Improvement in plasma illumination properties of ultrananocrystalline diamond films by grain boundary engineering

doi:10.1063/1.4817377

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Title:	Improvement in plasma illumination properties of ultrananocrystalline diamond films by grain boundary engineering
Authors:	K. J. Sankaran;K. Srinivasu;Chen, H. C.;Dong, C. L.;Leou, K. C.;Lee, C. Y.;Tai, N. H.;Lin, I. N.
Contributors:	淡江大學物理學系
Date:	2013-08-01
Issue Date:	2014-03-18 09:54:52 (UTC+8)
Publisher:	College Park: American Institute of Physics
Abstract:	Microstructural evolution of ultrananocrystalline diamond (UNCD) films as a function of substrate temperature (TS) and/or by introducing H2 in Ar/CH4 plasma is investigated. Variation of the sp 2 and sp 3 carbon content is analyzed using UV-Raman and near-edge X-ray absorption fine structure spectra. Morphological and microstructural studies confirm that films deposited using Ar/CH4 plasma at low TS consist of a random distribution of spherically shaped ultra-nano diamond grains with distinct sp 2-bonded grain boundaries, which are attributed to the adherence of CH radicals to the nano-sized diamond clusters. By increasing TS, adhering efficiency of CH radicals to the diamond lattice drops and trans-polyacetylene (t-PA) encapsulating the nano-sized diamond grains break, whereas the addition of 1.5% H2 in Ar/CH4 plasma at low TS induces atomic hydrogen that preferentially etches out the t-PA attached to ultra-nano diamond grains. Both cases make the sp 3-diamond phase less passivated. This leads to C2 radicals attaching to the diamond lattice promoting elongated clustered grains along with a complicated defect structure. Such a grain growth model is highly correlated to explain the technologically important functional property, namely, plasma illumination (PI) of UNCD films. Superior PI properties, viz. low threshold field of 0.21 V/μm with a high PI current density of 4.10 mA/cm2 (at an applied field of 0.25 V/μm) and high γ-coefficient (0.2604) are observed for the UNCD films possessing ultra-nano grains with a large fraction of grain boundary phases. The grain boundary component consists of a large amount of sp 2-carbon phases that possibly form interconnected paths for facilitating the transport of electrons and the electron field emission process that markedly enhance PI properties.
Relation:	Journal of Applied Physics 114(5), 054304(11pages)
DOI:	10.1063/1.4817377
Appears in Collections:	[Graduate Institute & Department of Physics] Journal Article

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