Control of Circularly Polarized Electroluminescence in Induced Twist Structure of Conjugate Polymer

An extremely high degree of circularly polarized photoluminescence (CPPL) and electroluminescence (CPEL) (dissymmetry factor values: |g_PL| = 0.72 and |g_EL| = 1.13) are generated from twisted stacking of achiral conjugated polymer induced by nonemitting chiral dopant of high helical twisting power for the first time. Using a theoretical analysis incorporating the Stokes parameter, the twisting angle and birefringence of the aligned conjugated polymer, and the degree of linear polarization in the emitted light are found to make a roughly equal contribution to the degree of CPEL as to the degree of CPPL. Moreover, it is also found that the location of the recombination zone within the emitting layer is a crucial parameter for determining the difference in the dissymmetry factor between CPEL and CPPL. This result is applied to an organic light‐emitting display to improve the luminous efficiency by 60%.     

Synthesis and influence of alkaline concentration on α-FeOOH nanorods shapes

α-FeOOH nanorods having uniform morphology were synthesized by water bath process. X-ray diffraction and transmission electron microscopy revealed that the single-crystalline orthorhombic α-FeOOH nanorods are about 10 nm in diameter and hundreds of nanometer in length. The effect of concentration of KOH on morphology of α-FeOOH nanorods was investigated. pH values of solution play an important role in the process of transformation of ferrihydrite into goethite. The inconsistent growth rate along different facets can be effected by pH values of the solution. The influence and growth mechanism of α-FeOOH nanorods were discussed in detail. This method may be widely used as reference to fabricate other inorganic one-dimensional nanostructured materials and easily realized in industrial-scale synthesis.     

Simultaneous Adjustment of Size and Helical Sense of Chiral Nanospheres and Nanotubes Derived from an Axially Racemic Poly(phenylacetylene)

Nanospheres and nanotubes with full control of their size and helical sense are obtained in chloroform from the axially racemic chiral poly(phenylacetylene) poly‐(R)‐ 1 using either Ag⁺ as both chiral inducer and cross‐linking agent or Na⁺ as chiral inducer and Ag⁺ as cross‐linking agent. The size is tuned by the polymer/ion ratio while the helical sense is modulated by the polymer/cosolvent (i.e., MeCN) ratio. In this way, the helicity and the size of the nanoparticles can be easily interconverted by very simple experimental changes.     

One-Dimensional Chiral Copper Iodide Chain-Like Structure Cu4I4(R/S-3-quinuclidinol)3 with Near-Unity Photoluminescence Quantum Yield and Efficient Circularly Polarized Luminescence

Chiral organic−inorganic hybrid metal halide materials have shown great potential for circularly polarized luminescence (CPL) related applications for their tunable structures and efficient emissions. Here, this work combines the highly emissive Cu₄I₄ cubane cluster with chiral organic ligand R/S-3-quinuclidinol, to construct a new type of 1D Cu-I chains, namely Cu₄I₄(R/S-3-quinuclidinol)₃, crystallizing in noncentrosymmetric monoclinic P2₁ space group. These enantiomorphic hybrids exhibit long-term stability and show bright yellow emission with a photoluminescence quantum yield (PLQY) close to 100%. Due to the successful chirality transfer from the chiral ligands to the inorganic backbone, the enantiomers show intriguing chiroptical properties, such as circular dichroism (CD) and CPL. The CPL dissymmetry factor (g_lum) is measured to be ≈4 × 10⁻³. Time-resolved photoluminescence (PL) measurements show long averaged decay lifetime up to 10 µs. The structural details within the Cu₄I₄ reveal the chiral nature of these basic building units, which are significantly different than in the achiral case. This discovery provides new structural insights for the design of high performance CPL materials and their applications in light emitting devices.     

Enhancement of antibacterial properties of Ag nanorods by electric field

Abstract

The effect of an electric field on the antibacterial activity of columnar aligned silver nanorods was investigated. Silver nanorods with a polygonal cross section, a width of 20–60 nm and a length of 260–550 nm, were grown on a titanium interlayer by applying an electric field perpendicular to the surface of a Ag/Ti/Si(100) thin film during its heat treatment at 700 °C in an Ar+H₂ environment. The optical absorption spectrum of the silver nanorods exhibited two peaks at wavelengths of 350 and 395 nm corresponding to the main surface plasmon resonance bands of the one-dimensional silver nanostructures. It was found that the silver nanorods with an fcc structure were bounded mainly by {100} facets. The antibacterial activity of the silver nanorods against Escherichia coli bacteria was evaluated at various electric fields applied in the direction of the nanorods without any electrical connection between the nanorods and the capacitor plates producing the electric field. Increasing the electric field from 0 to 50 V cm^?1 resulted in an exponential increase in the relative rate of reduction of the bacteria from 3.9×10^?2 to 10.5×10^?2 min^?1. This indicates that the antibacterial activity of silver nanorods can be enhanced by applying an electric field, for application in medical and food-preserving fields.     

Synthesis of Single-Crystalline Anatase TiO2 Nanorods With High-Performance Dye-Sensitized Solar Cells

Single-crystalline anatase TiO₂ nanorods have been prepared by solvothermal method using tetrabutylammonium hydroxide（TBAH） as a morphology controlling agent.The obtained TiO₂ nanorods are dominated by a large percentage of {010} facets.The power conversion efficiency of dye-sensitized solar cell（DSSC） based on anatase TiO₂ nanorods（8.66%） exhibits a significant improvement（35%） compared to that of P25 TiO₂（5.66%）.The high performance of the anatase TiO₂ nanorods solar cell is ascribed to their large percent of exposed {010} facets as well as balancing their surface areas and sizes.     

Self-assembly of luminescent twisted fibers based on achiral quinacridone derivatives

It is a great challenge to spontaneously assemble achiral molecules into twisted nanostructures in the absence of chiral substances. Here we show that two achiral centrosymmetric quinacridone (QA) derivatives, N,N′-di(n-hexyl)-1, 3, 8, 10-tetramethylquinacridone (C6TMQA) and N,N′-di(n-decyl)-1, 3, 8, 10-tetramethylquinac ridone (C10TMQA), can be employed as building blocks to fabricate well-defined twisted nanostructures by controlling the solvent composition and concentration. Bowknot-like bundles with twisted fiber arms were prepared from C6TMQA, whilst uniform twisted fibers were generated from C10TMQA in ethanol/THF solution. Spectroscopic characterization and molecular simulation calculations revealed that the introduction of ethanol into the solution could induce a staggered aggregation of C6TMQA (or C10TMQA) molecules and the formation of twisted nanostructures. Such twisted materials generated from achiral organic functional molecules may be valuable in the design and fabrication of new materials for optoelectronic applications. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

Hybrid p-type ZnO film and n-type ZnO nanorod p-n homo-junction for efficient photovoltaic applications

Simple hybrid p-n homo-junctions using p-type ZnO thin films and n-type nanorods grown on fluorine tin oxide (FTO) substrates for photovoltaic applications are described. The ZnO nanorods (1.5 μm) were synthesized via an aqueous solution method with zinc nitrate hexahydrate and hexamethylenetetramine on ZnO seed layers. The 10-nm-thick ZnO seed layers showed n-type conductivity on FTO substrates and were deposited with a sputtering-based method. After synthesizing ZnO nanorods, aluminum-nitride co-doped p-type ZnO films (200 nm) were efficiently grown using pre-activated nitrogen (N) plasma sources with an inductively-coupled dual-target co-sputtering system. The structural and electrical properties of hybrid p-n homo-junctions were investigated by scanning electron microscopy, transmittance spectrophotometry, and I-V measurements.     

Well-aligned Zn-doped tilted InN nanorods grown on r-plane sapphire by MOCVD

Well-aligned tilted Zn-doped InN nanorods have been grown successfully on r-plane sapphire in a horizontal metal-organic chemical vapor deposition system. All of the nanorods are symmetrically tilted in two opposite directions. X-ray diffraction and transmission electron microscopy measurements show that the nanorods are single-crystalline and have exactly the same epitaxial orientation as the a-plane InN film. The nanorod has a new cross sectional shape of an axial symmetry pentagon and the axis of symmetry is the c-axis of the crystal. Zn dopant plays a crucial role in the growth progress, being an important factor in controlling the morphology of the InN nanomaterials and their properties.     

Self-excited oscillation processes in porous-silicon-based structures

It was found that the dynamic current-voltage (_I-U) characteristics of the n-type porous-silicon-based structures upon prolonged room-temperature storage exhibit negative differential conductivity. Exposure of the samples to a vapor of polar molecules led to the development of self-excited oscillations both during the I-U measurements and in the course of reverse current relaxation in the structure studied. The observed effects are explained by the formation of deep surface energy levels and their charging by an electric current passing upon exposure to the atmosphere containing polar molecules.     

Fullerene Desymmetrization as a Means to Achieve Single‐Enantiomer Electron Acceptors with Maximized Chiroptical Responsiveness

Solubilized fullerene derivatives have revolutionized the development of organic photovoltaic devices, acting as excellent electron acceptors. The addition of solubilizing addends to the fullerene cage results in a large number of isomers, which are generally employed as isomeric mixtures. Moreover, a significant number of these isomers are chiral, which further adds to the isomeric complexity. The opportunities presented by single‐isomer, and particularly single‐enantiomer, fullerenes in organic electronic materials and devices are poorly understood however. Here, ten pairs of enantiomers are separated from the 19 structural isomers of bis[60]phenyl‐C61‐butyric acid methyl ester, using them to elucidate important chiroptical relationships and demonstrating their application to a circularly polarized light (CPL)‐detecting device. Larger chiroptical responses are found, occurring through the inherent chirality of the fullerene. When used in a single‐enantiomer organic field‐effect transistor, the potential to discriminate CPL with a fast light response time and with a very high photocurrent dissymmetry factor (g_ph = 1.27 ± 0.06) is demonstrated. This study thus provides key strategies to design fullerenes with large chiroptical responses for use as chiral components of organic electronic devices. It is anticipated that this data will position chiral fullerenes as an exciting material class for the growing field of chiral electronic technologies.     

CdS microflowers and interpenetrated nanorods grown on Si substrate: Structural,optical properties and growth mechanism

CdS semiconductor with different morphologies have been achieved by simple thermal evaporation of CdS powder at 1050 °C in a flowing Ar atmosphere. The products were characterized by X-ray diffraction, Scanning electron microscopy, Transmission electron microscopy and Photoluminescence. microflowers and interpenetrative nanorods of CdS were formed on catalyst free Si wafers at a temperature of 700 °C and 600 °C respectively. The flower like structures are composed of many interleaving nanorods which have the uniform diameter of about 700 nm and a well crystalline structure with [0001] as growth direction. The interpenetrative nanorods are found to be bounded with six side facets. X-ray diffraction studies revealed the hexagonal structure in both the products. The formation mechanism of microflowers and interpenetrated nanorods was discussed on the basis of nucleation growth kinetics. Room temperature photoluminescence spectra showed a strong green emission band (at ∼510 nm) from the CdS flower like structures, but on the other hand a red emission shoulder along with strong green emission band was observed for interpenetrative nanorods. These CdS micro/nanostructures with abundant morphologies may find applications in various micro/nanodevices, and the kinetics-driven morphology might be exploited to synthesize similar structures of other functional II–VI semiconductors.     

Shape‐Dependent Activity of Ceria for Hydrogen Electro‐Oxidation in Reduced‐Temperature Solid Oxide Fuel Cells

Single crystalline ceria nanooctahedra, nanocubes, and nanorods are hydrothermally synthesized, colloidally impregnated into the porous La_0.9Sr_0.1Ga_0.8Mg_0.2O_3‐δ (LSGM) scaffolds, and electrochemically evaluated as the anode catalysts for reduced temperature solid oxide fuel cells (SOFCs). Well‐defined surface terminations are confirmed by the high‐resolution transmission electron microscopy — (111) for nanooctahedra, (100) for nanocubes, and both (110) and (100) for nanorods. Temperature‐programmed reduction in H₂ shows the highest reducibility for nanorods, followed sequentially by nanocubes and nanooctahedra. Measurements of the anode polarization resistances and the fuel cell power densities reveal different orders of activity of ceria nanocrystals at high and low temperatures for hydrogen electro‐oxidation, i.e., nanorods > nanocubes > nanooctahedra at T ≤ 450 °C and nanooctahedra > nanorods > nanocubes at T ≥ 500 °C. Such shape‐dependent activities of these ceria nanocrystals have been correlated to their difference in the local structure distortions and thus in the reducibility. These findings will open up a new strategy for design of advanced catalysts for reduced‐temperature SOFCs by elaborately engineering the shape of nanocrystals and thus selectively exposing the crystal facets.     

Effects of temperature and ferromagnetism on the γ-Ni/γ′-Ni3Al interfacial free energy from first principles calculations

The temperature dependencies of the γ(f.c.c.)-Ni/γ′-Ni₃Al(L1₂) interfacial free energy for the {100}, {110}, and {111} interfaces are calculated using first-principles calculations, including both coherency strain energy and phonon vibrational entropy. Calculations performed including ferromagnetic effects predict that the {100}-type interface has the smallest free energy at different elevated temperatures, while alternatively the {111}-type interface has the smallest free energy when ferromagnetism is absent; the latter result is inconsistent with experimental observations of γ′-Ni₃Al-precipitates in Ni–Al alloys faceted strongly on {100}-type planes. The γ(f.c.c.)-Ni/γ′-Ni₃Al interfacial free energies for the {100}, {110}, and {111} interfaces decrease with increasing temperature due to vibrational entropy. The predicted morphology of γ′-Ni₃Al(L1₂) precipitates, based on a Wulff construction, is a Great Rhombicuboctahedron (or Truncated Cuboctahedron), which is one of the 13 Archimedean solids, with 6-{100}, 12-{110}, and 8-{111} facets. The first-principles calculated morphology of a γ′-Ni₃Al(L1₂) precipitate is in agreement with experimental three-dimensional atom-probe tomographic observations of cuboidal L1₂ precipitates with large {100}-type facets in a Ni-13.0 at.% Al alloy aged at 823 K for 4096 h. At 823 K this alloy has a lattice parameter mismatch of 0.004 ± 0.001 between the γ(f.c.c.)-Ni-matrix and the γ′-Ni₃Al-precipitates.     

Formation of rectangularly shaped Pd/Au bimetallic nanorods: evidence for competing growth of the Pd shell between the 110 and 100 side facets of Au nanorods

In this letter, we report the competing growth of a Pd shell on the {110} and {100} facets of Au nanorods (Au NRs). This results in the disappearance of unstable {110} facets and the formation of rectangularly shaped Pd/Au bimetallic nanorods that show only four stable {100} side surfaces. The energy minimization to a more stable morphology is believed to be the driving force for the formation of the rectangular shape of the Pd shell.     

The effect of the shape of nanorod arrays on the nanocarpet effect

The bundling of densely packed free-standing nanorods/nanotubes in a liquid environment, or the 'nanocarpet effect', has a direct impact on the stability of nanostructures used for chemical and biological sensors. Using glancing angle deposition, we prepared four different structures: vertically aligned, tilted, zigzag, and square spring Si nanorod arrays, and compared their stabilities after water treatment. We found that although the tilted nanorods were bent in the nanorod tilting direction, they did not form nanorod bundles, and this structure was the most stable one. The larger the tilting angle, i.e., the more inclined the nanorod was to the surface, the more stable the structure. We also found that the quasi-vertical nanorod structures, the zigzag and square spring structures, showed improved stabilities compared to vertically aligned nanorods. Furthermore, by properly depositing a capping layer on top of the vertically aligned nanorods, the structure became mechanically very stable while the high porosity nature of the nanorod array was maintained. This work is helpful for designing stable nanostructures used in a liquid environment.     

Ferromagnetism in Gd-doped CdS dilute magnetic semiconducting nanorods

Cd _x Gd_1?x S (x = 0–0.15) nanorods have been synthesized by solvothermal technique. X-ray diffraction study reveals that pure and Gd-doped CdS nanorods exhibits hexagonal wurtzite structure. Transmission electron microscopy reveals nanorods like morphology of synthesized CdS having 14 and 26 nm size of pure and 15 % doped CdS nanorods. UV–Visible absorption study confirms the blue shift in the energy band energy due to the quantum confinement effects. Photoluminescence spectra confirm the defect free nature of the synthesized nanorods with peaks emerging around 528 and 540 nm due to the green emission. The magnetic study shows that the pure and Gd-doped CdS nanorods exhibits ferromagnetic character and the magnetisation increased by five times from 0.074 to 0.422 emu/g upon Gd-doping.     

Ultrathin Anatase TiO2 Nanosheets for High‐Performance Photocatalytic Hydrogen Production

An ethanol solvothermal route has been developed to prepare ultrathin anatase TiO₂ nanosheets with dominant {001} facets (≈97%), a thickness of ≈2.5 nm, and a side length of ≈200 nm. The introduction of ethanol solvent significantly enhances the content of surface chemisorbed F^? on the TiO₂ nanosheet, which has a higher stability and further lowers the surface energy of {001} facets, giving rise to the large percentage of active {001} facets. Adopting well‐defined morphology, such nanosheets loaded with 1 wt% Pt exhibit an H₂ evolution rate as high as 17.86 mmol h^?1 g^?1, and the corresponding apparent quantum efficiency has been determined to be 34.2%.     

Shape control synthesis of low-dimensional calcium sulfate

Calcium sulfate nanorods, nanowires, nanobelts and sheets had been synthesized via a facile solution reaction of CaCl₂ and H₂SO₄ in mixed solvents of ethanol/N, N-dimethylformamide and deionized water at 35°C. The results indicated that well-crystallized CaSO₄ nanomaterials with different morphology were obtained by adjusting the volume ratio of ethanol/N, N-dimethylformamide to deionized water and the reaction time. Samples prepared at 35°C in mixed solvents of 50 mL ethanol and 30 mL water for 1 min and 2 h showed nanowire and sheet morphology, respectively. While increasing the volume ratio of ethanol to deionized water to 78/2, only nanorods were obtained. When N, N-dimethylformamide was employed to substitute ethanol, the sample heating at 35°C for 2 h was composed of nanowires in 50 mL N, N-dimethylformamide and 30 mL water. Higher volume ratio of N, N-dimethylformamide to deionized water caused the formation of nanorods.     

Faceting–roughening of twin grain boundaries

The coincidence site lattice (CSL) plays a similar role for grain boundaries (GB) as the crystal lattice plays for free surfaces. The most densely packed CSL is the twin-related CSL, characterized by an inverse density of coincidence sites Σ = 3. Phase diagrams in coordinates “relative temperature T/T _m—misorientation angle θ—inclination angle φ” were constructed for the twin GBs in Cu, Al, and Mo having different stacking fault energy γ. At low γ the twin GB remains faceted at all φ values and the number of crystallographically different facets increases with decreasing temperature. With increasing γ asymmetric twin GBs become more and more rough, and fewer facets appear with decreasing temperature. Also, with increasing γ the facets start to degenerate of into the first order rough-to-rough ridges. The behavior of twin GBs in Cu, Al, and Mo is compared with that of twin GBs in Zn.