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Study the wettability of III-N thin films with different bond ionicity and surface layers polarity
|L. Ostrovskaya 1, A. Vasin 2, O. Voznyy 4, Vitalij G. Deibuk 3, M. Sletov 3|
1. V.Bakul Institute for Superhard Materials, NAS, 2 Avtozavodskaya, Kyiv 254074, Ukraine
The subject of this work was to study the effect of chemical bonding rebuilding on the wettability of III-nitrides (from BN to InN). Structural (bond ionicity) and surface properties, associated with their wettability and surface free energy, for 0.5- to 2-μm thick GaN, AlN, InN films deposited on different substrates (Si, α-Al2O3) by a pyrolytic deposition from complex ammonium compounds of Al, Ga and In halides have been studied. BN films with the different fraction of cBN (from 10 to 70% cBN) have been grown by the ion beam assisted deposition technique on Si (111) p-type substrate at the temperature 400 оС in argon and nitrogen medium.
The contact angles for the liquids of different polarities (water, μ = 1,84 D and glycerol, μ = 0,28 D) on these films were measured by a sessile drop technique (drop diameter 0,5 – 1 mm) in air at room temperature 20 оС. The surface energy was calculated by Fowke’s equation using wetting angle measurement and was compared to the bond ionicity and the films surface layers polarity.
The analysis of chemical bonding is made in different models (Phillips’s ionicity, Vogl’s polarity and Garcia-Cohen’s charge asymmetry coefficient). The pseudopotential calculations of electronic charge distributions along the bonds and the charge asymmetry coefficients (BN - 0.35; GaN - 0.52; AlN - 0.61; InN - 0.64) allow us explain the wettability features of III-nitrides.
A correlation was noticed between the wettability and bond ionicity: the higher the bond ionicity of the film, the lower wetting angle values both for water and glycerol. Surface layers polarity also affects the wettability behavior: N-face of the film wetted better than Me-face. All the above results have been discussed along with the films surface energy parameter (its polar and dispersive components) as the surface-determined factors.
Presentation: poster at E-MRS Fall Meeting 2005, Symposium G, by Vitalij G. Deibuk
See On-line Journal of E-MRS Fall Meeting 2005
Submitted: 2005-05-12 13:19 Revised: 2009-06-07 00:44