Propagation of Structural Disorder in Epitaxially Connected Quantum Dot Solids from Atomic to Micron Scale

Nanocrystal (NC) solids are commonly prepared from nonpolar organic NC suspensions. In many cases, the capping on the NC surface is preserved and forms a barrier between the NCs. More recently, superstructures with crystalline connections between the NCs, implying the removal of the capping, have been reported, too. Here, we present large-scale uniform superstructures of attached PbSe NCs with a silicene-type honeycomb geometry, resulting from solvent evaporation under nearly reversible conditions. We also prepared multilayered silicene honeycomb structures by using larger amounts of PbSe NCs. We show that the two-dimensional silicene superstructures can be seen as a crystallographic slice from a 3-D simple cubic structure. We describe the disorder in the silicene lattices in terms of the nanocrystals position and their atomic alignment. The silicene honeycomb sheets are large enough to be used in transistors and optoelectronic devices.

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“…Such a decrease of the disorder with increasing number of attached layers of NCs was also observed for square lattices and cubic lattices. 50 …”

Section: Disorder Due To Nanocrystal Misalignment In the Silicene Latmentioning

confidence: 99%

Mono- and Multilayer Silicene-Type Honeycomb Lattices by Oriented Attachment of PbSe Nanocrystals: Synthesis, Structural Characterization, and Analysis of the Disorder

et al. 2018

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“…Nanoparticle self-assembly is an emerging route with tremendous potential to build novel nanostructured materials [1,2]. In the past two decades, increasing interest has been devoted toward the formation of 3D [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] and 2D [21][22][23][24][25][26][27][28][29][30][31][32] nanogeometric materials for optoelectronic applications [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47]. These nanomaterials are formed by the self-assembly of semiconductor nanocrystals (NCs) with the size of a few nanometers, and often with a roughly spherical shape, into various types of superstructures.…”

Section: Introductionmentioning

confidence: 99%

Understanding the Formation of PbSe Honeycomb Superstructures by Dynamics Simulations

Soligno

Vanmaekelbergh

2019

Phys. Rev. X

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Using a coarse-grained molecular dynamics model, we simulate the self-assembly of PbSe nanocrystals (NCs) adsorbed at a flat fluid-fluid interface. The model includes all key forces involved: NC-NC shortrange facet-specific attractive and repulsive interactions, entropic effects, and forces due to the NC adsorption at fluid-fluid interfaces. Realistic values are used for the input parameters regulating the various forces. The interface-adsorption parameters are estimated using a recently introduced sharpinterface numerical method which includes capillary deformation effects. We find that the final structure in which the NCs self-assemble is drastically affected by the input values of the parameters of our coarsegrained model. In particular, by slightly tuning just a few parameters of the model, we can induce NC selfassembly into either silicene-honeycomb superstructures, where all NCs have a f111g facet parallel to the fluid-fluid interface plane, or square superstructures, where all NCs have a f100g facet parallel to the interface plane. Both of these nanostructures have been observed experimentally. However, it is still not clear their formation mechanism, and, in particular, which are the factors directing the NC self-assembly into one or another structure. In this work, we identify and quantify such factors, showing illustrative assembled-phase diagrams obtained from our simulations. In addition, with our model, we can study the self-assembly dynamics, simulating how the NCs' structures evolve from few-NCs aggregates to gradually larger domains. For example, we observe linear chains, where all NCs have a f110g facet parallel to the interface plane as typical precursors of the square superstructure, and zigzag aggregates, where all NCs have a f111g facet parallel to the interface plane as typical precursors of the silicene-honeycomb superstructure. Both of these aggregates have also been observed experimentally. Finally, we show indications that our method can be applied to study defects of the obtained superstructures.

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“…Therefore, to establish the utility of NP films for optoelectronic applications, it is imperative to find ways to drive NP films from their insulating phase across a Metal-Insulator Transition (MIT) into a conducting phase. Various groups attempted to boost the mobility by boosting the inter-NP transition rate with a variety of methods, including: ligand engineering 25 – 27 , band-alignment engineering 28 , chemical-doping 29 , 30 , photo-doping 31 , metal-NP substitution 32 , epitaxial attachment of NPs 33 , 34 , and atomic layer deposition (ALD) methods 35 .…”

Section: Introductionmentioning

confidence: 99%

Metal-Insulator Transition in Nanoparticle Solids: Insights from Kinetic Monte Carlo Simulations

Vörös

Zimányi

2017

Sci Rep

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Progress has been rapid in increasing the efficiency of energy conversion in nanoparticles. However, extraction of the photo-generated charge carriers remains challenging. Encouragingly, the charge mobility has been improved recently by driving nanoparticle (NP) films across the metal-insulator transition (MIT). To simulate MIT in NP films, we developed a hierarchical Kinetic Monte Carlo transport model. Electrons transfer between neighboring NPs via activated hopping when the NP energies differ by more than an overlap energy, but transfer by a non-activated quantum delocalization, if the NP energies are closer than the overlap energy. As the overlap energy increases, emerging percolating clusters support a metallic transport across the entire film. We simulated the evolution of the temperature-dependent electron mobility. We analyzed our data in terms of two candidate models of the MIT: (a) as a Quantum Critical Transition, signaled by an effective gap going to zero; and (b) as a Quantum Percolation Transition, where a sample-spanning metallic percolation path is formed as the fraction of the hopping bonds in the transport paths is going to zero. We found that the Quantum Percolation Transition theory provides a better description of the MIT. We also observed an anomalously low gap region next to the MIT. We discuss the relevance of our results in the light of recent experimental measurements.

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Propagation of Structural Disorder in Epitaxially Connected Quantum Dot Solids from Atomic to Micron Scale

Cited by 43 publications

References 35 publications

Mono- and Multilayer Silicene-Type Honeycomb Lattices by Oriented Attachment of PbSe Nanocrystals: Synthesis, Structural Characterization, and Analysis of the Disorder

Mono- and Multilayer Silicene-Type Honeycomb Lattices by Oriented Attachment of PbSe Nanocrystals: Synthesis, Structural Characterization, and Analysis of the Disorder

Understanding the Formation of PbSe Honeycomb Superstructures by Dynamics Simulations

Metal-Insulator Transition in Nanoparticle Solids: Insights from Kinetic Monte Carlo Simulations

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