Novel method determining contact angle of liquid Au on solid Al ₂O₃ single crystal (0001) surface at 1373K

The contact angle in microscopic size is considered not always to be equal to that in macroscopic size. Recently, the authors [1] have investigated the contact angle of liquid Au on solid Al₂O₃ by using a micro-scale wetting method. In that research, however, it was very difficult to get clear information of the contact area. Therefore, the measurements showed considerably large scatter. In this study, a new method with a confocal scanning laser microscope utilizing He-Ne laser beam of 632.8nm and 1.5mW was employed to determine the contact angle in microscopic size. A small piece of gold particle was placed on a solid Al₂O₃ single crystal substrate which was polished to have the roughness of less than 0.1nm. With flowing a highly purified Ar gas, the sample was heated to 1373K. When the sample was melted to form a liquid drop of spherical shape, the height and width of the gold drop was measured by the confocal scanning laser microscope. The contact angle was then evaluated from the relationship between the height and width of the drop. [1] By applying this method, the contact angle of liquid Au of 100μm in radius on solid Al₂O₃ single crystal of (0001) facet was estimated to be 134 ± 3°. This result is almost the same as that (133-134°) by using the micro-scale wetting method.