TY - JOUR
T1 - Modifying Thermal Transport in Colloidal Nanocrystal Solids with Surface Chemistry
AU - Liu, Minglu
AU - Ma, Yuanyu
AU - Wang, Robert
N1 - Funding Information:
This work was supported by the Young Investigator Research Program of the Air Force Office of Scientific Research through award number FA9550-13-1-0163 and by the National Science Foundation through award number CBET-1227979. We thank Emmanuel Soignard for performing the X-ray reflectivity measurements. Wegratefully acknowledge the use of facilities within the LeRoy Eyring Center for Solid State Science and the Center for Solid State Electronics Research, both of which are located at Arizona State University.
PY - 2015/11/10
Y1 - 2015/11/10
N2 - We present a systematic study on the effect of surface chemistry on thermal transport in colloidal nanocrystal (NC) solids. Using PbS NCs as a model system, we vary ligand binding group (thiol, amine, and atomic halides), ligand length (ethanedithiol, butanedithiol, hexanedithiol, and octanedithiol), and NC diameter (3.3-8.2 nm). Our experiments reveal several findings: (i) The ligand choice can vary the NC solid thermal conductivity by up to a factor of 2.5. (ii) The ligand binding strength to the NC core does not significantly impact thermal conductivity. (iii) Reducing the ligand length can decrease the interparticle distance, which increases thermal conductivity. (iv) Increasing the NC diameter increases thermal conductivity. (v) The effect of surface chemistry can exceed the effect of NC diameter and becomes more pronounced as NC diameter decreases. By combining these trends, we demonstrate that the thermal conductivity of NC solids can be varied by an overall factor of 4, from ∼0.1-0.4 W/m-K. We complement these findings with effective medium approximation modeling and identify thermal transport in the ligand matrix as the rate-limiter for thermal transport. By combining these modeling results with our experimental observations, we conclude that future efforts to increase thermal conductivity in NC solids should focus on the ligand-ligand interface between neighboring NCs.
AB - We present a systematic study on the effect of surface chemistry on thermal transport in colloidal nanocrystal (NC) solids. Using PbS NCs as a model system, we vary ligand binding group (thiol, amine, and atomic halides), ligand length (ethanedithiol, butanedithiol, hexanedithiol, and octanedithiol), and NC diameter (3.3-8.2 nm). Our experiments reveal several findings: (i) The ligand choice can vary the NC solid thermal conductivity by up to a factor of 2.5. (ii) The ligand binding strength to the NC core does not significantly impact thermal conductivity. (iii) Reducing the ligand length can decrease the interparticle distance, which increases thermal conductivity. (iv) Increasing the NC diameter increases thermal conductivity. (v) The effect of surface chemistry can exceed the effect of NC diameter and becomes more pronounced as NC diameter decreases. By combining these trends, we demonstrate that the thermal conductivity of NC solids can be varied by an overall factor of 4, from ∼0.1-0.4 W/m-K. We complement these findings with effective medium approximation modeling and identify thermal transport in the ligand matrix as the rate-limiter for thermal transport. By combining these modeling results with our experimental observations, we conclude that future efforts to increase thermal conductivity in NC solids should focus on the ligand-ligand interface between neighboring NCs.
KW - colloidal nanocrystal
KW - ligand
KW - nanocrystal solid
KW - thermal conductivity
KW - thermal transport
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U2 - 10.1021/acsnano.5b05085
DO - 10.1021/acsnano.5b05085
M3 - Article
AN - SCOPUS:84952361279
SN - 1936-0851
VL - 9
SP - 12079
EP - 12087
JO - ACS nano
JF - ACS nano
IS - 12
ER -