Wettability of Amorphous Diamond-Like Carbons Deposited on Si and PMMA in Pulse-Modulated Plasmas

• Published in: IEEE transactions on plasma science 2012-07, Vol.40 (7), p.1837-1842
• Main Authors: Ta-Lun Sung, Yang, J. H.-C, Teii, K., Teii, S., Chung-Ming Liu, Wan-Yu Tseng, Li-Deh Lin, Ono, S.
• Format: Article
• Language: English
• Subjects: Amorphous carbon; biomedical coating; Carbon; Chemical bonds; chemical vapor deposition (CVD); Deformation; Diamond-like carbon; diamond-like carbon (DLC); Methane; optical emission; Plasmas; Polymethyl methacrylate; polymethyl methacrylate (PMMA); pulse; Rough surfaces; Silicon; Substrates; Surface roughness; wettability
• ISSN: 0093-3813; 1939-9375
• DOI: 10.1109/TPS.2012.2196057

Pulse-modulated direct-current methane plasmas are used to deposit amorphous diamond-like carbon films on Si and dentistry-use polymethyl methacrylate (PMMA) substrates as a function of the negative pulse voltage applied to the substrate (V max ). The films on PMMA show a transition from diamond-like to more graphitic carbon in the Raman spectra with increasing V max , dissimilar to those on Si. This is attributed to easy deformation of PMMA, leading to the low compressive stress of the films (1 to 2 GPa). The contact angle of water for the films on both Si and PMMA is large, ranging from 79° to 94° almost independent of V max , confirming that the films are hydrophobic despite the difference in carbon bonding state. The large dispersion component (41-43 mJ/m 2 ) of the surface free energy of the films measured from the contact angle of water and 1-bromonaphthalene indicates the high mass density of the films. The small polar component (0.2-3.5 mJ/m 2 ) is attributed to hydrogen saturation of the surface sites forming nonpolar C-H bonds and, thus, responsible for the hydrophobic behavior.