Comment on "Advanced field emission measurement techniques for research on modern cold cathode materials and their applications for transmission-type x-ray sources" [Rev. Sci. Instrum. 91, 083906 (2020)].

This Comment suggests that technological field electron emission (FE) papers, such as the paper under discussion [P. Serbun et al., Rev. Sci. Instrum. 91, 083906 (2020)], should use FE theory based on the 1956 work of Murphy and Good (MG), rather than a simplified version of FE theory based on the original 1928 work of Fowler and Nordheim (FN). The use of the 1928 theory is common practice in the technological FE literature, but the MG treatment is known to be better physics than the FN treatment, which contains identifiable errors. The MG treatment predicts significantly higher emission current densities and currents for emitters than does the FN treatment. From the viewpoint of the research and development of electron sources, it is counterproductive (and unhelpful for non-experts) for the technological FE literature to use theory that undervalues the performance of field electron emitters.