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

Abstract

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.Index Terms-Amorphous carbon, biomedical coating, chemical vapor deposition (CVD), diamond-like carbon (DLC), optical emission, polymethyl methacrylate (PMMA), pulse, wettability.

Enhanced Wettability of Cubic Boron Nitride Films by Plasma Treatment

“…The ICP treated films show a great reduction in contact angle of water down to almost zero degree (below the measurable limit of ~2º) independent of V b , where the drop spreads wholly over the film surface, so the films become superhydrophilic. This is wholly opposed to diamond and diamond-like carbons [12,13,15]. The inset shows a list of the dispersion (γ d ) and polar (γ p ) components of the apparent surface free energy (γ=γ d +γ p ) of some of the films calculated from the contact angle data of water and 1-bromonaphthalene by using the Owen and Wendt method [16].…”