Colloidal nanocrystal solids exhibit exceptional electronic and optical properties that make them attractive for electronic and optoelectronic devices.1 However, thermal transport properties also play an important role in such devices. For example, high thermal conductivities are desirable because this minimizes temperature rise during device operation, which subsequently leads to improved device performance and lifetime. Prior work on thermal transport in colloidal nanocrystal solids focused on ligand exchange strategies to modify thermal conductivity2, 3. In this work, we explore ligand cross-linking as a means to increase the thermal conductivity of nanocrystal solids.
Our investigation into modifying thermal transport with ligand cross-linking is inspired by recent work by Dreyer et al.4 They demonstrated that oleate ligands in iron oxide nanocrystal supercrystals can be cross-linked via thermal annealing, and that this cross-linking leads to large increases in Young’s modulus. Classical thermal transport theory indicates that increasing the Young’s modulus of a material should increase its speed of sound and consequently its thermal conductivity.
To investigate whether this classical design rule applies to nanocrystal solids, we report on our thermal conductivity studies of iron oxide nanocrystal films with cross-linked ligands. We utilize the 3ω method to measure thermal conductivity and our preliminary findings reveal that ligand cross-linking can increase the thermal conductivity by a factor of ~2. We also conduct effective medium approximation modeling to better understand the underlying origins of this thermal conductivity increase.
Boles, Michael A., Michael Engel, and Dmitri V. Talapin. "Self-assembly of colloidal nanocrystals: From intricate structures to functional materials." Chemical reviews 116.18 (2016): 11220-11289.
Ong, Wee-Liat, et al. "Surface chemistry mediates thermal transport in three-dimensional nanocrystal arrays." Nature Materials 12.5 (2013): 410-415.
Liu, Minglu, Yuanyu Ma, and Robert Y. Wang. "Modifying thermal transport in colloidal nanocrystal solids with surface chemistry." ACS nano 9.12 (2015): 12079-12087.
Dreyer, Axel, et al. "Organically linked iron oxide nanoparticle supercrystals with exceptional isotropic mechanical properties." Nature materials 15.5 (2016): 522-528.