Quantitative Analysis of Contact Angle of Water on SiC: Polytype and Polarity Dependence

Abstract

A SiC crystal mixed with 4H-, 6H-, and 15R-SiC polytypes and their wetting properties were characterized using precisely dispensed de-ionized (DI) water drops. Contact angles of a DI water drop on SiC surfaces were quantitatively determined by analyzing the sideview image of a DI water drop in contact with the SiC substrate with mixed polytypes using image analysis software. The contact angle measurements showed that the contact angle for the Si-face (0001) was approximately 4o ∼ 8o greater than that for the C-face (000-1) regardless of polytype. The surface roughness of both Si-face and C-face was measured using atomic force microscopy and confirmed to be nearly identical. Due to the difference in surface energy of polarity of SiC basal planes, the contact angle measured from the Si-face (0001) after native oxide removal showed significant decrease and it recovered over time by room temperature oxidation in air. In contrast, the contact angle measured from the C-face (000-1) after native oxide removal, showed significant decrease and it was maintained, even after room temperature oxidation for 24 h in air. We found that there is correlation between the wetting property of SiC polytypes of 4H-, 6H-, and 15 R and a difference in their surface potential energy corresponding to the hexagonality of each SiC polytype determined by the atomic arrangement.