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Abstract: The wettability and surface energy of hydrogenated amorphous carbon films (a-C:H) elaborated by distributed electron cyclotron resonance plasma were studied by contact angle measurements in relation to composition, structure and topography. Tetrahedral a-C:H (ta-C:H) showed relatively high water contact angle (CA) up to 82.3°, and low surface energy (E s), down to 25.3 mJ/m2. Hydrophobicity was found to increase with the intensity of the ion bombardment and with the tetrahedral character. A decrease of the dispersive component is responsible of the decrease of surface energy with substrate bias. Low mass-density polymer-like a-C:H (PLC) presents also a relatively high hydrophobicity with high water CA, up to 76.7°, and low surface energy values, down to 32.1 mJ/m2. Hydrophobicity is interpreted as resulting from a surface layer rich in sp2-carbon for ta-C:H and rich in C–H bonds for PLC. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

The effects of heavy-ion radiation over the electron field emission (EFE) properties of sulfur-doped nanocomposite carbon (n-C:S) films were investigated. Two identical sets of n-C:S films were prepared in a hot-filament chemical vapor deposition system using CH4, H2 and H2S. Films with various sp3 C and sp2 C fractions were present within each set. Raman spectroscopy revealed the composite nature of the films. One set of films was submitted to a 20 krad dose of energetic Si and Fe ions (GeV/amu) at Brookhaven National Laboratory''s alternating gradient synchrotron. Films originally having poor EFE properties showed a dramatic emission enhancement as a result of irradiation, while those having good EFE properties before irradiation showed a small emission improvement upon irradiation. This improved EFE behavior is explained as due to the formation of conductive trigonal carbon nano-channels within the tetragonally-bonded carbon matrix. The diameter of these trigonal carbon nano-channels is small enough to produce large local field enhancement, and large enough to withstand the relatively large emitted current densities. A mechanism is proposed for the creation of this graphitic carbon nano-wire network within the tetragonal carbon matrix upon energetic irradiation. The results suggest that radiation-hardened cold cathodes can be fabricated using nanocomposite carbon materials that would remain stable in their EFE properties while exposed to ionizing radiation. [Copyright &y& Elsevier]