Thermionic emission and work function of multiwalled carbon nanotube yarns

Thermionic emission from multiwalled carbon nanotubes (MWNTs) was investigated by using MWNT yarns. The work function of MWNT and thermionic emission constant of the yarn sample were both calculated from the thermionic emission data. The measured work function of MWNT is about $4.54--4.64\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The emission constant is larger than conventional thermionic cathode. Thermionic emission electron energy spectra at various temperatures have also been measured by using the MWNT yarn as the thermionic cathode in an electron momentum spectra instrument. The full width at half maximum of the spectra show a linear relation with the temperature. The carbon nanotube yarn may be used as thermionic cathode to replace the conventional cathode for their special properties.