Influence of Bulky Organo‐Ammonium Halide Additive Choice on the Flexibility and Efficiency of Perovskite Light‐Emitting Devices

Perovskite light‐emitting diodes (LEDs) require small grain sizes to spatially confine charge carriers for efficient radiative recombination. As grain size decreases, passivation of surface defects becomes increasingly important. Additionally, polycrystalline perovskite films are highly brittle and mechanically fragile, limiting their practical applications in flexible electronics. In this work, the introduction of properly chosen bulky organo‐ammonium halide additives is shown to be able to improve both optoelectronic and mechanical properties of perovskites, yielding highly efficient, robust, and flexible perovskite LEDs with external quantum efficiency of up to 13% and no degradation after bending for 10 000 cycles at a radius of 2 mm. Furthermore, insight of the improvements regarding molecular structure, size, and polarity at the atomic level is obtained with first‐principles calculations, and design principles are provided to overcome trade‐offs between optoelectronic and mechanical properties, thus increasing the scope for future highly efficient, robust, and flexible perovskite electronic device development.     

Lateral‐Polarity Structure of AlGaN Quantum Wells: A Promising Approach to Enhancing the Ultraviolet Luminescence

Aluminum‐gallium‐nitride alloys (Al _x Ga_{1– x} N, 0 ≤ x ≤ 1) can emit light covering the ultraviolet spectrum from 210 to 360 nm. However, these emitters have not fulfilled their full promise to replace the toxic and fragile mercury UV lamps due to their low efficiencies. This study demonstrates a promising approach to enhancing the luminescence efficiency of AlGaN multiple quantum wells (MQWs) via the introduction of a lateral‐polarity structure (LPS) comprising both III and N‐polar domains. The enhanced luminescence in LPS is attributed to the surface roughening, and compositional inhomogeneities in the N‐polar domain. The space‐resolved internal quantum efficiency (IQE) mapping shows a higher relative IQE in N‐polar domains and near inversion domain boundaries, providing strong evidence of enhanced radiative recombination efficiency in the LPS. These experimental observations are in good agreement with the theoretical calculations, where both lateral and vertical band diagrams are investigated. This work suggests that the introduction of the LPS in AlGaN‐based MQWs can provide unprecedented tunability in achieving higher luminescence performance in the development of solid state light sources.     

ESLD: An efficient and secure link discovery scheme for software‐defined networking

Software‐defined networking simplifies network management by decoupling the control plane from the data plane and centralizing it to the controller. As the brain of the network, the controller gains up‐to‐date holistic network visibility via topology discovery. However, as a key service of topology discovery, the link discovery service opens problems on efficiency and security. On the one hand, sending link discovery packets to all ports wastes not only the limited controller resources (such as CPU and memory) but also control channel bandwidth. On the other hand, attackers may use these packets to create fake links and perform link fabrication attack. Because of the centralized control paradigm, wasting controller resources may degrade network performance, and all the fake links may severely poison the network topology, even causing the denial of service or man‐in‐the‐middle attack. In this paper, we propose an efficient and secure link discovery scheme to improve link discovery performance and resist link fabrication attack caused by the software‐defined networking link discovery service. By adopting port classification technique and directionally transmitting packets to appropriate ports, our approach can reduce or eliminate redundant packets and improve link discovery performance. Meanwhile, we adopt the directional packet transmitting approach and the time‐marked hash‐based message authentication code authenticate scheme to resist the link fabrication attack. A prototype system is implemented on the basis of POX controller and Mininet simulator to evaluate our scheme. Simulation results demonstrate that our scheme can solve the link fabrication problems with less overload of both the control plane and the data plane.     

Performance Optimization of Vertical Nanowire‐based Piezoelectric Nanogenerators

The integrated nanogenerator (NG) based on vertical nanowire (NW) arrays is one of the dominant designs developed to harvest mechanical energy using piezoelectric nanostructures. Finite element method (FEM) simulations of such a NG are developed using ZnO NWs in compression mode to evaluate its performances in term of piezoelectric potential generated, capacitance, induced mechanical energy, output electrical energy, and efficiency. This evaluation is essential to correctly understand NG operation. Three main issues are highlighted. The mechanical and electrical structures of the NG as an integrated system are optimized, and strategies for concentrating the mechanical strain field in the NWs and increasing the force sensitivity are developed. In addition, the influence of NWs length and diameter on NG performances is investigated. The optimization results in a piezoelectric nano composite material where global performances are improved by mean of long and thin NWs.     

Catalyst‐Free GaN Nanorods Synthesized by Selective Area Growth

GaN nanorod formation on Ga‐polar GaN by continuous mode metalorganic chemical vapor deposition selective area growth (MOCVD SAG) is achieved under a relatively Ga‐rich condition. The Ga‐rich condition, provided by applying a very low V/III ratio, alters the growth rates of various planes of the defined nanostructure by increasing relative growth rate of the semi‐polar tilted m‐plane {1–101} that usually is the slowest growing plane under continuous growth conditions. This increased growth rate relative to the non‐polar m‐plane {1–100} and even the c‐plane (0001), permits the formation of GaN nanorods with nonpolar sidewalls. In addition, a new growth mode, called the NH₃‐pulsed mode, is introduced, utilizing the advantages of both the continuous mode and the lower growth rate pulsed mode to form nanorods. Finally, nanorods grown under the different growth modes are compared and discussed.     

MoO2/Mo2C Heteronanotubes Function as High‐Performance Li‐Ion Battery Electrode

Instead of carbon, Mo₂C is used to modify the MoO₂ material for the first time. The presence of highly conductive and electrochemical inactive Mo₂C decreases the resistance of the charge transport and enhances the structural stability of MoO₂ nanoparticles upon lithiation and delithiation, ensuring the superior cycling stability and high rate capability of the heteronanotubes. Cycled at 200 and 1000 mA g^?1 for 140 cycles, the discharge capacities of the MoO₂/Mo₂C heteronanotubes remain to be 790 and 510 mAh g^?1, respectively. This work demonstrates the potential of the novel heteronanotubes for application as an electrode material for high‐performance Li‐ion batteries.     

Hierarchical Carbon–Nitrogen Architectures with Both Mesopores and Macrochannels as Excellent Cathodes for Rechargeable Li–O2 Batteries

Lithium–oxygen batteries are attracting more and more interest; however, their poor rechargeability and low efficiency remain critical barriers to practical applications. Herein, hierarchical carbon–nitrogen architectures with both macrochannels and mesopores are prepared through an economical and environmentally benign sol–gel route, which show high electrocatalytic activity and stable cyclability over 160 cycles as cathodes for Li–O₂ batteries. Such good performance owes to the coexistence of macrochannels and mesopores in C–N hierarchical architectures, which greatly facilitate the Li⁺ diffusion and electrolyte immersion, as well as provide an effective space for O₂ diffusion and O₂/Li₂O₂ conversion. Additionally, the mechanism of oxygen reduction reactions is discussed with the N‐rich carbon materials through first‐principles computations. The lithiated pyridinic N provides excellent O₂ adsorption and activation sites, and thus catalyzes the electrode processes. Therefore, hierarchical carbon–nitrogen architectures with both macrochannels and mesopores are promising cathodes for Li–O₂ batteries.     

Full Color Emission in ZnGa2O4: Simultaneous Control of the Spherical Morphology,Luminescent, and Electric Properties via Hydrothermal Approach

ZnGa₂O₄ and ZnGa₂O₄: Mn²⁺/Eu³⁺ with uniform nanosphere (diameter about 400 nm) morphology have been synthesized via a facile hydrothermal approach. XRD, Raman spectra, XPS, FT‐IR, SEM, TEM, photoluminescence (PL), and cathodoluminescecne (CL) spectra are used to characterize the resulting samples. The controlled experiments indicate the dosage of trisodium citrate and pH values are responsible for shape determination of the ZnGa₂O₄ products. The possible fast crystallization–dissolution–recrystallization formation mechanism for these nanospheres is presented. Under UV light and low‐voltage electron beam excitation, ZnGa₂O₄, ZnGa₂O₄: Mn²⁺ and ZnGa₂O₄: Eu³⁺ emit bright blue, green, and red luminescence, respectively. Based on density functional theory calculations from first principles, the green and red emission are caused by the Mn 3d and Eu 4f electronic structures, respectively. Besides, the dependence of the CL intensity on the calcination temperature and electrical conductivity of the samples is presented. The ZnGa₂O₄: Mn²⁺ nanospheres have a higher CL intensity than that of bulk samples under the same excitation condition. The realization of three primary colors from a single host material suggests that full color display based on ZnGa₂O₄ nanospheres might be achievable, showing that these materials have potential applications in lighting and display fields.