Correlation between low threshold emission and C–N bond in nitrogen-doped diamond films

Abstract

A recent study demonstrated that electron emission occurs from conduction bands of heavily nitrogen (N)-doped diamond, utilizing the benefit of negative electron affinity [H. Yamaguchi et al., Phys. Rev. B 80, 165321 (2009)]. In addition, doping N-doped diamond films with dimethylurea (DMU) allowed high reproducibility. In this article, field emission properties of N-doped diamond films were compared between samples doped with DMU and one doped with urea. Fowler–Nordheim analysis and voltage-distance plot analysis showed that the barrier height for the urea-doped film was smaller than for DMU-doped counterparts, while the barrier height showed only a slight decrease when the DMU concentration in the reactant solution was changed from 10 to 1000 ppm. Ultraviolet photoelectron spectroscopy indicated that this difference in barrier height did not originate from the electron affinity. Time of flight secondary ion mass spectroscopy (TOF SIMS) exhibited that the concentration of C–N bonds in the urea-doped sample was an order of magnitude higher than in the two DMU-doped samples. This result suggests that only nitrogen atoms incorporated as C–N enhance the field emission properties of N-doped diamond films. Further TOF SIMS analysis of N-doped diamonds with urea or DMU doping may clarify the C–N distribution in relation to the electron emission under low electric fields.