Structural Color Formation of ZnO Nanorods Using Gold as a Seed and Reflective Layer

Traditional ZnO hydrothermal synthesis for producing nanostructured colors requires a ZnO seed layer and a reflective layer, which, in turn, requires high-temperature heat treatment. This requirement limits the choice of substrates to only those with a high heat resistance. Our study presents a simplified fabrication procedure to address the limitations of existing structured color fabrication methods and leverage the benefits of low-temperature solution processes. By depositing a Au layer on the substrate to function as a catalyst and reflective layer, we eliminated the need for seed and reflective layer fabrication and the associated heat treatment processes. The method employs hexamethylenetetramine (HMTA) hydrolysis to induce a chemical reaction with zinc nitrate hexahydrate and ammonia, thereby facilitating the formation of ZnO in a vertical structure and the production of structured color. We observed that the diameter and thickness of ZnO nanorods increased from 185 to 280 nm and from 60 to 210 nm, respectively, in proportion to the growth time, and we observed that the structural color changes with the variation of ZnO nanorods, which can express different colors. This method can be applied to polymer substrates as well as silicon wafers, providing an approach that minimizes the restrictions on substrate selection. It also has the advantage of being able to selectively generate structural color by controlling the growth time. The process can be used to fabricate nanomicroscale anticounterfeit patterns on flexible substrates and has potential applications in powerless sensors.