Transformation of ZnO nanorods into nanotubes and their field emission studies

Abstract

Synthesis of vertically well-aligned ZnO nanorods on Au coated silicon substrate by a facile electrochemical route has been carried out. The transformation of as-deposited ZnO nanorods into nanotubes was achieved via simple, single step, chemical etching process using KOH as etchant. The influence of various parameters of the etching, such as concentration of the etchant, bath temperature and duration on morphological features of the ZnO nanotubes has been investigated. It is observed that formation of ZnO nanotubes with smooth inner and outer surfaces is achieved when the etching was performed at 65 • C for 1 h duration, and at higher bath temperatures and longer durations, over etching of nanorods takes place. Field emission investigations of the ZnO nanorods and nanotubes were carried out at base pressure of 1 × 10 −8 mbar. The values of turnon field, corresponding to emission current density of 1 µA/cm 2 were observed to be 7.2 V/µm and 8.4 V/µm, corresponding to ZnO nanorods and nanotubes emitter respectively, and emission current density of ∼ 352.5 µA/cm 2 has been drawn from the ZnO nanotubes emitter at an applied field of 13.77 V/µm. The ZnO nanotubes emitter exhibits excellent emission current stability at the preset value of 1 µA over duration of 3 h, indicating its potential as electron source for practical applications.