Publications

ChemInform Abstract: Silica‐Supported Cationic Gold(I) Complexes as Heterogeneous Catalysts for Regio‐ and Enantioselective Lactonization Reactions.

Abstract The utility of the newly prepared catalysts is demonstrated by their application in the transformation of various allenoic acids to five‐ or six‐membered ring lactones.

Low temperature thin films formed from nanocrystal precursors

Nanocrystals of semiconductor compounds are produced. When they are applied as a contiguous layer onto a substrate and heated they fuse into a continuous layer at temperatures as much as 250, 500, 750 or even 1000.degree. K below their bulk melting point. This allows continuous semiconductor films in the 0.25 to 25 nm thickness range to be formed with minimal thermal exposure.

Ultra-Sensitive Biological Detection via Nanoparticle-Based Magnetically Amplified Surface Plasmon Resonance (Mag-SPR) Techniques

The report contains final reports from four separate projects co-funded by AFOSR/AOARD and Korean MEST. The four projects were (1) Ultra-Sensitive Biological Detection via Nanoparticle-Based Magnetically Amplified Surface Plasmon Resonance (Mag-SPR) Techniques; (2) Electronic, Photonic and Magnetic Properties of Natural and Modified DNA Complexes with Heavy Metals Ions; (3) Hierarchical Carbon Fiber Composites; and (4) Distributed Detection of Attacks/Intrusions and Prevention of Resource-Starvation Attacks in Mobile Ad Hoc Networks.

Molecular Weight, Osmotic Second Virial Coefficient, and Extinction Coefficient of Colloidal CdSe Nanocrystals

Membrane osmometry is used to measure osmotic pressures of dilute solutions containing quasispherical CdSe nanocrystals covered with polymer brushes in toluene in the range 31-45°C. Osmotic-pressure data, as a function of nanocrystal concentration, yield the molecular weight and the osmotic second virial coefficient of the nanocrystals; the latter is related to the potential of mean force between two nanocrystal particles in dilute solution. Coupled with molecular- weight data, extinction coefficients and oscillator strengths are also obtained for nanocrystals of various sizes in toluene. CdSe nanocrystal sizes were obtained either from transmission electron microscopy or from correlations between the wavelength of the absorbing peak and nanocrystal size. Osmotic-pressure data are reduced with a simple perturbed-hard-sphere equation of state; the perturbation is due to long-range (London dispersion) attraction and a short-range interaction potential. The only adjustable parameter, the strength of this short-range potential, shows two-body repulsion or attraction, depending on the sample and on solution conditions.

Threshold size for ambient metastability of rocksalt CdSe nanocrystals

Engineering gold-platinum core-shell nanoparticles by self-limitation in solution

Abstract Core-shell particles with thin noble metal shells represent an attractive material class with potential for various applications ranging from catalysis to biomedical and pharmaceutical applications to optical crystals. The synthesis of well-defined core-shell architectures remains, however, highly challenging. Here, we demonstrate that atomically-thin and homogeneous platinum shells can be grown via a colloidal synthesis method on a variety of gold nanostructures ranging from spherical nanoparticles to nanorods and nanocubes. The synthesis is based on the exchange of low binding citrate ligands on gold, the reduction of platinum and the subsequent kinetically hindered growth by carbon monoxide as strong binding ligand. The prerequisites for homogeneous growth are low core-binding ligands with moderate fast ligand exchange in solution, a mild reducing agent to mitigate homonucleation and a strong affinity of a second ligand system that can bind to the shell’s surface. The simplicity of the described synthetic route can potentially be adapted to various other material libraries to obtain atomically smooth core-shell systems.

Modular Synthesis of a Dual Metal–Dual Semiconductor Nano‐Heterostructure

Abstract Reported is the design and modular synthesis of a dual metal–dual semiconductor heterostructure with control over the dimensions and placement of its individual components. Analogous to molecular synthesis, colloidal synthesis is now evolving into a series of sequential synthetic procedures with separately optimized steps. We detail the challenges and parameters that must be considered when assembling such a multicomponent nanoparticle, and their solutions. This multicomponent nanosystem, Ru‐CdSe@CdS‐Pt, was designed to achieve charge carrier separation and directional transfer across different interfaces toward two separate redox catalysts. This heterostructure may potentially serve as a nanometric closed circuit photoelectrochemical cell.

Strain-dependent photoluminescence behavior in three geometries of CdSe/CdS nanocrystals

In recent years, a new generation of quantum confined colloidal semiconductor structures has emerged, with more complex shapes than simple quantum dots1, 2. These include nanorods3 and tetrapods4. Beyond shape, it is also now possible to spatially vary the electron and hole potentials within these nanoparticles by varying the composition. Examples of these new structures include seeded dots, rods, and tetrapods, which contain a CdSe core embedded within a CdS shell5, 6. These structures may have many uses beyond those envisioned for simple quantum dots, which are frequently employed in luminescent applications7. This paper is concerned with changes in the optoelectronic properties of tetrapods when the arms are bent. We demonstrate that seeded tetrapods can serve as an optical strain gauge, capable of measuring forces on the order of nanonewtons. We anticipate that a nanocrystal strain gauge with optical readout will be useful for applications ranging from sensitive optomechanical devices to biological force investigations.

Comb Polymer Architectures for Versatile Nanoparticle Assembly

Colloidal Synthesis of Hollow Cobalt Sulfide Nanocrystals - eScholarship

Formation of cobalt sulfide hollow nanocrystals through a mechanism similar to the Kirkendall Effect has been investigated in detail. It was found that performing the reaction at >120oC leads to fast formation of a single void ins ide each shell, whereas at room temperature multiple voids are formed within each shell, which can be attributed to strongly temperature-dependent diffusivities for vacancies. The void formation process is dominated by outward diffusion of cobalt cations; still, significant inward transport of sulfur anions can be inferred to occur as the final voids are smaller in diameter than the original cobalt nanocrystals. Comparison of volume distributions for initial and final nanostructures indicates excess apparent volume in shells implying significant porosity and/or a defective structure. Indirect evidence for shells to fracture during growth at lower temperatures was observed in shell size statistics and TEM of as-grown shells. An idealized model of the diffusional process imposes two minimal requirements on material parameters for shell growth to be obtainable within a specific synthetic system.

Band Gap Variation of Size- and Shape-Controlled Colloidal CdSe Quantum Rods

We report the band gaps of rodlike CdSe quantum dots with diameter varying from 3.0 to 6.5 nm and length from 7.5 to 40 nm. A qualitative explanation for the dependence of band gap on width and length is presented.

Micro-optical Tandem Luminescent Solar Concentrators

Traditional concentrating photovoltaic (CPV) systems utilize multijunction cells to minimize thermalization losses, but cannot efficiently capture diffuse sunlight, which contributes to a high levelized cost of energy (LCOE) and limits their use to geographical regions with high direct sunlight insolation. Luminescent solar concentrators (LSCs) harness light generated by luminophores embedded in a light-trapping waveguide to concentrate light onto smaller cells. LSCs can absorb both direct and diffuse sunlight, and thus can operate as flat plate receivers at a fixed tilt and with a conventional module form factor. However, current LSCs experience significant power loss through parasitic luminophore absorption and incomplete light trapping by the optical waveguide. Here we introduce a tandem LSC device architecture that overcomes both of these limitations, consisting of a PLMA polymer layer with embedded CdSe/CdS quantum dot (QD) luminophores and InGaP micro-cells, which serve as a high bandgap absorber on top of a conventional Si photovoltaic. We experimentally synthesize CdSe/CdS QDs with exceptionally high quantum-yield (99%) and ultra-narrowband emission optimally matched to fabricated III-V InGaP micro-cells. Using a Monte Carlo ray-tracing model, we show the radiative limit power conversion efficiency for a module with these components to be 30.8% diffuse sunlight conditions. These results indicate that a tandem LSC-on-Si architecture could significantly improve upon the efficiency of a conventional Si photovoltaic module with simple and straightforward alterations of the module lamination steps of a Si photovoltaic manufacturing process, with promise for widespread module deployment across diverse geographical regions and energy markets.

ChemRXiv: A Chemistry Preprint Server

ADVERTISEMENT RETURN TO ISSUEEditorialNEXTChemRXiv: A Chemistry Preprint ServerLaura L. Kiessling, Laura E. Fernandez, A. Paul Alivisatos, and Paul S. WeissCite this: ACS Nano 2016, 10, 10, 9053–9054Publication Date (Web):October 25, 2016Publication History Published online25 October 2016Published inissue 25 October 2016https://pubs.acs.org/doi/10.1021/acsnano.6b07008https://doi.org/10.1021/acsnano.6b07008editorialACS PublicationsCopyright © 2016 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views2926Altmetric-Citations6LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (179 KB) Get e-AlertscloseSUBJECTS:Nanoscience,Nanotechnology Get e-Alerts

Surfactant and temperature influence on Co nanocrystal structure and shape

Size-dependent electronic level structure of InAs nanocrystal quantum dots: Test of multiband effective mass theory

The size dependence of the electronic spectrum of InAs nanocrystals ranging in radius from 10–35 Å has been studied by size-selective spectroscopy. An eight-band effective mass theory of the quantum size levels has been developed which describes the observed absorption level structure and transition intensities very well down to smallest crystal size using bulk band parameters. This model generalizes the six-band model which works well in CdSe nanocrystals and should adequately describe most direct semiconductor nanocrystals with band edge at the Γ-point of the Brillouin zone.

New routes to control nanoparticle synthesis: general discussion

Yangwei Liu opened a general discussion of the paper by A. Paul Alivisatos: In the in situ TEM experiment, the NPs are actually moving in 3D with a range of several hundred nanometers. In the images and videos that were shown in the presentation,1 I was quite surprised that during the movement,

Electronic states of semiconductor clusters: Homogeneous and inhomogeneous broadening of the optical spectrum

The homogeneous (single-cluster) and inhomogeneous contributions to the low temperature electronic absorption spectrum of 35–50 Å diameter CdSe clusters are separated using transient photophysical hole burning. The clusters have the cubic bulk crystal structure, but their electronic states are strongly quantum confined. The inhomogeneous broadening of these features arises because the spectrum depends upon cluster size and shape, and the samples contain similar, but not identical, clusters. The homogeneous spectrum, which consists of a peak 140 cm−1 (17 meV) wide, with a phonon sideband and continuum absorption to higher energy, is compared to a simple molecular orbital model. Electron–vibration coupling, which is enhanced in small clusters, contributes to the substantial broadening of the homogeneous spectrum. The inhomogeneous width of the lowest allowed optical transition was found to be 940 cm−1, or seven times the homogeneous width, in the most monodisperse sample.