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Morphology and electron emission properties of nanocrystalline CVD diamond thin211 films

机译：纳米晶CVD金刚石薄膜211的形貌和电子发射特性

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Nanocrystalline diamond thin films have been produced by microwave plasma-211u001eenhanced chemical vapor deposition (MPECVD) using C(sub 60)/Ar/H(sub 2) or CH(sub 211u001e4)/Ar/H(sub 2) plasmas. Films grown with H(sub 2) concentration (le) 20% are 211u001enanocrystalline, with atomically abrupt grain boundaries and without observable 211u001egraphitic or amorphous carbon phases. The growth and morphology of these films 211u001eare controlled via a high nucleation rate resulting from low hydrogen 211u001econcentration in the plasma. Initial growth is in the form of diamond, which is 211u001ethe thermodynamic equilibrium phase for grains (le)5 nm in diameter. Once formed, 211u001ethe diamond phase persists for grains up to at least 15-20 nm in diameter. The 211u001erenucleation rate in the near-absence of atomic hydrogen is very high 211u001e((approximately) 10(sup 10) cm(sup (minus)2) sec(sup (minus)1)), limiting the 211u001eaverage grain size to a nearly constant value as the film thickness increases, 211u001ealthough the average grain size increases as hydrogen is added to the plasma. For 211u001ehydrogen concentrations less than (approximately)20%, the growth species is 211u001ebelieved to be the carbon dimer, C(sub 2), rather than the CH(sub 3)* growth 211u001especies associated with diamond film growth at higher hydrogen concentrations. 211u001eFor very thin films grown from the C(sub 60) precursor, the threshold field (2 to 211u001e(approximately)60 volts/micron) for cold cathode electron emission depends on the 211u001eelectrical conductivity and on the surface topography, which in turn depends on 211u001ethe hydrogen concentration in the plasma. A model of electron emission, based on 211u001equantum well effects at the grain boundaries is presented. This model predicts 211u001epromotion of the electrons at the grain boundary to the conduction band of 211u001ediamond for a grain boundary width (approximately) 3--4 (angstrom), a value 211u001ewithin the range observed by TEM.

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