The electron field emission (EFE) properties of microcrystalline diamond (MCD) films were markedly improved by using ultrananocrystalline diamond (UNCD) films as the nucleation layer. Thus formed MCD/UNCD composite films possess a low turn-on field ((E0)MCD/UNCD = 10.3 V/μm), which is even smaller than that for the underlying UNCD films ((E0)UNCD = 14.7 V/μm). However, the extent of the enhancement on EFE behavior of the MCD/UNCD films is strongly influenced by the characteristics of the UNCD nucleation layer. The improvement on EFE behavior of MCD/UNCD films is large when the UNCD nucleation layer was grown in H2-free Ar plasma (CH4/Ar/H2 (0%) = 2/98/0) and is small when the UNCD layer was grown in H2-containing Ar plasma (CH4/Ar/H2 (3%) = 2/95/3). Transmission electron microscopy (TEM) examinations reveal that, while both films contain large-grain and ultrasmall grain duplex microstructure, only the former contain nanographites, locating along the interface of large-grain and ultrasmall grain regions. Presumably, the nanographites form an interconnected path that improved the transport of electrons and markedly enhanced the EFE properties of the MCD/UNCD composite films.
Journal of Physical Chemistry C 115(28), pp.13894-13900