Understanding the temperature-dependent transformations of nanocrystal solids is critical to interpretation of temperature-dependent charge transport measurements and can inform our understanding of self-assembly processes. Using Grazing Incidence Small- and Wide-Angle X-ray Scattering (GISAXS and GIWAXS) and GPU-accelerated coarse-grained molecular dynamics simulations, we studied the distortion of colloidal PbS nanocrystal superlattices between room temperature and cryogenic temperatures. Experimental data show that, regardless of the nanocrystal size or dispersity, the superlattice reversibly distorts by contracting along one axis and expanding along two axes. Interestingly, hysteresis in the pathway is observed and attributed to a ligand order/disorder transition, which presents a thermodynamic barrier upon cooling which is absent during heating. These results reveal the central importance of the ligands and solvent in dictating superlattice structure upon cooling. This fundamental understanding also serves as a potential route for engineering chosen lattice polymorphs at a specific temperature.

Ligand-mediated structural transformations in PbS nanocrystal superlattices

256th National Meeting (2018)

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