Enhanced performances of triboelectric nanogenerators by filling hierarchical flower-like TiO2 particles into polymethyl methacrylate film

In this study, a flower-like TiO₂ filled polymethyl methacrylate (PMMA) composite is presented as a positive tribo-material to produce an excellent-performance triboelectric nanogenerator (TENG). By working in conjunction with polydimethylsiloxane (PDMS), the flat-surface PDMS/PMMA-flower TiO₂ TENG generates a voltage of 1200 V, a current of 139 mA m^-2 and an output power of 34.85 W m^-2, showing significant enhancement compared with its counterpart utilizing neat PMMA as the positive tribo-material under the same operating conditions, whose voltage is 620 V, current is 78 mA m^-2 and output power is 13.89 W m^-2, respectively. The performance of the TENG is highly dependent on filler loadings of TiO₂ flower particles in PMMA composites with an optimal filler loading of 40 wt% with the highest performances. The flower TiO₂ is vital to the enhanced performances of the TENG, which is due to the modified surface, the tailored dielectric constant and the space charge polarization. The TENG is capable of powering 600 light emitting diodes, a calculator and a digit display, and applied in self-powered electrophoretic deposition of oxide films. This work demonstrates a facile, low-cost approach for obtaining high-performance TENGs utilizing a PMMA-flower TiO₂ composite as the positive tribo-material for applications in sustainable power systems.

Quasi-One-Dimensional Charge Transport Can Lead to Nonlinear Current Characteristics in Organic Field-Effect Transistors

Nonlinearity in the current characteristics of organic field-effect transistor (OFET) devices has become a serious issue for accurate evaluation of the charge-carrier mobilities in organic semiconductors. In particular, in the case of several high-mobility materials, a kink appears in the transfer curves, and this nonlinearity has been generally interpreted as the result of poor contacts. Here, we describe another possible origin for the appearance of such a kink. Extensive molecular-scale device simulations indeed demonstrate that the quasi-1D nature of charge transport often encountered in organic crystals or highly oriented polymers can lead to significant transport through the bulk and result in nonlinearity of the transfer current characteristics if the actual charge injection is away from the channel. When this is the case, the low-gate voltage regime in fact does not overestimate the charge mobility along the channel direction.

Controlling the ferroelectric and resistive switching properties of a BiFeO3 thin film prepared using sub-5 nm dimension nanoparticles

In recent years, BiFeO₃ has attracted significant attention as an interesting multiferroic material in the exploration of fundamental science and development of novel applications. Our previous study (Phys. Chem. Chem. Phys.18, 2016, 25409) highlighted the interesting physicochemical features of BiFeO₃ of sub-5 nm dimension. The study also accentuated the existence of weak ferroelectricity at sub-5 nm dimensions in BiFeO₃. Based on this feature, we have prepared thin films using sub-5 nm BiFeO₃ nanoparticles and explored various physicochemical properties of the thin film. We report that during the formation of the thin film, the nanoparticles aggregated; particularly, annihilation of their nanotwinning nature was observed. Qualitatively, the Gibbs free energy change ΔG governed the abovementioned processes. The thin film exhibited an R3c phase and enhanced Bi-O-Fe coordination as compared to the sub-5 nm nanoparticles. Raman spectroscopy under the influence of a magnetic field shows a magnetoelectric effect, spin phonon coupling, and magnetic anisotropy. We report room-temperature ferroelectric behavior in the thin film, which enhances with the application of a magnetic field; this confirms the multiferroic nature of the thin film. The thin film shows polarization switching ability at multiple voltages and read-write operation at low bias (±0.5 V). Furthermore, the thin film shows negative differential-complementary resistive switching behavior in the nano-microampere current range. We report nearly stable 1-bit operation for 10² cycles, 10⁵ voltage pulses, and 10⁵ s, demonstrating the paradigm device applications. The observed results thus show that the thin films prepared using sub-5 nm BiFeO₃ nanoparticles are a promising candidate for future spintronics and memory applications. The reported approach can also be pertinent to explore the physicochemical properties and develop potential applications of several other nanoparticles.

Kinetic Monte Carlo Modeling of Charge Carriers in Organic Electronic Devices: Suppression of the Self-Interaction Error

Kinetic Monte Carlo (KMC) simulations have emerged as an important tool to help improve the efficiency of organic electronic devices by providing a better understanding of their device physics. In the KMC simulation of an organic device, the reliability of the results depends critically on the accuracy of the chosen charge-transfer rates, which are themselves strongly influenced by the site-energy differences. These site-energy differences include components coming from the electrostatic forces present in the system, which are often evaluated through electric potentials described by the Poisson equation. Here we show that the charge-carrier self-interaction errors that appear when evaluating the site-energy differences can lead to unreliable simulation results. To eliminate these errors, we propose two approaches that are also found to reduce the impact of finite-size effects. As a consequence, reliable results can be obtained at reduced computational costs. The proposed methodologies can be extended to other device simulation techniques as well.

Tunable room-temperature soft ferromagnetism in magnetoceramics of organometallic dendrimers

This article represents an introduction of new dendrimeric precursors to magnetic ceramics, and homometallic and heterometallic dendrimers with tunable magnetic properties.

Defective-Activated-Carbon-Supported Mn-Co Nanoparticles as a Highly Efficient Electrocatalyst for Oxygen Reduction

A highly active and durable cathodic oxygen reduction reaction (ORR) catalyst is synthesized by introducing a small amount of Mn-Co spinel into a kind of defective activated-carbon (D-AC) support. It is assumed that the synergetic coupling effects between the unique defects in the D-AC and the loaded Mn-Co spinel facilitate the ORR and enhance its durability.

Observation of nanotwinning and room temperature ferromagnetism in sub-5 nm BiFeO3 nanoparticles: a combined experimental and theoretical study

Particle size significantly affects the properties and therefore the potential applications of multiferroics. However, is there special particle size effect in BiFeO₃, which has a spiral modulated spin structure? This is still under investigation for sub-5 nm BiFeO₃. In this report, the structural, electronic and magnetic properties are investigated for chemically synthesized BiFeO₃ nanoparticles with an average size of 3 nm. We observed nanotwinning features in the specific size regime of the nanoparticles (2-4 nm). A weak Bi-O-Fe coordination and weak covalent nature has been observed in the nanoparticles through high-resolution electron energy loss spectroscopy and theoretical analysis, confirming that BiFeO₃ nanoparticles a retain rudimentary R3c phase even at sub-5 nm dimensions. The R3c phase of sub-5 nm BiFeO₃ nanoparticles has also been confirmed using Raman spectroscopy and Raman mapping of the vibrational modes. The nanoparticles display cluster spin glass, room temperature ferromagnetism, and a metamictization-davidite phase. The observation of weak magnetic entropy features confirmed the presence of a weak correlation between the magnetic and ferroelectric components. To support our experimental observations, we have simulated a sub-5 nm BiFeO₃ nanocluster. Using density functional theory, the ferromagnetic ground state and the presence of a weak covalent nature in the nanocluster is established considering the first Brillouin zone, thus confirming our experimental results. Finding of new physicochemical features in sub-5 nm BiFeO₃ would be beneficial for the understanding of the fundamental physical and chemical science as well as potential device development.

Conformal Pad-Printing Electrically Conductive Composites onto Thermoplastic Hemispheres: Toward Sustainable Fabrication of 3-Cents Volumetric Electrically Small Antennas

Electrically small antennas (ESAs) are becoming one of the key components in the compact wireless devices for telecommunications, defence, and aerospace systems, especially for the spherical one whose geometric layout is more closely approaching Chu’s limit, thus yielding significant bandwidth improvements relative to the linear and planar counterparts. Yet broad applications of the volumetric ESAs are still hindered since the low cost fabrication has remained a tremendous challenge. Here we report a state-of-the-art technology to transfer electrically conductive composites (ECCs) from a planar mould to a volumetric thermoplastic substrate by using pad-printing technology without pattern distortion, benefit from the excellent properties of the ECCs as well as the printing-calibration method that we developed. The antenna samples prepared in this way meet the stringent requirement of an ESA (ka is as low as 0.32 and the antenna efficiency is as high as 57%), suggesting that volumetric electronic components i.e. the antennas can be produced in such a simple, green, and cost-effective way. This work can be of interest for the development of studies on green and high performance wireless communication devices.

Magnetically separable Ag3PO4/NiFe2O4 composites with enhanced photocatalytic activity

A step wise growth process of APO nuclei leads to developing interesting morphologies of APO/NFO composites.

Facile fabrication of polycaprolactone/h-MoO3 nanocomposites and their structural, optical and electrical properties

Hexagonal molybdenum oxide (h-MoO₃) nanocrystals with a flower-like hierarchical structure were successfully incorporated into polycaprolactone (PCL) matrix by a simple solution casting technique.