Setting Carriers Free – Healing Faulty Interfaces Promotes Delocalization and Transport in Nanocrystal Solids

Walravens, Willem; Mahmoud, Nayyera; Geenen, Filip; Solano, Eduardo; Dendooven, Jolien; Tadjine, Athmane; Delerue, Christophe; Roelkens, Günther; Detavernier, Christophe; Hens, Zeger

doi:10.29363/nanoge.nfm.2018.208

Cited by 4 publications

(16 citation statements)

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“…To minimize the impact of dielectric screening, we analyzed the absolute absorptance of a series of QD superlattices built from PbSe or CdSe QDs. 15−17 Such samples combine a 0D confinement with a 2D geometry, 18 which makes that only minor corrections are needed for the screening of the electromagnetic field (see also Figure 1). More precisely, we calculated for the different QD samples the local field factor F, which is the ratio between the external and the local electric field using atomistic dielectric modeling (see Supporting Information S8) and found that |F| 2 ranges between 0.4 and 0.8.…”

Section: ■ Monolayer Qd Superlatticesmentioning

confidence: 99%

The Fine-Structure Constant as a Ruler for the Band-Edge Light Absorption Strength of Bulk and Quantum-Confined Semiconductors

et al. 2021

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Low-dimensional semiconductors have found numerous applications in optoelectronics. However, a quantitative comparison of the absorption strength of lowdimensional versus bulk semiconductors has remained elusive. Here, we report generality in the band-edge light absorptance of semiconductors, independent of their dimensions. First, we provide atomistic tight-binding calculations that show that the absorptance of semiconductor quantum wells equals mπα (m = 1 or 2 with α as the fine-structure constant), in agreement with reported experimental results. Then, we show experimentally that a monolayer (superlattice) of quantum dots has similar absorptance, suggesting an absorptance quantum of mπα per (confined) exciton diameter. Extending this idea to bulk semiconductors, we experimentally demonstrate that an absorptance quantum equal to mπα per exciton Bohr diameter explains their widely varying absorption coefficients. We thus provided compelling evidence that the absorptance quantum πα per exciton diameter rules the band-edge absorption of all direct semiconductors, regardless of their dimension.

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Section: ■ Monolayer Qd Superlatticesmentioning

confidence: 99%

The Fine-Structure Constant as a Ruler for the Band-Edge Light Absorption Strength of Bulk and Quantum-Confined Semiconductors

et al. 2021

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“…Healing of the defected interface at a high temperature can cause this type of rearrangement. 18 Other structures, such as trimers or higher order oligomers, are also more probable in the rod-like fusion conditions, which are later separated by size-selective precipitation.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…Nonetheless, such treatment can anneal the interface to a smoother one, removing imperfections in some cases. 18 Notably, the aforementioned intraparticle ripening mechanism works well for the homonymously oriented dimers.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Neck Barrier Engineering in Quantum Dot Dimer Molecules via Intraparticle Ripening

et al. 2021

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Coupled colloidal quantum dot (CQD) dimers represent a new class of artificial molecules composed of fused core/shell semiconductor nanocrystals. The electronic coupling and wave function hybridization are enabled by the formation of an epitaxial connection with a coherent lattice between the shells of the two neighboring quantum dots where the shell material and its dimensions dictate the quantum barrier characteristics for the charge carriers. Herein we introduce a colloidal approach to control the neck formation at the interface between the two CQDs in such artificial molecular constructs. This allows the tailoring of the neck barrier in prelinked homodimers formed via fusion of multifaceted wurtzite CdSe/CdS CQDs. The effects of reaction time, temperature, and excess ligands are studied. The neck filling process follows an intraparticle ripening mechanism at relatively mild reaction conditions while avoiding interparticle ripening. The degree of surface ligand passivation plays a key role in activating the surface atom diffusion to the neck region. The degree of neck filling strongly depends also on the initial relative orientation of the two CQDs, where homonymous plane attachment allows for facile neck growth, unlike the case of heteronymous plane attachment. Upon neck filling, the observed red-shift of the absorption and fluorescence measured both for ensemble and single dimers is assigned to enhanced hybridization of the confined wave function in CQD dimer molecules, as supported by quantum calculations. The fine-tuning of the particle interface introduced herein provides therefore a powerful tool to further control the extent of hybridization and coupling in CQD molecules.

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“…Moreover, an increase of the conductivity in the superlattice requires an annealing up to 150 °C. 24 While such an annealing cures small structural defects, it might alter the electrical activity of remnant defects or impurities and might not leave Au or Ag nanocrystals unaltered when they are used as substitutional dopants. So far, the nature of the doping has been found to vary depending on the chemistry used to prepare epitaxially connected QD superlattices.…”

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confidence: 99%

“…So far, the nature of the doping has been found to vary depending on the chemistry used to prepare epitaxially connected QD superlattices. 24,25 But the microscopic nature of doping in these superlattices is still unknown. It is not clear if doping is caused by a charge transfer from the remaining ligands, which affects all the QDs in the superlattice, or if doping is induced by isolated QDs that are defective and transfer extra free charge carriers to the superlattice.…”

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confidence: 99%

Quantum Dot Acceptors in Two-Dimensional Epitaxially Fused PbSe Quantum Dot Superlattices

et al. 2022

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Oriented attachment of colloidal quantum dots allows the growth of two-dimensional crystals by design, which could have striking electronic properties upon progress on manipulating their conductivity. Here, we explore the origin of doping in square and epitaxially fused PbSe quantum dot superlattices with low temperature scanning tunneling microscope and spectroscopy. Probing the density of states of numerous individual quantum dots reveals an electronic coupling between the hole ground states of the quantum dots. Moreover, a small amount of quantum dots shows a reproducible deep level in the band gap, which is not caused by structural defects in the 2 connections but arises from unpassivated sites at the {111} facets. Based on semiconductor statistics, these distinct defective quantum dots, randomly distributed in the superlattice, trap electrons, releasing a concentration of free holes, which is intimately related to the interdot electronic coupling. They act as acceptor quantum dots in the host quantum dot lattice, mimicking the role of dopant atoms in a semiconductor crystal.

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Setting Carriers Free – Healing Faulty Interfaces Promotes Delocalization and Transport in Nanocrystal Solids

Cited by 4 publications

References 0 publications

The Fine-Structure Constant as a Ruler for the Band-Edge Light Absorption Strength of Bulk and Quantum-Confined Semiconductors

The Fine-Structure Constant as a Ruler for the Band-Edge Light Absorption Strength of Bulk and Quantum-Confined Semiconductors

Neck Barrier Engineering in Quantum Dot Dimer Molecules via Intraparticle Ripening

Quantum Dot Acceptors in Two-Dimensional Epitaxially Fused PbSe Quantum Dot Superlattices

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