Collective topo-epitaxy in the self-assembly of a 3D quantum dot superlattice

• Published in: Nature materials Vol. 19; no. 1; pp. 49 - 55
• Main Authors: Abelson, Alex, Qian, Caroline, Salk, Trenton, Luan, Zhongyue, Fu, Kan, Zheng, Jian-Guo, Wardini, Jenna L., Law, Matt
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-01-2020; Nature Publishing Group
• Subjects: 639/301/357/1017; 639/301/357/551; 639/638/298/917; 639/638/298/923/966; 639/925/930/12; Biomaterials; Chemistry and Materials Science; Condensed Matter Physics; Lead selenides; Materials Science; Nanotechnology; Optical and Electronic Materials; Phase transitions; Quantum dots; Self-assembly; Superlattices
• ISSN: 1476-1122; 1476-4660
• DOI: 10.1038/s41563-019-0485-2

Epitaxially fused colloidal quantum dot (QD) superlattices (epi-SLs) may enable a new class of semiconductors that combine the size-tunable photophysics of QDs with bulk-like electronic performance, but progress is hindered by a poor understanding of epi-SL formation and surface chemistry. Here we use X-ray scattering and correlative electron imaging and diffraction of individual SL grains to determine the formation mechanism of three-dimensional PbSe QD epi-SL films. We show that the epi-SL forms from a rhombohedrally distorted body centred cubic parent SL via a phase transition in which the QDs translate with minimal rotation (~10°) and epitaxially fuse across their {100} facets in three dimensions. This collective epitaxial transformation is atomically topotactic across the 10
3
–10
5
QDs in each SL grain. Infilling the epi-SLs with alumina by atomic layer deposition greatly changes their electrical properties without affecting the superlattice structure. Our work establishes the formation mechanism of three-dimensional QD epi-SLs and illustrates the critical importance of surface chemistry to charge transport in these materials.
A structural investigation on the formation of 3D superlattices of colloidal PbSe quantum dots reveals a topotactic transition from the self-assembled phase of ligand-capped quantum dots to the epitaxially fused phase typical of conductive solids.