Theoretical problems arising in connection with development and operation of electron field emitters on the basis of carbon nanotubes are reviewed. The physical aspects of electron field emission that underlie the unique emission properties of carbon nanotubes (CNTs) are considered. Physical effects and phenomena affecting the emission characteristics of CNT cathodes are analyzed. Effects given particular attention include: the electric field amplification near a CNT tip with taking into account the shape of the tip, the deviation from the vertical orientation of nanotubes and electrical field-induced alignment of those; electric field screening by neighboring nanotubes; statistical spread of the parameters of the individual CNTs comprising the cathode; the thermal effects resulting in degradation of nanotubes during emission. Simultaneous consideration of the above-listed effects permitted the development of the optimization procedure for CNT array in terms of the maximum reachable emission current density. In accordance with this procedure, the optimum inter-tube distance in the array depends on the region of the external voltage applied. The phenomenon of self-misalignment of nanotubes in an array has been predicted and analyzed in terms of the recent experiments performed. A mechanism of degradation of CNT-based electron field emitters has been analyzed consisting of the bombardment of the emitters by ions formed as a result of electron impact ionization of the residual gas molecules.

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Graphene oxide produced by the standard Hammers method was annealed at various temperatures. The measurements indicate a monotone enhancement of the electric conductivity of the annealed graphene oxide samples with the increase of the annealing temperature. The most prominent jump in the conductivity (about five orders of magnitude) occurs between 150 and 180 • C. At the annealing temperature of 800 • C, the conductivity of reduced graphene oxide reaches the values typical for highly oriented pyrolytic graphite. The measurements demonstrate a non-linear character of conduction of reduced graphene oxide (RGO) samples, which manifests itself in a sensitivity of the sample conductivity to the magnitude of the applied voltage. This phenomenon is explained in terms of the percolation conduction mechanism of the RGO samples, in accordance with which the charge transport is provided by a limited number of percolation paths formed by contacting RGO fragments. A model simulation performed on the basis of the percolation mechanism of RGO conduction agrees qualitatively with the experimental data obtained.

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