Electron field emission properties of microcrystalline and nanocrystalline carbon thin films deposited by S-assisted hot filament CVD
ABSTRACT Results are reported on the electron field emission properties of microcrystalline and nanocrystalline carbon thin films grown on molybdenum substrates by S-assisted hot-filament chemical vapor deposition technique using methane (CH4), hydrogen sulfide (H2S), and hydrogen (H2) gas mixtures. Electron field emission measurements revealed that the S-assisted thin films have substantially lower turn-on fields and steep rising currents, for both microcrystalline and nanocrystalline carbon, as compared to those grown without sulfur. In order to study the property–structure correlations, we characterized the films’ microstructure with SEM, AFM and Raman spectroscopy (RS) techniques. It was found that sulfur addition causes significant microstructural changes in both micro- and nanocrystalline thin films. S-assisted films show smoother and finer-grained surfaces than those grown without it, and a higher content of non-diamond carbon (sp2-bonded C). Besides, although most of the S is expected to be electrically inactive, under the high doping conditions hereby employed, there may be a significant amount in donor states. The results are discussed in terms of the dual role of S by enhancing the creation of defects and the availability of conduction electrons.