Two-dimensional (2D) perovskites show great potential for optoelectronic applications due to their bandgap tunability, extremely large excition binding energy, and large crystal anisotropy compared with their three-dimensional counterparts. To fully explore exciton-based applications and improve their performance, it is essential to understand the exciton behavior in 2D perovskites. Here, we investigate exciton anisotropy within the crystallographic plane and cross plane of (C4H9NH3)2PbI4 2D perovskite crystals by polarization-resolved photoluminescence, reflection, and photoconductivity studies. We observe a polarization-dependent emission evolution and an enhanced self-trapped exciton emission with an oblique incident excitation from the cross plane. Furthermore, the anisotropy of excitons in (C4H9NH3)2PbI4 2D perovskite crystals is identified by polarization-resolved photoluminescence and photoconductivity measurement, and a completely opposite polarization-dependent behavior was observed for free excitons and self-trapped excitons. We attribute this different anisotropy to the existence of out-of-plane excitons and different optical selection rule for free excitons and self-trapped excitons. Our findings will shed light on designing and improving the performance of exciton-based optoelectronic devices in 2D perovskites.

Heterogeneous Au-Pt nanostructures have been synthesized using a sacrificial template-based approach. Typically, monodispersed Au nanoparticles are prepared first, followed by Ag coating to form core-shell Au-Ag nanoparticles. Next, the galvanic replacement reaction between Ag shells and an aqueous H(2)PtCl(6) solution, whose chemical reaction can be described as 4Ag + PtCl(6)(2-)→ Pt + 4AgCl + 2Cl(-), is carried out at room temperature. Pure Ag shell is transformed into a shell made of Ag/Pt alloy by galvanic replacement. The AgCl formed simultaneously roughens the surface of alloy Ag-Pt shells, which can be manipulated to create a porous Pt surface for oxygen reduction reaction. Finally, Ag and AgCl are removed from core-shell Au-Ag/Pt nanoparticles using bis(p-sulfonatophenyl)phenylphosphane dihydrate dipotassium salt to produce heterogeneous Au-Pt nanostructures. The heterogeneous Au-Pt nanostructures have displayed superior catalytic activity towards oxygen reduction in direct methanol fuel cells because of the electronic coupling effect between the inner-placed Au core and the Pt shell.

Building transient and flexible memristors is a promising strategy for developing emerging memory technologies. Here, a transient and flexible memristor based on a polymer nanocomposite, with a configuration of silver nanowire (AgNW)/citric acid quantum dot (CA QD)-polyvinyl pyrrolidone (PVP)/AgNW, is fabricated using a full-solution process method. The obtained device exhibits reversible resistive switching behavior and a dynamic random access memory (DRAM) storage feature, with the significant merits of a high ON/OFF ratio, low switching voltage, excellent reproducibility and desirable high flexibility, indicating outstanding memory characteristics such as low misreading, low power operation and low cost potential. Moreover, an operating mechanism of charge trapping/de-trapping of the quantum dots in the polymer matrix has been proposed. Importantly, the memristor can be disintegrated in water within 30 minutes, showing that it is a promising candidate for transient memories. This work paves a new way for potential use of this material in transient electronics, implanted electronics, data storage security and flexible electronic systems.

Concern about global climate change has led to research on low CO 2 emission in the process of the energy conversion of fossil fuel. One of the solutions is the conversion of fossil fuel into carbon-free energy carriers, hydrogen, and electricity with CO 2 capture and storage. In this paper, the main purpose is to investigate the thermodynamics performance of converting coal to a hydrogen and electricity system with chemical-looping reactors and to explore the influences of operating parameters on the system performance. Using FeO/Fe 3 O 4 as an oxygen carrier, we propose a carbon-free coproduction system of hydrogen and electricity with chemicallooping reactors. The performance of the new system is simulated using ASPEN PLUS software tool. The influences of the chemical-looping reactor's temperature, steam conversion rate, and O 2 /coal quality ratio on the system performance, and the exergy performance are discussed. The results show that a high-purity of H 2 (99.9%) is reached and that CO 2 can be separated. The system efficiency is 57.85% assuming steam reactor at 815°C and the steam conversion rate 37%. The system efficiency is affected by the steam conversion rate, rising form 53.17 to 58.33% with the increase of the steam conversion rate from 28 to 41%. The exergy efficiency is 54.25% and the losses are mainly in the process of gasification and HRSG.

BackgroundStaphylococcus aureus is associated with human skin and soft tissue infections (SSTIs); however, the involvement of virulence factors in different clinical presentations is unclear.MethodsWe analyzed methicillin-resistant S. aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) strains from Taiwan to determine correlations among the clinical characteristics of SSTIs, antimicrobial susceptibility and virulence factors of S. aureus with specific genetic backgrounds.ResultsWe identified 177 MRSA isolates and 130 MSSA isolates among the 307 SSTI-associated S. aureus isolates. Hospital-acquired (HA)- and community-acquired (CA)-MRSA isolates accounted for 61.6 % and 38.4 % of the isolates, respectively. Clinical presentations in SSTI patients differed significantly for the disease groups. Deep-seated MRSA infections presented with higher amputation rate than MSSA infections. MRSA isolates were all susceptible to linezolid, teicoplanin, and vancomycin, and >94 % of isolates were erythromycin- and clindamycin-resistant. Staphylococcal cassette chromosome (SCCmec) types IV, V, and VII were the most frequent in the CA-MRSA group (n = 68); types III, IV and V were the most frequent in the HA-MRSA group (n = 109). Panton-Valentine leukocidin (PVL) genes were significantly more frequent in CA-MRSA strains (75.0 %) than in HA-MRSA (33.0 %) and MSSA (24.6 %) and were found in 66.7 % (74/111) strains isolated from the abscess group. Exfoliatin A genes were more common in catheter-related exit-site MSSA infections (37.5 %) compared with other MSSA disease groups (P < 0.05). Exfoliatin B and superantigen exotoxin genes were uncommon in all SSTI disease types. Pulsotypes A (ST239), C, and D (ST59) were the predominant MRSA genotypes in deep-seated infections.ConclusionsIf not treated appropriately, deep-seated MRSA-associated infections present with higher amputation rates than deep-seated MSSA-associated infections. PVL-positive MRSA strains caused more frequently pus-forming lesions and less bacteremia and invasive diseases. Methods for discriminating CA-MRSA from HA-MRSA strains are now unreliable due to circulation of both ST 239 and ST 59 strains in the community and nosocomial settings. Initial antibiotic treatments should consider MRSA for patients with SSTIs in areas where MRSA is prevalent.