Formation of Epitaxially Connected Quantum Dot Solids: Nucleation and Coherent Phase Transition

Whitham, Kevin; Hanrath, Tobias

doi:10.1021/acs.jpclett.7b00846

Cited by 43 publications

(65 citation statements)

References 50 publications

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“…The unit cell angles of the OA‐capped mono‐ and multilayers are close to what is expected from a body‐centered cubic (BCC) superlattice seen from the <110> SL zone axis. Such symmetry and orientation have been observed in lead‐chalcogenide superlattices formed without ligand stripping . The thicker samples show symmetries close to a BCC structure even after ligand exchange.…”

supporting

confidence: 57%

“…On the other hand, initially a BCC lattice forms on the EG bath, likely due to the slower drying process . However, a large structural inhomogeneity is observed within and between samples without ligand treatment; the superlattice undergoes a slow transformation locally from BCC toward a simple cubic (SC) structure . This process occurs through a subphase‐mediated desorption of lead‐oleate from the CQD surface, giving rise to an oriented attachment .…”

mentioning

confidence: 99%

“…The addition of reactive ligands assists this process through removing the oleate ligands that act as spacers. The exposure of the facets transforms the lattice, which is expected to appear as a change in the angle from ≈70° to 90°, and a factor of 2 1/3 decrease in the lattice parameter …”

mentioning

confidence: 99%

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Electron Mobility of 24 cm² V⁻¹ s⁻¹ in PbSe Colloidal‐Quantum‐Dot Superlattices

et al. 2018

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Colloidal quantum dots (CQDs) are nanoscale building blocks for bottom-up fabrication of semiconducting solids with tailorable properties beyond the possibilities of bulk materials. Achieving ordered, macroscopic crystal-like assemblies has been in the focus of researchers for years, since it would allow exploitation of the quantum-confinement-based electronic properties with tunable dimensionality. Lead-chalcogenide CQDs show especially strong tendencies to self-organize into 2D superlattices with micrometer-scale order, making the array fabrication fairly simple. However, most studies concentrate on the fundamentals of the assembly process, and none have investigated the electronic properties and their dependence on the nanoscale structure induced by different ligands. Here, it is discussed how different chemical treatments on the initial superlattices affect the nanostructure, the optical, and the electronic-transport properties. Transistors with average two-terminal electron mobilities of 13 cm V s and contactless mobility of 24 cm V s are obtained for small-area superlattice field-effect transistors. Such mobility values are the highest reported for CQD devices wherein the quantum confinement is substantially present and are comparable to those reported for heavy sintering. The considerable mobility with the simultaneous preservation of the optical bandgap displays the vast potential of colloidal QD superlattices for optoelectronic applications.

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confidence: 57%

mentioning

confidence: 99%

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Electron Mobility of 24 cm² V⁻¹ s⁻¹ in PbSe Colloidal‐Quantum‐Dot Superlattices

et al. 2018

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Section: Assembly Of Cqd Thin Filmsmentioning

confidence: 99%

“…The different coordination numbers at the main facets resulting in different ligand binding energies make the ligand desorption easier from the {100} facets . The consequent appearance of large, uncovered surface areas at given directions, with highly enhanced orientation‐specific interactions and capacity to fuse, drives the formation of close‐to‐square, rhombic ordering in monolayers, and body‐centered cubic (BCC), rhombohedral, or (almost) simple cubic order in multilayer samples, with the {100} facets facing the subphase . The uncovered, reactive facets tend to epitaxially fuse through surface diffusion of atoms into the gap, resulting in a semiconnected structure, where some connections (necks) are as wide as the interacting facets, but the rest of the necks are missing and the gap increased …”

Section: Assembly Of Cqd Thin Filmsmentioning

confidence: 99%

Lead‐Chalcogenide Colloidal‐Quantum‐Dot Solids: Novel Assembly Methods, Electronic Structure Control, and Application Prospects

Balazs

Loi

2018

Advanced Materials

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Colloidal particles are formed and stabilized by surrounding the core with a surfactant shell that keeps the CQDs isolated and prevents charge transport though the arrays. [6] Replacing this shell by shorter molecules, so-called ligands, decreases the interparticle distance and increases the electronic coupling. This is thus a crucial step in forming conductive, practically relevant assemblies.Most early studies relied on a repetitive, layer-by-layer deposition and ligand exchange of CQDs to achieve thick conductive films, a method that resulted in the demonstration of field effect transistors and solar cells of noteworthy performances. [7][8][9][10][11][12][13][14][15] However, this technique only allows for limited control of the nanostructure and is not suitable for upscaling. The last few years brought several improvements in controlling the properties of CQD thin films with focus on both applications and the underlying science. [16,17] Current solar cells and transistors based on CQD arrays are on par with or better than the semiconducting polymer-based devices, showing the true prospects of these materials. [18][19][20] The most interesting feature of CQD solids is their enormous specific surface area; around one third of the atoms of a few nanometer CQDs are located at the surface, experiencing lower coordination than in bulk. Changing the dielectric or chemical environment thus has a significant effect on the overall properties. Much research has been conducted into this direction as well, leading to the ability to design the properties for applications.Here, we aim to show the most recent developments, put these results in perspective, and identify the limiting factors that limit further improvement in device performance. We focus on lead chalcogenides as they have been the subject of a variety of approaches to form solids, mainly because of their prospects in solar cell applications. However, the fundamental findings reported are valid for CQDs in general, and most methods can be used for other types of semiconductor nanocrystals as well. Although, numerous studies discuss the unique optical properties of CQDs, we have chosen to avoid their discussion here to be able to focus on the fabrication, electronic properties, and applications of CQD assemblies. In Section 2, two novel directions in sample fabrication of lead-chalcogenide CQD assemblies are discussed. The first one, the solution-phase ligand exchange, is relevant for mass production of devices, while the other, the self-assembly, is important for creating arrays with controlled nanostructure and order. Related to the difference in The quest for novel semiconductors with easy, cheap fabrication and tailorable properties has led to the development of several classes of materials, such as semiconducting polymers, carbon nanotubes, hybrid perovskites, and colloidal quantum dots. All these candidates can be processed from the liquid phase, enabling easy fabrication, and are suitable for different electronic and optoelectronic applications. Here, rece...

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Atomic Lattice Resolved Electron Tomography of a 3D Self‐Assembled Mesocrystal

Chu

Abelson

Qian

et al. 2023

Adv Funct Materials

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Complex 3D architectures of nanoscale building blocks can be created by selfassembly, but characterization of the atomic to mesoscale structure of such materials is limited by the difficulty of visualizing atoms across multiple length scales. Here, scanning transmission electron microscopy (STEM) and full-tilt tomographic reconstruction are used to image a single-crystalline region of a 3D epitaxially-fused PbSe quantum dot (QD) superlattice containing 633 QDs at a spatial resolution of 2.16 Å. The combined real-space and reciprocal-space analysis enables 3D mesoscale correlations of atomic lattice and superlattice order across hundreds of nanocrystals in 3D for the first time. Inhomogeneity in QD positional and orientational order reveals that the QD surface layers template the superlattice and that orientational entropy is higher in the interior layers than the surface layers. The measurement and analysis techniques presented here are applicable to a broad range of 3D nanostructured materials.

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Formation of Epitaxially Connected Quantum Dot Solids: Nucleation and Coherent Phase Transition

Cited by 43 publications

References 50 publications

Electron Mobility of 24 cm² V⁻¹ s⁻¹ in PbSe Colloidal‐Quantum‐Dot Superlattices

Electron Mobility of 24 cm² V⁻¹ s⁻¹ in PbSe Colloidal‐Quantum‐Dot Superlattices

Lead‐Chalcogenide Colloidal‐Quantum‐Dot Solids: Novel Assembly Methods, Electronic Structure Control, and Application Prospects

Atomic Lattice Resolved Electron Tomography of a 3D Self‐Assembled Mesocrystal

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Formation of Epitaxially Connected Quantum Dot Solids: Nucleation and Coherent Phase Transition

Cited by 43 publications

References 50 publications

Electron Mobility of 24 cm2 V−1 s−1 in PbSe Colloidal‐Quantum‐Dot Superlattices

Electron Mobility of 24 cm2 V−1 s−1 in PbSe Colloidal‐Quantum‐Dot Superlattices

Lead‐Chalcogenide Colloidal‐Quantum‐Dot Solids: Novel Assembly Methods, Electronic Structure Control, and Application Prospects

Atomic Lattice Resolved Electron Tomography of a 3D Self‐Assembled Mesocrystal

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Product

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Electron Mobility of 24 cm² V⁻¹ s⁻¹ in PbSe Colloidal‐Quantum‐Dot Superlattices

Electron Mobility of 24 cm² V⁻¹ s⁻¹ in PbSe Colloidal‐Quantum‐Dot Superlattices