Different etching evolution from initial to etched ZnO nanorods on substrates of dissimilar geometries

In this paper the influencing factors and their effects on the etching evolution from initial to etched ZnO nanorods (ZnONRs) were identified and investigated. Batches of ZnO nanorods were hydrothermally synthesized on planar, convex, and concave substrates, and then were etched in NaOH solution. It was found that not only the synthesizing and etching parameters but also the geometries of the substrates influence significantly the diameters, density, and orientation of both initial and etched ZnONRs. The larger the diameters of ZnONRs are, the more the oxygen vacancies on (001) crystal planes. It is at these oxygen vacancies that the etching process starts. Due to larger average diameters, initial ZnONRs on convex substrates are more readily etched than that on planar and concave ones. Thus uniform ZnO nanotubes (ZnONTs) appear quickest and most easily on convex substrates. The results can benefit the batch preparation, the performance improvement, and the process standardization of related ZnONR- and ZnONT-based devices and sensors.