Characterizations of Ag-catalyzed ZnO nanostructures prepared by vapor–solid mechanism

Abstract

This paper presents the synthesis and field emission characteristics of zinc oxide (ZnO) nanostructures grown on Ag-deposited Si substrate by using the vapor–solid (VS) mechanism. The morphology of the ZnO nanostructures was related to source and substrate temperatures. Nanowhiskers, nanotips and well-aligned nanorods were grown at substrate temperatures of 620, 650 and 680 °C, respectively. A strong bluish-green photoluminescence (PL) indicated that the nanostructures had many surface defects correlated with oxygen vacancies. Field emission analyses showed that the turn-on fields of ZnO nanowhiskers, nanotips and well-aligned nanorods were 4.5, 5.8 and 6.1 V/μm, respectively. The high emitter density and high aspect ratio of the well-aligned nanorods resulted in an enhancement in emission current density. Furthermore, the field emission stability of the well-aligned nanorods was better than that of the nanowhiskers and nanotips. The emission current densities of the ZnO nanowhiskers, nanotips and well-aligned nanorods, measured after continuous operation for 6 h, were approximately 2.05, 4.68 and 20.5 μA/cm 2, respectively.