Effect of adsorbates on field-electron emission from ZnO nanoneedle arrays

We studied the influence of adsorbates on field emission (FE) properties of well-aligned ZnO nanoneedle arrays with varying initial electric field, vacuum gap, and ambient pressure. The FE current exhibits hysteresis upon a loop of applied voltage. On applying an initial electric field of 3.85x10(6) V/m, the turn-on voltage increases similar to50%, Fowler-Nordheim plots show better linearity, as well as the hysteretic behavior can be annihilated. It is found that the FE current depends on the vacuum gap and the ambient pressure. The FE current increased sensitively with increasing the ambient pressure P when P