Chiral Luminescent Aza[7]helicenes Functionalized with a Triarylborane Acceptor and Near-Infrared-Emissive Doublet-State Radicals.

This paper presents new chiral luminescent molecules (N7-BMes2 and N7-TTM) using configurationally stable aza[7]helicene (1) as a universal heteroatom-doped chiral scaffold. The respective reactions of electron-donating 1 with a triarylborane acceptor via palladium-catalyzed Buchwald-Hartwig C-N coupling and with the open-shell doublet-state TTM radical via nucleophilic aromatic substitution (SN2Ar) resulted not only in tunable emissions from blue to the NIR domain but also in significantly enhanced emission quantum efficiency up to Φ = 50%.

Engineering Ultrathin Carbon Layer on Porous Hard Carbon Boosts Sodium Storage with High Initial Coulombic Efficiency.

Hard carbon (HC) has been widely adopted as the anode material for sodium ion batteries (NIBs). However, it is troubled by a low initial Coulombic efficiency (ICE) due to its porous structure. Herein, a graphitized and ultrathin carbon layer coating on HC is proposed to solve this challenge. The as-prepared porous carbon material coated with an ultrathin carbon layer composite (PCS@V@C) exhibits a cavity structure, which is prepared by using bis(cyclopentadienyl) nickel (CP-Ni) as the carbon source for outer coating, glucose carbon spheres as porous carbon, and introducing a silica layer to facilitate the coating process. When utilized as the anode for NIBs, the material shows an ICE increase from 47.1% to 85.3%, and specific capacity enhancement at 0.1 A g-1 from 155.3 to 216.7 mA h g-1. Moreover, its rate capability and cycling performance are outstanding, demonstrating a capacity of 140.3 mA h g-1 at 10 A g-1, and a retaining capacity of 225.6 mA h g-1 after 300 cycles at 0.1 A g-1 with the Coulombic efficiency of 100% at the second cycle. The excellent electrochemical performance of the PCS@V@C is attributed to the ultrathin carbon layer, which is beneficial for the formation of a stable solid electrolyte interphase (SEI) film. Therefore, this study provides a feasible surface modification method for the preparation of anode materials for NIBs with high specific capacity and ICE.

High-Energy Ball Milling Promoted Sulfur Immobilization for Constructing High-Performance Na-Storage Carbon Anodes.

Sulfur (S) doping is an effective method for constructing high-performance carbon anodes for sodium-ion batteries. However, traditional designs of S-doped carbon often exhibit low initial Coulombic efficiency (ICE), poor rate capability, and impoverished cycle performance, limiting their practical applications. This study proposes an innovative design strategy to fabricate S-doped carbon using sulfonated sugar molecules as precursors via high-energy ball milling. The results show that the high-energy ball milling can immobilize S for sulfonated sugar molecules by modulating the chemical state of S atoms, thereby creating a S-rich carbon framework with a doping level of 15.5 wt %. In addition, the S atoms are present mainly in the form of C-S bonds, facilitating a stable electrochemical reaction; meanwhile, S atoms expand the spacing between carbon layers and contribute sufficient capacitance-type Na-storage sites. Consequently, the S-doped carbon exhibits a large capacity (>600 mAh g-1), a high ICE (>90%), superior cycling stability (490 mAh g-1 after 1100 cycles at 5 A g-1), and outstanding rate performance (420 mAh g-1 at a high current density of 50 A g-1). Such excellent Na-storage properties of S-doped carbon have rarely been reported in the literatures before.

Edge Graphitized Oxygen-Rich Carbon Based on Stainless Steel-Assisted High-energy Ball Milling for High-Capacity and Ultrafast Sodium Storage.

Oxygen doping is an effective strategy for constructing high-performance carbon anodes in Na ion batteries; however, current oxygen-doped carbons always exhibit low doping levels and high-defect surfaces, resulting in limited capacity improvement and low initial Coulombic efficiency (ICE). Herein, a stainless steel-assisted high-energy ball milling is exploited to achieve high-level oxygen doping (19.33%) in the carbon framework. The doped oxygen atoms exist dominantly in the form of carbon-oxygen double bonds, supplying sufficient Na storage sites through an addition reaction. More importantly, it is unexpected that the random carbon layers on the surface are reconstructed into a quasi-ordered arrangement by robust mechanical force, which is low-defect and favorable for suppressing the formation of thick solid electrolyte interfaces. As such, the obtained carbon presents a large reversible capacity of 363 mAh g-1 with a high ICE up to 83.1%. In addition, owing to the surface-dominated capacity contribution, an ultrafast Na storage is achieved that the capacity remains 139 mAh g-1 under a large current density of 100 A g-1 . Such good Na storage performance, especially outstanding rate capability, has rarely been achieved before.

Surface-driven fast sodium storage enabled by Se-doped honeycomb-like macroporous carbon.

Selenium (Se) is an ideal doping agent to modulate the structure of carbon materials to improve their sodium storage performance but has been rarely investigated. In the present study, a novel Se-doped honeycomb-like macroporous carbon (Se-HMC) is prepared by a surface crosslinking method using diphenyl diselenide as the carbon source and SiO2 nanospheres as the template. Se-HMC has a high Se weight percentage above 10%, with a large surface area of 557 m2 g-1. Owing to the well-developed porous structure in combination with Se-assisted capacitive redox reactions, Se-HMC exhibits surface-dominated Na storage behaviors, thus presenting large capacity and fast Na storage capability. To be specific, Se-HMC delivers a high reversible capacity of 335 mA h g-1 at 0.1 A g-1, and after an 800-cycle repeated charge/discharge test at 1 A g-1, the capacity is stable with no dramatic loss. Remarkably, the capacity remains 251 mA h g-1 under a very large current density of 5 A g-1 (≈20 C), demonstrating an ultrafast Na storage process. As far as we know, such a good rate performance has been rarely achieved for carbon anodes before.

Enhanced Electromechanical Response in PVDF-BNBT Composite Nanofibers for Flexible Sensor Applications.

Wearable energy harvesters and sensors have recently attracted significant attention with the rapid development of artificial intelligence and the Internet of Things (IoT). Compared to high-output bulk materials, these wearable devices are mainly fabricated by thin-film-based materials that limit their application. Therefore, the enhancement of output voltage and power for these devices has recently become an urgent topic. In this paper, the lead-free bismuth titanate-barium titanate (0.93(Na0.5Bi0.5)TiO3-0.07BaTiO3(BNBT)) nanoparticles and nanofibers were embedded into the PVDF nanofibers. They produced high inorganic electrical voltage coefficients, high electromechanical coupling coefficients, and environmentally friendly properties that enhance the electromechanical performance of pure PVDF nanofibers, and they are all the critical requirements for modern flexible pressure sensors. In detail, PVDF and PVDF-based composites nanofibers were prepared by electrospinning, and different flexible sandwich composite devices were fabricated by the PDMS encapsulation method. As a result, the six-time enhancement maximum output voltage was obtained in a PVDF-BNBT (fiber)-based composite sensor compared to the pure PVDF one. Our results indicate that the output voltage of the pressure sensors has been significantly enhanced, and the development gate is enabled by analyzing the related physical process and influence mechanism.

Ferroelectric-Modulated MoS2 Field-Effect Transistors as Multilevel Nonvolatile Memory.

Ferroelectric field-effect transistors (FeFETs) with semiconductors as the channel material and ferroelectrics as the gate insulator are attractive and/or promising devices for application in nonvolatile memory. In FeFETs, the conductivity states of the semiconductor are utilized to explore the polarization directions of the ferroelectric material. Herein, we report FeFETs based on a few layers of MoS2 on a 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) single crystal with switchable multilevel states. It was found that the On-Off ratios can reach as high as 106. We prove that the interaction effect of ferroelectric polarization and interface charge traps has a great influence on the transport behaviors and nonvolatile memory characteristics of MoS2/PMN-PT FeFETs. In order to further study the underlying physical mechanism, we have researched the time-dependent electrical properties in the temperature range from 300 to 500 K. The separation of effects from ferroelectric polarization and interfacial traps on electrical behaviors of FeFETs provides us with an opportunity to better understand the operation mechanism, which suggests a fantastic way for multilevel, low-power consumption, and high-density nonvolatile memory devices.

Extended photo-response of ZnO/CdS core/shell nanorods fabricated by hydrothermal reaction and pulsed laser deposition.

Heterogenous nanostructures shaped with CdS covered ZnO (ZnO/CdS) core/shell nanorods (NRs) are fabricated on indium-tin-oxide by pulsed laser deposition of CdS on hydrothermally grown ZnO NRs and characterized through morphology examination, structure characterization, photoluminescence and optical absorption measurements. Both the ZnO cores and the CdS shells are hexagonal wurtzite in structure. Compared with bare ZnO NRs, the fabricated ZnO/CdS core/shell NRs present an extended photo-response and have optical properties corresponding to the two excitonic band-gaps of ZnO and CdS as well as the effective band-gap formed between the conduction band minimum of ZnO and the valence band maximum of CdS.

Extended photoresponse and multi-band luminescence of ZnO/ZnSe core/shell nanorods.

Aligned ZnO/ZnSe core/shell nanorods (NRs) with type-II energy band alignment were fabricated by pulsed laser deposition of ZnSe on the surfaces of hydrothermally grown ZnO NRs. The obtained ZnO/ZnSe core/shell NRs are composed of wurtzite ZnO cores and zinc blende ZnSe shells. The bare ZnO NRs are capable of emitting strong ultraviolet (UV) near band edge (NBE) emission at 325-nm light excitation, while the ZnSe shells greatly suppress the emission from the ZnO cores. High-temperature processing results in an improvement in the structures of the ZnO cores and the ZnSe shells and significant changes in the optical properties of ZnO/ZnSe core/shell NRs. The fabricated ZnO/ZnSe core/shell NRs show optical properties corresponding to the two excitonic band gaps of wurtzite ZnO and zinc blende ZnSe and the effective band gap between the conduction band minimum of ZnO and the valence band maximum ZnSe. An extended photoresponse much wider than those of the constituting ZnO and ZnSe and a multi-band photoluminescence including the UV NBE emission of ZnO and the blue NBE emission of ZnSe are observed.