Assembly of colloidal nanocrystals into open networks

Inorganic nanocrystals exhibit a wide variety of optical, electronic, chemical, and electrochemical functionality that is synthetically tunable based on their size and composition. Their properties and emerging methods for functionalizing their surfaces with specific chemical agents pose the exciting prospect to program the assembly of nanostructured materials whose properties depend intimately on both the characteristics of the building blocks and the mesoscale organization of these in the assembly. In this presentation, I describe novel strategies for assembling optically active nanocrystals into organized gel networks. In particular, theoretical frameworks predict open gel architectures when the extent of inter-particle bonding (i.e. valence) is constrained.[1] To achieve a chemically tunable valence, we functionalized semiconductor nanocrystals with highly charged chalcogenidometallates clusters that induce long range repulsive interactions.[2] The addition of controlled amounts of a cationic crosslinking agent determines the assembly of the nanocrystals into a low volume fraction gel. In another assembly strategy, short range attractive forces are induced between charge-stabilized nanocrystal colloids by the introduction of oligomeric polyethylene glycol (PEG). At low PEG concentrations, it can crosslink nanocrystals into a gel. At higher concentrations, PEG effectively passivates the nanocrystal surfaces, yet excess PEG can induce gel network assembly through the depletion attraction. The organization of the gel networks is characterized by small angle X-ray scattering, from which the fractal dimension that describes the gel topology is determined. We present an integrated approach leveraging theory, synthesis, characterization, and simulation to predict, realize, and analyze the formation of low volume fraction gels from colloidal nanocrystals with unusual optical properties in the visible and infrared spectral ranges. References: [1] BA Lindquist, RB Jadrich, DJ Milliron, TM Truskett, “On the Formation of Equilibrium Gels via a Macroscopic Bond Limitation,” J. Chem. Phys. 145 (2016), 074906. [2] A Singh, BA Lindquist, GK Ong, RB Jadrich, A Singh, H Ha, CJ Ellison, TM Truskett, DJ Milliron, “Linking Semiconductor Nanocrystals into Gel Networks through All-Inorganic Bridges,” Angew. Chem. Int. Ed. 54 (2015), 14840-14844

Carbon supported CdSe nanocrystals

Insights to the mechanism of CdSe nanoparticle attachment to carbon nanotubes following the hot injection method are discussed. It was observed that the presence of water improves the nanotube coverage while Cl containing media are responsible for the shape transformation of the nanoparticles and further attachment to the carbon lattice. The experiments also show that the mechanism taking place involves the right balance of several factors, namely, low passivated nanoparticle surface, particles with well-defined crystallographic facets, and interaction with an organics-free sp2 carbon lattice. Furthermore, this procedure can be extended to cover graphene by quantum dots.Comment: 5 pages, 5 figure

Gelation of Plasmonic Metal Oxide Nanocrystals by Polymer-Induced Depletion-Attractions

Gelation of colloidal nanocrystals (NCs) emerged as a strategy to preserve inherent nanoscale properties in multiscale architectures. Yet available gelation methods still struggle to reliably control nanoscale optical phenomena such as photoluminescence and localized surface plasmon resonance (LSPR) across NC systems due to processing variability. Here, we report on an alternative gelation method based on physical inter-NC interactions: short-range depletion-attractions balanced by long-range electrostatic repulsions. The latter are established by removing the native organic ligands that passivate tin-doped indium oxide (ITO) NCs while the former are introduced by mixing with small polyethylene glycol (PEG) chains. As we incorporate increasing concentrations of PEG, we observe a reentrant phase behavior featuring two favorable gelation windows; the first arises from bridging effects while the second is attributed to depletion-attractions according to phase behavior predicted by our unified theoretical model. The NCs remain discrete within the gel network, based on X-ray scattering and high-resolution transmission electron microscopy. The infrared optical response of the gel is reflective of both the NC building blocks and the network architecture, being characteristic of ITO NC LSPR with coupling interactions between neighboring NCs

3D characterization of CdSe nanoparticles attached to carbon nanotubes

The crystallographic structure of CdSe nanoparticles attached to carbon nanotubes has been elucidated by means of high resolution transmission electron microscopy and high angle annular dark field scanning transmission electron microscopy tomography. CdSe rod-like nanoparticles, grown in solution together with carbon nanotubes, undergo a morphological transformation and become attached to the carbon surface. Electron tomography reveals that the nanoparticles are hexagonal-based with the (001) planes epitaxially matched to the outer graphene layer.Comment: 7 pages, 8 figure

Genes Suggest Ancestral Colour Polymorphisms Are Shared across Morphologically Cryptic Species in Arctic Bumblebees

email Suzanne orcd idCopyright: © 2015 Williams et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited

What explains the North–South divide in Italian tax compliance? An experimental analysis

This is the author accepted manuscript. The final version is available from Palgrave Macmillan via the DOI in this recordI undertake a comparative study assessing the North–South divide in Italian tax compliance, employing the largest behavioral tax compliance experiment to date. Contrary to a large body of literature, I argue that willingness to pay taxes is constructed within a specific institutional environment and reflects the country’s quality of institutions. To test this hypothesis, I use controlled tax compliance experiments from four laboratories in Capua, Rome, Bologna, and Milan. By employing the experimental method, I am able to hold institutions constant allowing me to isolate cultural variation. Contrary to cultural explanations for tax compliance, when controlling the institutional environment, there is no difference in tax compliance. Furthermore, using social value orientation to compare prosociality, I also find no differences between the two regions. I therefore conclude that individuals’ relationship to their states shapes these behavioral differences in tax compliance.Funds for this research were provided by the European Research Council (Grant Agreement No. 295675 )

Type-II Colloidal Quantum Wells: CdSe/CdTe Core/Crown Heteronanoplatelets

Solution-processed quantum wells, also known as colloidal nanoplatelets (NPLs), are emerging as promising materials for colloidal optoelectronics. In this work, we report the synthesis and characterization of CdSe/CdTe core/crown NPLs exhibiting a Type-II electronic structure and Type-II specific optical properties. Here, based on a core-seeded approach, the CdSe/CdTe core/crown NPLs were synthesized with well-controlled CdTe crown coatings. Uniform and epitaxial growth of CdTe crown region was verified by using structural characterization techniques including transmission electron microscopy (TEM) with quantitative EDX analysis and X-ray diffraction (XRD). Also the optical properties were systematically studied in these Type-II NPLs that reveal strongly red-shifted photoluminescence (up to similar to 150 nm) along with 2 orders of magnitude longer fluorescence lifetimes (up to 190 ns) compared to the Type-I NPLs owing to spatially indirect excitons at the Type-II interface between the CdSe core and the CdTe crown regions. Photoluminescence excitation spectroscopy confirms that this strongly red-shifted emission actually arises from the CdSe/CdTe NPLs. In addition, temperature-dependent time-resolved fluorescence spectroscopy was performed to reveal the temperature-dependent fluorescence decay kinetics of the Type-II NPLs exhibiting interesting behavior. Also, water-soluble Type-II NPLs were achieved via ligand exchange of the CdSe/CdTe core/crown NPLs by using 3-mercaptopropionic acid (MPA), which allows for enhanced charge extraction efficiency owing to their shorter chain length and enables high quality film formation by layer-by-layer (LBL) assembly. With all of these appealing properties, the CdSe/CdTe core/crown heterostructures having Type-II electronic structure presented here are highly promising for light-harvesting applications

High-performance shape-engineerable thermoelectric painting

Output power of thermoelectric generators depends on device engineering minimizing heat loss as well as inherent material properties. However, the device engineering has been largely neglected due to the limited flat or angular shape of devices. Considering that the surface of most heat sources where these planar devices are attached is curved, a considerable amount of heat loss is inevitable. To address this issue, here, we present the shape-engineerable thermoelectric painting, geometrically compatible to surfaces of any shape. We prepared Bi2Te3-based inorganic paints using the molecular Sb2Te3 chalcogenidometalate as a sintering aid for thermoelectric particles, with ZT values of 0.67 for n-type and 1.21 for p-type painted materials that compete the bulk values. Devices directly brush-painted onto curved surfaces produced the high output power of 4.0 mW cm(-2). This approach paves the way to designing materials and devices that can be easily transferred to other applications.ope