Despite considerable research efforts, the influence of contact line tension during wetting at the nanoscale and its experimental determination remain challenging tasks. So far, molecular dynamics simulations and atomic force microscope measurements have contributed to the understanding of these phenomena. However, a direct measurement of the size dependence of the contact angle and the magnitude of the apparent line tension has not been realized so far. Here, we show that the contact angle is indeed dependent on the drop size for small drop diameters and determine the magnitude of the apparent line tension via liquid-metal based measurements of advancing and receding contact angle inside a scanning electron microscope. For this purpose, a robotic setup inside an electron microscope chamber and oxide-free Galinstan droplets—produced via an electromigration-based and focused ion beam irradiation-assisted process—are employed. Using the first-order correction of Young’s equation, we find an apparent line tension value of 4.02 × 10⁻⁷ J/m for Galinstan© on stainless steel.

We present a new technique to produce liquid metal spheres with customized diameters using electromigration. The liquid metal used is a versatile material, which is increasingly implemented in micromanipulation applications. The theories of mass transport activated by electromigration are compared with experimental results. The knowledge gained from the theory is used to optimize this method. Therefore, different tip designs with at constant current are used. The measurement results are presented to characterize the mass flow depending on a certain current density. These results show a direct correlation between the current applied and the mass flow of the liquid metal, as assumed by theory. At the end, a successful pick-and-place application with the investigated process is presented. This application will in future simplify the manipulation and the analysis of liquid metals on the small scale. [2018-0149]

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