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This work explores the characteristics of two-dimensional (2D) titanium carbide (Ti3C2 MXene) and utilizes first-principles study to weigh its potential for supercapacitor applications. Scanning electron microscopy images confirm the layered morphology of the MXene, and energy-dispersive X-ray spectroscopy (EDX) analysis supports the extraction of aluminum from the MAX phase. Fourier-transform infrared (FTIR) spectroscopy confirms the presence of oxygen-based functional groups on the surface of the MXene and X-ray diffraction (XRD) patterns validate its hexagonal crystalline structure. Cyclic voltammetry (CV) analysis reveals the presence of redox peaks, indicating the pseudocapacitive behaviour of the fabricated electrode. Additionally, galvanostatic charge–discharge (GCD) measurements yield a calculated specific capacitance of 370 F g−1. Electrochemical impedance spectroscopy (EIS) substantiates the low impedance resulting from the layered structure via the adequate adsorption/desorption of cations. The utilization of first-principles density functional theory (DFT) calculations reveals the merging of conduction and valence bands, signifying effective conductivity. Both the total and partial density of states cross the Fermi level, indicating a highly efficient charge mobility process. The combination of prominent surface redox reactions and excellent conductivity contributes to the superior specific capacitance of the fabricated electrode. Overall, these results highlight the excellent electrochemical properties of the Ti3C2 MXene electrode, declaring it as a promising candidate for supercapacitor applications. [ABSTRACT FROM AUTHOR]

Phase transitions are an intriguing yet poorly understood aspect of transition-metal-based materials; these phase transitions can result in changes to the refractive index, absorption coefficient, and other optical properties of the materials. Transition-metal-based materials exist in a variety of crystalline phases and also have metallic, semi-metallic, and semi-conducting characteristics. In this review, we demonstrate that alloyed W- and Mo-based dichalcogenides enable phase transitions in structures, with phase transition temperatures that are tunable across a wide range using various alloy models and modern DFT-based calculations. We also analyze the tuning the optical bandgap of the metal oxide nanoparticles through doping of the transition metal in a manner that is suitable for optical switching and thermal imaging. After the introduction and a brief illustration of the structures and their exceptional properties, we discuss synthetic methodologies and their application as part of important strategies toward the enhanced performance of transition-metal-based dichalcogenides and oxides. In the end, our conclusion highlights the prospects of 2D materials as phase transition materials due to their advantages in terms of scalability and adaptability. [ABSTRACT FROM AUTHOR]

Condensation of moisture on the epitaxial graphene on 6H-SiC was observed below room temperature despite continuous nitrogen flow on the graphene surface. Raman peaks associated with ice were observed. A combination of peaks in the frequency range of 500–750 cm−1, along with a broad peak centered at ~1327 cm−1, were also observed and were assigned to airborne contaminants. The latter is more important since its position is in the frequency range where the defect-associated D band of graphene appears. This band can be easily misunderstood to be the D band of graphene, particularly when the Raman spectrum is taken below room temperature. This peak was even observed after the sample was brought back to room temperature due to water stains. This work highlights the importance of careful Raman investigation of graphene below room temperature and its proper insulation against moisture. [ABSTRACT FROM AUTHOR]

Zinc sulfide (ZnS) thin films with variable structural, optical, electrical, and thermoelectric properties were obtained by changing the source-to-substrate (SSD) distance in the physical-vapor-thermal-coating (PVTC) system. The films crystallized into a zinc-blende cubic structure with (111) preferred orientation. The films had a wide 3.54 eV optical band gap. High-quality homogenous thin films were obtained at 60 mm SSD. The sheet resistance and resistivity of the films decreased from 1011 to 1010 Ω/Sq. and from 106 to 105 Ω-cm, when SSD was increased from 20 mm to 60 mm, respectively. The phase and band gap were also verified by first principles that were in agreement with the experimental results. Thermoelectric characteristics were studied by using the semi-classical Boltzmann transport theory. The high quality, wide band gap, and reduced electrical resistance make ZnS a suitable candidate for the window layer in solar cells. [ABSTRACT FROM AUTHOR]

Ferromagnetism is explored in Cr3C2 from microscopic to electronic levels and the spin coupling is attributed to the p electrons of the nearest‐neighbor carbon atoms around the Cr–C atomic interactions. By using the spin‐polarized density functional calculations, four models are formulated. The models reveal that the C atoms seated in tri‐prism I site can induce magnetic moments and the C vacancies can also take part in the induced magnetic moment. The p–d orbital interactions between C interstitial atom and Cr atom contribute to two asymmetric states of majority and minority spins and lead to weak magnetic moments. The C interstitial atoms and C vacancies in the crystal lattice of Cr3C2 are observed by high‐resolution transmission electron microscopy and electron‐spin resonance (ESR) techniques. The magnetic properties of Cr3C2 are investigated by a superconducting quantum interference device. [ABSTRACT FROM AUTHOR]

Since the successful separation of graphene from its bulk counterpart, two-dimensional (2D) layered materials have become the focus of research for their exceptional properties. The layered hexagonal boron nitride (h-BN), for instance, offers good lubricity, electrical insulation, corrosion resistance, and chemical stability. In recent years, the wide-band-gap layered h-BN has been recognized for its broad application prospects in neutron detection and quantum information processing. In addition, it has become very important in the field of 2D crystals and van der Waals heterostructures due to its versatility as a substrate, encapsulation layer, and a tunneling barrier layer for various device applications. However, due to the poor adhesion between h-BN and substrate and its high preparation temperature, it is very difficult to prepare large-area and denseh-BN films. Therefore, the controllable synthesis of h-BN films has been the focus of research in recent years. In this paper, the preparation methods and applications of h-BN films on III–V compounds are systematically summarized, and the prospects are discussed. [ABSTRACT FROM AUTHOR]

Broad and low‐intensity Raman peaks are usually expected from nanocrystalline thin semiconductor films. The inherently weak Raman scattering phenomenon can be further deteriorated by unwanted background signals preventing the successful Raman analysis of an analyte. In this study, the resonant and surface‐enhanced Raman scattering techniques were combined to detect CuO and Cu2O phases in the partially oxidized nanocrystalline copper film that were otherwise undetectable. Heat treatment resulted in increased oxidation and phase transition from multiphase to single CuO phase that was in situ observed by temperature‐dependent Raman measurements. Detailed understanding of the film properties and substrate interaction was made by using several characterization techniques. [ABSTRACT FROM AUTHOR]

Flexible sensors with excellent sensitivity and stable performance are attracting more and more attention in emerging electronics. Herein, silver microflakes (AgMFs) as conductive filler in polyaniline (PANI)/polyurethane (PU) matrix are used to prepare the AgMFs/PANI/PU strain sensor by simple mixing and curing process. The AgMFs/PANI/PU strain sensor has high sensitivity (GF=173.66), ultra‐short response time (10 ms), and reassuring cycle stability (>4000 times). Excellent sensor performance demonstrates its unlimited potential for health monitoring, such as joint motion, breathing and pulse beat. [ABSTRACT FROM AUTHOR]

Resonant Raman scattering is highly desired for material study. It is experimentally not easy to reach the resonant scattering interaction between an incident photon and a material due to the limited available laser wavelengths. In this study, by employing silver plasmonic nanoparticles deposited on glass substrate and by in situ adjusting the cadmium sulfide (CdS) band gap through heat treatment, resonant Raman scattering condition (laser wavelength of 514.5 nm) was fully achieved in nanocrystalline CdS thin films. The dramatically enhanced Raman scattering allowed us to in situ monitor the phase transition that occurred during the heat treatment and to quantitatively characterize the fraction of the zincblende (cubic) CdS in the main base of wurtzite (hexagonal) CdS. Raman multi-phonon and the corresponding high-order scattering modes were observed due to the much enhanced surface nanoplasmonic electric field. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The concentration and small size of nanodiamonds (NDs) plays a crucial role in the mechanical performance of epoxy-based nanocomposites by modifying the interface strength. Herein, we systemically analyzed the relation between the high concentration and small size of ND and the fracture properties of its epoxy-based nanocomposites. It was observed that there is a two-fold increase in fracture toughness and a three-fold increase in fracture energy. Rationally, functionalized-NDs (F-NDs) showed a much better performance for the nanocomposite than pristine NDs (P-NDs) because of additional functional groups on its surface. The F-ND/epoxy nanocomposites exhibited rougher surface in contrast with the P-ND/epoxy, indicating the presence of a strong interface. We found that the interfaces in F-ND/epoxy nanocomposites at high concentrations of NDs overlap by making a web, which can efficiently hinder further crack propagation. In addition, the de-bonding in P-ND/epoxy nanocomposites occurred at the interface with the appearance of plastic voids or semi-naked particles, whereas the de-bonding for F-ND/epoxy nanocomposites happened within the epoxy molecular network instead of the interface. Because of the strong interface in F-ND/epoxy nanocomposites, at high concentrations the de-bonding within the epoxy molecular network may lead to subsequent cracks, parallel to the parent crack, via crack splitting which results in a fiber-like structure on the fracture surface. The plastic void growth, crack deflection and subsequent crack growth were correlated to higher values of fracture toughness and fracture energy in F-ND/epoxy nanocomposites. [ABSTRACT FROM AUTHOR]

A series of alluaudite Na2Fe3− xMn x(PO4)3 microcompounds, which self-assembled from primary nanorods, were prepared successfully through a solvothermal method. As a promising candidate cathode for sodium-ion batteries, it is necessary to obtain a deeper understanding of the relationship between the structure and physicochemical properties of these materials. The local electronic and geometric environments were systematically investigated, for the first time, by using a combination of soft/hard X-ray absorption, IR, and Mössbauer spectroscopy. The results show that the electrochemical performance is not only associated with morphology, but also with the electronic and crystalline structure. With the introduction of manganese into the lattice, the long-range order maintains the isostructural framework and the lattice parameters expand as expected. However, for short-range order, PO4 tetrahedra and MO6 octahedra (M=Fe and Mn) become more severely distorted as a function of Mn concentration. Meanwhile, larger MnO6 octahedra will compress the space of FeO6 octahedra, which will result in stronger core/electron-electron interactions for Fe, as characterized by hard/soft X-ray absorption spectra. These slight changes in the electronic and local structures lead to different electrochemical performances with changes to the manganese content. Moreover, other physicochemical properties, such as magnetic behavior, are also confirmed to be correlated with these different electron interactions and local geometric environments. [ABSTRACT FROM AUTHOR]

Surface plasmon (SP) enhancement of photoluminescence (PL) from a green-emitting InGaN/GaN quantum well (QW) using nanoparticles (NPs) made of different metals and their combinations was investigated. The NPs were formed by annealing the metal films in N2 followed by rapid cooling. Four-fold enhancement in PL intensity was achieved using random metal NPs made of Cu on Mg (Cu-Mg) double metal film that was more than two folds of the enhancement observed by AgNPs. Reversing the order of metal film deposition (Mg on Cu) resulted in much lower PL intensity due to significantly different NPs size distribution as the given annealing conditions did not cause homogeneous alloying of the two metals. The results pave the way for the application of NPs of relatively low-cost unconventional metals and their combinations in the SP enhancement of LEDs. [ABSTRACT FROM AUTHOR]

A small Boron ion (B-ion) dose of 5 × 1014 cm−2 was implanted in a GaN epilayer at an energy of 50 keV, and the sample was subjected to high-temperature rapid thermal annealing (RTA). The resonant Raman spectrum (RRS) showed a strong characteristic of a photoluminescence (PL) emission peak associated with GaN before B-ion implantation and RTA treatment. The PL signal decreased significantly after the B-ion implantation and RTA treatment. The analysis of temperature-dependent Raman spectroscopy data indicated the activation of two transitions in B-ion-implanted GaN in different temperature ranges with activation energies of 66 and 116 meV. The transition energies were estimated in the range of 3.357–3.449 eV through calculations. This paper introduces a calculation method that can be used to calculate the activation and transition energies, and it further highlights the strong influence of B-ion implantation on the luminesce of GaN. [ABSTRACT FROM AUTHOR]

Surface plasmon (SP)-enhanced quantum-well (QW) LEDs have proved their potential in replacing conventional lighting devices for their high-performance capabilities in ultraviolet (UV), blue and green spectral ranges. The SP-enhanced QW-LEDs have applications in light emission enhancement, light polarization, color conversion, and speed modulation. The electric field of the plasmonic mode of a metal couples with the exciton energy of QWs in resonance results in efficiency enhancement to several folds. The strength of the SP–QW coupling is mainly influenced by the type of metal used for SP enhancement, the metal nanostructure geometry, and the penetration depth of the SP fringing field in the p-GaN. The use of an appropriate dielectric interlayer between the metal and the p-GaN allows further control over SP resonance with QW emission wavelength. The penetration depth defines the p-GaN thickness and the QW period number for effective SP–QW coupling. The optimization of these parameters is key to achieve high efficiencies in SP-enhanced QW-LEDs for various applications. This review explains the SP enhancement mechanism and the key challenges facing the SP enhancement of QW-LEDs. The main factors that affect the SP–QW coupling have been explained in detail based on recent reports devoted to this field. [ABSTRACT FROM AUTHOR]

Developing sodium-ion batteries (SIBs) with high initial coulombic efficiency (ICE) and long-term cycling stability is crucial to meet energy storage device requirements. Designing anode materials that could exhibit high ICE is a promising strategy to realize enhanced energy density in SIBs. A trifunctional network binder substantially improves the electrochemical performance and ICE, providing excellent mechanical properties and strong adhesion strength. A rationally designed electrode material and binder can achieve high ICE, long cycling performance, and excellent specific capacity. Here, a NiS/NiS 2 heterostructure as an anode material and a trifunctional network binder (SA-g-PAM) are designed for SIBs. Unprecedently, the anode comprising of an SA-g-PAM binder achieved the highest ICE of 90.7% and remarkable cycling stability for 19000 cycles at a current density of 10 A g -1 and maintained the specific capacity of 482.3 mAh g -1 even after 19000 cycles. This exciting work provides an alternate direction to the battery industry for developing high-performance electrode materials and binders with high ICE and excellent cycling stability for energy storage devices.