title: Correlating superlattice polymorphs to internanoparticle distance, packing density, and surface lattice in assemblies of PbS nanoparticles.
abstract: Assemblies of 3.5 nm PbS nanoparticles (NPs) nucleate in three dominant superlattice polymorphs: amorphous, body-centered-cubic (bcc) and face-centered-cubic (fcc) phase. This superlattice relationship can be controlled by the inter-NP distance without changing the NP size. Upon increase of inter-NP distance, the packing density decreases, and the capping molecules at NP surfaces change in structure and accordingly modify the surface energy. The driving force for NP assembly develops from an entropic maximization to a reduction of total free energy through multiple interactions between surface molecules and NPs and resulting variation of surface molecules. Upon long-term aging and additional thermal treatment, fcc undergoes a tetragonal distortion and subsequently transforms to bcc phase, and simultaneously, the NPs embedded in supercrystals reduce surface energy primarily in {200} facets. Linking molecule-NP interactions with a series of changes of packing density and surface lattice spacings of NPs allows for an interpretation of principles governing the nucleation, structure stability, and transformation of PbS NP-assembled supercrystals.
authors: Cornell High Energy Synchrotron Source, Cornell University, Ithaca, New York 14853, United States. zw42@cornell.edu
authors: Zhongwu
authors: Z
authors: Wang
authors: Constanze
authors: C
authors: Schliehe
authors: Kaifu
authors: K
authors: Bian
authors: Darren
authors: D
authors: Dale
authors: William A
authors: WA
authors: Bassett
authors: Tobias
authors: T
authors: Hanrath
authors: Christian
authors: C
authors: Klinke
authors: Horst
authors: H
authors: Weller