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

Nature materials (2019-10-16)
Alex Abelson, Caroline Qian, Trenton Salk, Zhongyue Luan, Kan Fu, Jian-Guo Zheng, Jenna L Wardini, Matt Law

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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1-Octadecene, technical grade, 90%
(3-Mercaptopropyl)trimethoxysilane, 95%
Ferrocene, 98%
Carbon tetrachloride, anhydrous, ≥99.5%
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Tetrachloroethylene, anhydrous, ≥99%
Ammonium thiocyanate, 99.99% trace metals basis
Toluene-d8, anhydrous, 99.6 atom % D