Self-organization Of Nanocrystals Research Articles

Three-Dimensional Superlattice of PbS Quantum Dots in Flakes.

In the last two decades, many experiments were conducted in self-organization of nanocrystals into two- and three-dimensional (3D) superlattices and the superlattices were synthesized and characterized by different techniques, revealing their unusual properties. Among all characterization techniques, X-ray diffraction (XRD) is the one that has allowed the confirmation of the 3D superlattice formation due to the presence of sharp and intense diffraction peaks. In this work, we study self-organized superlattices of quantum dots of PbS prepared by dropping a monodispersed colloidal solution on a glass substrate at different temperatures. We showed that the intensity of the low-angle XRD peaks depends strongly on the drying time (substrate temperature). We claim that the peaks are originated from the 3D superlattice. Scanning electron microscopy images show that this 3D superlattice (PbS quantum dots) is formed in flake’s shape, parallel to the substrate surface and randomly oriented in the perpendicular planes.

Multi-scale simulations of apatite–collagen composites: from molecules to materials

We review scale-bridging simulation studies for the exploration of atomicto-meso scale processes that account for the unique structure and mechanic properties of apatite-protein composites. As the atomic structure and composition of such complex biocomposites only partially is known, the first part (i) of our modelling studies is dedicated to realistic crystal nucleation scenarios of inorganic-organic composites. Starting from the association of single ions, recent insights range from the mechanisms of motif formation, ripening reactions and the self-organization of nanocrystals, including their interplay with growth-controlling molecular moieties. On this basis, (ii) reliable building rules for unprejudiced scale-up models can be derived to model bulk materials. This is exemplified for (enamel-like) apatite-protein composites, encompassing up to 106 atom models to provide a realistic account of the 10 nm length scale, whilst model coarsening is used to reach μm length scales. On this basis, a series of deformation and fracture simulation studies were performed and helped to rationalize biocomposite hardness, plasticity, toughness, self-healing and fracture mechanisms. Complementing experimental work, these modelling studies provide particularly detailed insights into the relation of hierarchical composite structure and favorable mechanical properties.

Tic-Tac-Toe Binary Lattices from the Interfacial Self-Assembly of Branched and Spherical Nanocrystals

The self-organization of nanocrystals has proven to be a versatile route to achieve increasingly sophisticated structures of materials, where the shape and properties of individual particles impact the final functionalities. Recent works have addressed this topic by combining various shapes to achieve more complex arrangements of particles than are possible in single-component samples. However, the ability to create intricate architectures over large regions by exploiting the shape of multiply branched nanocrystals to host a second component remains unexplored. Here, we show how the concave shape of a branched nanocrystal, the so-called octapod, is able to anchor a sphere. The two components self-assemble into a locally ordered monolayer consisting of an intercalated square lattice of octapods and spheres, which is reminiscent of the "tic-tac-toe" game. These tic-tac-toe domains form through an interfacial self-assembly that occurs by the dewetting of a hexane layer containing both particle types. By varying the experimental conditions and performing molecular dynamics simulations, we show that the ligands coating the octapods are crucial to the formation of this structure. We find that the tendency of an octapod to form an interlocking-type structure with a second octapod strongly depends on the ligand shell of the pods. Breaking this tendency by ligand exchange allows the octapods to assemble into a more relaxed configuration, which is able to form a lock-and-key-type structure with a sphere, when they have a suitable size ratio. Our findings provide an example of a more versatile use of branched nanocrystals in self-assembled functional materials.

Chiral quantum supercrystals with total dissymmetry of optical response.

Since chiral nanoparticles are much smaller than the optical wavelength, their enantiomers show little difference in the interaction with circularly polarized light. This scale mismatch makes the enhancement of enantioselectivity in optical excitation of nanoobjects a fundamental challenge in modern nanophotonics. Here we demonstrate that a strong dissymmetry of optical response from achiral nanoobjects can be achieved through their arrangement into chiral superstructures with the length scale comparable to the optical wavelength. This concept is illustrated by the example of the simple helix supercrystal made of semiconductor quantum dots. We show that this supercrystal almost fully absorbs light with one circular polarization and does not absorb the other. The giant circular dichroism of the supercrystal comes from the formation of chiral bright excitons, which are the optically active collective excitations of the entire supercrystal. Owing to the recent advances in assembly and self-organization of nanocrystals in large superparticle structures, the proposed principle of enantioselectivity enhancement has great potential of benefiting various chiral and analytical methods, which are used in biophysics, chemistry, and pharmaceutical science.

Spontaneous Formations of Superlattices and Supracrystals from Various Forms of Mn3O4 Nanocrystals

In this work, we demonstrate a one-step approach for synthesis and construction of self-assembled superlattices (SLs) or supracrystals (SCs) using Mn3O4 nanocrystal building blocks. The Mn3O4 crystals have been prepared from simple starting chemicals; only oleylamine and manganese acetate are involved in the synthesis. Surprisingly, shape-controlled Mn3O4 nanocrystals (e.g., spheres, cubes, plates, or rice) have been obtained by just tuning precursor concentration, temperature, and reaction time. A process scheme has been devised as a guide for morphological control. Furthermore, due to surface modification with oleylamine molecules and the presence of strong interactive forces (such as dipole–dipole and van der Waals interactions) among the Mn3O4 nanocrystals, stringent requirements for formation of SLs and SCs have been relaxed in terms of shape uniformity and size monodispersity. The self-organization of nanocrystals is a fast spontaneous process requiring no additional postgrowth treatments. The proje...

ChemInform Abstract: Uncovering Molecular Processes in Crystal Nucleation and Growth by Using Molecular Simulation

AbstractReview: 120 refs.

Atomistic modelling of ion aggregation from solution and the self-organization of nanocrystals and nanocomposite biomaterials

We present a recently developed simulation method forexploring the mechanisms of crystal nucleation from solu-tion. By efficient tackling of the time-length scale prob-lem, molecular dynamics simulations allow very detailedinsights into the association of ions from solution and thedevelopment of structural motifs resulting in the nuclea-tion of nanocrystals. Our studies of ionic self-organizationinclude ripening reactions, such as proton transfer eventsand the interplay with growth-controlling molecules. Theformer issue is illustrated by the example of Zn

Self-Organization of Nanocrystals in Polymer Brushes. Application in Heterojunction Photovoltaic Diodes

We present a new approach to achieving order in molecular semiconductors via alignment of polymer chains using surface-initiated polymerization. Polyacrylate brushes grown from transparent conducting electrodes, with triarylamine side groups as hole-transporting components, show characteristics of high mobilities for hole transport. Solution processing a second component with favorable enthalpic interactions can form a composite with mesoscale order and be exploited for heterojunction diodes. We find substantial uptake of CdSe nanocrystals (with diameter in the range 2.5-2.8 nm), and such composites show photovoltaic quantum efficiencies of up to 50%.