Oscillation of wettability of molten Cu islands on SiO2

Abstract Contact-angle oscillation of liquid Cu islands on amorphous or single-crystal SiO 2 was observed in situ by an ultrahigh vacuum scanning electron microscope. The oscillation period changes from 100 to 0.1 s depending on island diameter and substrate temperature in ranges from 10 to 0.1 μm and from 1080 to 1130°C, respectively. The higher the substrate temperature and the smaller the island radius, the shorter the oscillation period. Oscillation phenomena were investigated on various kinds of metal islands and substrate materials in order to reveal the mechanism for contact-angle oscillation. The origin of the contact-angle oscillation is explained by the geometrical change of the interface profile of the molten island in a period of the oscillation caused by reaction or dissolution with the substrate.