  Thermal properties in the metal/graphene (Gr) systems are analyzed by using
an atomistic phonon transport model based on Landauer formalism and
first-principles calculations. The specific structures under investigation
include chemisorbed Ni(111)/Gr, physisorbed Cu(111)/Gr and Au(111)/Gr, as well
as Pd(111)/Gr with intermediate characteristics. Calculated results illustrate
a strong dependence of thermal transfer on the details of interfacial
microstructures. In particular, it is shown that the chemisorbed case provides
a generally smaller interfacial thermal resistance than the physisorbed due to
the stronger bonding. However, our calculation also indicates that the weakly
chemisorbed interface of Pd/Gr may be an exception, with the largest thermal
resistance among the considered. Further examination of the electrostatic
potential and interatomic force constants reveal that the mixed bonding force
between the Pd and C atoms results in incomplete hybridization of Pd and
graphene orbital states at the junction, leading effectively to two phonon
interfaces and a larger than expected thermal resistance. Comparison with
available experimental data shows good agreement. The result clearly suggests
the feasibility of phonon engineering for thermal property optimization at the
interface.
