| In this dissertation, we have conducted fundamental studies for the phenomena of subcontinuum thermal transport in solids. Instead of using a phenomenological model based on the overall macroscale thermal behavior of solids, e.g., Fourier law of heat conduction, we studied the actual carriers of thermal energy, electrons and phonons, and captured their dynamics using Boltzmann transport equation (BTE). We have developed a novel lattice Boltzmann method (LBM), based on BTE, to successfully capture the transient sub-continuum thermal behavior in the solids. The virtues of being inherently transient in nature, ease in hybridizing with other physical models with broad length and time-scales, and ease of parallelizability of the algorithm made LBM as our natural choice.; We first developed LBM to accurately model the dynamics of phonons, which are primary energy carriers in semiconductors, to study sub-continuum thermal transport in semiconductors. The model is verified against different hierarchical schemes under their range of applicability and against the available experimental results. LBM successfully captured various sub-continuum effects, such as hot-spots generation, ballistic thermal transport, and temperature slip at the boundaries, which were not previously captured by continuum based models. In addition, anisotropic thermal conductivity for silicon thin films, depending upon the device dimensions and material's microstructure, is predicted by our model. Simple representative equations, capturing the predictions made by our LBM simulations, are formulated and can be used as a correction factor for subcontinuum effects in a continuum based thermal solvers. Rigorous boundary and multilayer treatments are also incorporated in our model to achieve accurate device level thermal modeling.; Since metals have two coupled energy carriers, electrons and phonons, we extended our methodology developed for phonons to electrons and simulated the coupled electrons and phonons sub-systems in the metals. We accurately captured the dynamics of both electrons and phonons inside the metals without simplifying either of the two subsystems. We demonstrated our coupled LBM scheme for metals via simulating thin gold films heating by ultra-short laser pulses and studied the effect of electron-phonon coupling on the thermal behavior of metals.; LBM developed in this work will enhance the nanotechnology by providing a better understanding of the thermal phenomena in the sub-continuum domain and will assist in developing a sub-continuum thermal design tool in electronics and data storage industry for systems such as silicon-on-insulator transistors, heat assisted magnetic recording, and phase change media, etc. |
