Abstract
Microstructural evolution as a function of substrate temperature (T S ) for conducting ultrananocrystalline diamond (UNCD) films is systematically studied. Variation of the sp 2 graphitic and sp 3 diamond content with T S in the films is analysed from the Raman and near-edge x-ray absorption fine structure spectra. Morphological and microstructural studies confirm that at T S =700°C well-defined acicular structures evolve. These nanowire structures comprise sp 3 phased diamond, encased in a sheath of sp 2 bonded graphitic phase. T S causes a change in morphology and thereby the various properties of the films. For T S =800°C the acicular grain growth ceases, while that for T S =700°C ceases only upon termination of the deposition process. The grain-growth process for the unique needle-like granular structure is proposed such that the CN species invariably occupy the tip of the nanowire, promoting an anisotropic grain-growth process and the formation of acicular structure of the grains. The electron field emission studies substantiate that the films grown at T S =700°C are the most conducting, with conduction mediated through the graphitic phase present in the films. © 2012 IOP Publishing Ltd.