High current field emission behavior of carbon nanofiber film: Adsorbate effects

We report high current-density field emission from carbon nanofiber (CNF) films synthesized using electroplated Ni catalysts. High-density thick CNFs, which had many protrusions with small tip radii and a solid structure without hollow cores, were formed on gold-buffer layers. The maximum emission current of 3.67mA was measured from the area of 4.9×10−3cm2, corresponding to the current density of 750mA∕cm2. There was a distinctive hysteresis in emission-current versus voltage (I-V) curves corresponding to the ramping direction of bias voltage, which led us to divide I-V curves into three distinguishable regimes: adsorbate-enhanced, intermediate, and intrinsic emission regimes. The deviations between up- and down-sweep emission currents, and the slope change in Fowler-Nordheim curves were most prominent in intermediate emission regime. Based on systematic field emission measurements, such as variations of chamber pressure and bias-voltage sweep speed, and temporal variation of emission current at fixed bias voltages, we propose that the observed emission behavior of CNFs stemmed from the desorption and readsorption of adsorbates during emission measurements.