Controlled wettability of diamond/β-SiC composite thin films for biosensoric applications

Abstract

The wettability of different diamond/β-SiC composite thin film surfaces has been studied before and after chemical treatment by measuring contact angles in both static and dynamic modes; the water contact angle varies from 92.6 ± 2.5° to 32.7 ± 2.8° as the β-SiC content in the composite films (after chemical treatment) increases. The thermodynamic surface tension components of the film surfaces are calculated by using Owens-Wendt-Rabel-Kaelbles and van Osss methods. The increase in hydrophilicity is attributed to the increase in the total surface energy, which is induced by the increase of the Lewis acid-base surface tension component (γAB). The point of zero charge (PZC) of the film surfaces was determined to be at pH 4. Additionally, a composite film surface with a wettability gradient was also fabricated; here, the water contact angle varies from 86.7° at the left edge to 25.1° at the right edge of the film surface. To analyze the molecular scale origin of the observed contact angle variations, time-of-flight secondary ion mass spectrometry was employed to understand the surface termination of the "as-deposited" and "treated" diamond/β-SiC composite films. The controlled wettability was explained by the correlation of the surface termination with the measured contact angle. This work shows that diamond/β-SiC composite thin film surfaces provide varied surface energies that can serve as substrates for diverse biotechnological activities that require different surface wettabilities. © 2010 American Chemical Society.