Microcontact Printing of Organic Self-Assembled Monolayers for Patterned Growth of Well-Aligned ZnO Nanorod Arrays and their Field-Emission Properties

This paper describes a simple method for preparing well-aligned ZnO nanorod arrays in a more tunable fashion, which enables the synthesis of nanorods directly in various patterns and the easy control of the array density. This method is based on a combination of the microcontact printing process for patterning and a solution approach for depositing ZnO nanorods. The growth behavior between the contact and noncontact areas is investigated. Different formation mechanisms are proposed, and it is found that the key difference between nanorod and microrod forms was the ZnO seed layer and the van der Waals force at specific conditions. The role of self-assembled monolayers of octadecyl-trichloro-silane in the reaction solution is also discussed. Wettability of the surfaces is assessed by measuring the water contact angle, and the results show significant variation with surface morphology, from 17.6° to 123.6°. The lowest turn-on applied field strength is 4.65 V/μm at the current density of 10 μA/cm², which is achieved by the lowest array density of nanorods. The field-emission characteristics of the nanorods are found to be highly reproducible. The results could be valuable for the application of field-emission-based devices using ZnO nanorod arrays as cathode materials.