Field emission studies on electrochemically synthesized ZnO nanowires

Nanocrystalline zinc oxide (ZnO) films were synthesized using cathodic reduction of Zn foil in aqueous electrolyte of different molar concentrations containing ZnCl₂ and H₂O₂, followed by annealing at 400 °C in air. An X-ray diffractometer (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) were used for characterization. The XRD patterns exhibited a set of well-defined diffraction peaks corresponding to the wurtzite phase of ZnO. SEM and TEM images clearly revealed the formation of randomly oriented ZnO nanowires having lengths of several microns and diameters less than 100 nm. From the field emission studies, the threshold field values, required to draw emission current density of ∼1 μA/cm² were found to be 1.44, 1.36 and 1.5 V/μm for nanowires synthesized using 0.002, 0.004 and 0.016 M electrolyte concentrations, respectively. All Folwer–Nordheim (F–N) plots showed non-linear behavior indicating semiconducting nature of the emitters. The ZnO nanowires exhibited good emission current stability at the pre-set value of ∼10 μA over a duration of 6 h. The simplicity of the synthesis route coupled with the promising emission properties made the electrochemically synthesized ZnO nanowires a suitable candidate for high-current density applications.