The fracture behavior of a single-crystal Al-nanoplate with an edge crack under tensile loading was simulated using a molecular statics technique to evaluate crack growth resistance in Al. The crack length was determined using a stiffness method. A parabolic function fitted from simulation results was used to predict the crack length from the stiffness value extracted from unloading curves. Based on energy considerations, crack growth resistance was calculated. Crack growth resistance rose sharply in the initial stages of crack growth, and with an additional crack extension, it increased gradually to converge to a constant far exceeding the fracture toughness predicted by the Griffith criterion. This trend in the crack growth resistance curve was closely related to the amorphous zone formed at the crack tip after the onset of crack propagation.

Silicon carbide (SiC) is the main semiconductor alternative for low loss high voltage devices. The wide energy band gap also makes it suitable for extreme environment electronics, including very high temperatures. Operating integrated electronics at 500–600 °C poses several materials challenges. However, once electronics is available for these high temperatures, the added challenge is designing integrated circuits capable of operating in the entire range from room temperature to 500 °C. Circuit designers have to take into account parameter variations of resistors and transistors, and models are needed for several temperatures. A common circuit design technique to manage parameter variations between different transistors, without wide temperature variations, is to use negative feedback in amplifier circuits. In this paper we show that this design technique is also useful for adapting to temperature changes during operation. Two different amplifier designs in SiC are measured and simulated from room temperature up to 500 °C.

To study the formation mechanism and stability of the phase in the interface of tungsten carbide particles reinforced iron matrix composites, the composites were fabricated by spark plasma sintering (SPS) technique and combined with first-principles calculation. It was found that Fe3W3C compound was stable from the perspective of both thermodynamics and mechanical properties based on our calculations. Interfacial reaction product of tungsten carbide particles reinforced iron matrix composites was M6C. Experimental results indicated that the samples prepared by SPS did not appear interfacial reaction zone, while, interfacial reaction zone appeared for the remelted samples. With the increasing remelting temperature, the width of the interface reaction zone increased because the mutual diffusion occurred at the interface between tungsten carbide particles and matrix. Its formation mechanism was 3Fe + 3/2W2C → Fe3W3C + 1/2C. Our research might provide a theoretical guidance in controlling the interface of tungsten carbide particles reinforced iron matrix composites.

Layered molybdenum disulfide (MoS2) has attracted great attention owing to its unique properties. However, synthesizing large area thin film with high crystal quality and uniformity remains a challenge. The present study explores large scale MoS2 growth methods, i.e., two-step method of sputtering-chemical vapor deposition and direct sputtering method, and applies them to fabricate field effect transistors and supercapacitors, respectively. The thickness modulated MoS2 films by two-step method exhibited high field effect mobility [∼12.24 cm2/(V s)] and current on/off ratio (∼106). The direct sputtering of MoS2 demonstrated excellent electrochemical performance with a high capacitance (∼30 mF/cm2) and cyclic stability upto 5000 cycles. Our growth methods reported here for the large scale MoS2 with high uniformity can trigger the development of several important technologies in two-dimensional materials.

Hot indirect extrusion behaviors of fully dense 3 mol% Y2O3-stabilized ZrO2 polycrystals with a grain size of 80 nm were investigated by using a conical graphite die. During early extrusion at 1843 K and a constant compression stress of 60–80 MPa, the relative moving billet velocity (v 0) shows a sharp maximum, followed by a continuous decrease until it reaches a steady-state v 0 value. Visual observations of the material flow by using graphite foil markers indicate that the deformation zone at the steady-state v 0 is well represented by a spherical velocity field. The decrease in v 0 corresponds to the transition from heterogeneous to homogeneous deformation. The stress exponent (n) of 2.07 was obtained from the log–log plots of the steady-state v 0 versus the external applied stress that is compensated by threshold and sliding friction stresses. This n value suggests plastic deformation through grain-boundary sliding in indirect extrusion.

With the advent of flexible, wearable and portable electronic products, flexible lithium-ion batteries (LIBs) and electrochemical capacitors (ECs), which are able to withstand repeated deformation or bending, have attracted considerable attention as one type of energy-storage device. However, the fabrication of these flexible electrodes is the main bottleneck in the practical utilization and application of these energy-storage devices. Up to now, enormous efforts have been made in addressing the shortcomings and remarkable improvements have also been achieved. So a systematic review of the status and progresses is highly required. In this review, we first make a short introduction about the challenges faced in the conventional batteries and capacitors. Then, we summarize the recent improvements in flexible and wearable LIBs and ECs with a focus on the flexible active materials and substrates. Finally, we discuss the prospects and challenges towards the practical applications of the flexible electrodes in the future.

AlGaN/GaN heterostructures were grown by metal–organic chemical vapor deposition (MOCVD) on sp2-bonded BN using AlN as a nucleation layer. The best x-ray diffraction rocking curve full-width-at-half-maximums (FWHMs) are 0.13° and 0.17° for the GaN (0002) and ( $10\bar 12$ ) diffraction peaks. Hall-effect measurements show room temperature mobility near 2000 cm/V·s with sheet carrier density of ∼1 × 1013 cm−2, comparable to the best values obtained on sapphire using Fe-doped GaN buffers. The best low temperature mobility of the 2-dimensional electron gas (2DEG) is ∼33,000 cm2/V·s; indicating that the dominant scattering mechanism limiting the transport of 2DEG is interface roughness. Good quality BN grown directly onto sapphire is shown to be effective for reducing parallel conduction that exists due to residual donor impurities in the buffer. Luminescence measurements indicate good optical quality of the GaN/BN/sapphire. The residual strain in the GaN layer is found to be almost completely eliminated when it is released from the substrate.

Due to gravitational self-compression, the pressure in planetary interiors can reach millions of times the atmospheric pressure. Such high pressure has a significant influence on their rheology. In the present paper, we focus on how pressure in the range of the Earth's lower mantle may influence the structure of a MgO {310}/[001] tilt boundary. The defected structure of the grain boundary (GB) will be described through its dislocation, disclination, and generalized-disclination (g-disclination) density fields. At first, the strain and rotation fields in the boundary area at different pressures are derived from the discrete atomic positions simulated by first-principles calculations. For each pressure, the discontinuities of displacement, rotation, and strain in the boundary area are continuously rendered by dislocation, disclination, and g-disclination density fields, respectively. These density fields measured at different pressures are compared to provide understanding on how pressure does influence the GB structures in Earth materials.

We have reported the chemical blending carbonization method to obtain microporous carbon with high surface area for application as electrode materials in supercapacitors. Aliphatic dicarboxylic acids with different methylene numbers (n = 2, 4, 6, and 8) react with phenolic resin (PF) during curing process. Abundant micropores are created in the carbon matrix after the decomposition of grafted or blocked diacids at temperature higher than 400 °C. The specific surface area (SSA) of the carbonized blending system increases with the diacid chain length, but decreases after n > 4 of the chain length. The maximum SSA of the blending system is up to 605.9 m2/g, which increased approximately 68% compared to that of the neat carbonized PF. Electrochemical investigation indicates that the highest specific capacitances of the blending system reaches 175 F/g at a specific current of 0.1 A/g in 30 wt% KOH aqueous electrolyte. Furthermore, the capacitance maintenance achieves 82.8% as the current density enlarged 55 times.

In this paper, taking into account the external loading, growth strain, creep, and bending deformation during the metallic high-temperature oxidation, a residual stress evolution model is developed according to the force- and moment-equilibrium equations. In this model, oxidation kinetic relationship (the stress-dependent growth rate) is related to the stress in the oxide scale, not classical parabolic law. If and only if the stress in the scale or the activation volume is equal to zero, this relationship can reduce to the parabolic law. Then the stress-dependent oxidation kinetics is compared with the stress-independent one (the parabolic law). Finally, effects of the external loading on the stress distribution in the oxide scale, the curvature of the system and the scale thickness are discussed, and numerical results show that the tensile external loading decreases the oxidation stress and promotes the growth rate of the oxidation layer.

A series of novel KLaSr3−x (PO4)3F:xEu2+ phosphors were synthesized for the first time. The crystal structure, photoluminescence properties, concentration quenching, decay analysis, and the temperature dependent luminescence properties were investigated in detail. The unit cell parameters for KLaSr3(PO4)3F were estimated to be a = 9.8997 Å, c = 7.4075 Å, and V = 628.7 Å3. The photoluminescence excitation spectrum of KLaSr3(PO4)3F:Eu2+ shows a broad band from 225 nm to 450 nm with a maximum at about 320 nm. KLaSr3−x (PO4)3F:xEu2+ phosphors exhibit a wide emission band ranging from 425 to 550 nm. KLaSr3(PO4)3F:Eu2+ phosphors exhibit good thermal stability up to 423 K. KLaSr3(PO4)3F:Eu2+ was fabricated with commercial green (Ba,Sr)SiO4:Eu2+ and red CaAlSiN3:Eu2+ phosphors to obtain a white-light-emitting diode. All the results demonstrate that KLaSr3(PO4)3F:Eu2+ are promising blue phosphors for white-light ultraviolet light-emitting diode applications.

In this study, surface texturing and hydrogenated amorphous carbon (a-C:H) diamond-like carbon (DLC) coating was combined to evaluate the coating performance at various temperatures in oil lubricated reciprocating sliding tests. Micro dimples were created by laser surface texturing on M2 steel using a Pico second laser. DLC coating was deposited by hybrid magnetron sputtering on textured substrates. Textured a-C:H showed stable coefficient of friction at 30, 80, and 125 °C compared to un-textured a-C:H. At 30 °C, graphitization was not observed for both textured and un-textured DLC coating. Graphitization was more pronounced in the case of un-textured a-C:H at 80 and 125 °C. Results show that, at all temperatures tested (30–125 °C), DLC textured samples showed higher wear resistance compared to un-textured DLC coating. The improvement in wear resistance can be explained by the lower graphitization of textured DLC coating. Lower graphitization in the case of textured DLC might be due to the wear particle capturing and lubricant retention ability of textures.

Using the peeling-induced splitting method, the effect of the irradiation of ultraviolet (UV) light on the formation of surface gratings on the surface of PMMA(Poly(Methyl Methacrylate))-based films is investigated at room temperature. The thickness of the PMMA-based films is in range of 236–534 nm, and the irradiation dose is in range of 0–5 J/cm2. Surface gratings are formed on the surface of the irradiated PMMA-based films. The spatial wave length is a linear function of the film thickness, independent of the UV doses used. The peeling-induced splitting process introduces compressive stress on the surface of the PMMA-based films, much larger than the corresponding surface energy. The magnitude of the apparent surface force increases with the increase of the film thickness. All the surface gratings formed have amplitudes approximately in the same range.

Structural characterization, quantitative phase analysis, and morphological behavior of biomineralized deposits in human pancreas [pancreatic stones (PSs)] have been carried out using infrared (IR)-spectroscopy, scanning electron microscopy (SEM), powder x-ray diffraction, and thermogravimetry - differential scanning calorimetry (TG–DSC). The fourier transform infrared (FT-IR) spectra indicated that the primary composition of PSs was calcium carbonate. An x-ray powder diffraction phase quantification using the Rietveld method revealed that five of the pancreatic calculi were composed exclusively of calcite (CAL) and the remaining four contained small amounts of vaterite and aragonite in addition to the CAL phase. The crystallite size of CAL in the PSs study varied between 104(6) and 181(2) nm. The SEM images of pancreatic calculi showed a variety of crystal morphologies for biogenic CAL crystallites such as, thin plates, spherulites, prisms, and cylindrical laths. Thermogravimetric analysis of PS1 reveals that biogenic CAL is stable up to 910 K, above which temperature CAL transforms into calcium oxide.

We demonstrate fabrication and characterization of photovoltaic (PV) devices made using pencil, paper, and commonly available economical chemicals with a power conversion efficiency of ∼1.8%. The current collecting electrode of the device composed of multilayered graphene (MuLG) was hand-drawn on the cellulosic paper using an H2B pencil. CdSe quantum dots (QD) were used for charge generation, and 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) as a bridging molecule to facilitate transfer of the photo-induced charges to the electrodes through MuLG. MuLG acted both as charge carrier and current collector electrode. The device fabrication and testing were accomplished in a wet lab under ambient conditions with minimum use of sophisticated instrumentation. The materials and devices were characterized using UV–visible, fluorescence, x-ray diffraction spectroscopy, and scanning and transmission electron microscopy. I–V characteristics of the PV devices fabricated on paper and polyester transparency substrates were performed using a solar simulator (AM 1.5) under ambient wet laboratory conditions. The use of pencil and paper makes the device fabrication simple, environmentally responsible, and accessible to layperson thus opening a new window for low cost PV and opto-electronic devices.

GeTe–Sb2Te3 superlattices have attracted major interest in the field of phase-change memories due to their improved properties compared with their mixed counterparts. However, their crystal structure and resistance-switching mechanism are currently not clearly understood. In this work epitaxial GeTe–Sb2Te3 superlattices have been grown with different techniques and were thoroughly investigated to unravel the structure of their crystalline state with particular focus on atomic stacking and van-der-Waals bonding. It is found that, due to the bonding anisotropy of GeTe and Sb2Te3, the materials intermix to form van-der-Waals heterostructures of Sb2Te3 and stable GeSbTe. Moreover, it is found through annealing experiments that intermixing is stronger for higher temperatures. The resulting ground state structure contradicts the dominant ab-initio results in the literature, requiring revisions of the proposed switching mechanisms. Overall, these findings shed light on the bonding nature of GeTe–Sb2Te3 superlattices and open a way to the understanding of their functionality.

The co-doped ZnB2O4:Eu3+, Tb3+ phosphor was prepared by a thermal conversion method using Zn[B3O3(OH)5]·H2O:Eu3+, Tb3+ as the precursor, which was characterized by energy dispersive x-ray spectrometer, x-ray powder diffraction, infrared, scanning electron microscopy, and photoluminescence. The effects of doped concentration, calcining temperature, and calcining time of precursor on the luminescence property of ZnB2O4: Eu3+, Tb3+ phosphor were investigated. The results showed that the ZnB2O4: Eu3+, Tb3+ phosphor with maximum luminescent intensity was obtained by calcining the precursor at 900 °C for 6 h. It is found that the ZnB2O4: Eu3+, Tb3+ phosphor prepared by this method exhibits much stronger emission intensity than that synthesized by conventional high temperature solid-state method. Meanwhile, ZnB2O4: Eu3+, Tb3+ also has stronger emission intensity and higher red to orange ratio than those of ZnB2O4: Eu3+.

Laves phase NbCr2-based composites toughened with different volume fractions of Cr phase were fabricated by spark plasma sintering (SPS). The microstructural evolution and mechanical properties of these spark plasma sintered NbCr2/Cr composites were investigated. The mechanical properties evaluations indicate that the introducing of Cr phase consolidated by SPS has a beneficial effect on the mechanical properties of the NbCr2 Laves phase. When the content of Cr phase in the NbCr2 Laves phase increases to 30 wt%, the hardness measured by a Berkovich nanoindenter operated with the continuous stiffness measurements mode attains the maximum value of 13.44 GPa, which is increased by about 56% over the as-cast NbCr2 Laves phase. More importantly, the room-temperature fracture toughness of the NbCr2-30wt%Cr alloy is increased to 18.9 MPa·m1/2, which is 16 times higher than that of the as-cast NbCr2 Laves phase (1.2 MPa·m1/2). The microstructural analysis indicates that the residual of Cr phase and formation of Nb solid solution can provide remarkable toughening of the NbCr2 Laves phase by fine grain toughening, dual ductile phase toughening, and interface toughening mechanisms. A possible formation mechanism of Nb solid solution during SPS has been proposed by considering the composition distribution.

Mechanical properties are of fundamental importance in materials science and engineering, and have been playing a great role in various materials applications in the human history. Measurements of mechanical properties of 2-dimensional (2D) materials, however, are particularly challenging. Although various types of 2D materials have been intensively explored in recent years, the investigation of their mechanical properties lags much behind that of other properties, leading to lots of open questions and challenges in this research field. In this review, we first introduce the nanoindentation technique with atomic force microscopy to measure the elastic properties of graphene and 2D transition metal dichalcogenides. Then we review the effect of defects on mechanical properties of 2D materials, including studies on naturally defective chemical-vapor-deposited and intentionally defective 2D materials. Lastly, we introduce a nano-electromechanical device, resonators, built on the basis of the excellent mechanical properties of 2D materials.

Boron cluster chemistry roared to life in the 20th century with seminal discoveries outlining the incredibly versatile chemistry of boron, producing a range of neutral and ionic boron compounds that paved the way for a robust suite of hybrid materials that incorporate these electronically delocalized inorganic clusters with the additional organic flexibility. Looking toward further materials research in the 21st century, these stable, inorganic polyhedral borane clusters discovered during previous century will provide a particularly fertile ground for exploration. These stable clusters have already seen significant exploration, but their utility has been obscured by classical synthetic routes using highly toxic neutral borane compounds. This incongruity is quite ironic given the current variety of medical explorations conducted with the essentially nontoxic dodecahedral borane dianion. This article will lay out some essential context and outline key synthetic studies that may dramatically simplify access to these unique compounds to a broader community of materials scientists and engineers.