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The optical absorption and photoluminescence spectra of multi-alkali photocathodes are presented. The value of the band gap of multi-alkali photocathodes is determined by analysis of these spectra. It has been shown that the band gap Eg is equal to 1.3-1.4 eV. The value of the work function is also determined and the conclusion is drawn that multi-alkali photocathodes are photocathodes with negative or nearly zero electron affinity.

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Field-emission characteristics of carbon layers with very long (up to several mm) and sparse nanotubes (nanofilaments) have been investigated. For such layers field emission current of 10μA is registered at very low average electric field Eav=0.16V∕μm and the values of the field amplification coefficient β reach 45 000. It has been found that, at electric fields corresponding to the onset of the field emission, the emitting nanotubes are stretched towards the anode. At high emission currents (exceeding 30–50μA), one or several luminous filaments have been observed in the gap between the sample and the anode. These luminous filaments are carbon nanotubes (nanofilaments) heated by the emission current.