In our previous work [1,2], we observed complicated behavior of field-induced electron emission from nanocarbon films in non-stationary (pulsed) electric field, including strong temporal dispersion with characteristic times as large as about 10μs. At the investigated materials, the emission current is produced at numerous low-aspect-ratio active centers. These centers can be expected to interact - for instance, via current-induced voltage drop at nanocarbon grains. Thus, the emitter surface represents a kind of 2d medium with spatial and temporal dispersion, principally suitable for development of oscillations and waves. Detection and characterization of these oscillatory phenomena can give new information on properties, performance and interaction of efficient emission centers. To investigate fluctuations of emission pattern with area resolution, we use the apparatus schematically showed in Fig. 1. Anode 4 and cathode guard electrode 3 form 2.5 mm-wide quasi-planar field gap in a vacuum chamber pumped typically to 10{sup}(-7) Torr. The studied emitting structure 2 is placed behind an orifice in the guard electrode. Heater 1 serves for conditioning of the sample prior to its investigation. Electrons extracted from the sample pass through a 2 mm-diameter diaphragm in the anode to strike the phosphor screen 5 deposited at a polished end of light-guide bunch 6. Emission images can be observed at the other end of the bunch, outside of the vacuum chamber. To measure a signal representing emission current density at a selected spatial position, the light flux from the corresponding image spot is collected with an optic fiber probe 7 and then directed to a photomultiplier 8. The present system includes four such data channels. Usually, four probes are arranged in quadratic or linear array with 100-150μm period, and whole array is scanned across the image to obtain measurable signal magnitudes at all data inputs.
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