Dual Plasmons with Bioinspired 3D Network Structure Enabling Ultrahigh Efficient Solar Steam Generation.

Plasmonic nanomaterials such as Au, Ag, and Cu are widely recognized for their strong light-matter interactions, making them promising photothermal materials for solar steam generation. However, their practical use in water evaporation is significantly limited by the trade-off between high costs and poor stability. In this regard, we introduce a novel, nonmetallic dual plasmonic TiN/MoO3-x composite. This composite features a three-dimensional, urchin-like biomimetic structure, with plasmonic TiN nanoparticles embedded within a network of plasmonic MoO3-x nanorods. As a solar absorber, the TiN/MoO3-x composite achieves a high evaporation rate of ∼2.05 kg m-2 h-1 with an energy efficiency up to 106.7% under 1 sun illumination, outperforming the state-of-the-art plasmonic systems. The high photothermal stability and unique dual plasmonic nanostructure of the TiN/MoO3-x composite are demonstrated by advanced in situ laser-heating transmission electron microscopy and photon-induced near-field electron microscopy/electron energy-loss spectroscopy, respectively. This work provides new inspiration for the design of plasmonic materials.

The Role of Local DFT+U Minima in the First-Principles Modeling of the Metal-Insulator Transition in Vanadium Dioxide.

The DFT+U method is frequently employed to improve the first-principles description of strongly correlated materials. However, it is prone to deliver metastable electronic minima. While these local minima of the DFT+U method are often considered to be computational artifacts, their physical meaning and relationship to true excited states remains unclear. In this work, the possibility of theoretically modeling transformations in the solid state that require thermal or optical excitations of electrons is explored, taking into account the metastable states of the computationally undemanding DFT+U formalism. For this purpose, we choose to examine the example of the VO2 metal-insulator transition. Metastable states that are located on different electronic potential energy surfaces are found to correspond to experimentally observed VO2 phases. The identified metastable electronic states can be used to model the collapse of the VO2 band gap at elevated temperatures and upon photoexcitation as well as other monoclinic-monoclinic phase transformations. The results suggest that local DFT+U minima can indeed carry physical meaning, while they remain under-reported in theoretical literature on transition metal oxides like VO2.

How optical excitation controls the structure and properties of vanadium dioxide.

We combine ultrafast electron diffraction and time-resolved terahertz spectroscopy measurements to link structure and electronic transport properties during the photoinduced insulator-metal transitions in vanadium dioxide. We determine the structure of the metastable monoclinic metal phase, which exhibits antiferroelectric charge order arising from a thermally activated, orbital-selective phase transition in the electron system. The relative contribution of the photoinduced monoclinic and rutile metals to the time-dependent and pump-fluence-dependent multiphase character of the film is established, as is the respective impact of these two distinct phase transitions on the observed changes in terahertz conductivity. Our results represent an important example of how light can control the properties of strongly correlated materials and demonstrate that multimodal experiments are essential when seeking a detailed connection between ultrafast changes in optical-electronic properties and lattice structure.

Density-Based Descriptors of Redox Reactions Involving Transition Metal Compounds as a Reality-Anchored Framework: A Perspective.

Description of redox reactions is critically important for understanding and rational design of materials for electrochemical technologies, including metal-ion batteries, catalytic surfaces, or redox-flow cells. Most of these technologies utilize redox-active transition metal compounds due to their rich chemistry and their beneficial physical and chemical properties for these types of applications. A century since its introduction, the concept of formal oxidation states (FOS) is still widely used for rationalization of the mechanisms of redox reactions, but there exists a well-documented discrepancy between FOS and the electron density-derived charge states of transition metal ions in their bulk and molecular compounds. We summarize our findings and those of others which suggest that density-driven descriptors are, in certain cases, better suited to characterize the mechanism of redox reactions, especially when anion redox is involved, which is the blind spot of the FOS ansatz.

Tailored Waveform of Dielectric Barrier Discharge to Control Composite Thin Film Morphology.

Nanocomposite thin films of TiO2 in a polymer-like matrix are grown in a filamentary argon (Ar) dielectric barrier discharge (DBD) from a suspension of TiO2 nanoparticles in isopropanol (IPA). The sinusoidal voltage producing the plasma is designed to independently control the matrix growth rate and the transport of nanoparticle (NP) aggregates to the surface. The useful FSK (frequency shift keying) modulation mode is chosen to successively generate two sinusoidal voltages: a high frequency of 15 kHz and a low frequency ranging from 0.5 to 3 kHz. The coating surface coverage by the NPs and the thickness of the matrix are measured as a function of the FSK parameters. The duty cycle between these two signals is varied from 0 to 100%. It is observed that the matrix thickness is mainly controlled by the power of the discharge, which largely depends on the high-frequency value. The quantity of NPs deposited in the composite thin film is proportional to the duration of the low frequency applied. The FSK waveform has a double modulation effect, allowing us to obtain a uniform coating as the NPs are not affected by the high frequency and the matrix growth rate is limited when the low frequency is applied. When it is close to a frequency limit, the low frequency acts like a filter for the NP aggregates. The higher the frequency, the smaller the size of the aggregates transferred to the surface. By changing only the FSK modulation parameters, the thin film can be switched from superhydrophobic to superhydrophilic, and under suitable conditions, a nanocomposite thin film is obtained.

Colloidal Metal Nanoparticles Prepared by Laser Ablation and their Applications.

This review article highlights the recent advances of the synthesis and application of metal nanoparticles (NPs) fabricated via pulsed laser ablation in liquid (PLAL) phase and also introduces relevant NP formation mechanisms. Although wet-chemical approaches have been well established to synthesize colloidal metal NPs with various components and structures, some inherent drawbacks, such as reaction residuals and/or contaminations, largely limit some of their applications. The PLAL method has recently been developed as an alternative approach and received increasing attention for colloidal NP preparation, without involving complicated chemical reactions. In certain cases, by using PLAL, ligand-free and surface-clean NPs can be obtained and well dispersed in liquid, leading to the formation of a "surface-clean" NP dispersion. This unique feature renders PLAL-synthesised metal NPs attractive candidates for many interesting applications in catalysis, biology, sensing, and clean energy generation and storage. We conclude this review by proposing several interesting research directions and future challenges, from PLAL fabrication to applications. We hope this review can serve as a good reference and help with the further development of PLAL-NPs and their diverse applications.

Accurate theoretical and experimental characterization of optical grating coupler.

Periodic structures, acting as reflectors, filters, and couplers, are a fundamental building block section in many optical devices. In this paper, a three-dimensional simulation of a grating coupler, a well-known periodic structure, is conducted. Guided waves and leakage characteristics of an out-of-plane grating coupler are studied in detail, and its coupling efficiency is examined. Furthermore, a numerical calibration analysis is applied through a commercial software package on the basis of a full-wave finite-element method to calculate the complex propagation constant of the structure and to evaluate the radiation pattern. For experimental evaluation, an optimized grating coupler is fabricated using electron-beam lithography technique and plasma etching. An excellent agreement between simulations and measurements is observed, thereby validating the demonstrated method.

Optical properties of epitaxial CaxBa1-xNb2O6 thin film based rib-waveguide structure on (001) MgO for electro-optic applications.

In this work, optical properties of epitaxial CaxBa1-xNb2O6, CBN (x = 0.28) thin film based waveguides are studied at 1550 nm optical communications wavelength. CBN thin films are deposited epitaxially on MgO substrates using Pulsed Laser Deposition and characterized by prism coupling to extract the refractive index and propagation loss. It is shown that the 2 µm-thick epitaxial CBN thin films have a refractive index close to the bulk form and the CBN planar waveguides have a propagation loss of 4.3 ± 0.5 dB/cm. 1 cm-long rib waveguide structures were fabricated using a high density plasma etching. Their propagation losses were measured by the cutback method at 8.4 ± 0.6 dB/cm.

Construction of Ultrathin BiVO4-Au-Cu2O Nanosheets with Multiple Charge Transfer Paths for Effective Visible-Light-Driven Photocatalytic Degradation of Tetracycline.

In this study, unique BiVO4-Au-Cu2O nanosheets (NSs) are well designed and multiple charge transfer paths are consequently constructed. The X-ray photoelectron spectroscopy measurement during a light off-on-off cycle and redox capability tests of the photo-generated charge carriers confirmed the formation of Z-scheme heterojunction, which can facilitate the charge carrier separation and transfer and maintain the original strong redox potentials of the respective component in the heterojunction. The ultrathin 2D structure of the BiVO4 NSs provided sufficient surface area for the photocatalytic reaction. The local surface plasmon resonance (LSPR) effect of the electron mediator, Au NPs, enhanced the light absorption and promoted the excitation of hot electrons. The multiple charge transfer paths effectively promoted the separation and transfer of the charge carrier. The synergism of the abovementioned properties endowed the BiVO4-Au-Cu2O NSs with satisfactory photocatalytic activity in the degradation of tetracycline (Tc) with a removal rate of ≈80% within 30 min under visible light irradiation. The degradation products during the photocatalysis are confirmed by using ultra-high performance liquid chromatography-mass spectrometry and the plausible degradation pathways of Tc are consequently proposed. This work paves a strategy for developing highly efficient visible-light-driven photocatalysts with multiple charge transfer paths for removing organic contaminants in water.

High electrochemical performance of nickel cobaltite@biomass carbon composite (NiCoO@BC) derived from the bark of Anacardium occidentale for supercapacitor application.

Biomass carbon-based materials are highly promising for supercapacitor (SC) electrodes due to their availability, environment-friendliness, and low cost. Herein, an easy energy-saving hydrothermal process was used to produce NiCo2O4/NiOOH (NiCoO) composites with biomass carbon (BC) derived from the bark of Anacardium occidentale (AO) at different synthesis time durations (2 h, 4 h, 8 h, 16 h). The structural and morphological properties of the samples were analysed using XRD, Raman spectroscopy, XPS, SEM, TEM and BET, and the results exhibit the presence of carbon inserted into the nickel-cobalt hydroxide matrix. The NiCoO@BC composite synthesized in 4 h (NiCoO@BC(4 h)) displays a good specific capacitance of 475 F g-1 at 0.5 A g-1 and a low equivalent series resistance (ESR) value of 0.36 Ω. It shows a good coulombic efficiency of 98% and retains 86% of the capacitance after 4000 cycles. The asymmetric supercapacitor (ASC) device (NiCoO@BC(4 h)//AC) assembled using activated carbon (AC) as a negative electrode displays 20 W h kg-1 energy density and 900 W kg-1 power density at 1 A g-1. The stability test shows a good coulombic efficiency of 99% and 78% capacitance retention after 15 000 cycles. These findings imply that NiCoO@BC composites have outstanding electrochemical properties, making them suitable as SC electrode materials.

Asymmetric fracture dislocation of the hips: case report.

Bilateral asymmetric hip fracture dislocation is an extremely rare entity. The injury is caused by a high velocity mechanism. We reported a case of bilateral hip fracture dislocation and its management. A 30-year-old man with no previous medical or surgical history was involved in a road accident involving a high-speed collision between two trucks. X-rays of the pelvis revealed asymmetrical bilateral fracture-luxation of the hips. The reduction of the hips was done under general anesthesia. Asymmetrical bilateral traumatic dislocation fracture of the hip is a rare serious injury. Reduction must be performed within 6 hours. Short- and long-term monitoring of the patient is essential.

Silver nanoparticle enhanced metal-organic matrix with interface-engineering for efficient photocatalytic hydrogen evolution.

Integrating plasmonic nanoparticles into the photoactive metal-organic matrix is highly desirable due to the plasmonic near field enhancement, complementary light absorption, and accelerated separation of photogenerated charge carriers at the junction interface. The construction of a well-defined, intimate interface is vital for efficient charge carrier separation, however, it remains a challenge in synthesis. Here we synthesize a junction bearing intimate interface, composed of plasmonic Ag nanoparticles and matrix with silver node via a facile one-step approach. The plasmonic effect of Ag nanoparticles on the matrix is visualized through electron energy loss mapping. Moreover, charge carrier transfer from the plasmonic nanoparticles to the matrix is verified through ultrafast transient absorption spectroscopy and in-situ photoelectron spectroscopy. The system delivers highly efficient visible-light photocatalytic H2 generation, surpassing most reported metal-organic framework-based photocatalytic systems. This work sheds light on effective electronic and energy bridging between plasmonic nanoparticles and organic semiconductors.

Effect of surface oxidation on the interaction of 1-methylaminopyrene with gold nanoparticles.

The effect of the surface chemistry of gold nanoparticles (GNPs) on the GNP-amine (-NH(2)) interaction was investigated via conjugating an amine probe--1-methylaminopyrene (MAP) chromophore--with three Au colloidal samples of the same particle size yet different surface chemistry. The surface of laser-irradiated and ligand-exchanged-irradiated GNPs is covered with acetonedicarboxylic ligands (due to laser-introduced citrate oxidization) and citrate ligands, respectively, and both surfaces contain oxidized Au species which are essentially lacking for the citrate-capped GNPs prepared by the pure chemical approach. Both laser-irradiated samples show inferior adsorption capacity of MAP as compared with the purely chemically prepared GNPs. Detailed investigations indicate that MAP molecules mainly complex directly with Au atoms via forming Au-NH(2)R bonds, and the oxidization of the GNP surface strongly influences the ratio of this direct bonding to the indirect bonding originating from the electrostatic interaction between protonated amine (-NH(3)(+)) and negatively charged surface ligands. The impact of the oxidized GNP surface associated with the laser treatment is further confirmed by aging experiment on GNP-MAP conjugation systems, which straightforwardly verifies that the surface oxidation leads to the decrease in the MAP adsorption on GNPs.

Dependence of gold nanoparticle production on pulse duration by laser ablation in liquid media.

The dependence on laser fluence and laser pulse duration of size, size distribution and concentration of gold nanoparticles synthesized by laser ablation in liquid media was investigated. It was demonstrated that increasing laser energy from 1 to 5 mJ/pulse enhances the ablation rate by a factor of 100. The behavior of the ablation rate, hence of the nanoparticle concentration, as a function of pulse duration (varied from 40 fs to 200 ps) was found to strongly differ from that in air, which can be explained by photoionization and important losses of laser energy in the femtosecond regime. The optimal pulse duration for maximum ablation rate in liquid media was found to be equal to 2 ps.

The Origin of the Thermochromic Property Changes in Doped Vanadium Dioxide.

Vanadium dioxide is a promising material for novel smart window applications due to its reversible metal-insulator transition which is accompanied by a change in its optical properties. The transition temperature (TMIT) can be controlled via elemental doping, but the reduction of TMIT is generally coupled with a decrease of the optical contrast between the two phases. To better understand how the contrast is fundamentally connected to TMIT, the thermochromic properties of doped VO2 were theoretically investigated across the metal-insulator transition from first principles. Different dopants and their interaction with the VO2 host structure as well as different modes of doping were studied in detail. It was found that the transition temperature change is mainly related to the stabilization of the high-temperature metallic phase due to lattice deformations which are caused by the presence of the dopant ion. Inherent limitations to the thermochromic performance of VO2 substitutionally doped by the replacement of vanadium cations with other species were found, and alternative approaches were proposed. Specifically, a charge-neutral substitution of oxygen or an oxygen substitution in combination with interstitial doping without net charge transfer between the dopant atoms and VO2 were identified as promising avenues to ensure a low TMIT and no loss of optical contrast in vanadia-based smart window materials.

Versatile metal-wire waveguides for broadband terahertz signal processing and multiplexing.

Waveguides play a pivotal role in the full deployment of terahertz communication systems. Besides signal transporting, innovative terahertz waveguides are required to provide versatile signal-processing functionalities. Despite fundamental components, such as Bragg gratings, have been recently realized, they typically rely on complex hybridization, in turn making it extremely challenging to go beyond the most elementary functions. Here, we propose a universal approach, in which multiscale-structured Bragg gratings can be directly etched on metal-wires. Such an approach, in combination with diverse waveguide designs, allows for the realization of a unique platform with remarkable structural simplicity, yet featuring unprecedented signal-processing capabilities. As an example, we introduce a four-wire waveguide geometry, amenable to support the low-loss and low-dispersion propagation of polarization-division multiplexed terahertz signals. Furthermore, by engraving on the wires judiciously designed Bragg gratings based on multiscale structures, it is possible to independently manipulate two polarization-division multiplexed terahertz signals. This platform opens up new exciting perspectives for exploiting the polarization degree of freedom and ultimately boosting the capacity and spectral efficiency of future terahertz networks.

Electrically tunable sign of capacitance in planar W-doped vanadium dioxide micro-switches.

Negative capacitance (NC) in a planar W-doped VO2 micro-switch was observed at room temperature in the low-frequency range 1 kHz-10 MHz. The capacitance changed from positive to negative values as the W-doped VO2 active layer switched from semiconducting to metallic state under applied voltage. In addition, a capacitance-voltage hysteresis was observed as the applied voltage was cycled from -35 to 35 V. These observations suggest that NC results from the increase of the electrically induced conductivity in the active layer. This NC phenomenon could be exploited in advanced multifunctional devices including ultrafast switches, field-effect transistors and memcapacitive systems.

Enhanced Electrochemical Behavior of Peanut-Shell Activated Carbon/Molybdenum Oxide/Molybdenum Carbide Ternary Composites.

Biomass-waste activated carbon/molybdenum oxide/molybdenum carbide ternary composites are prepared using a facile in-situ pyrolysis process in argon ambient with varying mass ratios of ammonium molybdate tetrahydrate to porous peanut shell activated carbon (PAC). The formation of MoO2 and Mo2C nanostructures embedded in the porous carbon framework is confirmed by extensive structural characterization and elemental mapping analysis. The best composite when used as electrodes in a symmetric supercapacitor (PAC/MoO2/Mo2C-1//PAC/MoO2/Mo2C-1) exhibited a good cell capacitance of 115 F g-1 with an associated high specific energy of 51.8 W h kg-1, as well as a specific power of 0.9 kW kg-1 at a cell voltage of 1.8 V at 1 A g-1. Increasing the specific current to 20 A g-1 still showcased a device capable of delivering up to 30 W h kg-1 specific energy and 18 kW kg-1 of specific power. Additionally, with a great cycling stability, a 99.8% coulombic efficiency and capacitance retention of ~83% were recorded for over 25,000 galvanostatic charge-discharge cycles at 10 A g-1. The voltage holding test after a 160 h floating time resulted in increase of the specific capacitance from 74.7 to 90 F g-1 at 10 A g-1 for this storage device. The remarkable electrochemical performance is based on the synergistic effect of metal oxide/metal carbide (MoO2/Mo2C) with the interconnected porous carbon. The PAC/MoO2/Mo2C ternary composites highlight promising Mo-based electrode materials suitable for high-performance energy storage. Explicitly, this work also demonstrates a simple and sustainable approach to enhance the electrochemical performance of porous carbon materials.

Homodyne Solid-State Biased Coherent Detection of Ultra-Broadband Terahertz Pulses with Static Electric Fields.

We present an innovative implementation of the solid-state-biased coherent detection (SSBCD) technique, which we have recently introduced for the reconstruction of both amplitude and phase of ultra-broadband terahertz pulses. In our previous works, the SSBCD method has been operated via a heterodyne scheme, which involves demanding square-wave voltage amplifiers, phase-locked to the THz pulse train, as well as an electronic circuit for the demodulation of the readout signal. Here, we demonstrate that the SSBCD technique can be operated via a very simple homodyne scheme, exploiting plain static bias voltages. We show that the homodyne SSBCD signal turns into a bipolar transient when the static field overcomes the THz field strength, without the requirement of an additional demodulating circuit. Moreover, we introduce a differential configuration, which extends the applicability of the homodyne scheme to higher THz field strengths, also leading a two-fold improvement of the dynamic range compared to the heterodyne counterpart. Finally, we demonstrate that, by reversing the sign of the static voltage, it is possible to directly retrieve the absolute THz pulse polarity. The homodyne configuration makes the SSBCD technique of much easier access, leading to a vast range of field-resolved applications.

Probing the role of thermal vibrational disorder in the SPT of VO[Formula: see text] by Raman spectroscopy.

Phase competition in transition metal oxides has attracted remarkable interest for fundamental aspects and technological applications. Here, we report a concurrent study of the phase transitions in undoped and Cr-doped VO[Formula: see text] thin films. The structural, morphological and electrical properties of our films are examined and the microstructural effect on the metal-insulator transition (MIT) are highlighted. We further present a distinctive approach for analyzing the Raman data of undoped and Cr-doped VO[Formula: see text] thin films as a function of temperature, which are quantitatively correlated to the electrical measurements of VO[Formula: see text] films to give an insight into the coupling between the structural phase transition (SPT) and the MIT. These data are also combined with reported EXAFS measurements and a connection between the Raman intensities and the mean Debye-Waller factors [Formula: see text] is established. We found that the temperature dependence of the [Formula: see text] as calculated from the Raman intensity retraces the temperature profile of the [Formula: see text] as obtained from the EXAFS data analysis. Our findings provide an evidence on the critical role of the thermal vibrational disorder in the VO[Formula: see text] phase transitions. Our study demonstrates that correlating Raman data with EXAFS analysis, the lattice and electronic structural dynamics can be probed.