Table of contents

Vacuum degree online detection of vacuum interrupter has been a great challenge for decades. In this letter, a novel approach based on laser induced breakdown spectroscopy (LIBS) was proposed to solve this tough problem, which is suitable for non-intrusive, electro-magnetic interference free and remote detection. The spectral lines of Cu, H, N and O elements from the interrupter shield were detected for a large gas pressure range from p  =  1  ×  10⁻³ Pa to 1  ×  10⁵ Pa. It was found that the spectral intensities of O and H increase monotonically with gas pressure, in contrast the spectral intensity of Cu first decreases slightly and then increases. Their intensity ratios, especially for that of Cu to O, change dramatically and monotonically with the gas pressure when p  ⩽  0.1 Pa, indicating that they can be used for determining the vacuum degree values. Spectral ratio method fundamentally reduces the influences of the possible variation in measuring distance and the laser power fluctuation, making LIBS a promising method for vacuum degree online detection of vacuum interrupters.

Hybrid perovskites have achieved tremendous success as a light absorber in solar cells during the past few years. However, the stability issue casts shadow on their practical applications. Perovskite oxides may offer an alternative. In this study, the metal–insulator transition in perovskite neodymium nickelates (NdNiO₃) is systematically tuned by adjusting the oxygen partial pressure during film growth. Room temperature insulating films with different band gaps are obtained. Testing photovoltaic cells have been prepared by combining the nickelates with Nb-doped SrTiO₃, and photovoltaic performance has been optimized. Our study offers a new route for designing novel photovoltaic materials.

Integration of 1D carbon nanotubes and 2D graphene sheets through covalent bonding can create novel 3D nanoporous hybrid nanostructures that inherit unique mechanical, thermal, electrical and chemical properties of their building blocks and even have new properties in three dimensions. Great progress has been made in developing 3D carbon nanotube–graphene nanoarchitectures for various applications such as mechanical cushions, thermal sinkers, transistors, and renewable energy conversion. This review presents the recent advances in synthesis and analysis of the 3D nanostructures. Emphasis is put on design principles, molecular structures, processes and properties of the materials.

Regardless of the synthetic method, developing high magnetic coercivity in ferromagnetic nanowires (NWs) with large diameters has been a challenge over the past two decades. Here, we report on the synthesis of highly coercive cobalt NW arrays with diameters of 65 and 80 nm, which are embedded in porous anodic alumina templates with high-aspect-ratio pores. Using a modified electrochemical deposition method enabled us to reach room temperature coercivity and remanent ratio up to 3000 Oe and 0.70, respectively, for highly crystalline as-synthesized hcp cobalt NW arrays with a length of 8 μm. The first-order reversal curve (FORC) analysis showed the presence of both soft and hard magnetic phases along the length of the resulting NWs. To develop higher coercive fields, the length of the NWs was then gradually reduced in order from bottom to top, thereby reaching NW sections governed by the hard phase. Consequently, this resulted in record high coercivities of 4200 and 3850 Oe at NW diameters of 65 and 80 nm, respectively. In this case, the FORC diagrams confirmed a significant reduction in interactions between the magnetic phases of the remaining sections of NWs. At this stage, x-ray diffraction (XRD) and dark-field transmission electron microscopy analyses indicated the formation of highly crystalline bamboo-like sections along the [0 0 2] direction during a progressive pulse-controlled electrochemical growth of NW arrays under optimized parameters. Our results both provide new insights into the growth process, crystalline characteristics and magnetic phases along the length of large diameter NW arrays and, furthermore, develop the performance of pure 3d transition magnetic NWs.

We propose a spherical cloak described by a non-singular asymmetric elasticity tensor $\mathbb{C}$ depending upon a small parameter $\eta,$ that defines the softness of a region one would like to conceal from elastodynamic waves. By varying η, we generate a class of soft spheres dressed by elastodynamic cloaks, which are shown to considerably reduce the scattering of the soft spheres. Importantly, such cloaks also provide some wave protection except for a countable set of frequencies, for which some large elastic field enhancement can be observed within the soft spheres. Through an investigation of trapped modes in elasticity, we supply a good approximation of such Mie-type resonances by some transcendental equation. Our results, unlike previous studies that focused merely on the invisibility aspects, shed light on potential pitfalls of elastodynamic cloaks for earthquake protection designed via geometric transforms: a seismic cloak needs to be designed in such a way that its inner resonances differ from eigenfrequencies of the building one wishes to protect. In order to circumvent this downfall of field enhancement inside the cloaked area, we introduce a novel generation of cloaks, named here, mixed cloaks. Such mixed cloaks consist of a shell that detours incoming waves, hence creating an invisibility region, and of a perfectly matched layer (PML, located at the inner boundary of the cloaks) that absorbs residual wave energy in such a way that aforementioned resonances in the soft sphere are strongly attenuated.

The designs of mixed cloaks with a non-singular elasticity tensor combined with an inner PML and non-vanishing density bring seismic cloaks one step closer to a practical implementation. Note in passing that the concept of mixed cloaks also applies in the case of singular cloaks and can be translated in other wave areas for a similar purpose (i.e. to smear down inner resonances within the invisibility region).

High-luminous efficacy white light-emitting diodes (LEDs) were realized by using GaN-based thin-film (TF) flip-chip (FC) LEDs with phosphor–silicone encapsulation. The TFFC-LEDs were fabricated by electrode isolation, FC configuration, copper electroplating, and laser lift-off (LLO) techniques. During the fabrication process, the high-defect undoped GaN layer was eliminated by inductively coupled plasma (ICP) etching to lower the absorption loss. Then, the exposed N-face n-GaN surface formed after the ICP etching was systematically studied through control of the temperature, time and concentration of the KOH solution to acquire hexagonal cones with high extraction efficiency. It is found that the external quantum efficiency was improved by a maximum value of 169% for the TFFC-LEDs with optimized surface hexagonal cones compared to TFFC-LEDs with flat surfaces. To further improve the output power, the chip size and n-contact via holes of the TFFC-LEDs were increased. A maximum luminous efficacy of 139 lm W⁻¹ was realized for white LEDs (5700 K, 350 mA, 2.98 V) using these TFFC-LEDs with phosphor–silicone encapsulation. In addition, these white LEDs also have a lower junction temperature of 87 °C even at 700 mA. These results indicate that the proposed TFFC-LEDs are promising for use in automotive and solid-state lighting applications.

This report describes the effect of quantum interference on the absorption of light in a quantum emitter and metamaterial system. The system was comprised of a dielectric substrate doped with quantum emitters and metallic split ring resonators that included metallic rods. At the interface between the dielectric substrate and the metal are surface plasmon polaritons; these interact with excitons, which are present in quantum emitters. Quantum interference occurs due to the interaction between excitons and surface plasmon polaritons. It is also considered that excitons decay from an excited state to the ground state due to the radiative and nonradiative decay processes. The quantum interference phenomenon occurs between excitons decay rates. The density matrix method is used to calculate the absorption of light in the presence of both radiative and nonradiative processes. It is found that there is a decrease in the absorption of light by metamaterial hybrids due to quantum interference. There is also an increase in the absorption of light when the resonant frequencies of two excitons are in resonance with the surface plasmon polariton. Absorption peaks are shifted and broadened due to the surface plasmon polariton coupling. These findings suggest that the optical absorption properties of a metamaterial hybrid can be tuned by doping the supporting substrate with quantum emitters.

We report an experimental scheme for high performance sensing by an all-metal meta-surface (AMMS) platform. A dual-band resonant absorption spectrum with a bandwidth down to a single-digit nanometer level and an absorbance up to 89% is achieved due to the surface lattice resonances supported by the resonators array and their hybridization coupling with the particle plasmon resonances. The sensing application in the analysis of the sodium chloride solution has been demonstrated, where remarkable changes from a spectral 'dark state' to 'bright state' and vice versa are observed. Sensing performance factors of the figure of merit exceeding 50 and the spectral intensity change related FoM* up to 1075 are simultaneously achieved. The corresponding detection limit is as low as 8.849  ×  10⁻⁶ RIU. These features make such an AMMS-based sensor a promising route for efficient bio-chemical sensing, etc.

Coexistence of volatile and nonvolatile resistive switching characteristics in a single Cu/ZrO₂/Pt device was demonstrated by controlling the current compliance (I_CC). The grain boundaries as well as the increased amount of oxygen vacancies in the polycrystalline ZrO₂ films offer the opportunity to reduce the switching kinetics and to engineer the dimension and density of the conductive filaments (CFs). Only one CF with an atomic scale diameter was formed when the I_CC was lower, whereas this tiny CF was unstable and would be annihilated spontaneously when the applied voltage reduced to zero, exhibiting a typical volatile property. The size of the CF grew with the further increasing of the I_CC. Quantized conductance was observed during the switching process, corresponding to the atomic-size variation of the CF. However, robust multiple CFs were formed and dominate the totally nonvolatile switching behaviors when a large enough I_CC was adopted. This work demonstrates the feasibility of modulating the switching kinetics to realize the volatile and nonvolatile characteristics for high-density storage and neuromorphic applications.

We present a study of germanium as n-type dopant in wurtzite GaN films grown by plasma-assisted molecular-beam epitaxy, reaching carrier concentrations of up to 6.7  ×  10²⁰ cm⁻³ at 300 K, well beyond the Mott density. The Ge concentration and free carrier density were found to scale linearly with the Ge flux in the studied range. All the GaN:Ge layers present smooth surface morphology with atomic terraces, without trace of pits or cracks, and the mosaicity of the samples has no noticeable dependence on the Ge concentration. The variation of the GaN:Ge band gap with the carrier concentration is consistent with theoretical calculations of the band gap renormalization due to electron–electron and electron–ion interaction, and Burstein–Moss effect.

In spite of the large amount of tribological work carried out to explain the friction and wear mechanism in diamond-like carbon (DLC) films, some of the core issues relating to the evolution of reactive species across sliding interfaces and their role on the friction and wear mechanism remain unclear. The phase composition, film density and hydrogen content present in a DLC film can be tailored by substrate biasing during film deposition to achieve a nearly vanishing friction coefficient. Furthermore, nitrogen doping in DLC films significantly improves wear resistance, and sliding occurs in a nearly wearless regime. Undoped and nitrogen-doped DLC films exhibit a nearly frictionless value with ultra-low wear behavior when tests are performed in argon, nitrogen and methane atmospheres. The antifriction and antiwear properties of the DLC films were improved with the reduction of adsorbed oxygen impurities on the film surface. This behavior was understood by correlating the oxygen impurities present at the surface/subsurface region of the DLC film while using x-ray photoelectron spectroscopy and depth-resolved Auger electron spectroscopy.

The electrical characteristics of Au/MgZnO:Ga (GMZO) Schottky contact, which is fabricated using a dual ion beam sputtering system, have been investigated using current–voltage (I–V) and capacitance–voltage (C–V) measurements over a wide temperature range of 80 to 300 K. The apparent Schottky barrier height (SBH) and ideality factor obtained from the I–V measurements are observed to increase and reduce, respectively, with increasing measurement temperature. This anomalous observation in the behaviour of the SBH is in good agreement with the predictions of a double Gaussian distribution (DGD) of the inhomogeneous SBH at a metal–semiconductor (MS) interface. The values of the SBH as determined from C–V measurements are expectedly higher than those extracted from I–V measurements. The DGD model is observed to fit with experimentally obtained data for the temperature-dependent SBH with mean values of the SBH of 0.95 and 0.54 eV and standard deviations of 0.131 and 0.072 eV in the temperature range of 160–300 K and 80–160 K, respectively. The larger value of the SBH standard deviation confirms more SBH inhomogeneity at the MS interface, and these inhomogeneities are attributed to the presence of deep level or surface level interface states. The calculated interface states density is seen to vary from 6.46  ×  10¹⁴ eV⁻¹ cm⁻² at E_C-0.27 eV to 1.58  ×  10¹⁴ eV⁻¹ cm⁻² at E_C-0.74 eV, where E_C is the bottom of a conduction band at 300 K.

To investigate the role surface traps play in the charge injection and transfer behavior of alumina-filled epoxy composites, surface traps with different trap levels are introduced by different surface modification methods which include dielectric barrier discharges plasma, direct fluorination, and Cr₂O₃ coating. The resulting surface physicochemical characteristics of experimental samples were observed using atomic force microscopy, scanning electron microscopy and fourier transform infrared spectroscopy. The surface potential under dc voltage was detected and the trap level distribution was measured. The results suggest that the surface morphology of the experimental samples differs dramatically after treatment with different surface modification methods. Different surface trap distributions directly determine the charge injection and transfer property along the surface. Shallow traps with trap level of 1.03–1.11 eV and 1.06–1.13 eV introduced by plasma and fluorination modifications are conducive for charge transport along the insulating surface, and the surface potential can be modified, producing a smoother potential curve. The Cr₂O₃ coating can introduce a large number of deep traps with energy levels ranging from 1.09 to 1.15 eV. These can prevent charge injection through the reversed electric field formed by intensive trapped charges in the Cr₂O₃ coatings.

Using first-principles calculations, we propose a new class of materials, Janus silicene, which is silicene asymmetrically functionalized with hydrogen and halogen atoms. Formation energies and phonon dispersion indicated that all the Janus silicene systems exhibit good kinetic stability. As compared to silicane, all Janus silicene systems are direct band gap semiconductors. The band gap of Janus silicene can take any value between 1.91 and 2.66 eV by carefully tuning the chemical composition of the adatoms. In addition, biaxial elastic strain can further reduce the band gap to 1.11 eV (under a biaxial tensile strain up to 10%). According to moderate direct band gap, these materials demonstrate potential applications in optoelectronics, exhibiting a very wide spectral range, and they are expected to be highly stable under ambient conditions.

Micro and nano-patterning of surfaces is an increasingly popular challenge in the field of the miniaturization of devices assembled via top-down approaches. This study demonstrates the possibility of depositing sub-micrometric localized coatings—spots, lines or even more complex shapes—made of amorphous hydrogenated carbon (a-C:H) thanks to a moving XY stage. Deposition was performed on silicon substrates using chemical vapor deposition assisted by an argon atmospheric-pressure plasma jet. Acetylene was injected into the post-discharge region as a precursor by means of a glass capillary with a sub-micrometric diameter. A parametric study was carried out to study the influence of the geometric configurations (capillary diameter and capillary-plasma distance) on the deposited coating. Thus, the patterns formed were investigated by scanning electron microscopy and atomic force microscopy. Furthermore, the chemical composition of large coated areas was investigated by Fourier transform infrared spectroscopy according to the chosen atmospheric environment. The observed chemical bonds show that reactions of the gaseous precursor in the discharge region and both chemical and morphological stability of the patterns after treatment are strongly dependent on the surrounding gas. Various sub-micrometric a-C:H shapes were successfully deposited under controlled atmospheric conditions using argon as inerting gas. Overall, this new process of micro-scale additive manufacturing by atmospheric plasma offers unusually high-resolution at low cost.

We fabricated a highly transmitted Ag–In₂O₃/glass nanocomposite material through a sol–gel method plus a controlled gas. Microstructural analysis revealed that the Ag and In elements in the Ag–In₂O₃ nanostructure exist in two forms: crystalline Ag nanoparticles and non-crystalline In₂O₃. And the crystalline Ag nanoparticles show the small size, uniform distribution and good dispersion in the glass host, thus triggering the surface plasmon resonance (SPR) effect and the quantum confinement effect. Remarkably, the Ag–In₂O₃/glass nanocomposite material exhibits the high transmittance greater than 70% in almost the whole visible spectral range. Open-aperture Z-scan technique further showed a typical two-photon absorption effect in the Ag–In₂O₃/glass nanocomposite material, where the nonlinear absorption coefficient was determined to be ~1.1  ×  10⁻⁹ cm W⁻¹, and interestingly, the normalized transmittance decreased with increasing input fluence. The present results blaze a new path to develop the metal/glass nanocomposite materials with high transmittance, significant nonlinear absorption effects and potential optical limiting behavior. In addition, the mechanism on the nonlinear absorption effects were also discussed in this paper, such as the SPR effect, the quantum confinement effect, the thermal effects, the nonlinear scattering effect and the resonant nonlinear effect.

Multi-walled carbon nanotubes and single-walled carbon nanotubes show great potential for the application as an electromagnetic interference shielding material. In this paper, the electromagnetic interference shielding the effectiveness of a composite surface coated single/multi-walled carbon nanotube hybrid buckypaper was measured, which showed an average shielding effectiveness of ~55 dB with a buckypaper thickness of 50 µm, and bukypaper density of 0.76 g cm⁻³, it is much higher than other carbon nanotube/resin materials when sample thickness is on the similar order. The structural, specific surface area and conductivity of the buckypapers were examined by field-emission scanning electron microscopy, specific surface area analyzer and four probes resistance tester, respectively.

The compound semiconductor HgI₂ has been widely studied and employed as a material for ionizing radiation detection. Monocrystal growth is an intricate method for obtaining materials for this application. With the aim of finding a simpler and more effective way to develop ionizing radiation detectors, we employed HgI₂ nanostructures subjected to a hydrothermal treatment and then pressed for this purpose. In the synthesis procedure, aqueous solutions of Hg(NO₃)₂ and NaI were mixed until their reaction completed and the suspension obtained was then placed in a homemade autoclave and heated at 120 °C for 2, 10 or 24 h. We confirmed the HgI₂ tetragonal phase by powder XRD in all cases, independently of the synthesis conditions employed. Nanoparticles were characterized by their size and morphology by TEM. We used the HgI₂ nanostructures to obtain a pellet by applying 0.7 GPa of pressure at room temperature. The pellet was then used to construct the detector, and we studied the electrical properties of the detector and its response to ²⁴¹Am sources of different exposure rates. The resistivity and signal-to-noise ratio obtained are of the order of those reported for HgI₂ detectors assembled with monocrystals. The results obtained in this work encourage us to work further on this topic, improving the method, scaling the detector's size and studying its spectrometric grade.