Tailoring of polycrystalline diamond surfaces from hydrophilic to superhydrophobic via synergistic chemical plus micro-structuring processes

MONTAÑO-FIGUEROA, A. GABRIELA; ALCANTAR-PEÑA, JESUS J.; TIRADO, PABLO; ABRAHAM, ALEJANDRO; DE OBALDIA, ELIDA; AUCIELLO, ORLANDO

CARBON

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2018 vol. 139 p. 361 - 368

0008-6223

The wettability properties of the surfaces of polycrystalline diamond films, grown by Hot Filament Chemical Vapor Deposition, with different grain sizes, ranging from microcrystalline diamond (MCD), to nanocrystalline diamond (NCD), to ultrananocrystalline diamond (UNCD), were successfully tailored from as-grown flat semi-hydrophobic to hydrophilic surfaces, via oxygen (O2) plasma treatment, to highly-hydrophobic by carbon tetrafluoride (CF4) plasma treatment, and to super-hydrophobic diamond surface, via synergistic tailoring of surface chemistry and 3-D texturing. Raman spectroscopy analysis and secondary electron microscopy revealed the Hydrogen-surface termination and increased grain size, respectively, of the diamond films. Atomic Force Microscopy imaging of the plasma-treated UNCD films revealed no significant change in the surface roughness after either O2 or CF4 treatments. Nevertheless, a surface-chemistry alteration was confirmed by X-ray Photoelectron Spectroscopy. Finally, the synergistic combination of 3-D surface structuring and plasma-induced fluorine atoms surface termination of UNCD films produced a superhydrophobic state as revealed by a Water Contact Angle (WCA) close to ∼174°, thus producing the highest superhydrophobic surface of diamond material demonstrated today. The metastable Cassie-Baxter state, for the superhydrophobic 3-D UNCD surface, was demonstrated via a close correlation between the mathematical calculation based on the Cassie-Baxter Model and the experimental measurement of the WCA.