Nanoscale Wetting and Its Connection with Macroscopic Young's Equation

Wetting behavior of liquids plays a key role in the wet cleaning process of semiconductor fabrication, and quantitative evaluation of the solid-fluid interfacial tensions using molecular dynamics (MD) simulation is needed for the understanding, control, and design of the process. In this report, we summarize the basic features of the interfacial tensions from a microscopic viewpoint, and we show two basic approaches - called the mechanical and thermodynamic routes - to calculate solid-fluid interfacial tensions by MD simulations, which enable the microscopic understanding of Young's equation at the nanoscale as the basis of wetting physics. In the mechanical route, the local stress anisotropy appearing around the interfaces is related to the interfacial tensions through original Bakker's equation and its extended versions developed by the present authors. On the other hand, in the thermodynamic route, the solid-related interfacial tensions are extracted as the free energy difference from a reference system.