Molecular Models for Gas-Wall Interactions
Orateur : Arjan JH Frijns
Eindhoven University of Technology, Department of Mechanical Engineering, The Netherlands
Abstract : Gas flows in micro- and nanosystems are of great importance for various applications in semiconductor industry. Rarefaction and the small length scales in micro- and nanosystems cause the Navier-Stokes equation to break down, making the CFD solution invalid. For such conditions, particle based methods, such as Molecular Dynamics (MD) are preferred. For modelling gas flows and heat transfer, the interaction between the gas and the solid walls is essential. However, water-silicon/silica interaction is generally not well modeled for non-reactive MD. Furthermore, computation time increases rapidly when the wall molecules are explicitly modeled in MD simulations. To save computation time, implicit boundary functions are often used. Steele’s potential has been used in studies of fluid-solid interface for a long time. However this approach is limited to van der Waals force interactions between electrically neutral surfaces and argon-like molecules (Lennard-Jones potentials). In this presentation, the idea of Steele’s potential is extended in order to simulate water-silicon/silica interactions. A new wall potential model is developed based on electronegativity-equalization method (EEM) based ReaxFF empirical force field and the non-reactive molecular dynamics package PumMa which allows a tabulated potential function as a input. Contact angle simulations with these tabulated wall potentials have been performed in order to validate the wall potential model. They resulted (non-fitted) contact angles of 129 ͦ for pure silicon, of 0 ͦ for silica-quartz, and of 40 ͦ for silica-cristobalite. These values are in agreement with experimental values.
Date et lieu : le Vendredi 23 Septembre à 11h, salle 250, IUSTI