Original Contributions to the Theory of Phonon Transport in Low-Dimensional Materials for Thermoelectric Applications

Thermoelectric materials that efficiently convert heat to electricity offer a pathway for waste heat recovery in Nigerian gas flaring infrastructure and industrial processes, where significant thermal energy is currently lost to the atmosphere. Enhancing the thermoelectric efficiency of materials requires simultaneous optimisation of electronic and phonon transport properties, which is only tractable through rigorous theoretical modelling at the nanoscale. This study makes original contributions to the theory of phonon transport in low-dimensional carbon and chalcogenide nanostructures relevant to thermoelectric applications, applying non-equilibrium Green's function formalism and Boltzmann transport equation approaches. Novel analytical expressions are derived for the phonon mean free path spectrum in graphene nanoribbons with realistic edge disorder, extending existing theory to account for the distinctive phonon scattering geometry of defect-rich interfaces. The lattice thermal conductivity of MoSe2-MoTe2 lateral heterostructures is computed from first principles and compared with available experimental data, achieving agreement within 8 percent. A figure of merit optimisation framework is developed that identifies edge passivation configurations maximising the ratio of electronic to phonon conductance in graphene nanoribbon thermoelectric junctions. The theoretical predictions provide guidance for experimental synthesis programmes at Nigerian university physics laboratories. Keywords: phonon transport, thermoelectric, graphene nanoribbon, non-equilibrium Green's function, low-dimensional materials