Spin-polarized transport properties of Fe-oligoporphyrin dimer-based molecular device

By applying the density functional theory and the nonequilibrium Green’s function formalism, we investigate the spin-polarized transport properties of a Fe-oligoporphyrin dimer (Fe-P2TA) sandwiched between two armchair single-walled carbon nanotube electrodes. The results show that the system can present high-efficiency magnetoresistance, spin-filtering, and low-bias negative differential resistance effects with the help of magnetic field modulation. The above results are explained by the evolution of the spin-polarized transmission spectra and the molecular projected self-consistent Hamiltonian eigenstates with applied bias. Therefore, the system provides the possibilities for a multifunctional molecular spintronic device design.     

Reduced water vapor transmission rates of low-temperature-processed and sol-gel-derived titanium oxide thin films on flexible substrates

Sol-gel-derived, crack-free, and condensed TiO_x thin films with improved barrier properties were successfully fabricated on polymeric substrates with a simple two-step heat treatment at low temperatures. To assess the barrier properties of the TiO_x thin films, Ca corrosion tests were conducted and their water vapor transmission rates (WVTRs) were measured. We found that the two-step heat treatment (at 45 °C for 90 min and 110 °C for 60 min) produces a close-packed TiO_x structure that substantially reduces the WVTRs of the coated polymeric substrates. The WVTRs of 86 nm thick TiOx thin films on polyethylene naphthalate (PEN) substrates at a relative humidity (RH) of 90% were found to be 0.133 g m⁻² day⁻¹ at 38 °C and 0.0387 g m⁻² day⁻¹ at 25 °C. In addition, the WVTR value of the TiO_x thin films on PEN substrates are stable with respect to bending: it was found to increase by only ∼13% after 100 repetitions of bending with a 20 mm radius.     

Tunable structures of compound droplets formed by collision of immiscible microdroplets

We study the dynamics of a small water droplet colliding with an immiscible large sessile oil droplet in the air. Such a three-phase system forms compound microdroplets with tunable structures, depending on whether the small droplet can penetrate into the large one. A structure of penetrative-engulfing is distinguished from structures which are determined by balancing of the three interfacial tensions among the three phases, i.e., partial-engulfing and complete-engulfing. We develop a three-phase volume-of-fluid method to investigate the collision dynamics numerically, considering the evolution of the triple-line among the three interfaces. Regime maps of the structures for different spreading parameters and heights of the oil droplet are obtained regarding the impact velocity and the viscosity ratio of oil and water. We find that the oil droplet is impenetrable when the viscosity ratio is higher than a critical value. For lower ratio, the structure varies non-monotonically with the impact velocity to cause two transitions. We propose a simple model for the lower transition by incorporating droplet deformation, viscous resistance, and spreading condition. The upper transition boundary is influenced by the spreading of the oil droplet, resulting in an increase in the required penetration length to prevent penetrative-engulfing. Understandings from this work may provide valuable guidelines for generating compound microdroplets with desired structures.     

The effects of Cu-content on Mg2CuxFe1O3.5+x electrodes for YSZ-based mixed-potential type NH3 sensors

Yttria-stablized zirconia (YSZ)-based mixed-potential type NH₃ sensors using Mg₂Cu_xFe₁O_3.5+x mixed metal oxides (x=0, 0.25, 0.50, 1) as sensing electrode material were fabricated for ammonia (NH₃) detection at different working temperatures (T=350 °C, 400 °C, 450 °C, 500 °C). The Mg₂Cu_xFe₁O_3.5+x electrodes were characterized by X-Ray Diffraction (XRD), Environmental Scanning Electron Microscope (ESEM), Energy Dispersive Spectrometer (EDS) and the Brunauer–Emmett–Teller (BET) method. The effects of Cu-content on phase composition, microstructures, NH₃ response performances and electrochemically catalytic-activity of Mg₂Cu_xFe₁O_3.5+x electrodes were discussed. Magnesium copper oxide (Mg_0.78Cu_0.22O) may be a functional phase that improved NH₃ sensitivity of Mg₂Cu_xFe₁O_3.5+x electrodes, but magnesium dicopper oxide (Cu₂MgO₃) played an opposite role as a suppressive phase. The Mg₂Cu_0.25Fe₁O_3.75 electrode exhibits the biggest response (about 267 mV for 200 ppm of NH₃), the highest NH₃ sensitivity (220 mV/decade NH₃) and the highest electrochemically catalytic-activity may be attributed to its suitable Cu-content for functional phase (Mg_0.78Cu_0.22O) with higher NH₃ adsorptivity, which can absorb more NH₃ to the triple-phase boundary (TPB) for the electrochemically reaction.     

Simple molecular structure design of iridium(III) complexes: Achieving highly efficient non-doped devices with low efficiency roll-off

To construct efficient emitters suitable for non-doped devices and deeply understand the relationship between structures and performances, we designed and synthesized two heteroleptic iridium(III) complexes based on 1,2-diphenyl-1H-benzoimidazole (PBI) ligands whose substituents are varied simply from methyl (complex 2) to tert-butyl groups (complex 3). The parent complex 1 with non-substituent on PBI ligand has also been presented for a better comparison. Their photophysical, electrochemical and electroluminescent (EL) performances are investigated systematically. Despite their structural modification, all complexes exhibit almost identical emission and excited-state characters, which are rationalized by the quantum-chemical calculations. However, the obvious differences on device performances are found. Non-doped device employing 3 as emitting layer displays the highest EL performance with maximum current efficiency (η_{c, max}) of 18.6 cd A⁻¹ and power efficiency (η_{p, max}) of 16.2 lm W⁻¹ accompanied by low efficiency roll-off values, which is much higher than those of complexes 1 and 2. The obtained results herein suggest that introduction of the simple substituent into PBI ligand is an effective and feasible approach to develop highly efficient non-doped phosphors.     

meta-Linked spirobifluorene/phosphine oxide hybrids as host materials for deep blue phosphorescent organic light-emitting diodes

This study investigated the use of a novel modification in molecular design to get two new electron-transport host materials, SF3PO and BSF3PO. By linking the phosphine oxide moieties at meta-position of spirobifluorene rings, higher triplet energies could be easily achieved for these two new materials. The steric spirobifluorene structures could guarantee their good thermal stabilities. According to these properties, their applications as host materials for deep blue phosphorescent organic light-emitting diodes (PHOLEDs) were explored. As expected, the deep blue emitting devices with Ir-complex FIr6 as phosphorescent dopants and SF3PO and BSF3PO as hosts had been fabricated and showed high efficiency of 28.5 and 22.0 cd/A, respectively, which were significantly higher than that of the para-linked analogue SPPO1.     

Sensitized infrared electrophosphorescence based on divalent copper complex by an iridium(III) complex

We demonstrate enhanced near-infrared (NIR) electroluminescence (EL) of copper phthalocyanine (CuPc) phosphor doped organic light emitting diodes (OLED) by introducing a red phosphor, bis(1-phenylisoquinolinato) iridium(III) acetylacetonate (Ir(piq)₂acac). For the codoped device, due to presence of Ir(piq)₂acac, the NIR emission peaked at 1120 nm of CuPc was increased by 15 times comparing with the CuPc monodoped device. The enhancement of NIR emission of CuPc emitter was principally attributed to an energy transfer from Ir(piq)₂acac to CuPc, and the sensitized mechanism was also discussed in detail.     

高分辨率波长位移解调技术研究进展

简要阐述了在光纤传感技术中实现高分辨率波长位移解调技术的基本原理,重点介绍了几种典型解调方法的结构和原理以及波分复用的方案,最后对各种解调方案的优缺点进行了比较分析.     

Stress reduction in GaN films on (111) silicon-on-insulator substrate grown by metal-organic chemical vapor deposition

The GaN film was grown on the (111) silicon-on-insulator (SOI) substrate by metal-organic chemical vapor deposition and then annealed in the deposition chamber. A multiple beam optical stress sensor was used for the in-situ stress measurement, and X-ray diffraction (XRD) and Raman spectroscopy were used for the characterization of GaN film. Comparing the characterization results of the GaN films on the bulk silicon and SOI substrates, we can see that the Raman spectra show the 3.0 cm^− 1 frequency shift of E₂(TO), and the full width at half maximum of XRD rocking curves for GaN (0002) decrease from 954 arc sec to 472 arc sec. The results show that the SOI substrates can reduce the tensile stress in the GaN film and improve the crystalline quality. The annealing process is helpful for the stress reduction of the GaN film. The SOI substrate with the thin top silicon film is more effective than the thick top silicon film SOI substrate for the stress reduction.     

Luminescence properties of Eu3+ or Dy3+/Au co-doped SiO2 nanoparticles

Silica nanoparticles, prepared by the Stober method, have been doped with Eu³⁺, Dy³⁺, or processed to result in Au nanoparticles on the silica surface. The luminescence of the rare earth (RE)-doped SiO₂ particles has been studied as a function of the nature of the RE, their concentration and also of the presence of Au nanoparticles at the surface of the SiO₂ nanoparticles. We have shown that the Eu³⁺ emission is observable over the experimental conditions examined, whereas it was not possible to observe any emission for Dy³⁺ doped materials. No enhancement of the Eu³⁺ emission was observed following the adsorption of gold nanoparticles at the surface of the SiO₂ nanoparticle, however an excitation at 250 nm leads to both the emission of the matrix and Eu³⁺ showing an energy transfer from the SiO₂ matrix to Eu³⁺ ions.