO nanorods grown by a solution-based method increased from 0 to 6 × 10 ¹⁰ cm^-2. For the given range of the amine concentration, surface energy increased from 31 mN m^-1 to 64 mN m^-1. While its dispersive component showed weak correlation with the amine concentration, its polar component increased from less than 1 mN m^-1 to 20 mN m^-1, indicating that the reactive amine molecules induced the change of the nanorod density in our experimental system. These results suggest that the use of mixed SAMs can be applied to various material systems with a new perspective for controlling the density of nanorod arrays.