Efficient field emission from vertically grown planar ZnO nanowalls on an ITO-glass substrate

Vertically grown planar ZnO nanowalls, with typical dimensions of 40-80 nm thickness and several micrometers wide, were electrodeposited on an indium-tin-oxide (ITO)-glass substrate at 70 °C. X-ray photoelectron spectroscopy (XPS) studies reveal that the nanowalls consist of ZnO covered with a Zn(OH)(2) overlayer. An x-ray diffraction (XRD) study shows that these nanowalls have the wurtzite structure and are highly crystalline. The corresponding Raman and photoluminescence spectra further indicate the presence of oxygen deficiency. These ZnO nanowalls exhibit excellent field emission performance, with not only a considerably lower turn-on field of 3.6 V µm(-1) (at 0.1 µA cm(-2)) but also a higher current density of 0.34 mA cm(-2) at 6.6 V µm(-1) than most ZnO nanowires and other one-dimensional nanostructures reported to date.