Entropic, Enthalpic, and Kinetic Aspects of Interfacial Nanocrystal Superlattice Assembly and Attachment

Whitham, Kevin; Smilgies, Detlef‐M.; Hanrath, Tobias

doi:10.1021/acs.chemmater.7b04223

Cited by 46 publications

(41 citation statements)

References 91 publications

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“…In similar experiments [73,85,87], self-assembly of NCs into square superlattices was observed, with all NCs oriented with a f100g facet parallel to the superlattice plane, and with oriented attachment between PbSe NCs by opposite f100g facets also performed. Although the relevant forces involved in the formation of these superlattices are known [93], the precise mechanisms are far from understood. In particular, it is not clear yet why the PbSe NCs form square superlattices in some cases and silicene-honeycomb superlattices in others.…”

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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Section: Introductionmentioning

confidence: 99%

Understanding the Formation of PbSe Honeycomb Superstructures by Dynamics Simulations

Soligno

Vanmaekelbergh

2019

Phys. Rev. X

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“…Recently, time-resolved X-ray scattering methods have been demonstrated to be a powerful tool for studying the NC assembly in real time under controlled experimental conditions. [10][11][12][13][14][15][16][17][18][19][20] The majority of these reports utilize the grazing-incidence small-angle X-ray scattering (GISAXS) technique for the in situ measurements of the self-assembly of colloidal NCs upon solvent evaporation. [11][12][13][14][15]19 However, the GISAXS geometry is limited to the surface characterization due to small incident angles of the X-ray beam and cannot deliver information about bulk superlattice structure.…”

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confidence: 99%

Coexistence of hcp and bct Phases during In Situ Superlattice Assembly from Faceted Colloidal Nanocrystals

Lokteva

Koof

Walther

et al. 2019

J. Phys. Chem. Lett.

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We study the in situ self-assembly of faceted PbS nanocrystals from colloidal suspensions upon controlled solvent evaporation using time-resolved small-angle X-ray scattering and X-ray crosscorrelation analysis. In our bulk-sensitive experiment in transmission geometry, the superlattice crystallization is observed in real time revealing a hexagonal closed-packed (hcp) structure followed by formation of a body-centered cubic (bcc) superlattice. The bcc superlattice undergoes continuous tetragonal distortion in the solvated state shortly after its formation, resulting in the body-centered tetragonal (bct) structure. Upon solvent evaporation, the bct superstructure becomes more pronounced with the still coexisting hcp phase. These findings corroborate the existing simulations of assembling cuboctahedral-shaped particles and illustrate that we observed the predicted equilibrium states. This work is essential for a deeper understanding of the fundamental forces that direct nanocrystal assembly including nanocrystal shape and ligand coverage. TOC GRAPHICSKEYWORDS. Small angle X-ray scattering (SAXS), X-ray cross correlation analysis (XCCA), evaporative induced self-assembly, lead sulfide (PbS), time-resolved superlattice crystallization.

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“… 63 At such small distances, epitaxial connections occur to minimize the free energy of the system. 4 , 5 , 48 , 56 , 63 , 64 The potential for eliminating dangling bonds leads to a strong enthalpic driving force; in the case of 7 nm Pd cubes, more than 1000 atomic bridges per {100} face will be formed.…”

Section: Resultsmentioning

confidence: 99%

Quantifying Strain and Dislocation Density at Nanocube Interfaces after Assembly and Epitaxy

Agrawal

Patra

Altantzis

et al. 2020

ACS Appl. Mater. Interfaces

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Nanoparticle self-assembly and epitaxy are utilized extensively to make 1D and 2D structures with complex shapes. High-resolution transmission electron microscopy (HRTEM) has shown that single-crystalline interfaces can form, but little is known about the strain and dislocations at these interfaces. Such information is critically important for applications: drastically reducing dislocation density was the key breakthrough enabling widespread implementation of light-emitting diodes, while strain engineering has been fundamental to modern high-performance transistors, solar cells, and thermoelectrics. In this work, the interfacial defect and strain formation after self-assembly and room temperature epitaxy of 7 nm Pd nanocubes capped with polyvinylpyrrolidone (PVP) is examined. It is observed that, during ligand removal, the cubes move over large distances on the substrate, leading to both spontaneous self-assembly and epitaxy to form single crystals. Subsequently, atomically resolved images are used to quantify the strain and dislocation density at the epitaxial interfaces between cubes with different lateral and angular misorientations. It is shown that dislocation- and strain-free interfaces form when the nanocubes align parallel to each other. Angular misalignment between adjacent cubes does not necessarily lead to grain boundaries but does cause dislocations, with higher densities associated with larger rotations.

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Entropic, Enthalpic, and Kinetic Aspects of Interfacial Nanocrystal Superlattice Assembly and Attachment

Cited by 46 publications

References 91 publications

Understanding the Formation of PbSe Honeycomb Superstructures by Dynamics Simulations

Understanding the Formation of PbSe Honeycomb Superstructures by Dynamics Simulations

Coexistence of hcp and bct Phases during In Situ Superlattice Assembly from Faceted Colloidal Nanocrystals

Quantifying Strain and Dislocation Density at Nanocube Interfaces after Assembly and Epitaxy

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