The diamond-solution interface: the surface energy of hydrogen terminated nanocrystalline CVD diamond derived from conta
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The diamond-solution interface: the surface energy of hydrogen terminated nanocrystalline CVD diamond derived from contact angle measurements Stoffel D. Janssens1, Sien Drijkoningen1, Marc Saitner1, Hans-Gerd Boyen1, Ken Haenen1, 2, Patrick Wagner1, 2 1 Institute for Materials Research (IMO), Hasselt University, BE-3590 Diepenbeek, Belgium 2 IMOMEC, IMEC vzw, BE-3590 Diepenbeek, Belgium ABSTRACT In this work, a determination of the surface energy for hydrogen terminated nanocrystalline diamond grown with microwave plasma enhanced chemical vapor deposition is presented. Five identical hydrogen terminated nanocrystalline diamond layers of ~150 nm thick are deposited on silicon substrates and examined with X-ray photoelectron spectroscopy to determine the surface groups and possible surface contaminations. In order to evaluate the surface energy, contact angle measurements are performed using the sessile drop method in combination with data analysis based on the ‘Owens, Wendt, Rabel and Kaelble’ method. Four different experimental approaches to evaluate the surface energy of hydrogen terminated nanocrystalline diamond are discussed. INTRODUCTION Nanocrystalline diamond is a versatile material that is currently being put forward as a material of choice for a variety of applications that make use of its surface properties. Therefore it is interesting to find reliable ways of investigating its surface properties. This work presents an experimental study of the surface energy of hydrogen terminated nanocrystalline diamond (NCD:H) by measuring contact angles using the sessile drop method. Data analysis is based on the ‘Owens, Wendt, Rabel and Kaelble’ (‘OWRK’) method [1, 2]. However, this method can be combined with different experimental approaches, usually differing in starting assumptions for the data treatment and/or the used liquids for the contact angle measurements. In this work, the following four experiments are conducted and the results are compared: 1. 2. 3. 4.
water, ethylene glycol and diiodomethane (pure liquids) multiple alcohol/water solutions (values used from the article of Hong and Chen [3]) multiple alcohol/water solutions (calibrated with a variety of polymers) multiple alcohol/water solutions (calibrated with a variety of calibrated polymers)
Experiment 1 is the standard way to determine surface energies and this method leads to no significant polar interactions on the surface after data analysis, which is expected from NCD:H, which is hydrophobic in nature [4]. However, the last two methods do show polar interactions on the surface to a certain extent. A possible explanation for this phenomenon is the presence of a higher adhesion force between alcohol (ethanol) and the NCD:H surface than between water and the NCD:H film. This would mean that the last two experiments lead to erroneous data because of the presence of a thin layer of alcohol on NCD:H, effectively leading to a water on alcohol system instead of the envisaged alcohol/water mixture on an NCD:H surface. Therefore,
Experiment.1 which is
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