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We report an unsurpassed solution characterization technique based on analytical ultracentrifugation, which demonstrates exceptional potential for resolving particle sizes in solution with sub-nm resolution. We achieve this improvement in resolution by simultaneously measuring UV/Vis spectra while hydrodynamically separating individual components in the mixture. By equipping an analytical ultracentrifuge with a novel multi-wavelength detector, we are adding a new spectral discovery dimension to traditional hydrodynamic characterization, and amplify the information obtained by orders of magnitude. We demonstrate the power of this technique by characterizing unpurified CdTe nanoparticle samples, avoiding tedious and often impossible purification and fractionation of nanoparticles into apparently monodisperse fractions. With this approach, we have for the first time identified the pure spectral properties and band-gap positions of discrete species present in the CdTe mixture., Max-Planck Society; BASF SE, Ludwigshafen; National Institutes of Health (RR022200); NSF (ACI-1339649); National Science Foundation (TG-MCB070039N); DFG ("PE 427/28-1")

Wir berichten über eine Weiterentwicklung auf Grundlage der analytischen Ultrazentrifugation, durch welche Partikelgrößen direkt in Lösung mit Sub-nm-Auflösung charakterisiert werden können. Erreicht wird diese Auflösung durch die simultane Messung von UV/Vis-Spektren, während die einzelnen Komponenten der Mischung hydrodynamisch aufgetrennt werden. Durch die Aufrüstung der analytischen Ultrazentrifuge mit einem neuartigen Multiwellenlängendetektor wird der traditionellen hydrodynamischen Charakterisierung eine weitere spektrale Dimension hinzugefügt, was den Informationsgehalt vervielfacht. Die Leistungsfähigkeit der Messmethode wird durch die Charakterisierung von CdTe-Nanopartikeln verdeutlicht, wobei keine Aufreinigung und Fraktionierung der Nanopartikeln in einzelne, scheinbar monodisperse Fraktionen erforderlich ist. Durch unsere Untersuchungen konnten wir zum ersten Mal die reinen spektralen Eigenschaften und Bandlücken von diskreten CdTe-Nanopartikelspezies in einer Mischung messen. published

We report on an efficient assembly approach to a variety of electrostatically stabilized all-inorganic semiconductor nanocrystals (NCs) via their linking with appropriate ions into multibranched gel networks. These all-inorganic non-ordered 3D assemblies can combine strong interparticle coupling which facilitates charge transport between the NCs with their diverse morphology, composition, size, and functional capping ligands. Moreover, the resulting dry gels (aerogels) are highly porous monolithic structures, which preserve the quantum confinement of their building blocks. The inorganic semiconductor aerogel made of 4.5 nm CdSe colloidal NCs, capped with iodide ions and bridged with Cd2+ ions, exhibited a surface area as high as 146 m2/g.

A novel colloidal synthesis of copper selenide nanosheets (NSs) with lateral dimensions of up to 3 μm is developed. This material is used for the fabrication of flexible conductive films prepared via simple drop-casting of the NS dispersions without any additional treatment. The electrical performance of these coatings is benchmarked against copper selenide spherical nanocrystals (SNCs) in order to demonstrate the advantage of 2D morphology of the NSs for flexible electronics. In this contest, Cu2−xSe SNC films exhibit higher conductivity but lower reproducibility due to the formation of cracks leading to discontinuous films. Furthermore, the electrical properties of the films deposited on different flexible substrates following their bending, stretching and folding are studied. A comparison of Cu2−xSe SNC and CuSe NS films reveals an increased stability of the CuSe NS films under mechanical stress applied to the samples and their improved long-term stability in air.

The absolute electronic energy levels in Hg-doped CdTe semiconductor nanocrystals (CdHgTe NCs) with varying sizes/volumes and Hg contents are determined by using cyclic voltammetry (CV) measurements and density functional theory (DFT) -based calculations. The electrochemical measurements demonstrate several distinct characteristic features in the form of oxidation and reduction peaks in the voltammograms, where the peak positions are dependent on the volume of CdHgTe NCs as well as on their composition. The estimated absolute electronic energy levels for three different volumes, namely 22, 119 and 187 nm(3) with 2.7±0.3 % of Hg content, show strong volume dependence. The volume-dependent shift in the characteristic reduction and oxidation peak potential scan can be attributed to the alteration in the energetic band positions owing to the quantum confinement effect. Moreover, the composition (Cd/Hg=98.3/1.7 and 97.0/3.0) -dependent alteration in the electronic energy levels of CdHgTe NCs for two different samples with similar volumes (ca. 124±5 nm(3) ) are shown. Thus obtained electronic energy level values of CdHgTe NCs as a function of volume and composition demonstrate good congruence with the corresponding absorption and emission spectral data, as well as with DFT-based calculations. DFT calculations reveal that incorporation of Hg into CdTe NCs mostly affects the energy levels of conduction band edge, whereas the valence band edge remains almost unaltered.

The n‐type semiconductor system Bi2Te3Bi2Se3 is known as a low‐temperature thermoelectric material with a potentially high efficiency. Herein, a facile approach is reported to synthesize core/shell heterostructured Bi2Te2Se/Bi2Te3 nanosheets (NSs) with lateral dimensions of 1–3 μm and thickness of about 50 nm. Bi2Te3 and Bi2Se3, as well as heterostructured Bi2Te2Se/Bi2Te3 NSs are obtained via colloidal synthesis. Heterostructured NSs show an inhomogeneous distribution of the chalcogen atoms forming selenium and tellurium‐rich layers across the NS thickness, resulting in a core/shell structure. Detailed morphological studies reveal that these structures contain nanosized pores. These features contribute to the overall thermoelectric properties of the material, inducing strong phonon scattering at grain boundaries in compacted solids. NSs are processed into nanostructured bulks through spark plasma sintering of dry powders to form a thermoelectric material with high power factor. Electrical characterization of our materials reveals a strong anisotropic behavior in consolidated pellets. It is further demonstrated that by simple thermal annealing, core/shell structure can be controllably transformed into alloyed one. Using this approach pellets with Bi2Te2.55Se0.45 composition are obtained, which exhibit low thermal conductivity and high power factor for in‐plane direction with zT of 1.34 at 400 K.

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Hierarchical superstructures formed by self-assembled nanoparticles exhibit interesting electrochemical properties that can potentially be exploited in Li-ion batteries (LIBs) as possible electrode materials. In this work, we tested two different morphologies of CuS superstructures for electrodes, namely, tubular dandelion-like and ball-like assemblies, both of which are composed of similar small covellite nanoparticles. These two CuS morphologies are characterized by their markedly different electrochemical performances, suggesting that their complex structures/morphologies influence the electrochemical properties. At 1.12Ag-1, the cells made with CuS tubular structures delivered about 420mAhg-1, and at 0.56Ag-1, the capacity was as high as about 500mAhg-1 with good capacity retention. Their ease of preparation and processing, together with good electrochemical performance, make CuS tubular dandelion-like clusters attractive for developing low-cost LIBs based on conversion reactions.

Mixed metal–semiconductor nanocrystal aerogels are fabricated, which are light-emitting and highly porous macroscopic monoliths. Thiol-stabilized CdTe and Au nanoparticles from aqueous synthesis act as building blocks for the hybrid material. The Au colloids undergo a surface-modifi cation to enhance the particle stability and achieve thiol functionalities. A photochemical treatment is applied for the gelation process which is found to be reversible by subsequent addition of thiol molecules. Via supercritical drying aerogels are formed. The variation of the initial CdTe to Au nanoparticle ratio permits a facile tuning of the content and the properties of the resulting aerogels. The obtained structures were characterized by means of optical spectroscopy, electron microscopy, elemental analysis, and nitrogen physisorption.

Four alternating arylamino-functionalized copolymers were synthesized in a Suzuki copolymerization applying 4, 4′-(2,7-dibromo-9H-fluorene-9,9-diyl)dianiline, 4,4′-(2,7-dibromo-9H-fluorene-9,9-diyl)bis(N,N-diphenylaniline), 4-(3,6-dibromo-9H- carbazol-9-yl)aniline and 4-(3,6-dibromo-9H-carbazol-9-yl)-N,N-diphenylaniline in combination with 2,2′-(9,9-dioctyl-9H-fluorene-2,7-diyl)bis(1,3,2-dioxaborinane). The resulting novel alternating copolymers were fully characterized. The copolymers revealed blue light emission and wide optical bandgaps of at least 2.93 eV for the fluorene-based and 3.07 eV for the carbazole-based polymers. The amino-functions allow to tie semiconducting CdTe nanocrystals (NCs) and to synthesize a series of composites with CdTe NCs. Moreover, tuning the emission color over a wide range by tying these CdTe NCs results in a facile preparation of organic–inorganic semiconductor composites with emission colors “a la carte.” © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

5 páginas, 5 figuras.-- et al., A novel all-inorganic electroluminescent device is demonstrated based on highly luminescent CdTe nanocrystals intercalated within a laminar hydrotalcite-like structure. The laminar scaffold acts to both support and distribute the CdTe nanocrystals. The device is synthesized using simple wet chemical processes at room temperature in ambient conditions. It has high thermal stability, operating continuously up to 90 °C, and a maximum efficiency at J = 0.12 A cm−2. The device is targeted at the automotive industry., The authors acknowledge funding from the EU FP6 project “Stabilight” (Grant No. 017328).

A straightforward approach to the fabrication of quantum-dot (QD)-in-polymer solid composites with a tunable content of the nanoparticles is presented. This procedure includes the colloidal synthesis of QDs based on CuInS2 with their subsequent shelling with ZnS and ligand exchange with two molecules containing monomer units. These QDs, on the one hand, retain their bright photoluminescence after the exchange. On the other hand, their functionalized surface bears double-bond-containing groups that are copolymerizable with common monomers such as styrene and methyl methacrylate via free radical polymerization. The composites possess an enhanced photostability, in particular polystyrene-based solids, being tested in a focus of a powerful irradiation. During this treatment, an interesting light-soaking effect consisting in a significant enhancement of the photoluminescence is observed. Owing to their superior stability under the light irradiation, these composites are very promising for application in low-cost solar-energy devices such as photovoltaic windows, solar concentrators, spectral converters. Perspectives of the practical application of the composites are well supported by Monte Carlo simulations. The developed method of surface engineering can be applied to a wide range of other QDs to incorporate them into a polymer matrix and fabricate highly transparent and stable composites.