Nitrogen-Incorporated Boron-Doped Nanocrystalline Diamond Nanowires for Microplasma Illumination

Abstract

The origin of nitrogen-incorporated boron-doped nanocrystalline diamond (NB-NCD) nanowires as a function of substrate temperature (T-s) in H-2/CH4/B2H6/N-2 reactant gases is systematically addressed. Because of Ts, there is a drastic modification in the dimensional structure and microstructure and hence in the several properties of the NB-NCD films. The NB-NCD films grown at low Ts (400 degrees C) contain faceted diamond grains. The morphology changes to nanosized diamond grains for NB-NCD films grown at 550 degrees C (or 700 degrees C). Interestingly, the NB-NCD films grown at 850 degrees C possess one-dimensional nanowirelike morphological grains. These nanowire-like NB-NCD films possess the co-existence of the sp(3)-diamond phase and the sp(2)-graphitic phase, where diamond nanowires are surrounded by sp(2)-graphitic phases at grain boundaries. The optical emission spectroscopy studies stated that the CN, BH, and C-2 species in the plasma are the main factors for the origin of nanowire-like conducting diamond grains and the materialization of graphitic phases at the grain boundaries. Moreover, conductive atomic force microscopy studies reveal that the NB-NCD films grown at 850 degrees C show a large number of emission sites from the grains and the grain boundaries. While boron doping improved the electrical conductivity of the NCD grains, the nitrogen incorporation eased the generation of graphitic phases at the grain boundaries that afford conducting channels for the electrons, thus achieving a high electrical conductivity for the NB-NCD films grown at 850 degrees C. The microplasma devices using these nanowire-like NB-NCD films as cathodes display superior plasma illumination properties with a threshold field of 3300 V/mu m and plasma current density of 1.04 mA/cm(2) with a supplied voltage of 520 V and a lifetime stability of 520 min. The outstanding plasma illumination characteristics of these conducting nanowire-like NB-NCD films make them appropriate as cathodes and pave the way for the utilization of these materials in various microplasma device applications.