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.     

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.     

Low core loss of Fe85Si2B8P4Cu1 nanocrystalline alloys with high Bs and B800

The Fe–Si–B–P–Cu nanocrystalline alloys exhibit high saturation magnetic flux density (B_s) as well as good soft magnetic properties such as low coercivity, high effective permeability and low magnetostriction after nanocrystallization. In this paper, the Fe₈₅Si₂B₈P₄Cu₁ alloy has been newly developed. On the viewpoint of magnetic softness, the Fe₈₅Si₂B₈P₄Cu₁ nanocrystalline alloy reveals low core loss (W) at a commercially frequency of 50 Hz in the maximum induction (B_m) range of up to 1.75 T, and the W in the B_m range of less than 1.8 T is smaller than that of the highest-graded oriented Si-steel due to high magnetic flux density at 800 A/m (B₈₀₀) of above 1.8 T and excellent magnetic softness originated from much higher Fe content and uniform nanocrystalline structure with small magnetostriction. The electrical resistivity (ρ) is relative higher than Si-steels. Thus the Fe–Si–B–P–Cu alloys are attractive for applying to magnetic parts such as motors, transducers, choke-coils and so-forth.     

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...     

In-situ formation of Ni (oxy)hydroxide on Ni foam as an efficient electrocatalyst for oxygen evolution reaction

A binder-free Ni (oxy)hydroxide on Ni foam was prepared through an in-situ electrochemical activation method. Ni (oxy)hydroxide is active for the oxygen evolution reaction. The Ni (oxy)hydroxide directly formed on the surface of Ni foam as a binder-free catalyst not only exhibited large electrochemically active area, but also displayed low interfacial electronic resistance and low charge transfer resistance. Therefore, the optimized Ni (oxy)hydroxide exhibits an overpotential of 288 and 370 mV at 10 and 500 mA cm⁻², respectively, in 1.0 M KOH for the oxygen evolution reaction, as well as favorable during 240 h at 100 mA cm⁻².     

Sol-gel fabrication of NiO and NiO/WO3 based electrochromic device on ITO and flexible substrate

Electrochromic devices (ECDs) with reversible transmittance change represent a promising alternative to smart windows. However, the low−cost facile fabrication of ECDs, particularly flexible devices, remains challenging. In this study, novel NiO is synthesized by a solid state method, and the as−prepared NiO is introduced as an electrochromic anodic layer and fabricated onto a transparent conductive electrode (indium tin oxide, ITO or flexible silver nanowires, AgNW) by a sol–gel spin coating and low temperature annealing (80 °C-150 °C). The solvent, thickness of NiO, and annealing temperature are evaluated to obtain higher ECD performance. NiO/ITO ECDs exhibit very high transmittance variation (ΔT = ~84%) at 700 nm with applied potentials of −3.0 and 0 V. The stability and transmittance variation of NiO/ITO are significantly improved in the presence of a WO₃ cathodic electrode at lower applied voltages of 1.5 to 0 V. The low processing temperature of 80 °C demonstrates the potential of the flexible ECDs. The flexible NiO–WO₃ device achieves a transmittance variation of ~38% at 700 nm with applied potential of 2.0 and 0 V, and retains the ECD performance. The application of low−cost solution−processed NiO and NiO/WO₃−based ECDs in flexible transparent conductive electrodes provides a new pathway for the fabrication of optical devices and printed electronics.     

High-temperature microstructural evolution of SiCN fibers derived from polycarbosilane with different C/N ratios

Research into the high-temperature microstructural evolution of SiCN ceramic fibers is important for the aerospace application of advanced ceramic matrix composites in harsh environments. In this work, we studied the microstructural evolution of SiCN fibers with different C/N ratios that derived from polycarbosilane fibers at the annealing temperature range of 1400∼1600 °C. These results showed that the phase separation of SiC_xN_y phase and the two-dimension grain growth process of free carbon nanoclusters could be processed at the researched temperature range. As the annealing temperature increased to 1600 °C, the crystallization of amorphous SiC and Si₃N₄ could be detected. SEM and Raman analysis showed that the decomposition and carbothermal reduction of the Si₃N₄ phase at high temperatures played primary roles in contributing to the fiber strength degradation. Thus, a higher C/N ratio, which is beneficial for inhibiting the decomposition of amorphous Si₃N₄, helps SiCN fibers retain high tensile strength at high temperatures.     

Solar hydrogen evolution over native visible-light-driven Sn3O4

Low-cost semiconductor photocatalysts that can efficiently harvest solar energy and generate H₂ from water or alcohols will be critical to future hydrogen economies. Co-catalyst loading and/or doping of foreign element at host material have been crucial for semiconductor photocatalyst to produce significant H₂ evolution, so far. We synthesized native-visible-light driven Sn₃O₄ photocatalyst, which significantly catalyzed hydrogen evolution from various alcohol solutions under irradiation of visible light (λ > 400 nm), without co-catalyst. The H₂ production reaction proceeded through hydroxyalkyl radical reaction in the methanol solution. The apparent quantum yield was 0.4% for the Sn₃O₄ competitive to that of visible-light-sensitive co-catalyst loaded doped photocatalyst. The enhanced hydrogen evolution is attributed to the desirable band gap and band edge positions (CBM and VBM) of the Sn₃O₄ for H₂ production in visible light, which would originate from atomically layered structure of Sn₃O₄. The Sn₃O₄ material is good promising photocatalyst for solar hydrogen production from alcohols.     

A closed-host bi-layer dense/porous solid electrolyte interphase for enhanced lithium-metal anode stability

Thanks to its high specific capacity and low electrochemical potential, lithium metal is an ideal anode for next-generation high-energy batteries. However, the unstable heterogeneous surface of lithium gives rise to safety and efficiency concerns that prevent it from being utilized in practical applications. In this work, the formation of a closed-host bi-layer solid electrolyte interphase (SEI) improves the stability of lithium metal anode. This is successfully realized by forming an interconnected porous LiF-rich artificial SEI in contact with Li metal, and a dense, stable in-situ formed upper layer SEI. The porous layer increases the number of Li/LiF interfaces, which reduces local volume fluctuations and improves Li⁺ diffusion along these interfaces. Additionally, the tortuous porous structure guides uniform Li⁺ flux distribution and mechanically suppresses dendrite propagation. The dense upper layer of the SEI accomplishes a closed-host design, preventing continuous consumption of active materials. The duality of a dense top layer with porous bottom layer led to extended cycle life and improved rate performance, evidenced with symmetric cell testing, as well as full cell testing paired with sulfur and LiFePO₄ (LFP) cathodes. This work is a good example of a rational design of the SEI, based on comprehensive consideration of various critical factors to improve Li-metal anode stability, and highlights a new pathway to improve cycling and rate performances of Li metal batteries.