SPECTRAL-ANALYSIS OF FIELD-EMISSION CURRENT FLUCTUATIONS FROM A CARBON-FIBER FIELD EMITTER

The spectral analysis of field emission current fluctuations from a vapour-grown carbon-fibre field emitter has been carried out at two pressure conditions, 1 x 10(-8) mbar and 1 x 10(-9) mbar. These fluctuations consist of steps and spikes or 'digital pulses', and are characteristic of a graphite emitter. At low residual gas pressure the autocorrelation function decays exponentially with two time constants of the corresponding power spectrum Lorentzian type, indicating that these fluctuations originate mostly from 'flip-flop' or 'switching' of an adatom between two equivalent sites. At higher residual gas pressure the autocorrelation function decays exponentially with a single time constant, while the corresponding power spectrum does not correspond to the Lorentzian type. The tip morphology has been studied by field ion microscopy at liquid nitrogen temperature. It has been suggested that two sets of adsorption sites on these planes may be responsible for the flip-flop mechanism leading to the observed fluctuations,