This paper considers phonon transport behavior in graphene nanoribbons (GNRs) that bridge semi-infinite graphene contacts. The work employs an atomistic Green’s function method to investigate phonon wave effects in zigzag and armchair edge ribbons. Phonon transmission functions and thermal conductances are found to be sensitive to the edge shape of structures. The thermal conductances of GNRs with different widths are normalized by the quantum of thermal conductance to reveal the relation between number of phonon modes and conductance as a function of temperature. In addition, the phonon transmission functions of nano ribbons with defects are evaluated by artificially creating mismatches at interfaces. By comparing the transmission function of different defect patterns and the corresponding thermal conductances, the reduction of phonon transport is quantified. The length of defects is found to be important to phonon transport. Constriction effects are also studied at abrupt mismatched interfaces, and the reduction of thermal conductance is found to be moderately high.

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