Enhanced field emission from pulsed laser deposited nanocrystalline ZnO thin films on Re and W

Nanocrystalline ZnO thin films have been deposited on rhenium and tungsten pointed and flat substrates by pulsed laser deposition method. An emission current of 1 nA with an onset voltage of 120 V was observed repeatedly and maximum current density similar to 1.3 A/cm(2) and 9.3 mA/cm(2) has been drawn from ZnO/Re and ZnO/W pointed emitters at an applied voltage of 12.8 and 14 kV, respectively. In case of planar emitters (ZnO deposited on flat substrates), the onset field required to draw 1 nA emission current is observed to be 0.87 and 1.2 V/mu m for ZnO/Re and ZnO/W planar emitters, respectively. The Fowler-Nordheim plots of both the emitters show nonlinear behaviour, typical for a semiconducting field emitter. The field enhancement factor beta is estimated to be similar to 2.15x10(5) cm(-1) and 2.16x10(5) cm(-1) for pointed and 3.2x10(4) and 1.74x10(4) for planar ZnO/Re and ZnO/W emitters, respectively. The high value of beta factor suggests that the emission is from the nanometric features of the emitter surface. The emission current-time plots exhibit good stability of emission current over a period of more than three hours. The post field emission surface morphology studies show no significant deterioration of the emitter surface indicating that the ZnO thin film has a very strong adherence to both the substrates and exhibits a remarkable structural stability against high-field-induced mechanical stresses and ion bombardment. The results reveal that PLD offers unprecedented advantages in fabricating the ZnO field emitters for practical applications in field-emission-based electron sources.