Theoretical Study On Phonon Scattering And Thermophysical Properties

Phononics, a new science and technology for processing information with phonons/heatand for controlling heat, has emerged as one of the hottest spots in nanoscience andnanotechnology.Various primary thermal (phononic) devices, have been proposed theoretically.The rapid development of nanotechnology has enabled the fabrication of structures muchsmaller than the mean free path of electrons and phonons,such as thermal rectifier, thermaltransistor, thermal logical gate, and thermal memory. Because of the potential applications ofgraphene and its derived nanostructures in phononics and the increased power dissipation innanoelectronics, which undermines the correct functionality of devices and limits their lifetime,phonon transport on this scale is of significant interest. Apart from the effort to minimize heatgeneration, an efficient heat management scheme is necessary.It has been shown that the thermal conductivity in graphene is high and dominated byphonons. High thermal conductance was predicted as well in graphene nanoribbons(GNRs).Which is unfortunate, however, that the phonon gas model is not perfect, and thephysical picture of phonon transform is not clear, especially for nano low dimensionalstructures whose spatial confinement will lead to a complicate phonon dispersion relations.This work introduces the classification of AGNRs and ZGNRs with different width and thedetail analysis process of brillouin zone, using the force constant method (FCM) to describe allthe phonon dispersion relations without linear approximation and isotropic, and the analysis ofgroup velocities and density of states of different phonon branches are performed, thencalcuated specific heat of different phonon branches. The resistive umklapp phonon-phononscattering rate can be calculated in the standard general approximation for dielectric crystals.The expression has been used successfully for graphene, carbon nanotubes,and GNRs. Byusing of the relaxation time approximation, the expression of thermal conductivity can derivedfrom the Boltzmann equation and Fourier law. All the programs are written through Matlab toobtain intuitive schematic diagrams. Based on the simulated calculation of thermal conductivity,GNRs shows high thermal conductivity similar to graphene.The research result declares that GNRs have excellent thermal conduction properties andthe value of thermal conductivity depends on the its length, width, the boundary conditions andother conditions. The above theoretical analysis construct soild foundation for futureexperiments and further theoretical study.