Reverse Non-Equilibrium Molecular Dynamics Demonstrate That Surface Passivation Controls Thermal Transport at Semiconductor-Solvent Interfaces

Daniel C. Hannah, J. Daniel Gezelter, Richard D. Schaller, George C. Schatz

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

We examine the role played by surface structure and passivation in thermal transport at semiconductor/organic interfaces. Such interfaces dominate thermal transport in semiconductor nanomaterials owing to material dimensions much smaller than the bulk phonon mean free path. Utilizing reverse nonequilibrium molecular dynamics simulations, we calculate the interfacial thermal conductance (G) between a hexane solvent and chemically passivated wurtzite CdSe surfaces. In particular, we examine the dependence of G on the CdSe slab thickness, the particular exposed crystal facet, and the extent of surface passivation. Our results indicate a nonmonotonic dependence of G on ligand-grafting density, with interfaces generally exhibiting higher thermal conductance for increasing surface coverage up to 0.08 ligands/Å2 (75-100% of a monolayer, depending on the particular exposed facet) and decreasing for still higher coverages. By analyzing orientational ordering and solvent penetration into the ligand layer, we show that a balance of competing effects is responsible for this nonmonotonic dependence. Although the various unpassivated CdSe surfaces exhibit similar G values, the crystal structure of an exposed facet nevertheless plays an important role in determining the interfacial thermal conductance of passivated surfaces, as the density of binding sites on a surface determines the ligand-grafting densities that may ultimately be achieved. We demonstrate that surface passivation can increase G relative to a bare surface by roughly 1 order of magnitude and that, for a given extent of passivation, thermal conductance can vary by up to a factor of 2 between different surfaces, suggesting that appropriately tailored nanostructures may direct heat flow in an anisotropic fashion for interface-limited thermal transport.

Original languageEnglish
Pages (from-to)6278-6287
Number of pages10
JournalACS nano
Volume9
Issue number6
DOIs
Publication statusPublished - Jun 23 2015

Keywords

  • heat conduction
  • nanocrystals
  • nonequilibrium molecular dynamics
  • phonons
  • simulations
  • thermal transport

ASJC Scopus subject areas

  • Materials Science(all)
  • Engineering(all)
  • Physics and Astronomy(all)

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