Abstract
We use molecular dynamics simulations and the lattice-based scattering boundary method to compute the thermal conductance of finite-length Lennard-Jones superlattice junctions confined by bulk crystalline leads. The superlattice junction thermal conductance depends on the properties of the leads. For junctions with a superlattice period of four atomic monolayers at temperatures between 5 and 20 K, those with mass-mismatched leads have a greater thermal conductance than those with mass-matched leads. We attribute this lead effect to interference between and the ballistic transport of emergent junction vibrational modes. The lead effect diminishes when the temperature is increased, when the superlattice period is increased, and when interfacial disorder is introduced, but is reversed in the harmonic limit.
Highlights
Semiconductor superlattice nanostructures have received considerable research attention since their first appearance in the 1970s.1,2 They have applications in solid state lighting and thermoelectric energy conversion due to the size-tunability of their electronic properties
We describe the three techniques used in Section III: the thermal circuit model, non-equilbrium MD (NEMD) simulations, and the Landauer transport formula with the scattering boundary method (SBM)
The length dependence of the thermal conductance for superlattice junctions with two, four, and eight atomic monolayers per thin film at average temperatures of 20 K and 40 K were extracted from NEMD simulations
Summary
Semiconductor superlattice nanostructures have received considerable research attention since their first appearance in the 1970s.1,2 They have applications in solid state lighting and thermoelectric energy conversion due to the size-tunability of their electronic properties. Semiconductor superlattice nanostructures have received considerable research attention since their first appearance in the 1970s.1,2. They have applications in solid state lighting and thermoelectric energy conversion due to the size-tunability of their electronic properties. The possibility of tuning superlattice design for low thermal conductivity provides a potential path to optimizing the thermoelectric figure of merit. Computational work on thermal transport within superlattices has been performed using equilibrium[6,7] and non-equilibrium[6,8,9,10,11,12,13] molecular dynamics (MD) simulations. Work has been done using perturbative anharmonic lattice dynamics calculations, using force constants from both analytical potentials and from density functional theory calculations.[14,15,16]
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