This paper presents a new evaluation method of wettability between solid and liquid metals in ultra-high vacuum. An argon ion sputter cleaning process of the specimen and a highly magnified observation of the contact angles by scanning electron microscope were adopted to obtain the most reliable experimental values of the contact angles. It was actually found that the wettability between silver and tungsten, that had been thought to be poor, was rather good, when both of the surfaces were perfectly cleaned in ultra-high vacuum. The contact angles for various liquid metals on tungsten were also determined using this experimental method. The empirical tight binding calculations were performed and the local density of states was used to evaluate the wetting interaction energy. The calculated local values were qualitatively proportional to the experimental values of the interaction energies. In order to control wettability, it is necessary to control the electronic states of the substrate surface.
