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A new facility for high-pressure diffraction and spectroscopy using diamond anvil high-pressure cells has been built at the Advanced Light Source on Beamline 12.2.2. This beamline benefits from the hard X-radiation generated by a 6 Tesla superconducting bending magnet (superbend). Useful x-ray flux is available between 5 keV and 35 keV. The radiation is transferred from the superbend to the experimental enclosure by the brightness preserving optics of the beamline. These optics are comprised of: a plane parabola collimating mirror (M1), followed by a Kohzu monochromator vessel with a Si(111) crystals (E/{Delta}E {approx} 7000) and a W/B{sub 4}C multilayer (E/{Delta}E {approx} 100), and then a toroidal focusing mirror (M2) with variable focusing distance. The experimental enclosure contains an automated beam positioning system, a set of slits, ion chambers, the sample positioning goniometry and area detectors (CCD or image-plate detector). Future developments aim at the installation of a second end station dedicated for in situ laser-heating on one hand and a dedicated high-pressure single-crystal station, applying both monochromatic as well as polychromatic techniques.

Quantum dot surfaces can have a substantial effect on their physical, chemical, and optoelectronic properties. When the chemistry that occurs at the surface of nanocrystals is studied, critical insights can be gained into the fundamental structural, thermodynamic, and optical properties of quantum dot materials providing a valuable guide for how to best adapt them for desired applications. Colloidal quantum dots are often terminated with organic ligands that consist of a long aliphatic chain and a head group that binds tightly to the nanocrystal surface. While extensive work has been done to understand how ligand head groups influence quantum dot properties, studies to unravel the influence of the organic ligand tail on ligands and surface reaction equilibria are incomplete. To further investigate the driving forces of quantum dot surface modification, a series of ligand exchange reactions with oleic acid were performed on indium phosphide quantum dots, initially terminated with straight-chain carboxylates of variable lengths. The reaction was monitored using isothermal titration calorimetry and ¹H NMR to determine the extent of each reaction and its associated thermodynamics. From these measurements, interligand interactions were observed to be dependent on the length of the straight-chain ligand. A modified Ising model was used to investigate the enthalpic and entropic effects contributing to these ligand exchanges and reveal that interligand interactions play a much larger role than previously thought. Additional experimentation with phosphonic acid ligand exchange reveals complexity in the reaction mechanism but further illustrates the significant impact of ligand tail group length on thermodynamics, even in cases where there is a large difference in head group binding energy.

An optical ruler based on ultrahigh-resolution colocalization of single fluorescent probes is described in this paper. It relies on the use of two unique families of fluorophores, namely energy-transfer fluorescent beads (TransFluoSpheres) and semiconductor nanocrystal quantum dots, that can be excited by a single laser wavelength but emit at different wavelengths. A multicolor sample-scanning confocal microscope was constructed that allows one to image each fluorescent light emitter, free of chromatic aberrations, by scanning the sample with nanometer scale steps with a piezo-scanner. The resulting spots are accurately localized by fitting them to the known shape of the excitation point-spread function of the microscope. We present results of two-dimensional colocalization of TransFluoSpheres (40 nm in diameter) and of nanocrystals (3–10 nm in diameter) and demonstrate distance-measurement accuracy of better than 10 nm using conventional far-field optics. This ruler bridges the gap between fluorescence resonance energy transfer, near- and far-field imaging, spanning a range of a few nanometers to tens of micrometers.

We propose a design for a concentrated photovoltaic (CPV) module with features that can capture both direct and diffuse sunlight. This approach uses a luminescent solar concentrator (LSC) sheet that includes quantum dots, and a tailored optical coating that enhances concentration and delivery of sunlight to the micro-PV cells. In addition, the light not captured by the quantum dots impinges on a tandem solar cell beneath the LSC sheet. The design of the LSC focuses on lowering the number of expensive micro-PV cells needed within the concentrator waveguide, thus reducing system costs while maintaining high efficiency. The design also allows the module to be effective without a tracking system, making it attractive to all PV markets.

The self-assembly of nanocrystals enables new classes of materials whose properties are controlled by the periodicities of the assembly, as well as by the size, shape, and composition of the nanocrystals. While self-assembly of spherical nanoparticles has advanced significantly in the past decade, assembly of rod-shaped nanocrystals has seen limited progress due to the requirement of orientational order. Here, the parameters relevant to self-assembly are systematically quantified using a combination of diffraction and theoretical modeling; these highlight the importance of kinetics on orientational order. Through drying-mediated self-assembly, we achieve unprecedented control over orientational order (up to 96% vertically oriented rods on 1 cm(2) areas) on a wide range of substrates (ITO, PEDOT:PSS, Si(3)N(4)). This opens new avenues for nanocrystal-based devices competitive with thin film devices, as problems of granularity can be tackled through crystallographic orientational control over macroscopic areas.

Monitoring of visible light sensitized reduction of CO₂ at Cu nanoparticles in aqueous solution by rapid-scan ATR FT-IR spectroscopy on the time scale of seconds allowed structural identification of a one-electron intermediate and demonstrated its kinetic relevancy for the first time. Isotopic labeling (¹²C: 1632, 1358, 1346 cm^-1; ¹³C: 1588, 1326, 1316 cm^-1) revealed a species of carbon dioxide dimer radical anion structure, most likely bound to the catalyst surface through carbon. Intermediacy of Cu-C(═O)OCO₂^- surface species is in agreement with a recently proposed mechanism for electrocatalytic CO₂ reduction at Cu metal nanoparticles based on Tafel slope analysis. Spontaneous decrease of the intermediate after termination of the photosensitization pulse (Sn porphyrin excited at 405 nm) was accompanied by the growth of HCO₃^-. CO was produced as well, but sensitive detection required photolysis for tens of minutes. A direct kinetic link between a C₂O₄^- surface intermediate and the CO product was also demonstrated for photocatalyzed CO₂ reduction at aqueous CdSe nanoparticles, where first order growth of a Cd-C(═O)OCO₂^- species was accompanied by rise of CO (monitored by a fast Ni complex trap) and HCO₃^- showing a distinct induction period. The detection of the one-electron surface intermediate and confirmation of its catalytic relevancy was enabled by the delivery of electrons one-by-one by the photosensitization method. The observation of carbon dioxide dimer radical anion points to approaches for rate enhancements of heterogeneous CO₂ reduction by creating catalytic environments that favor formation of this intermediate.

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionCorrection to Tetrapod Nanocrystals as Fluorescent Stress Probes of Electrospun NanocompositesShilpa N. Raja, Andrew C. K. Olson, Kari Thorkelsson, Andrew J. Luong, Lillian Hsueh, Guoqing Chang, Bernd Gludovatz, Liwei Lin, Ting Xu, Robert O. Ritchie, and A. Paul Alivisatos*Cite this: Nano Lett. 2013, 13, 11, 5762Publication Date (Web):October 14, 2013Publication History Published online14 October 2013Published inissue 13 November 2013https://pubs.acs.org/doi/10.1021/nl4035785https://doi.org/10.1021/nl4035785correctionACS PublicationsCopyright © 2013 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 Views686Altmetric-Citations1LEARN 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 (98 KB) Get e-Alertsclose Get e-Alerts

The kinetics of solid-solid phase transitions are explored using pressure-induced structural transformations in Si nanocrystals. In agreement with the predictions of homogeneous deformation theories, large elevations in phase transition pressure are observed in nanocrystals as compared to bulk Si, and high pressure x-ray diffraction peak widths indicate an overall change in nanocrystal shape upon transformation. In addition, unlike the BC8 phase recovered in bulk Si, amorphous Si nanoclusters are obtained upon release of pressure, providing an example of kinetic size control over solid phases.

A nanoscale, visible-light, self-sensing stress probe would be highly desirable in a variety of biological, imaging, and materials engineering applications, especially a device that does not alter the mechanical properties of the material it seeks to probe. Here we present the CdSe–CdS tetrapod quantum dot, incorporated into polymer matrices via electrospinning, as an in situ luminescent stress probe for the mechanical properties of polymer fibers. The mechanooptical sensing performance is enhanced with increasing nanocrystal concentration while causing minimal change in the mechanical properties even up to 20 wt % incorporation. The tetrapod nanoprobe is elastic and recoverable and undergoes no permanent change in sensing ability even upon many cycles of loading to failure. Direct comparisons to side-by-side traditional mechanical tests further validate the tetrapod as a luminescent stress probe. The tetrapod fluorescence stress–strain curve shape matches well with uniaxial stress–strain curves measured mechanically at all filler concentrations reported.

Understanding electronic dynamics in multiexcitonic quantum dots (QDs) is important for designing efficient systems useful in high power scenarios, such as solar concentrators and multielectron charge transfer. The multiple charge carriers within a QD can undergo undesired Auger recombination events, which rapidly annihilate carriers on picosecond time scales and generate heat from absorbed photons instead of useful work. Compared to the transfer of multiple electrons, the transfer of multiple holes has proven to be more difficult due to slower hole transfer rates. To probe the competition between Auger recombination and hole transfer in CdSe, CdS, and CdSe/CdS QDs of varying sizes, we synthesized a phenothiazine derivative with optimized functionalities for binding to QDs as a hole accepting ligand and for spectroscopic observation of hole transfer. Transient absorption spectroscopy was used to monitor the photoinduced absorption features from both trapped holes and oxidized ligands under excitation fluences where the averaged initial number of excitons in a QD ranged from ∼1 to 19. We observed fluence-dependent hole transfer kinetics that last around 100 ps longer than the predicted Auger recombination lifetimes, and the transfer of up to 3 holes per QD. Theoretical modeling of the kinetics suggests that binding of hole acceptors introduces trapping states significantly different from those in native QDs passivated with oleate ligands. Holes in these modified trap states have prolonged lifetimes, which promotes the hole transfer efficiency. These results highlight the beneficial role of hole-trapping states in devising hole transfer pathways in QD-based systems under multiexcitonic conditions.

We observe the assembly of CdS nanorod superlattices by the combination of a DC electric field and solvent evaporation. In each electric-field (1 V/microm) assisted assembly, CdS nanorods (5 nm x 30 nm) suspended initially in toluene were observed to align perpendicular to the substrate. Azimuthal alignment along the nanorod crystal faces and the presence of stacking faults indicate that both 2D and 3D assemblies were formed by a process of controlled super crystal growth.

Discrete DNA-gold nanoparticle conjugates with DNA lengths as short as 15 bases for both 5 and 20 nm gold particles have been purified by anion-exchange HPLC. Conjugates comprising short DNA (<40 bases) and large gold particles (> or =20 nm) are difficult to purify by other means and are potential substrates for plasmon coupling experiments. Conjugate purity is demonstrated by hybridizing complementary conjugates to form discrete structures, which are visualized by TEM.

A solution-phase synthesis of monodisperse SnTe nanocrystals via the reaction of bis[bis(trimethylsilyl)amino]tin(II) with trioctylphosphine telluride in oleylamine is demonstrated. The obtained SnTe nanocrystals are single-crystalline particles with a cubic rock-salt crystal structure. The size of the SnTe nanocrystals can be precisely tuned in the range of 4.5−15 nm by tailoring the reaction temperature and stabilizer concentration. These SnTe nanocrystals exhibit size-tunable band gap energies of 0.38−0.8 eV. The narrow size-distributions allow assembling SnTe nanocrystals into 3-dimensional superlattices.