Title
Pyramid-shaped wurtzite CdSe nanocrystals with inverted polarity Pyramid-shaped wurtzite CdSe nanocrystals with inverted polarity
Author
Faculty/Department
Faculty of Sciences. Physics
Publication type
article
Publication
Subject
Physics
Chemistry
Engineering sciences. Technology
Source (journal)
ACS nano
Volume/pages
9(2015) :8 , p. 8537-8546
ISSN
1936-0851
ISI
000360323300085
Carrier
E
Target language
English (eng)
Full text (Publishers DOI)
Affiliation
University of Antwerp
Abstract
We report on pyramid-shaped wurtzite cadmium selenide (CdSe) nanocrystals (NCs), synthesized by hot injection in the presence of chloride ions as shape-directing agents, exhibiting reversed crystal polarity compared to former reports. Advanced transmission electron microscopy (TEM) techniques (image-corrected high-resolution TEM with exit wave reconstruction and probe-corrected high-angle annular dark field-scanning TEM) unequivocally indicate that the triangular base of the pyramids is the polar (000 (1) over bar) facet and their apex points toward the [0001] direction. Density functional theory calculations, based on a simple model of binding of Cl- ions to surface Cd atoms, support the experimentally evident higher thermodynamic stability of the (000 (1) over bar) facet over the (0001) one conferred by Cl- ions. The relative stability of the two polar facets of wurtzite CdSe is reversed compared to previous experimental and computational studies on Cd chalcogenide NCs, in which no Cl-based chemicals were deliberately used in the synthesis or no Cl- ions were considered in the binding models. Self-assembly of these pyramids in a peculiar clover-like geometry, triggered by the addition of oleic acid, suggests that the basal (polar) facet has a density and perhaps type of ligands significantly different from the other three facets, since the pyramids interact with each other exclusively via their lateral facets. A superstructure, however with no long-range order, is observed for clovers with their (000 (1) over bar) facets roughly facing each other. The CdSe pyramids were also exploited as seeds for CdS pods growth, and the peculiar shape of the derived branched nanostructures clearly arises from the inverted polarity of the seeds.
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Full text (open access)
https://repository.uantwerpen.be/docman/irua/3e2f8f/127807.pdf
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