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


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 103–105 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.

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Fig. 1: Fabrication and ligand chemistry of PbSe QD epi-SLs.
Fig. 2: Structure of the oleate-capped QD SL films.
Fig. 3: Structure of the epi-SL films.
Fig. 4: The phase transition pathway.
Fig. 5: Effect of ALD alumina infilling on the epi-SLs.

Data availability

The datasets generated and/or analysed during the current study are available from the corresponding author on reasonable request.


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This work was supported by the UC Office of the President under the UC Laboratory Fees Research Program Collaborative Research and Training Award LFR-17-477148. We thank C. Zhu, E. Schaible and A. Liebman-Pelaez for training and assistance on Beamline 7.3.3 of the Advanced Light Source, T. Aoki for TEM assistance, Q. Lin for X-ray diffraction assistance and D. Smilgies for the use of his GISAXS software and useful correspondence. This research used resources of the Advanced Light Source, which is a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231. Materials characterization was performed at the user facilities of the UC Irvine Materials Research Institute, which include instrumentation funded in part by the National Science Foundation Major Research Instrumentation Program under grant no. CHE-1338173.

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Correspondence to Matt Law.

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Supplementary Information

Supplementary Methods, Figs. 1–23, Tables 1–6 and references.

Supplementary Video S1

Phase transition from an oleate-capped to epitaxially fused colloidal quantum dot superlattice

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Abelson, A., Qian, C., Salk, T. et al. Collective topo-epitaxy in the self-assembly of a 3D quantum dot superlattice. Nat. Mater. 19, 49–55 (2020).

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