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  • NANOSCALE THERMAL CONDUCTION CHARACTERISATION IN THIN FILM SYSTEMS
    (2018) Khaled, Mohammad
    Thesis
    The characteristic length of the thin film systems used nowadays in nanoscale thermoelectric and microelectric devices are comparable to the mean free path and wavelength of energy carriers. As a result, the application of classical theorise to characterise thermal transport at the nanoscale is questionable. However, it is essential to understand the underlying physics of heat propagation in thin film systems to control, manipulate, and manage thermal properties in micro and nanodevices. Understanding thermal properties by experiment are challenging, especially for materials with low thermal conductivity and small mean free path (MFP). On the other hand, molecular dynamics (MD) allows investigation of sophisticated crystalline, bulk, interface and surface effects of thermal conduction problem with accuracy, fidelity, and reliability. Nevertheless, the computational results of MD can suffer from the wrong choice of critical parameters, unfit empirical potentials for thermal application and provide unreliable thermal conductivity. Moreover, the dependence of the thermal boundary resistance (TBR) on temperature, thin film's dimension, and defects are not systematically assessed for the important thin films in the thermal application. To solve this problem, a systematic equilibrium molecular dynamics (EMD), addressing the critical issues in thermal conduction characterisation is proposed at the classical temperature range, where thermal conduction is dominated by phonons. The model has been validated by investigating the thermal conduction of Si and dielectrics used in thin film systems. The issue with empirical potential is addressed by critically assessing the performance of a potential on the basis of thermal conductivity, atomic energy and phonon density of state prediction. Later, thin film systems are studied to understand relative phonon propagation at the interface and quantify TBR's dependence on interface area, interfacial distance as well as temperature. Finally, the thermal resistance of thin film systems with defects is characterised to understand realistic phonon propagation scenario in the thermal application of thin film systems.