(222v) Simulating Nanoscale Thermal Transport in Nanoscale Systems

The ever increasing demand for higher performances in NEMS/MEMS and hard disk drives (HDDs) has resulted in decreasing the dimensions further into nanoscale, where thermal management via heat transfer is increasingly important due to significantly higher heat dissipation and operating temperatures. For example, state-of-the-art recording technology in the benchmark example of HDDs called heat assisted magnetic recording (HAMR) results in swift degradation of nanoscale lubricant, carbon overcoat (COC), and magnetic layers, leading to magnetic media corrosion which is detrimental to HDD operation. In addition, the lack of thorough understanding of the temperature profiles introduced by the hotspot and energy management throughout these materials also exacerbates the problem. 

To address this issue, in this study we will investigate the transient heat transfer in nano-scale thin films in HDI when a hotspot is created. Since traditional conduction models like Fourier law are not suitable due to dominant sub-continuum effects such as ballistic thermal transport and temperature slip at the boundaries, we utilize a lattice Boltzmann method (LBM) for phonons and electrons (which are primary carriers of energy) in the nano-scale thermal modeling. LBM originates from the non-equilibrium methodology of Boltzmann transport equations (BTEs) and is computationally efficient due to easy parallelization with capabilities of easily handling complex geometries.  Another advantage of LBM formulation in this system arises from the capability to accurately account for the temperature slip at the boundaries and interfaces, which is critical for energy management in HDDs. This is done by modeling phonon scattering (a) at the system boundaries, where a specularity factor P is introduced, which represents the fraction of carriers undergoing diffusive scattering at the boundary, accounting for the surface roughness, and (b) at the interface of two layers, where the transmission coefficient  obtained from the diffusive mismatch model is applied, representing total fraction of energy transmitted across the interface. Our results of in-plane and out of plane thermal transport mechanism and temperature profiles in realistic thin film structures with complex grain boundary interfaces as well as heat transfer between each adjacent layers will provide a clear physical understanding of the dynamics at nanoscale systems. In addition, our study will also lead to providing novel design criteria for efficient thermal management in these systems.