Molecular Dynamics Simulation of Thin Films with Rough and Asymmetric Interfaces

Thermal rectification is a phenomenon in which thermal transport is preferred in one direction over the opposite. Though observations of thermal rectification have been elusive, it could be useful in many applications such as thermal management problems at the micro/nano scale for electronics cooling. The current work explores the possibility of thermal rectifying devices with the use of interfaces and shows that pristine, imperfect and asymmetric interfaces in thin films can result in a difference in the effective thermal conductivity when the temperature gradient is reversed. The asymmetric geometries investigated in the device include hemispherical and ellipsoidal shapes. The rectifying behavior originates from the difference in the frequency content between two temperature reservoirs. More massive elements will produce different frequencies that reflect preferentially at a nanostructured interface whose features are of the order of the phonon wavelength. At a constant temperature difference of 20K we calculate a different heat flux or effective thermal conductivity depending on the direction of the temperature gradient. Results show a difference of approximately 70% in the effective thermal conductivity for opposite directions.