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Colloidal CdSe 0‑Dimension Nanocrystals and Their Self-Assembled 2‑Dimension Structures
journal contribution
posted on 2018-02-20, 22:04 authored by Yuanyuan Liu, Baowei Zhang, Hongsong Fan, Nelson Rowell, Maureen Willis, Xiaotong Zheng, Renchao Che, Shuo Han, Kui YuWe
report on a particular type of CdSe nanocrystals (NCs) that
exhibit a single optical absorption doublet. The two peaks in the
doublet are relatively sharp with a full width half-maximum as narrow
as 10 nm. The peak positions vary with passivation ligands (at ∼426
and ∼453 nm for amine ligand passivation and at ∼432
and ∼460 nm for carboxylate ligand passivation). To date, it
has been generally concluded that these NCs have a two-dimension (2D)
morphology with 1D quantum confinement. Here, we report that zero-dimension
(0D) NCs with 3D quantum confinement can exhibit a very similar static
optical feature consisting of a sharp absorption doublet. We show
that our as-prepared CdSe NCs (without further purification) were
mainly 0D NCs, as observed when they were deposited on transmission
electron microscopy (TEM) grids directly from toluene or hexane dispersions.
We further demonstrate that it was possible to alter this 0D morphology
by using dispersion additives and/or purification solvents to result
in the appearance of 2D NCs under TEM. Although the 0D and self-assembled
2D NCs displayed similar static optical features, the two morphologies
behaved quite differently in polarized emission. The 2D NCs exhibited
detection angle dependent polarized emission, whereas the 0D NCs do
not. Our findings indicate that a well-like morphology can be induced
by the presence of hexadecylamine (HDA) in the dispersion with sonication
for amine-passivated 0D NCs or by the use of ethanol during purification
with dispersion storage for carboxylate-passivated 0D NCs. In this
way, it is possible to manipulate the NC morphology for a targeted
application through the appropriate post-treatment. This study highlights
that more sophisticated theoretical studies are required to account
for the experimental observations in which both 0D NCs and their self-assembled
2D NC products display similar static optical features.
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carboxylate-passivated 0 D NCscarboxylate ligand passivationHDAself-assembled 2 D NCs3 D quantum confinementamine-passivated 0 D NCs1 D quantum confinement0 D morphologyTEMamine ligand passivation2 D NCsabsorption doubletself-assembled 2 D NC products display0 D NCstransmission electron microscopyas-prepared CdSe NCs
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