This article is a review of research on nanostructured high-entropy alloys with emphasis on those made by the severe plastic deformation methods of mechanical alloying and high-pressure torsion. An example of thin film refractory metal alloys made by magnetron sputtering is also presented. The article will begin with a discussion of the seminal research of B.S. Murty and co-workers who first produced nanocrystalline high-entropy alloys by mechanical alloying of powders. This will be followed by a listing of research, in mostly chronological order, of mainly 3d transition metal alloys made nanocrystalline by mechanical alloying. Research on the well-studied Cantor alloy, from the literature and the author’s laboratory will be presented. The author’s and co-worker’s research on a low-density high-entropy alloy with single-phase fcc or hcp structure and an extremely high strength (hardness)-to-weight ratio will be described.

The present status of R&D for various types of solar cells is presented by overviewing research and development projects for solar cells in Japan as the PV R&D Project Leader of the New Energy and Industrial Technology Development Organization (NEDO) and the Japan Science and Technology Agency (JST). Developments of high-efficiency solar cells such as 44.4% (under concentration) and 37.9% (under 1-sun) InGaP/GaAs/InGaAs 3-junction solar cells by Sharp, 26.6% crystalline Si heterojunction back-contact (HBC) solar cells by Kaneka, 22.3% CIGS solar cells by Solar Frontier have been demonstrated under the NEDO PV R&D Project. 15.0% efficiency has also been attained with 1 cm2 perovskite solar cell by NIMS under the JST Project. This article also presents analytical results for efficiency potential of high-efficiency solar cells based on external radiative efficiency (ERE), open-circuit voltage loss and fill factor loss. Crystalline Si solar cells, GaAs, III–V compound 3-junction and 5-junction, CIGSe, and CdTe solar cells have efficiency potential of 28.5%, 29.7%, 42%, 43%, 26.5%, and 26.5% under 1-sun condition, respectively, by improvements in ERE.

GaN field-effect transistors with impressive power switching characteristics have been demonstrated. Preventing their widespread field deployment are reliability and instability concerns. Some emanate from the use of a dielectric in the gate stack. Under typical operation, the gate dielectric comes periodically under intense electric field. This causes trapping and detrapping of electrons and introduces transient shifts in the threshold voltage, a phenomenon known as Bias-Temperature Instability (BTI). A high electric field also results in the formation of defects inside the dielectric. Over time, the defects accumulate and eventually result in the abrupt creation of a conducting path that shorts the dielectric and renders the device inoperable. This process, known as Time-Dependent Dielectric Breakdown (TDDB), often imposes a maximum lifetime for the FET technology. This article presents a methodology for the study of BTI and TDDB in insulated-gate GaN FETs. Our findings paint a picture of BTI and TDDB that in many respects is similar to that of Si transistors but with some unique characteristics. Understanding the physics and developing appropriate lifetime models is essential to enabling the deployment of this important new power electronics technology.

In this study, TiO2 photoanodes doped with samarium ions via a method of hydrothermal treatment were used to fabricate dye-sensitized solar cells (DSSCs). Different doping concentrations were investigated on the effects of the cell’s performance. Some techniques including XRD, scanning electron microscopy, HRTEM, XPS, UV-Vis, photoluminescence were used to characterize the morphology, structure, and optic properties of the prepared photoanodes. The photovoltaic performance of the fabricated cells was further evaluated by measuring the current density–voltage (J–V) curves. It was found that: (1) The down-conversion luminescence effect derived from samarium doping could enhance the light-harvesting ability. (2) Compared with the undoped sample, the samarium-doped cells exhibited enhanced photovoltaic performance. Among the cells with different doping concentrations, the cell TiO2:0.015 Sm showed the best power conversion efficiency of 6.08% with a high open-circuit voltage (V oc) and a short-circuit current density (J sc).

This article presents innovative work undertaken to evaluate the auxetic composite materials developed using weft-knitted fabrics with negative Poisson’s ratio (NPR) produced from high-tenacity filaments of para-aramid (p-AR) and polyamide. The aim of this study is to develop polymeric composite materials reinforced with auxetic knitted fabrics and to evaluate the degree of transference of the auxetic behavior from the fibrous reinforcement to the composite produced. The results show that the NPR values remained in the composites. Regardless of the type of resin used, either epoxy or polyester, the highest values were obtained for samples produced with p-AR auxetic knitted fabrics. The NPR composites developed within this work present great potential for applications in industrial areas, including personal protection products, such as bulletproof vests, helmets, knee, and elbow protectors, and in all other areas where energy absorption is a key factor to be considered.

Persistent evolution and scaling down of integrating circuits have created a need to identify new thermoelectric materials that can be exploited to convert dissipated heat into electrical energy. We demonstrate that thermoelectric performance of silicene nanoribbons (SiNRs) can be enhanced by introducing nanopores We observe that with the incorporation of pores, thermal conductance of SiNRs is reduced which in turn leads to enhancement of thermoelectric performance (high ZT). Although the Seebeck coefficient degrades in the presence of pore, the conductivity exhibits an improved pattern, in effect contributing to better performance. In this paper, our aim is to tune the pore to its optimal dimension so as to enhance the overall thermoelectric efficiency and to study the effect of passivation at the pore edges on the thermoelectric parameters. It is further analyzed that with the pore passivation, the thermal conductance exhibits a width-dependent oscillating behavior. Ballistic transport regime and semi-empirical method using Huckel basis set are used to obtain the electrical properties, while the Tersoff potential is used for the phononic system.

We introduce the idea that the electronic band structure of a charge density wave system may mimic that of graphene. In that case, a class of materials quite different from graphene might be opened up to exploit graphene’s remarkable properties. For such materials, their dynamical rather than static properties are crucial. The charge density wave system requires a wave geometry simply related to graphene and self-consistency among the electrons which requires the net Coulomb and phonon-mediated parts of the electron–electron interactions to be attractive. Our model leads to an analytical expression for the total energy in terms of the effective electron mass µ, the electron density ρ0, and the strength ${\tilde v_K}$ of the net electron–electron interaction. We examine the limitations set upon ${\tilde v_K}$ by self-consistency, stability, and the approximation in the electronic state calculation and find them to be mutually compatible.

The size and strain-rate dependence of plastic deformation in Au microspheres of diameter ranging from 0.8 to 6.0 µm was investigated at room-temperature using flat-punch micro-compression testing. The contact yield stress was observed to increase with decreasing microsphere diameter. The apparent activation volume, V*, associated with the rate dependent plastic deformation remained essentially constant between 4 and 6b 3 for 0.8 and 1.0 µm spheres over strains up to 20% whereas it increased from 12 to 42b 3 for the larger 3.0 and 6.0 µm diameter specimens. The initiation of plastic deformation within the microspheres was also found to be highly dependent upon sphere diameter and strain rate with associated V*, and apparent activation energy, Q*, values of 0.4b 3 and 0.02 eV for 0.8 µm diameter spheres increasing to 4.1b 3 and 0.16 eV for 6.0 µm diameter spheres. These values indicate that initial plasticity is controlled by heterogeneous nucleation events that are consistent with a surface self-diffusion mechanism.

Stretchability of polyimide-supported nanocrystalline Au films with a thickness ranging from 930 to 20 nm was evaluated by uniaxial tensile testing. The results show that the fracture strain gradually decreased with decreasing the film thickness. Such degraded stretchability depends on plastic deformation mechanisms associated with the length scales. As the film thickness is larger than 90 nm, local thinning in the grown grains contributed to the high stretchability. Full dislocation behaviors including dislocation pileup in the 930 nm-thick film, the activation of Frank–Read dislocation source in the 170 nm-thick film and the grain boundary dislocation source in the 90 nm-thick film were dominated plastic deformation. As the film thickness is less than 40 nm, low stretchability of thin films resulted from intergranular fracture, and partial dislocation behaviors became prevailed. Evident grain growth happened in the films studied except for the 20 nm-thick film, which is expected to be involved in the stretchability of the nanocrystalline metal films on flexible substrates.

Super-black carbon aerogel sleeves (CAS) with different reflectivities and a clear aperture had been made, by the sol–gel polycondensation of resorcinol (R) and formaldehyde (F) under the catalysis of sodium carbonate (C), and was used to eliminate stray light. We explained that the subwavelength structure is the main factor that leads to the low reflectivity of CA and constructed a simple optical system to measure the exit power from CAS in different directions. We proved that different CASs have different matting effects, and all of these CASs have better matting effects than that of monolithic graphite that has higher reflectivity. To show the fine angular resolution ability of CAS, we measured the faculae from the reflected light of a compact disc and found that the CAS with a clear aperture of 1.0 mm is the best. The super-black CAS could be used in precision optical instruments and to eliminate stray light in the optical.

To improve the quality of horizontal continuous casting bronze thin slab, especially the end quality of the thin slab, three methods were proposed; (i) using silicon steel sheet at the ends of the traveling magnetic field (TMF), (ii) change in the length of TMF, and (iii) reduction in the ends current intensity of TMF. Then, the effect of these methods on the magnetic field, flow and solidification of thin slab was studied both numerically and experimentally. Results show that the use of silicon steel sheet is the best method to modify the magnetic field intensity distribution. Due to the electromagnetic field shielding effect of silicon steel sheet, when the silicon steel sheet with 150 mm length and 0.5 mm thickness was applied, the magnetic field intensity at the ends of TMF was reduced to about half of the original. However, the magnetic field intensity in the middle of TMF did not change, which assists the elimination of the strong flow of the melt at the ends of the mold and uniform the solidification shell of the melt. Then, the bronze thin slab can be successfully cast without any crack defects at the ends.

The aim of this study is to investigate the effects of different master alloys containing Ti, B, and Zr on the structure and tensile properties of thin-section A356 aluminum alloy in as-cast and T6-treated conditions. Microstructural examinations were performed using light optical and scanning electron microscopy. The results showed that the addition of 0.1 wt% Ti, 0.05 wt% B, and 0.1 wt% Zr decreases the average grain size of the cast alloy from 840 μm to 387 μm, 236 μm, and 363 μm, respectively. This structural refinement results in the variation of the α-Al primary phase distribution mode from dendritic to rosettelike. It has been found that 0.6 wt% Al–8B master alloy (0.05 wt% B) is the strongest to refine the structural parameters. This leads to the enhancement of both ultimate tensile strength and elongation values from 208 MPa and 6.2% in as-cast to 290 MPa and 12.5% in B-refined alloy at T6-treated conditions. In addition, the presence of more fine dimples on the fracture surfaces of the T6-treated specimens revealed that T6-treatment encourages ductile mode of fracture.

Effects of Zn content on microstructures and mechanical properties of as-cast Mg–4Y–xZn alloys (x = 1, 2, 3, 4) have been studied in the article. The results indicate that the X phase is formed firstly, and the X phase, X + W phases, and W phase precipitated in order when the Zn contents increased from 1 to 4 wt%. The secondary dendritic arm spacing of the tested alloys first decrease as the Zn content increases within the range of 1–2% and then it increases. The ultimate tensile strength (UTS) and elongation of the four experimental alloys increase until the addition of Zn reaches to 3%, with the maximum values of 213.6 MPa and 11.82%, respectively. Besides, the fracture behaviors of Mg–4Y–1Zn, Mg–4Y–2Zn, and Mg–4Y–3Zn were a quasi-cleavage fracture, while Mg–4Y–4Zn belonged to cleavage.

Ni/Sn–xZn/Ni (x = 1, 5, 9 wt%) joints were used to investigate the effect of Zn content on interfacial reactions during reflow under a temperature gradient. Asymmetrical growth and transformation of intermetallic compounds (IMCs) occurred between the cold and hot end interfaces. Faster IMC growth at the cold end and a more prompt IMC transformation at the hot end in a lower Zn content solder joint were identified due to the more thermomigration-induced Zn and Ni atomic fluxes toward the cold end. The main diffusion species into IMC layers changed from Zn atoms at the early stage to Sn and Ni atoms at the later stage. As a result, the IMC evolution followed (Ni,Zn)3Sn4 → Ni3Sn4 in the Ni/Sn–1Zn/Ni joint, Ni5Zn21 → τ phase → Ni3Sn4 in the Ni/Sn–5Zn/Ni joint, and Ni5Zn21 → τ phase in the Ni/Sn–9Zn/Ni joint along with the reflow time. A higher Zn content could effectively inhibit the dissolution of the hot-end Ni substrate and restrain the growth rate of the cold-end interfacial IMCs.

Mg–3Al–Zn alloy with the addition of Al and Si as a eutectic alloy was subjected to conventional hot rolling. The corresponding mechanical properties, microstructure evolution, and dynamic recrystallization mechanism were investigated by optical microscope, scanning electron microscope, electron backscattered diffraction (EBSD), and tensile tests. The experimental results indicated that the Mg–3(Al–Si)–Zn alloy had a microstructure refinement, thus rendering an enhanced mechanical properties in comparison with the Mg–3Al–Zn alloy. The refined Mg2Si particles could act as potential nucleation sites for recrystallization in as-rolled Mg–3(Al–Si)–Zn alloy sheets, which resulted in more completely recrystallized regions through particle stimulated nucleation and a weakened basal texture compared to Mg–3Al–Zn alloy. The improvement in the tensile strength of the as-rolled Mg–3(Al–Si)–Zn alloy can be attributed to grain refinement and second phase strengthening caused by the refined Mg2Si particles.

2-(3,4 epoxycyclohexyl)ethyltrimethoxysilane (EETMS)/3-glycidoxypropyltrimethoxysilane (GPTMS) mediated, in situ synthesis of functional palladium (Pd) nanocomposites over the graphene oxide (GO) surface is reported. The prepared nanocomposites viz, Pd/EETMS, Pd/GPTMS, Pd/GO/EETMS, and Pd/GO/GPTMS, are encapsulated into mesoporous (2–10 nm) silica-alginate beads to primarily serve the development of cost-effective catalyst for on-board generation of hydrogen. Major findings involve: (i) the synthesis of porous silica alginate beads, with the controlled pore sizes (2–10 nm) as a function of concentration of alkoxysilanes, (ii) onboard release of hydrogen from the decomposition of hydrazine, which is evaluated as: (1) time-dependent disappearance of the N–N bond stretching band at 1069 cm−1 based on the FTIR spectroscopy, (2) volumetric estimation of the equimolar hydrogen using methylene blue (MB); (3) catalytic reduction of p-nitroaniline (PNA). The decomposition of high concentration of hydrazine is made possible using very low concentration of palladium. On calcination the efficiency of catalysts found to enhance further. The noteworthy finding is probing the hydrogen evolution using FTIR spectroscopy. Hydrogen selectivity of ∼100% is obtained from the most efficient catalyst (Pd/GO/EETMS-623 K).

In this work, we reported the growth of cadmium-free Ag-doped Zn–In–S nanocrystals (NCs) with effective photoluminescence (PL) via a hot-injection strategy. The effects of the nucleation temperatures, reaction times, and Ag-doping concentrations on the PL properties of Ag-doped Zn–In–S NCs were investigated systematically. The as-synthesized NCs exhibit color-tunable PL emissions covering a broad visible range of 472–585 nm. After being passivated by a protective ZnS shell, the PL quantum yield (QY) of the resultant NCs was greatly improved up to 33%. With the increase of the Ag-doping level, the PL is significantly intensified due to the improved concentration of Ag ions which provides more holes to recombine with electrons from the bottom of the conduction band. This also makes the emission via the dopant energy level become a powerful, competitive advantage for the NCs with higher Ag-doping levels, resulting in a longer lifetime and higher PL QY. These results suggest that tailoring the Ag-doping level can be a powerful strategy to control the optical properties of Ag-doped Zn–In–S NCs.

Palladium (Pd) nanostructures have been actively adapted for various applications and their properties and applicability closely depend on their shape, size, and density. In this paper, the evolution of self-assembled Pd nanostructures on the hexagonal c-plane GaN is presented by the systematical control of Pd deposition amount (DA) at distinctive temperatures. Pd nanostructures of various configurations, sizes, and densities are demonstrated based on the solid-state dewetting of Pd thin films and a clear distinction in the growth regimes is observed. Three growth regimes are clearly observed depending on the variation of DA, i.e., (i) the agglomeration of Pd nanoparticles, (ii) the coalescence of wiggly Pd nanostructures, and finally (iii) the growth of nanovoids and layers. Owing to the temperature-dependent dewetting process, the growth regimes are markedly shifted, resulting in the distinctive Pd nanostructures within the identical DA range. The results are discussed in conjunction with the surface diffusion, Volmer–Weber and coalescence growth model, and surface/interface energy minimization mechanism. In addition, the evolution of optical properties, emission band, and lattice properties are probed by reflectance, photoluminescence, and Raman spectroscopy, which exhibit varying spectral intensity and peak positions according to the surface morphology of Pd nanostructures.

In this work, the hybrid carbon nanofibers (Cu2O/CNFs) containing cuprous oxide (Cu2O) nanoparticles were prepared by a convenient electrospinning method and following a carbonization treatment. The morphology, composition, and microstructure of the Cu2O/CNFs were characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffractometer. The as-prepared Cu2O/CNFs exhibited a stronger absorption in the range of 250–700 nm. The band gap energy of the Cu2O/CNFs was estimated to be 2.0 eV. Due to the synergistic effect between photocatalytic activity of Cu2O and excellent adsorption capacity of CNFs, the obtained Cu2O/CNFs exhibited excellent photocatalytic activity for degradation of rhodamine B (RhB) and phenol. The possible mechanism for degradation of RhB and phenol degradation were also discussed. The resultant hybrid carbon composites offer the significant advantages, such as low dosage, high catalytic activity, easy recycling, and excellent stability. We hope that the resultant hybrid composite Cu2O/CNFs could be applied as catalytic materials for further application in the future.