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Natural bioinspired hierarchically ordered architectures from the nanoscale to the macroscale are achieved in graphene/ZrB 2 hybrid composites to improve their toughness using graphene oxide. Two types of films containing different volumes of graphene oxide are self-assembled with ZrB 2 or SiC micro particles through a vacuum-assisted filtration method. Scanning electron microscopy images show that ceramic particles are homogeneously distributed in a continuous multilayer graphene oxide network, forming a nano-micro hierarchical structure. Tensile tests are employed to test the strength of these films. The spark plasma sintering method is utilized to construct micro-macro structural order through densifying two types of alternately stacked films containing different volumes of graphene oxide. Indentation tests reveal alternately compressive and tensile layers are achieved after the sintering process. By combining different structural features spanning several length scales, the composites exhibit a unique combination of high strength (522 MPa) and toughness (9.5 MPa m 0.5 ); in particular, the fracture toughness is more than double that of the composite without the hierarchical architecture. The toughening mechanisms are also analyzed at different length scales. This bioinspired material-independent approach should be employed in the designing and processing of materials for structural, high-temperature and energy related applications.

Carbon-bonded carbon fiber (CBCF) composites consist of chopped carbon fibers network by vitreous carbon at the intersections with high porosity, low thermal conductivity and high-temperature resistance. To further enhance mechanical properties of CBCF composites, nanostructured modification can inspire the creation of CBCF composites with tunable mechanical properties. Here, we report an self-grown strategy to prepare carbon nanotubes (CNTs) and ZrB2-modified CBCF composites with a green and single-step process without any foreign gases. The CNTs-ZrB2 was directly self-grown in CBCF matrix from zirconium (Zr) and boron (B)-contained polymeric precursors during thermal pyrolysis. Results showed that the CNTs are uniformly dispersed in the composites with several hundred micrometers length. The CNTs play a significant role on improving mechanical properties of CBCF composites by pulling-out and bridging effect compared with CBCF composites without CNTs.

Porous ZrB 2 –SiC (ZS) ceramics with different volume fractions of porosity, i.e. 8.7%, 17.9% and 27.3% and different mean pore diameter, i.e. 2.21, 3.65 and 4.23 μm, were fabricated using partial hot pressing, in order to investigate the effect of the porosity and pore size on their mechanical and thermal properties as well as thermal shock performance. Particular emphasis was placed in the study on thermal shock fracture resistance. The critical temperature difference, Δ T c , of porous ZS herein was found to increase slightly with increasing porosity. This phenomenon is inconsistent with most previous researches on other material systems. However, it was well explained from the viewpoints of both physical properties and microstructures of the material, which provides new perspectives and a deeper understanding of how porosity and pore-size affect Δ T c . The Δ T c was also observed to increase as pore size decrease. It could tailor the thermal shock resistance of ZS ceramic and obtain porous ZS ceramic with both high thermal shock fracture resistance and high thermal shock damage resistance, using the above porosity and pore-size dependence of physical properties.

Compared to traditional optical domes, domes of sapphire coated with films can effectively reduce emissivity and increase transmittance. The purpose of this work is to investigate the thermal radiation effect on sapphire optical dome coated with yttrium oxide by a radio frequency magnetron sputtering method. The emissivity of sapphire coated with Y2O3 films is studied by both numerical and experimental methods. The results indicate that the emissivity of sapphire substrate is reduced effectively with increasing the thickness of the Y2O3 film. In addition, a finite element model is developed to simulate the radiation intensity of the optical dome. The thermal responses indicate that the maximum temperature is reduced apparently compared with the uncoated sapphire as Y2O3 film thicknesses increase. The average irradiance distribution at different film thicknesses with time shows that the self-thermal radiation disturbance of sapphire optical dome delays 0.93 s when the thickness of Y2O3 film is 200 μm, which can guarantee the dome works properly and effectively even in a harsh environment.

The chemical composition, structure and mechanical properties of hafnium oxide films with different nitrogen constituents were investigated. X-ray photoelectron spectrum analysis showed that nitrogen atoms acted as oxygen substitution and interstitial atoms. The crystalline features exhibited no change during nitrogen doping. Nevertheless, the films with high compressive stress displayed significantly enhanced mechanical properties. The enhanced mechanism could mainly be attributed to the dislocation obstacle motion by inserting nitrogen atoms.

SiOC and SiZrOC ceramics were obtained starting from the hydrosilane system without and with zirconium n-propoxide (Zr(OnPr)4) by sol–gel route. The precursor architectures indicated that the presence of Si H bonds leads to a different cross-linking mechanism of SiZrOC precursor, where the Si H bonds were involved in the formation of Si O Zr bonds. The presence of Zr caused a lower content of sp3 carbon in SiZrOC ceramics. At above 1400 °C, the sp3-C/Si ratio in both ceramics increased due to carbothermal reduction, especially rapidly for SiOC ceramics, suggesting the carbothermal reduction in SiZrOC ceramics has been strongly suppressed with the presence of ZrO2. Raman spectroscopy showed the graphitization degree of free carbon increased with temperature in both ceramics, but was always lower in SiZrOC ceramics. The SiZrOC ceramics has been found to exhibit remarkably high temperature stability with respect to carbothermal decomposition up to 1600 °C in comparison with the SiOC ceramics.

Carbon nanosheet–coated micron zirconium diboride particles were achieved by an atmospheric chemical vapor deposition in the presence of methane gas without catalyst. The microstructures and carbon structure for the novel particles were characterized by scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. In addition, the growth process of hybrid particles was analyzed by thermodynamic theory. The results showed that zirconium diboride particles were coated by carbon nanosheets uniformly. The carbon nanosheets/zirconium diboride particles were employed to fabricate ceramic composite using spark plasma sintering process. The fracture toughness of the composite was improved up to 5.9 MPa·m0.5 with only 0.9 wt% of carbon nanosheets, which was 40.9% higher than that of the composite without carbon nanosheets. The toughening mechanisms were mainly known as carbon nanosheets crack bridging and pulling out which lead to the formation of crack deflection in the novel composite.

In this study, novel KCaY(PO4)2:Dy3+, Eu3+ (KCYP:Dy3+, Eu3+) nanophosphor has been successfully prepared by a facile solution-combustion route. The crystal structure, morphological and microstructural features, and photoluminescence (PL) properties of KCYP:Dy3+, Eu3+ nanophosphor, as well as its thermal properties, have been studied. Investigations based on XRD, FTIR and Raman verify the formation of single-phased and well-crystallized KCYP:Dy3+, Eu3+. SEM and TEM observations reveal that the KCYP:Dy3+, Eu3+ nanophosphor displays uniform spherical morphology with an average particle size of about 47 nm. The optimal concentrations of Dy3+ and Eu3+ ions in KCYP were determined to be 3 mol% and 7 mol%, respectively. Under near-ultraviolet (NUV) excitation, individual Dy3+- or Eu3+-doped samples exhibit characteristic PL emissions in their respective regions. As for the Dy3+, Eu3+ co-doped KCYP, energy transfer has been confirmed happening from Dy3+ to Eu3+ via an electric dipole–dipole interaction, and the critical distance (Rc) was calculated to be 17.07 A. Our experiments reveal that it is easy to produce warm white or tunable emissions by regulating the Eu3+ content. Moreover, the single-component KCYP:3%Dy3+, 7%Eu3+ nanosized phosphor has a very low correlated color temperature (2766 K) and a high color-rendering index (Ra = 81.6). The quenching temperature (T0.5) of the KCYP:Dy3+, Eu3+ nanophosphor was found to be higher than 220 °C, indicating its superior thermal resistance. Consequent three rounds of the heating–cooling cycle experiments demonstrate no occurrence of thermal degradation. These findings suggest that this nanophosphor is a promising candidate for application in NUV-pumped glareless warm-white LED.

The composite film of carbon nanotubes and silicon carbide nanowires was synthesized directly on the silicon substrate by the catalyst-assisted method. The carbon nanotubes crimped together decorated with silicon carbide nanowires covering the whole substrate. The appropriate amount of aluminum powders is a crucial factor to achieve the composite film. The composite film exhibited excellent intrinsic superhydrophobicity without any further functionalization. By using the nano/micropillar composite structure model, the presence of silicon carbide nanowires is found to be the key factor that results in the superhydrophobicity of the films. The feasible synthesis of the superhydrophobic coating could have potential application in water-repelling devices, like biochemical sensors and microfluidic systems. Keywords: Composite film, Superhydrophobic, Self-cleaning, Pillar structure model

SiBOC ceramics with highly graphitized free carbon were prepared from sol–gel derived pre-ceramic gels followed by pyrolysis at 1000–1600 °C under nitrogen. The effects of boron incorporation on the precursor architecture, microstructure and crystallization of SiBOC ceramics were discussed. The experimental results showed that the incorporation of boron had little effect on the silicon bonding environment in SiBOC precursor and led to a higher ceramic yield of 89%. The crystallization of both β-SiC and free carbon was enhanced in SiBOC ceramics. Raman spectra showed that the intensity ratio of D to G band was very small for the SiBOC ceramics pyrolyzed at 1600 °C, indicating the highly ordering and graphitization of free carbon. The clear presence of D׳ band at 1610 cm −1 in Raman spectra suggested the partial substitution of C with B atoms in graphite layer, which significantly promoted the graphitization of free carbon. The turbostratic graphite with 10–20 layers graphene was observed by TEM.

For the first stage, a metastable β titanium alloy, Ti–3.5Al–5Mo–4V–2Cr–2Sn–2Zr–1Fe reinforced with trace amounts of TiB whiskers and TiC particles was fabricated by vacuum arc melting process and hot forging followed by heat treatment at 780 °C/740 °C, then by aging at 500 °C, 550 °C, 570 °C and 600 °C. For the second stage, the unreinforced titanium alloy was also fabricated by the same process. The microstructural characteristics were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Traces of TiB whiskers and TiC particles (2.2 vol.%) with a volume ratio of 2:3 synthesized in situ exerted a hybrid reinforcing effect on the β titanium alloy. The reinforcements were uniformly distributed in the matrix and the elastic modulus was improved about 25 GPa. Ultimate tensile strength and yield strength achieves about 1625 MPa and 1500MPa respectively, with ductility at 7% when the aging temperature is 500 °C. The ductility of (TiB + TiC)/(Ti–3.5Al–5Mo–4 V–2Cr–2Sn–2Zr–1Fe) matrix composite could be enhanced by increasing the aging temperatures. After 780 °C followed by aging at 570 °C, excellent strength and plasticity properties were obtained (ultimate tensile strength of matrix alloy is 1350 MPa with elongation of 18% and ultimate tensile strength of composite is 1500 MPa with elongation of 13%). Keywords: Microstructure, High strength titanium alloy, Heat treatment, Tensile properties, Titanium matrix composite

Improving open-circuit voltage is critical to improving the performance of diamond nuclear battery. ZnO films have been successfully used as the electron transport layer of diamond Schottky nuclear battery in this work. The open-circuit voltage of device with ZnO layer is increased from 1.03 to 1.43 V and the conversion efficiency is increased by 100% to 1.42% compared with device without ZnO layer. By comparing the device structure diagram and potential distribution before and after adding the ZnO layer, we try to find out the cause of the increase in open-circuit voltage. This research provides a new way to improve the open-circuit voltage and conversion efficiency of nuclear batteries.

With the advent of the 5G era, the efficient and large-scale preparation of high thermal conductivity materials is viewed as a challenge in the heat conduction and dissipation of electronic components. In this work, poly (diallyl dimethyl ammonium chloride) (PDDA) was used to combine nanodiamond (ND) particles with boron nitride nanosheets (BNNS) by electrostatic interactions. The filler and polyvinyl alcohol (PVA) were mixed to prepare a large-area, flexible, insulating, and high thermal conductivity composite film by the doctor blade method. Considering the high cost of ND, when keeping the filler content at 30 wt%, the introduction of few ND on BNNS (ND/BNNS, 3/100, w/w) enhanced the in-plane thermal conductivity of the composite film from 11.29 to 15.49 W/m·K (pure PVA film~0.22 W/m·K). Given these advantages, this composite film shows promising applications in next-generation portable and flexible electronic devices.

Advanced electromagnetic wave (EMW) absorbing materials with low-cost, lightweight, high absorption efficiency and wide absorption frequency are extremely desirable for solving electromagnetic radiation. Herein, an excellent microwave absorber composed of NiCo2S4 nanosheets decorated three-dimensional (3D) hierarchically porous carbon derived from biomass was successfully designed and constructed via a facile strategy for the first time. The results shown that the morphology and EMW absorption ability of 3D NiCo2S4/C hybrid composites could be synchronously tailored just by controlling the initial content of cetyltrimethyl ammonium bromide (CTAB) as a surfactant, and a substantial enhancement of microwave absorption performance could be achieved after the introduction of NiCo2S4 nanosheets, resulting from the matched impedance and the enhanced attenuation constant. The optimized NiCo2S4/C composites exhibit strong EMW absorption abilities, whose minimum reflection loss (RLmin) value reaches −64.74 dB with an ultra-thin thickness of 1.91 mm, and the effective absorption bandwidth (EAB, RL ≤ − 10 dB) is up to 5.26 GHz ranging from 9.22 to 14.48 GHz, which could also cover the entire X-band within 2.23–2.31 mm thickness. This work provides a new sight to design and prepare next-generation microwave absorbers with high absorption efficiency and wide absorption frequency through a low-cost, sustainable and effective method.

The modern portable and wearable electronic devices have been put forward a claim on flexibility, transparency and lightweight. Triboelectric nanogenerator (TENG) has attracted great attention as basic component of independent power source due to its outstanding characteristics. Here, a simple and efficient approach was demonstrated to modify poly-(dimethylsiloxane) (PDMS) in order to both improve the output electrical performance of TENG and optimize its hydrophobility as well. The 4 cm2 TENG consisting of PDMS-perfluorododecyl trichlorosilane (FDTS) friction layer and copper nanowires (Cu NWs)/reduced graphene oxide (RGO) electrode, exhibits high output voltage and large transfer charge quantity of 125 V and 80 nC, where the corresponding electrical performances are larger with several times than that of pristine PDMS-based TENG. A voltage of 105.8V can be obtained even under the ambient condition with high humidity of ~60%. The improvements are attributed to the reaction between FDTS and PDMS, introducing fluorine element to absorb more electrons and increasing dielectric constant. Moreover, the fabricated TENG remains high visible transmittance (70.1%) and good flexibility as energy sources which can satisfy the demands of portable and wearable electronic devices.

Amorphous boron powders were applied to grow boron-doped diamond (BDD) films with chemical vapor deposition method. The material is nontoxic and noncorrosive compared to conventional boron sources such as boroethane. The mechanism for using solid boron source as the dopant in low temperature and low pressure has been explained with a non-equilibrium thermodynamic coupling model and optical emission spectroscopic analysis. The BDD film was utilized in a non-enzymatic glucose sensor. A porous Au/Ni layer was then placed on the BDD surface for enhanced sensitivity. The electrode was characterized by scanning electron microscopy, Raman spectra, X-ray diffraction, cyclic voltammograms and amperometric responses. Typically operated at a voltage of 500 mV, it demonstrated fast response to glucose thanks to its large surface, rapid electron transfer, and synergetic effects between Au and Ni. Two specific linear ranges are found, one between 0.02 and 2 mM, and a second one between 2 and 9 mM. The detection limit and the best sensitivity are 2.6 μM and 157.5 μAmM−1 cm−2.

As thermal interface materials, polymers are limited by its low thermal conductivity. In this work, a three-dimensional bi-network structure consisting of chemical vapor deposition graphene foam and close-stacked nanodiamonds was constructed in epoxy matrix via a template method. The obtained composites exhibit interesting properties: significant thermal conductivity enhanced efficiency per unit of fillers (74.33%) based on pure epoxy matrix, and excellent electrical conductivity (0.256 S/cm) compared with epoxy matrix (4.58exp-14 S/cm). Finite Element Analysis based on the design of the dual networks was carried out to confirm the heat transfer mechanism, and it is proved that composites with GF/ND bi-network have a lower temperature gradient. That provides a novel insight of improvement method for thermal conductivity by construction of a three-dimension bi-network structure.

Hydrogen has been deemed as an ideal substitute fuel to fossil energy because of its renewability and the highest energy density among all chemical fuels. One of the most economical, ecofriendly, and high-performance ways of hydrogen production is electrochemical water splitting. Recently, 2D transition metal dichalcogenides (also known as 2D TMDs) showed their utilization potentiality as cost-effective hydrogen evolution reaction (HER) catalysts in water electrolysis. Herein, recent representative research efforts and systematic progress made in 2D TMDs are reviewed, and future opportunities and challenges are discussed. Furthermore, general methods of synthesizing 2D TMDs materials are introduced in detail and the advantages and disadvantages for some specific methods are provided. This explanation includes several important regulation strategies of creating more active sites, heteroatoms doping, phase engineering, construction of heterostructures, and synergistic modulation which are capable of optimizing the electrical conductivity, exposure to the catalytic active sites, and reaction energy barrier of the electrode material to boost the HER kinetics. In the last section, the current obstacles and future chances for the development of 2D TMDs electrocatalysts are proposed to provide insight into and valuable guidelines for fabricating effective HER electrocatalysts.

Electrode surfaces with superhydrophobic and conductive properties exhibit a unique energy-mass transfer behavior in electrolytes. Therefore, the rational design of electrode surface structures, conductivity, and infiltration performance is expected to yield more efficient electrochemical reactions and solve the gas-deficit problem that hinders many underwater gas-consuming reaction systems. In this paper, hydrogenated carbon nano-onions displaying superhydrophobicity and conductivity were prepared by microwave plasma-enhanced chemical vapor deposition, which exhibited remarkable transferability and designability. The fabricated carbon nano-onions were used to modify the surfaces of various materials and structures toward their application to self-cleaning, oil-water separation, and enabling highly effective underwater oxygen-consuming reactions. Systematic analyses of the different wetting states of the superhydrophobic electrodes coated with the fabricated carbon nano-onions indicated that the different wetting states have important effects on their behaviors for underwater nucleation reactions, thus changing the efficiency of underwater oxygen-consuming reaction systems. The results reveal that designing a superhydrophobic electrode with a Wenzel-Cassie coexistent underwater wetting state, rather than a Cassie state or Wenzel state, is the key to enabling highly effective underwater oxygen-consuming reactions.

Transition metal oxides have recently been demonstrated as highly attractive anodes for high-capacity lithium ion batteries, whose electrochemical properties could be further improved through rational architecture design and incorporating reliable conductive network. Herein, mesoporous γ-Fe2O3 spheres/graphene aerogel composites were synthesized via a solvothermal pathway followed by suitable annealing. Experimental results reveal the uniform mesoporous structure and well-dispersed γ-Fe2O3 spheres with the size of 300-400 nm embedded in the mesopores of the graphene aerogel network. Compared with α-Fe2O3/graphene aerogel and pure γ-Fe2O3, the as-synthesized composite delivers, at the first cycle, a high discharging capacity of 1080 mAh g-1 at current density of 200 mA g-1. Even at much higher current density of 8000 mA g-1, satisfactory discharging capacities of 421.5 mAh g-1 can still be achieved. Upon 100 charging-discharging cycles, the specific capacity of as high as 890.5 mAh g-1 at 200 mA g-1 is maintained. The enhanced electrochemical properties could be attributed to their favorable three-dimensional graphene aerogel network, which accounts for the improved structural stability and electronic conductivity of γ-Fe2O3 during the lithiation/delithiation process.

The impact behavior of human skull sandwich cellular bones with gradient geometric feature is investigated using theoretical and numerical methods. To predict the structural impact performance theoretically, the skull bone is considered as a multi-layer sandwich structure where the effect of the number of layers on its impact behavior is discussed. Three sections with different porosities and thicknesses obtained from the rebuilt 3D skull model are selected, and the numerical simulation is carried out to illustrate the reliability of the theoretical model. A close agreement between the numerical and theoretical results is observed. Moreover, the energy absorption capacity of the skull in the theoretical model is further demonstrated by experimental results of the human skull under impact loading from the literature. Numerical and experimental results show that the theoretical model can effectively predict the impact performance of the skull cellular bone. Therefore, this study can provide a reliable theoretical basis for the evaluation of the mechanical behavior of the human skull under dynamic loads.

The Al2O3/YAG:Ce3+ eutectics (170 mm x 90 mm x 20 mm) with different Ce3+ concentrations, which could be used as structural members and new type of fluorescent materials, were grown by the horizont ...

The appearance of polycrystalline diamond (PCD) at the edges of deposited layers is a major obstacle in MPCVD diamond growth process. In this work, diamond growth states with various substrate thicknesses were simulated to obtain the distribution of electric field intensity, electron density and temperature on the substrate surface. The simulation results indicate that the distribution of surface plasma can be controlled by the design of substrate thickness, thus affecting the growth of diamond. Three samples with different substrate thicknesses were grown and the variation of crystal quality from the edges to the centers was analyzed by Raman spectroscopy. The growth results showed that as the thickness of the substrate decreased, the formation of PCD rim was inhibited. One reason for this phenomenon is that the plasma density at the edges and corners decreases when a thinner substrate is used, which suppresses the probability of two-dimensional nucleation and defect formation.

We propose a strategy to realize a vertically parallel multilayered distribution of microdiamonds in a polymeric matrix by pre-constructing layers with abundantly stacked microdiamonds. Silicone-based composites with this microdiamond arrangement exhibit interesting material properties in the through-plane direction: significant increments in thermal conductivity (335% that of composites with a random structure at a similar low loading of 24.7 vol%), and excellent dielectric properties as thermal interface materials for applications such as radars. Novel numerical models focused on this design of microdiamond arrangement are proposed to further understand mechanism of thermal conductivity increment and are found to match thermal conductivity and tendency of composites with this type of microdiamond distribution. It is revealed that adjusting microstructures in pre-constructed microdiamond layers is regarded as an effective strategy to improve further thermal conductivity of composites.

Compared with conventional anti-reflective film, an anti-reflective sub-wavelength surface structure provides an ideal choice for a sapphire optical window especially in harsh environments. However, it is still a challenge to obtain a sapphire anti-reflective surface microstructure because of its high hardness and chemical inertness. In this paper, combined with optical simulation, we proposed a facile method based on the anodic oxidation of aluminum film and following epitaxial annealing. Al thin film was deposited on a sapphire substrate by magnetron sputtering, and anodic oxidation was then performed to prepare surface pore-like structures on the Al film. Followed by two-step annealing, both the anodic oxidized coating and underlying unoxidized Al film were transformed totally into alumina. The parameters of anodic oxidation were analyzed to obtain the optimal pore-like structures for the antireflection in the mid-infrared and visible spectrum regions, respectively. Finally, the optimized surface sub-wavelength nanostructure on sapphire can increase the transmittance by 7% in the wavelength range of 3000–5000 nm and can increase 13.2% significantly for visible spectrum region, respectively. Meanwhile, the surface wettability can be also manipulated effectively. The preparation of surface pore-like sub-wavelength structure by the annealing of anodic oxidized aluminum film on sapphire is a feasible, economical and convenient approach and can find the applications for various optoelectronic fields.

Macroporous SiOC ceramics have been prepared by the pyrolysis of the preceramic precursor obtained from methyltrimethoxysilane and dimethyldimethoxysilane. The structural evolution of the sol–gel derived SiOC ceramics at high temperatures was investigated using SEM, TG, FTIR, XRD and Raman spectra. The SiOC xerogel exhibited a porous structure consisting of cross-linked spherical gel particles. The structural rearrangement appeared and the SiOC ceramic particles changed from spherical to irregular shape after thermal pyrolysis. The ceramic yield was found to be approximately 70% until 1400 °C, and decreased to 38% at 1600 °C owing to carbothermal reduction. The SiC nanorods were in situ formed from macroporous SiOC ceramic wall at 1600 °C. The β-SiC nanocrystals precipitated from the SiOC matrix at 1400 °C and grew up to 4.6 nm at 1600 °C. The graphitization degree of free carbon increased with the increase of pyrolysis temperature.

The preferentially oriented In2O3 thin films were prepared on glass substrates by conventional magnetron sputtering with Ar+ plasma exposure at room temperature. Based on the x-ray diffraction, x-ray photoelectron spectroscopy, and UV photoelectron spectroscopy results, it was found that the Ar+ plasma exposure not only enhanced the low-temperature crystallization of In2O3 thin films, but also led to a dramatic improvement in the work function. Furthermore, it demonstrated that the shift mechanism of the work function in In2O3 thin films mainly combined with theelimination of oxygen defects and the change of the preferential orientation of In2O3 film surface.

Interface engineering has emerged as a fertile and efficacious approach to turn functional properties in the field of film systems. In this work, the interfacial properties of sputtered yttrium oxide films on zinc sulfide substrate (Y 2 O 3 /ZnS) were analyzed by transmission electron microscopy (TEM), X-ray photoelectron spectrum (XPS) depth profile and nano-scratch measurement. An interface layer with the depth of 20 nm between Y 2 O 3 film and ZnS substrate was directly observed by TEM. Under different film growth conditions, although the interfacial features including interfacial width and composition distribution exhibit similar behavior, it is found that higher cohesive strength is obtained under a special substrate bias voltage of −160 V at low substrate temperature. Such an enhanced mechanical property can be understood by the role of physisorbed oxygen in the interfacial region, in which less physisorbed oxygen with van der Waals bonds leads to a strong adhesion. Our results provide a favorable strategy to achieve strong adhesion between oxide and sulfide at low temperature, which are urgent in future micro-electric applications.

The coupling effect between nitrogen-vacancies (VN) and aluminum-interstitial sites (Ali) is investigated theoretically and experimentally in AlN helices. First-principles calculations predict a photoluminescence emission peak at approximately 600 nm in AlN doped with complex-defect (VNAli). A typical long afterglow (persistent luminescence) was observed in unintentionally doped AlN helices by introducing the complex-defect of (VNAli). An analysis of the luminescent characteristics indicated that the mechanism behind this afterglow is the complex-defect level and complex-defect density. These findings may further enrich the thoughts of defects in the wide band gap semiconductor of AlN.

An original catalytic method has been proposed to synthesize carbon nanotubes (CNTs)–ZrB2–ZrO2 heterostructures using ZrB2 polymeric precursor. The pyrolysized gases from the ZrB2 polymeric precursor are identified to be the carbon sources for CNTs growth. A parametric study is conducted to control the CNTs growth by optimizing parameters such as synthesis temperature and catalyst content. Observations show that the in situ grown CNTs are homogeneously dispersed in the powders, and the structure and the amount of CNTs are significantly dependent on the synthesis parameters. There are two kinds of grown CNTs existed in the produced hybrid heterostructures: (i) the kinking structured CNTs that are disordered and incomplete graphitization; (ii) the improved and graphitized CNTs. The ZrB2 polymeric precursor during thermal pyrolysis provides capable of supplying substantial carbon source for CNTs nucleation and growth by homogeneous vapor–liquid–solid reactions.

Carbon-based nanomaterials provide an attractive perspective to replace precious Pt-based electrocatalysts for oxygen reduction reaction (ORR) to enhance the practical applications of fuel cells. Herein, we demonstrate a one-pot direct transformation from graphitic-phase C3N4 (g-C3N4) to nitrogen-doped graphene. g-C3N4, containing only C and N elements, acts as a self-sacrificing template to construct the framework of nitrogen-doped graphene. The relative contents of graphitic and pyridinic-N can be well-tuned by the controlled annealing process. The resulting nitrogen-doped graphene materials show excellent electrocatalytic activity toward ORR, and much enhanced durability and tolerance to methanol in contrast to the conventional Pt/C electrocatalyst in alkaline medium. It is determined that a higher content of N does not necessarily lead to enhanced electrocatalytic activity; rather, at a relatively low N content and a high ratio of graphitic-N/pyridinic-N, the nitrogen-doped graphene obtained by annealing at 900 °C (NGA900) provides the most promising activity for ORR. This study may provide further useful insights on the nature of ORR catalysis of carbon-based materials.

This paper investigates the influence of deposition conditions on the properties of yttrium oxide thin films. The paper focuses on the texture, optical and mechanical properties. With this objective, a series of yttrium oxide thin films with different thicknesses were deposited by direct current (DC) unbalanced reactive magnetron sputtering at high and low pumping speed. By changing the oxygen flow, depositions were performed in the three characteristic deposition modes for reactive magnetron sputtering, i.e., metallic, transition and poisoned mode. By using an oxygen flow directed to the substrate, full oxidation of the samples, as shown by X-ray photoelectron spectroscopy (XPS), in the three modes is obtained. Crystallographic characterization by X-ray diffraction (XRD) shows that films crystallize in the cubic phase with a strong (222) out-of-plane orientation at low oxygen flow. As the oxygen flow increases a mixture of cubic and monoclinic phase is obtained. In poisoned mode, the films consist of the cubic phase with preferred (420) orientation. Scanning electron microscopy (SEM) cross sections show, with increasing oxygen flow, a loss of the columnar structure. As the oxygen flow rates increase through the metallic, transition, and the poisoned mode, the grain size becomes gradually smaller. An overview diagram of all experimental results uncovers that the textural changes are closely linked to the oxygen partial pressure rather than the oxygen flow. The optical properties of films were investigated by spectroscopic ellipsometry (SE). The films with a columnar structure demonstrate superior hardness and modulus as well as the high plasticity.

In order to understand the growth behavior of yttrium oxide films driven by thermodynamics and kinetics, two fundamental growth parameters, substrate heating and biasing, were investigated to control film structure and properties comprehensively. We observed two distinct areas, normal deposition area (area 1) and abnormal deposition area (etching area, area 2) at different substrate bias voltages regardless of the substrate temperature. X-ray diffraction (XRD) results show that heating promotes cubic phase formation, whereas ion bombardment induces monoclinic phase growth. Atomic force microscopy (AFM) measurements exhibit that the ions slightly enlarge the surface islands in area 1, whereas they flatten and smoothen the surface in area 2. X-ray photoelectron spectroscopy (XPS) results demonstrate that high temperature suppresses the physisorbed oxygen, and the ion bombardment favorably selects oxygen etching in area 1, causing excess oxygen vacancies. This selectivity almost disappears in area 2. Furthermore, the refractive index and band gap can be enhanced by both substrate temperature and bias voltage. The surface wettability of films can be modulated by the surface chemical composition.

In this paper, ZnO thin films with different thicknesses grown on Si (1 0 0) substrates by atomic layer deposition (ALD) method were annealed in nitrogen at the temperatures ranging from 200 to 900 °C. The influences of film thickness and annealing temperature on the structural and optical properties of the ZnO films were systematically investigated by XRD, SEM and RT-PL. All the ALD-ZnO thin films show polycrystalline hexagonal wurtzite structure and a high preferential c-axis orientation. The results show that the crystallinity quality and luminescence performance are both improved by increasing the film thickness. In addition, the loss of oxygen which results in the formation of oxygen vacancies (VO) is the main reason for the green emission dominating visible band of annealed ZnO thin films. The visible band is dominated by different kinds of defects including oxygen vacancies (VO and V O + ), and interstitial oxygen (IO) with increasing annealing temperature. High-quality ZnO thin films with good luminescence performance can be obtained for the films annealed at 800 °C in nitrogen.

Pt nanoparticles supported on Vulcan XC-72 carbon black have been synthesized by a facile solvothermal method. The obtained Pt/C catalysts are characterized by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), and transmission electron microscopy (TEM) analysis to identify Pt mean size and Pt content. The results of electrochemical measurements demonstrate that the Pt/C catalyst prepared at the reaction temperature of 140 °C and the reaction time of 2 h shows the biggest initial electrochemical area with an initial electrochemically active specific surface area (ESA) of 70.6 m2gPt−1, the highest electrocatalytic stability with an ESA loss of 48.7% after 1,000 CV cycles, and the best electrocatalytic activity and stability toward methanol oxidation reaction (MOR) with a specific activity of 0.6 mA cm−2 and a retention rate (the ratio of the final current density to the maximum current density) after 3,600 s of 42.8%. Moreover, the electrochemical performance of homemade Pt/C catalyst is superior to that of commercial Pt/C catalyst, suggesting that the solvothermal synthesis is a promising method for preparing Pt based catalyst.

Transparency in the infrared (IR) light region and high conductivity for electromagnetic (EM) shielding performance are contradicting properties for conventional window materials. It is challenging to explore a new class of materials with both IR transmittance and high electrical conductivity. Herein, middle-IR transmittance and EM-shielding performance are realized by graphene network fabrics (GNFs). GNFs are fabricated by chemical vapor deposition using copper mesh with different geometric constructions as the sacrificial substrate. The structure of GNFs endows the as-fabricated material high IR transmittance, good electrical conductivity, and EM-shielding efficiency. The grid parameter τ with regard to the square aperture and wire width exerts a profound effect on the EM-shielding performance. The highest EM-shielding efficiency is 12.86 dB at 10 GHz with a transmittance of 70.85% at 4500 nm. Meanwhile, the highest IR light transmittance is 87.85% with an EM-shielding efficiency of 4 dB. Based on the experimental and theoretical analyses, the EM-shielding efficiency is prominently dependent on microwave absorption.

In order to improve the oxidation resistance of carbon-bonded carbon fiber composites, a multi-composition coating consisting of multilayer ZrB2-SiC whiskers(SiCw)-borosilicate/ZrB2-MoSi2-SiCw-borosilicate was prepared on the surface of ZrB2-modified carbon-bonded carbon fiber composites (M-CBCF) by a rapid sintering method in trace amounts of oxygen environment. The inner-layer ZrB2-SiCw-borosilicate was first prepared by instantaneous vacuum-impregnation to seal the surface pores of M-CBCF, and the outer-layer ZrB2-MoSi2-SiCw-borosilicate was obtained by slurry spraying. The multilayer-coated composites were embedded in graphite powders and sintered at 1723 K for 10 min in atmosphere. The results showed that the prepared ZrB2-SiCw-borosilicate/ZrB2-MoSi2-SiCw-borosilicate coating had remarkable oxidation resistance and could protect M-CBCF from high-temperature erosion. The weight loss rate of the double-layer-coated composites was only 0.44% after oxidation for 100 min at 1773 K, while the weight loss rate of inner-layer-coated composites reached 25.35%. The oxidation resistance of multilayer coating was mainly attributed to the high viscosity of glass phase, matched thermal expansion coefficient and the toughening effect of SiCw.

Small but strong carbon nanotubes (CNTs) are fillers of choice for composite reinforcement owing to their extraordinary modulus and strength. However, the mechanical properties of the nanocomposites are still much below those for mechanical parameters of individual nanotubes. The gap between the expectation and experimental results arises not only from imperfect dispersion and poor load transfer but also from the unavailability of strong polymers that can be effectively utilized within the composites of nanotubes. Aramid nanofibers (ANFs) with analogous morphological features to nanotubes represent a potential choice to complement nanotubes given their intrinsic high mechanical performance and the dispersible nature, which enables solvent-based processing methods. In this work, we showed that composite films made from ANFs and multiwalled CNTs (MWCNTs) by vacuum-assisted flocculation and vacuum-assisted layer-by-layer assembly exhibited high ultimate strength of up to 383 MPa and Young's modulus (stiffness) of up to 35 GPa, which represent the highest values among all the reported random CNT nanocomposites. Detailed studies using different imaging and spectroscopic characterizations suggested that the multiple interfacial interactions between nanotubes and ANFs including hydrogen bonding and π-π stacking are likely the key parameters responsible for the observed mechanical improvement. Importantly, our studies further revealed the attractive thermomechanical characteristics of these nanocomposites with high thermal stability (up to 520 °C) and ultralow coefficients of thermal expansion (2-6 ppm·K(-1)). Our results indicated that ANFs are promising nanoscale building blocks for functional ultrastrong and stiff materials potentially extendable to nanocomposites based on other nanoscale fillers.

Nanoscale materials having size- and shape-dependent interactions with light provide flexible opportunities for harvesting solar energy. Photocatalysts based on semiconductor nanoparticles (NPs) have been the most effective materials for the conversion of light into chemical energy, the efficiency of which can be further enhanced by the incorporation of metallic NPs forming hybrid nanostructures. The structural parameters of not only constituent components but also the resultant hybrid nanostructures are critical for the optimization of photocatalytic performance of composite catalysts. Here we demonstrated the successful size control over ZnO hexagonal pyramids (HPs) for the first time. The smallest HPs showing the best photocatalytic properties were used for further Au attachment. Interestingly, we found that most of the Au NPs preferred to grow on the apexes of the basal plane. Very occasionally, Au NPs at the tip of ZnO HPs can be observed. The role of light in promoting the reduction of gold salt by ...

Sharp local structure, like the leading edge of hypersonic aircraft, confronts a severe aerodynamic heating environment at a Mach number greater than 5. To eliminate the danger of a material failure, a semi-active thermal protection system is proposed by integrating a metallic heat pipe into the structure of the leading edge. An analytical heat-balance model is established from traditional aerodynamic theories, and then thermal and mechanical characteristics of the structure are studied at Mach number 6–8 for three refractory alloys, Inconel 625, C-103, and T-111. The feasibility of this simple analytical method as an initial design tool for hypersonic aircraft is assessed through numerical simulations using a finite element method. The results indicate that both the isothermal and the maximum temperatures fall but the von Mises stress increases with a longer design length of the leading edge. These two temperatures and the stress rise remarkably at a higher Mach number. Under all investigated hypersonic conditions, with a 3 mm leading edge radius and a 0.15 m design length, the maximum stress exceeds the yield strength of Inconel 625 at Mach numbers greater than 6, which means a material failure. Moreover, both C-103 and T-111 meet all requirements at Mach number 6–8.

Ultra-high temperature ceramics (UHTCs) are composed of ZrC, ZrB2, HfC, HfB2, HfN and TaC and their melting points are higher than 3000℃. They are a vital class of high temperature structural materials and have attracted a great deal of attention in the past two decades in fundamental research and in technological applications. The ZrB2-SiC and HfB2-SiC UHTC composites, in particular, have excellent oxidation/ablation resistance, moderate thermal shock resistance and high strength retention at elevated temperature. They can survive oxidizing environments at temperatures of 2000℃ and higher. These properties make them the most promising materials for use in extreme environments such as hypersonic flight, atmospheric re-entry, and rocket propulsion. ZrB2-based and HfB2-based UHTCs have similar oxidation and ablation behaviors however as ZrB2-based UHTCs are lighter and less expensive, they are used as aerospace materials. Here we provide a comprehensive review of UHTC composites including their preparation, mechanical properties, thermal shock resistance, oxidation/ablation properties and thermal response, with a particular focus on ZrB2-based UHTCs. UHTCs were generally fabricated by hot pressing, spark plasma sintering, pressureless sintering, reactive hot pressing and sinter forging. Hot pressing is the dominant densification technique for the preparation of UHTCs. The flexural strength of UHTCs decreases with an increase in grain size and it exhibits a strong correlation with the size of the SiC particulates. However, the fracture toughness trend is not consistent with that of strength and therefore the matching of grain size becomes important. UHTCs display plasticity at elevated temperature and their brittle-to-ductile transition temperature (1500℃) strongly depends on the grain size and the purity of the grain boundaries. Catastrophic failure occurs easily during the heating or cooling process. The thermal shock resistance of UHTCs is a major issue for future applications. The methods used to improve the thermal shock resistance of UHTCs are summarized from critical thermal shock temperature and strength retention rate after thermal shock testing points of view. The oxidation behavior of UHTCs significantly depends on the temperature and the temperature limits of the applications of these materials are analyzed. The effect of the additives on the overall performance of the resultant composites as well as the relationship between material composition, microstructure and performance are also discussed in detail. This provides useful insights into effective design principles to optimize the overall structural performance of ultra-high temperature ceramic composites according to special service environments. The remaining challenges and future outlook of this field are also addressed.