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Abstract: Most attempts to emulate the mechanical properties of strong and tough natural composites using helicoidal films of wood‐derived cellulose nanocrystals (w‐CNCs) fall short in mechanical performance due to the limited shear transfer ability between the w‐CNCs. This shortcoming is ascribed to the small w‐CNC‐w‐CNC overlap lengths that lower the shear transfer efficiency. Herein, we present a simple strategy to fabricate superior helicoidal CNC films with mechanical properties that rival those of the best natural materials and are some of the best reported for photonic CNC materials thus far. Assembling the short w‐CNCs with a minority fraction of high aspect ratio CNCs derived from tunicates (t‐CNCs), we report remarkable simultaneous enhancement of all in‐plane mechanical properties and out‐of‐plane flexibility. The important role of t‐CNCs is revealed by coarse grained molecular dynamics simulations where the property enhancement are due to increased interaction lengths and the activation of additional toughening mechanisms. At t‐CNC contents greater than 5% by mass the mixed films also display UV reflecting behaviour. These damage tolerant optically active materials hold great promise for application as protective coatings. More broadly, we expect the strategy of using length‐bidispersity to be adaptable to mechanically enhancing other matrix‐free nanoparticle ensembles. [ABSTRACT FROM AUTHOR]

Cesium-based perovskite nanocrystals (NCs) have outstanding photophysical properties improving the performances of lighting devices. Fundamental studies on excitonic properties and hot-carrier dynamics in perovskite NCs further suggest that these materials show higher efficiencies compared to the bulk form of perovskites. However, the relaxation rates and pathways of hot-carriers are still being elucidated. By using ultrafast transient spectroscopy and calculating electronic band structures, we investigated the dependence of halide in Cs-based perovskite (CsPbX3 with X=Br, I, or their mixtures) NCs on the hot-carrier relaxation processes. All samples exhibit ultrafast (<0.6 ps) hot-carrier relaxation dynamics with following order: CsPbBr3 (310 fs)>CsPbBr1.5I1.5 (380 fs)>CsPbI3 NC (580 fs). These result accounts for a reduced light emission efficiency of CsPbI3 NC compared to CsPbBr3 NC. [ABSTRACT FROM AUTHOR]

The spatiotemporal regulation of light-gated ion channels is a powerful tool to study physiological pathways and develop personalized theranostic modalities. So far, most existing light-gated channels are limited by their action spectra in the ultraviolet (UV) or visible region. Simple and innovative strategies for the specific attachment of photoswitches on the cell surface without modifying or genetically encoding channel structures, and more importantly, that enable the remote activation of ion-channel functions within near-infrared (NIR) spectral window in living systems, remain a challenging concern. Herein, metabolic glycan biosynthesis is used to achieve site-specific covalent attachment of near-infrared-light-mediated lanthanide-doped upconversion nanocrystals (UCNs) to the cell surface through copper-free click cyclization. Upon irradiation with 808 nm light, the converted emission at 480 nm could activate a light-gated ion channel, channelrhodopsins-2 (ChR2), and thus remotely control the cation influx. This unique strategy provides valuable insights on the specific regulation membrane-associated activities in vivo. [ABSTRACT FROM AUTHOR]

0D transition metal phosphides (TMPs) nanocrystals (NCs)-2D ultrathin black phosphorus (BP) heterostructure (Ni2P@BP) have been synthesized via a facile sonication-assisted exfoliation followed by a solvothermal process. Compared with the bare BP, the specially designed Ni2P@BP architecture can enhance the electrical conductivity (from 2.12 × 102 to 6.25 × 104 S m-1), tune the charge carrier concentration (from 1.25 × 1017 to 1.37 × 1020 cm-3), and reduce the thermal conductivity (from 44.5 to 7.69 W m-1 K-1) at 300 K, which can be considered for multiple applications. As a result, the Ni2P@BP exhibits excellent Li storage properties and high hydrogen evolution reaction electrocatalytic activities. The Ni2P@BP shows improved Li diffusion kinetics (e.g., the Li ions diffusion coefficient increases from 1.14 × 10-14 cm2 s-1 for pure BP nanosheets to 8.02 × 10-13 cm2 s-1 for Ni2P@BP). In addition, the Ni2P@BP electrode sustains hydrogen production with almost unchanged activity over 3000 cycles, which indicates its good chemical stability when operating under strong reducing environment. [ABSTRACT FROM AUTHOR]

In this work, self-assembled Ge quantum dot (QD) formation in a dielectric matrix is explored. Of particular interest were their structural and optical properties, in order to understand the stress build-up in such a process and its impact on the material properties during processing. To this end, thin films consisting of (Ge + SiO2)/SiO2 multilayers grown by RF magnetron sputtering were deposited at room temperature. Annealing of such films at 873 K in inert N2 atmosphere produced, at the position of the Ge-rich SiO2 layers, a high lateral density (about 1012 cm−2) of Ge QDs with a good crystallinity. SiO2 spacer layers separated the adjacent Ge-rich layers, where the Ge QDs were formed with a diameter of about the size of the (Ge + SiO2) as-deposited layer thickness, and created a good vertical repeatability, confirmed by the appearance of a Bragg sheet in two-dimensional small-angle X-ray scattering patterns. The structural analysis, by wide-angle X-ray diffraction, grazing-incidence small-angle X-ray scattering and transmission electron microscopy, has shown that the described processing of the films induced large compressive stress on the formed QDs. Optical analysis by time-resolved photoluminescence (PL) revealed that the high density of crystalline Ge QDs embedded in the amorphous SiO2 matrix produced a strong luminescence in the visible part of the spectrum at 2-2.5 eV photon energy. It is shown that the decay dynamics in this energy range are very fast, and therefore the transitions that create such PL are attributed to matrix defects present in the shell surrounding the Ge QD surface (interface region with the matrix). The measured PL peak, though wide at its half-width, when analysed in consecutive short spectral segments showed the same decay dynamics, suggesting the same mechanism of relaxation. [ABSTRACT FROM AUTHOR]

The formation of cluster structures on the surface of fullerite C60/C70 and its composites with nanosilica (A-300, AM1-300 and A-300+AM1-300) with hydrochloric acid in a hydrophobic environment was studied by means of low-temperature 1H NMR spectroscopy. It was established that the surface of fullerite crystals can separate hydrochloric acid solution into its components, and in the environment of weakly polar organic solvent, CDCl3, the substantial fraction of water exists in a weakly associated state. It was shown that the composite nanosystems made of fullerite and silica (A-300, AM1-300 and their 1 : 1 mixture), the adsorption of hydrochloric acid predominantly occurs on a silica part of the composite. Addition of dimethyl sulfoxide to the medium results in formation of several types of clusters on the surface, which include water molecules, hydrogen chloride and dimethyl sulfoxide, wherein less associated forms are localized predominantly on the surface of the fullerite (their number is maximal for the combined (A-300 + AM1-300)/C60 composites). Therefore the features of the cluster structures and their site of localization in the volume of the solid phase can be controlled by varying the content of the composite nanosystem. [ABSTRACT FROM AUTHOR]

Electron paramagnetic resonance (EPR) spectroscopy complemented with X-ray diffraction, X-ray fluorescence, and optical spectroscopy was used to study nanocrystalline CeO2 powder samples that exhibit weak room-temperature ferromagnetism. EPR lines assigned to the Ce3+ trigonal sites were found for the first time in cerium dioxide that contains a trace impurity of Mn2+. This finding indicates that manganese dopant facilitates the conversion of the oxidation state of Ce4+ to Ce3+ in nanocrystalline CeO2. Our results support the view that Ce3+/Ce4+ pairs along with defects on the surface of nanoparticles are responsible for the ferromagnetism in CeO2. The EPR study reveals that the charge-transfer mechanism proposed recently is more suitable to explain the origin of room-temperature ferromagnetism in CeO2 than the F+-centers exchange interactions. [ABSTRACT FROM AUTHOR]

When 300 kV cryo-EM images at Scherzer focus are acquired from ∼100 nm thick three-dimensional protein nanocrystals using a Falcon 2 direct electron detector, Fourier transformation can reveal the crystalline lattice to surprisingly high resolutions, even though the images themselves seem to be devoid of any contrast. Here, it is reported how this lattice information can be enhanced by means of a wave finder in combination with Wiener-type maximum-likelihood filtering. This procedure paves the way towards full three-dimensional structure determination at high resolution for protein crystals. [ABSTRACT FROM AUTHOR]

Crystallization of biological macromolecules such as proteins implies several prerequisites, for example, the presence of one or more initial nuclei, sufficient amounts of the crystallizing substance and the chemical potential to provide the free energy needed to force the process. The initiation of a crystallization process itself is a stochastic event, forming symmetrically assembled nuclei over kinetically preferred protein-dense liquid clusters. The presence of a spatial repetitive orientation of macromolecules in the early stages of the crystallization process has so far proved undetectable. However, early identification of the occurrences of unit cells is the key to nanocrystal detection. The optical properties of a crystal lattice offer a potential signal with which to detect whether a transition from disordered to ordered particles occurs, one that has so far not been tested in nanocrystalline applications. The ability of a lattice to depolarize laser light depends on the different refractive indices along different crystal axes. In this study a unique experimental setup is used to detect nanocrystal formation by application of depolarized scattered light. The results demonstrate the successful detection of nano-sized protein crystals at early stages of crystal growth, allowing an effective differentiation between protein-dense liquid cluster formation and ordered nanocrystals. The results are further verified by complementary methods like X-ray powder diffraction, second harmonic generation, ultraviolet two-photon excited fluorescence and scanning electron microscopy. [ABSTRACT FROM AUTHOR]

ABSTRACT PolyHIPEs of ethylene glycol dimethacrylate (EGDMA) and styrene/divinylbenzene were prepared by polymerization of water-in-oil high internal phase emulsions (HIPEs) within high pressure liquid chromatography (HPLC) columns. The columns were incorporated into a HPLC system affixed to an inductively-coupled plasma mass spectrometer, and their potential for the separation of engineered nanoparticles was investigated. Triplicate injections of 5 and 10 nm gold particles injected onto a poly(styrene- co-divinylbenzene) polyHIPE column produced an average difference in retention time of 135 s. On a poly(EGDMA) column, triplicate injections of dysprosium containing polystyrene particles of 52 and 155 nm produced a difference in retention time of 8 s. In both cases the smaller particles eluted from the column first. Comparison, using scanning electron microscopy, of the polyHIPE columns after the separations, against freestanding monoliths produced from the same HIPEs, revealed no apparent change in the internal porous structure of the polyHIPEs. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41229. [ABSTRACT FROM AUTHOR]

We have investigated the IR photoluminescence (PL) behavior of Cu-doped β-FeSi2 nanocrystals (β-NCs) embedded in Si layers. The diffusion rate of Cu atom was controlled by annealing. The most appropriate condition brought the largest intensities of both the intrinsic A band emission at 0.803 eV by 214% and the acceptor related C band emission at ∼0.75 eV by 582% in comparison with those of non-doped β-NCs. Rutherford backscattering spectrometry (RBS) revealed increase of Cu atoms in the Si layer with β-NCs with increasing the anneal duration. The C band enhancement surely is originated from increase of a density of state at acceptor levels relating to increase of Cu in β-lattice. Photocarrier injection PL measurements (PCI-PL) reveal that the enhancement of the A band emission may be attributed to a controlled migration process of holes with a repeated trap process due to Cu-doping into the Si phase. This dynamic condition leads to an increase of valence band offset at the β-NCs/Si heterointerfaces where the migration of holes from the β-NCs to Si is prevented, so that a radiative recombination rate can be enhanced. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

We investigate the luminescence properties of Ce3+ ions in Ce-doped SiO1.5 thin films containing Si nanocrystals (Si-ncs) by means of steady-state photoluminescence (PL), time-resolved PL and PL excitation spectroscopy. Strong Ce-related blue luminescence is observed with the naked eye at room temperature. The Ce-related lumines-cence is found to ncrease with the Ce content in the films while simultaneously, the Si-nc-related luminescence decreases. Moreover, the decay time of the Si-nc related luminescence decreases for increasing Ce concentrations thus suggesting a possible indirect excitation of the Ce3+ ions via Si-ncs. However, PL excitation measurements show that Ce3+ ions are mainly directly excited with only a negligible influence of the Si-ncs. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The properties of nanostructured cobalt in the fields of magnetic, catalytic and biomaterials depend critically on Co close packing. This paper reports a structural analysis of nanosized cobalt based on the whole X-ray diffraction (XRD) pattern simulation allowed by the Debye equation. The underlying structural model involves statistical sequences of cobalt layers and produces simulated XRD powder patterns bearing the concurrent signatures of hexagonal and cubic close packing (h.c.p. and f.c.c.). Shape, size distribution and distance distribution between pairs of atoms are also modelled. The simulation algorithm allows straightforward fitting to experimental data and hence the quantitative assessment of the model parameters. Analysis of two samples having, respectively, h.c.p. and f.c.c. appearance is reported. Extended X-ray absorption fine-structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectra are simulated on the basis of the model, giving a tool for the interpretation of structural data complementary to XRD. The outlined structural analysis provides a rigorous structural basis for correlations with magnetic and catalytic properties and an experimental reference for ab initio modelling of these properties. [ABSTRACT FROM AUTHOR]

Amorphous calcium carbonate phases, either synthesized artificially or generated biogenically, can be identified from broadened peaks in X-ray or electron diffraction profiles. It is conceivable that randomly oriented nanocrystals, approximately 1 nm in size, could give rise to coherent diffraction profiles that are characterized as amorphous. The coherent diffraction profiles for 200 keV electrons, as might be used in an electron microscope, and Cu Kα X-rays were calculated for needle-shaped calcite crystals bounded by {1121} facets and rhomb-shaped crystals bounded by {1014} facets. Crystals of about 1.0 nm in size gave a profile that is consistent with the X-ray measurements of amorphous calcium carbonate. The relative intensity of high-angle broadened peaks and changes in the IR spectrum are best explained by disorder in the nanocrystallites. The presence of randomly oriented nanocrystallites also explains the lack of optical birefringence. [ABSTRACT FROM AUTHOR]

N-doped nanocrystalline TiO2 is synthesized successfully through a simple ammonia-modified hydrolysis-solvothermal process. It is demonstrated that the resulting TiO2 doped with an appropriate amount of N exhibits high visible photocatalytic activities for the degradation of gas-phase acetaldehyde and liquid-phase phenol, which is attributed to its increased visible adsorption, appropriate crystallinity, and good dispersibility, whereas its UV activity is decreased. On the basis of the atmosphere-controlled surface photovoltage spectra, it is found that the doped N species can capture the photogenerated holes so as to be favorable for photogenerated charge separation, so it is suggested that its decreased UV activity results from its weak adsorption of O2 compared with that of undoped TiO2, as shown by the O2 temperature-programed desorption curves. Interestingly, the photocatalytic activity of the resulting N-doped TiO2 under visible or UV irradiation can be improved further by promoting O2 adsorption after modification with an appropriate amount of phosphoric acid. [ABSTRACT FROM AUTHOR]

The carboxysome is a giant protein complex that acts as a metabolic organelle in cyanobacteria and some chemoautotrophs. Its outer structure is formed by the assembly of thousands of copies of hexameric shell protein subunits into a molecular layer. The structure determination of a CcmK1 shell protein mutant (L11K) from the β-carboxysome of the cyanobacterium Synechocystis PCC6803 led to challenges in structure determination. Twinning, noncrystallographic symmetry and packing of hexameric units in a special arrangement led to initial difficulties in space-group assignment. The correct space group was clarified after initial model refinement revealed additional symmetry. This study provides an instructive example in which broken symmetry requires a new choice of unitcell origin in order to identify the highest symmetry space group. An additional observation related to the packing arrangement of molecules in this crystal suggests that these hexameric shell proteins might have lower internal symmetry than previously believed. [ABSTRACT FROM AUTHOR]

Smart Catalyst: The cyclical diffusion of nanometer‐sized nickel clusters into and out of the perovskite structure under elevated temperature and reducing and oxidizing atmosphere could in situ redeliver and redisperse Ni, thereby reinforcing the anti‐coking and ‐sintering of Ni during oxidative reforming of CH4. [ABSTRACT FROM AUTHOR]

Anorganische Nanostrukturen: Legierte 10 nm große Cu2ZnSn(S1−xSex)4 ‐ Wurtzitnanokristalle (mit variabler Zusammensetzung x=0 – 1) wurden durch Heißinjektion synthetisiert. Photolumineszenz(PL) ‐ Spektren der Kristalle zeigen eine Bandlücke zwischen 0.9 – 1.4 eV, die über die Zusammensetzung der Nanokristalle gesteuert werden kann und direkt mit dem Verhältnis von Schwefel zu Selen korreliert (siehe Bild). [ABSTRACT FROM AUTHOR]

This paper reviews the synthesis and characterization of several transparent glass-ceramics with optical active nanocrystals. Glass-ceramics containing ferroelectric Srx Ba1-x Nb2 O6 nanocrystals with an ellipsoidal shape show optical phase modulations in the presence of alternative electric fields. In the glass-ceramics with Ba2 Ti Si2 O8 ( BTS) nanocrystals, BTS crystalline layers with a thickness of approximately 120 nm are formed at the surface and ellipsoidal-shaped crystallites with a diameter of 100-200 nm are dispersed in the glass matrix. Some Te O2-based and Ge O2-based glasses show a prominent nanocrystallization. RE-doped Ca F2 nanocrystals are patterned in a spatially selected region by laser irradiations. The size, morphology, and dispersion state of nanocrystals should be carefully checked in each glass system and composition. The basic concept for the design of glass system and composition is also discussed. Some data on optical active performances in transparent glass-ceramics with nanocrystals were introduced. [ABSTRACT FROM AUTHOR]

We report an observation of shape-induced phase transition from wurtzite to zinc blende phase of encapsulated CdSe nanoclusters in mesoporous silica. Presence of both the phases is also observed in the as-grown sample before encapsulation. Role of interfacial energy in the energetic mesopores, as the possible origin of phase transition, is thus ruled out, as the samples are encapsulated subsequent to their synthesis in the soft chemistry route. Electron-phonon coupling in the resonant Raman spectroscopic studies, using different energies for clusters of different phase and shape, thereby confirms the presence of both the wurtzite and the zinc blende phases. Transmission electron microscopic studies are used for the direct evidence of the shape-induced solid-solid phase transition between two crystalline phases, for the first time. Small fluctuation of energies, in the form of shape, during its growth may be the driving force for the observed phenomenon, as the surface energy of both the phases stabilizes to the same value. Thus, finally, specific shapes can be used as one of the ways to differentiate the resulting phases. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Lead tungstate PbWO4 nanocrystals in transparent lead borate glass-ceramics containing Er3+ ions were fabricated. Luminescence spectra at about 1530 nm due to main 4 I13/2-4 I15/2 laser transition of Er3+ ions were examined for glass samples before and after heat treatment. Near-infrared luminescence of Er3+ ions in glass-ceramics is enhanced and long-lived in comparison to precursor glasses. It suggests that the Er3+ ions are partially incorporated into PbWO4 crystalline phase. [ABSTRACT FROM AUTHOR]

Nanocrystalline phase-pure metal fluorides MF2 (M: Ca, Sr, Ba) are obtained by simple mixing or shaking of alkaline earth hydroxides with NH4F. [ABSTRACT FROM AUTHOR]