Dynamics and Interaction of Active Centers at Nanocarbon Electron Emitters

摘要

Enhanced electron field-induced emission from layers composed by nanocarbon low-aspect-ratio (i.e. not very elongated) particles still doesn't have complete theoretic explanation. Our previous experimental results [1,2] indicated that this phenomenon can be possibly attributed to the effect of non-stationary electric field component associated with kHz- or MHz-frequency current fluctuations. "Non-conservative" rf field action in a heterogeneous system can affect electron energy distributions thus facilitating extraction of electrons into vacuum. This work was aimed to demonstrate presence of rf field and investigate properties of field-induced emission current fluctuations with spatial resolution. The presented early experiments were performed with a strongly non-uniform sample of nanoporous carbon (NPC, [3]) using the scheme and techniques described in detail in [4]. The sample produced full emission current up to 20μA for 12-18 kV dc voltage applied to 2.5 mm-wide cathode-anode gap. Comparison of area-resolved current density waveforms and their frequency spectra obtained for different probe positions revealed a few possible types of current fluctuations' scenarios. For some of the emission image spots, averaged spectra were almost uniform, similar to "white noise" frequency distributions (curve 1 in Fig. 1). Though, the corresponding current waveforms, being disordered over the most part of their length, included intervals of periodic and even quasi-harmonic modulation. At other probe positions, relatively low-frequency components (below 100 kHz) prevailed in the oscillatory spectra, as it is showed by curve 2 in Fig. 1. Low-current-density signals often had the form of a succession ofμs-long "bursts" with falls practically to zero level in pauses between them.