Controllable size and photoluminescence of ZnO nanorod arrays on Si substrate prepared by microwave-assisted hydrothermal method

High-quality ZnO nanorod arrays were grown on silicon substrates by microwave-assisted hydrothermal method. A ZnO seed layer deposited by magnetron sputtering was used for promoting nanorod growth. Process optimization indicates that the size and surface density of nanorods can be controlled individually by varying process parameters including precursor concentration, heating temperature, and heating time. The photoluminescence performance of the nanorods is closely dependent on the mean size of the rods. Reducing rod diameter leads to decreased UV emission and visible emission intensity ratio, which has been attributed to the increased impurities or defects on the rod surface. The present results provide a feasible approach to modify the optical properties of transparent ZnO nanorod arrays.     

Average vs. local structure and composition-property phase diagram of K0.5Na0.5NbO3-Bi½Na½TiO3 system

Phase diagram of the solid solution system K_0.5Na_0.5NbO₃- Bi_½Na_½TiO₃ [(1-x)KNN-xBNT] has been established from dielectric permittivity measurement and structure analyses. The unit cell volumes continuously decrease depending on the composition, while the local structure maintains distortions away from the cubic average structure in the range 0.10 ≤ x ≤ 0.90. No clear correspondence for the temperatures of phase transition exists between structural studies and physical properties. The dielectric behavior is depicted successively from normal ferroelectric, diffuse phase transition, re-entrant-like relaxor, relaxor + dipolar glass-like relaxor, BNT-like relaxor with the increase of BNT. A comprehensive composition-property phase diagram for this system has been given to understand the various ferroelectric phenomena. The result could be mainly elucidated by the nanoclusters and the disorder driven nucleation of polar nanoregions contributed by a valence mismatch at one of the cation sites.     

High mobility and low operation voltage organic field effect transistors by using polymer-gel dielectric and molecular doping

In this work, we present a method to increase the performance in solution processed organic field effect transistors (OFET) by using gel as dielectric and molecular doping to the active organic semiconductor. In order to compare the performance improvement, Poly (methylmethacrylate) (PMMA) and Poly (3-hexylthiophene-2,5-diyl) P3HT material system were used as a reference. Propylene carbonate (PC) is introduced into PMMA to form the gel for using as gate dielectric. The mobility increases from 5.72×10⁻³ to 0.26 cm² V s^–1 and operation voltage decreases from −60 to −0.8 with gel dielectric. Then, the molecular dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) is introduced into P3HT via co-solution. The mobility increases up to 1.1 cm² V s^–1 and the threshold voltage downs to −0.09 V with doping. The increase in performance is discussed in terms of better charge inducing by high dielectric properties of gel and trap filling due to the increased carrier density in active semiconductor by molecular doping.     

Development of a knowledge-based system for materials management

In the past, many mistakes have been made in selecting the best materials for a given task. Thus, tools for humans to optimise the selection of materials will be valuable assets, particularly when the field of application is broad, the problem complex, the operating envelope variable, or the environment is aggressive. In this paper, a methodology for construction of a generic computer materials selector is described. A knowledge structure is presented in which materials selection and failure analysis are at opposite ends of a spectrum of materials performance. An example of the selection of a coating for marine use is given. Besides being of great value to designers, the tool is of considerable potential use for general materials information systems and computer-based learning modules.     

Vanadium nitride based CoFe prussian blue analogues for enhanced electrocatalytic oxygen evolution

The development of efficient and stable nonprecious-metal catalysts remains a challenge for electrochemical water oxidation in practical applications. Prussian blue analogues (MM′-PBAs, A_xM_y [M′ (CN)₆]_z·nH₂O: A = alkali metal; M/M’ = transition metals), as a kind of potential electrocatalyst candidate for oxygen evolution reaction (OER), are rarely studied. Herein, by a facile coprecipitation method, CoFe–PBAs were in-situ grown on the surface of highly conductive vanadium nitride (VN) particles. The hybrid CoFe–PBAs/VN achieves the amelioration of the poor conductivity of bare CoFe–PBAs and the increase in the density of Co²⁺ active sites due to electron interaction. Compared with bare CoFe–PBAs (overpotential of 398 mV at 10 mA cm⁻² and Tafel slope of 78.35 mV dec⁻¹), the CoFe–PBAs/VN manifests a remarkably enhanced electrocatalytic activity for OER (lower overpotential of 290 mV at 10 mA cm⁻² and a smaller Tafel slope of 39.72 mV dec⁻¹), which is superior among PBAs and PBAs-derived materials reported as electrocatalysts for OER. Besides, this hybrid material behaves an excellent long-term durability. High conductivity of VN and electron interaction between VN and CoFe–PBAs contribute to the promoted catalytic performance. This study provides a novel strategy using VN substrates to support PBAs-based catalysts so as to obtain highly active and stable electrocatalysts towards practical applications.     

Luminescent ionic lattice occupation and wide tunable emission spectra of La2MgZrO6:Bi3+,Eu3+ double perovskite phosphors for white light LED

La₂Mg_1-x/2Zr_1-x/2O₆:xBi³⁺(x=0.01-0.035,abbreviated as LMZ:Bi³⁺) and La_2-yMg_0.99Zr_0.99O₆:0.02Bi³⁺,yEu³⁺(y=0.1-0.11,abbreviated as LMZ:Bi³⁺,Eu³⁺) double-perovskite phosphors were prepared through high-temperature solid-phase method.The emission spectrum of LMZ:xBi³⁺(x=0.01-0.035)phosphors excited at 353 nm is asymmetric in the range be...     

Self-supported Ni2P nanotubes coated with FeP nanoparticles electrocatalyst (FeP@Ni2P/NF) for oxygen evolution reaction

Bimetallic phosphides have been widely investigated as electrocatalysts for oxygen evolution reaction (OER) due to their efficient activity and environmental friendliness. While the reasonable design and controllable synthesis of bimetallic phosphide with typical nanostructure is still a great challenge. Hence, we put forward a novel and straightforward way for constructing FeP nanoparticles coated Ni₂P ultrathin nanotube arrays on the surface of Ni foil (FeP@Ni₂P/NF), which is synthesized through two steps of electrodeposition and subsequent in-situ phosphorization process. The obtained FeP@Ni₂P/NF shows excellent electrochemical activity for OER, and it only needs potential of 1.52 V vs. RHE to reach the current density of 50 mA cm⁻² in an alkaline media. The excellent electrocatalytic activity of FeP@Ni₂P/NF mainly benefits from: (i) the synergistic effect between FeP and Ni₂P promoting electron transfer; (ii) the formation of the unique 3D ultrathin nanotube arrays increasing the quantity of active sites and avoiding the agglomeration of catalysts during testing. In addition, the influence of reaction condition on the electrochemical activity for OER has also been investigated through altering the phosphorization temperature of precursor.     

Three-dimensional Ni2P–MoP2 mesoporous nanorods array as self-standing electrocatalyst for highly efficient hydrogen evolution

Electrochemical hydrogen evolution reaction (HER) via the splitting of water has required electrocatalysts with cost-effectiveness, environmentally friendliness, high catalytic activity, and superior stability to meet the hydrogen economy in future. In this context, we report the successful synthesis of self-standing mesoporous Ni₂P–MoP₂ nanorod arrays on nickel foam (Ni₂P–MoP₂ NRs/3D-NF) through an effective phosphidization of the corresponding NiMoO₄ NRs/3D-NF. The as-synthesis Ni₂P–MoP₂ NRs/3D-NF, as an efficient HER electrocatalyst, exhibits small overpotential of 82.2 and 124.7 mV to reach current density of 10 and 50 mA cm⁻², a low Tafel slope of 52.9 mV dec⁻¹ and it retains its catalytic performance for at least 20 h in alkaline condition. Our work also offers a new strategy in designing and using transition metal phosphide-based 3D nanoarrays catalysts with enhanced catalytic efficiency for mass production of hydrogen fuels.     

Equivalent constitutive equations of honeycomb material using micro-polar theory to model thermo-mechanical interaction

For describing the properties for micro-polar cellar material, the definitions of representative element as well as the corresponding equivalent physical quantities in cellular are introduced in this paper. It involves the Cauchy stress, couple stress, displacement gradient, strain, torsion tensor, temperature gradient and the heat flux respectively. The general principle and mode of solving the boundary value problem with respect to the construction of the equivalent constitutive equations is investigated, and the thermo-mechanical interaction is modeled for the micro-polar cellar material. In the context, a standard method for formulizing the boundary value problem in accordance with the specified representative element volume (REV) is developed, and thereupon the equivalent constitutive equations are deduced. For honeycomb materials, the analytical formula for the equivalent elastic coefficient tensor, temperature coefficients of equivalent stress, equivalent Fourier coefficients and the temperature gradient coefficients of couple stress of the honeycomb materials would be formed.