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Effect of adsorbates on field emission from flame-synthesized carbon nanotubes

We report the influence of adsorbates on field emission from flame-synthesized patterned carbon nanotubes (CNTs) by varying current–voltage sweep operational modes (continuous and pulsed) and vacuum pressure. Based on the gas adsorption and desorption effect, three distinguishable emission regimes—intrinsic adsorption, field-induced adsorption enhanced and current-induced desorption regimes—were proposed to interpret the nonlinearity of Fowler–Nordheim plots. The field-emission current versus applied voltage curves exhibited distinctive vacuum-pressure- and sweep-speed-dependent hysteresis upon a loop of anode voltage. This hysteresis was attributed to the absorption–desorption of adsorbates due to the large surface defects of the flame-synthesized CNTs. Such flame-synthesized CNTs with distinctive gas-absorption ability may have potential application in gas-sensing field-emission devices.