Effect of chain conformation in the phonon transport across a Si-polyethylene single-molecule covalent junction

We use nonequilibrium molecular dynamics simulations to study heat transfer across molecular junctions formed by alkane chains covalently bonded to crystalline silicon leads. We focus our studies on the role of chain conformation on phonon transport across junctions and along the chain. We find that in the case of straight chains, all trans conformations, the silicon-polyethylene junction conductance is 180 pW/K, and heat flows ballistically, i.e. with no resistance, along the chain. The introduction of gauche conformations (kinks) leads to a nonzero thermal resistance of the chain and also reduces the junction conductance to 100 pW/K. The chain thermal resistance is proportional to the number of gauche conformations indicating that they act as strong and independent phonon scattering centers. We attribute the 80% enhancement in junction conductance during extension from coiled to straight chain conformation to ballistic (coherent) phonon transport along a straight chain. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3592296]