Synthesis and ignition of energetic CuO/Al core/shell nanowires

Energetic thermites (mixtures of Al and metal oxides), due to their high energy densities, have broad applications in propulsion, thermal batteries, waste disposal, and power generation for micro systems. Reducing the sizes of Al and metal oxides down to the nanoscale has been shown to be effective in increasing their reaction rates and reducing their ignition delays. However, it remains a challenge to create mixtures of Al and metal oxides with nanoscale uniformity. Here we report synthesis and ignition studies on thermites with a new nanostructure, i.e., CuO/Al core/shell nanowires (NWs). The CuO NW cores were synthesized by the thermal annealing of copper films and served as templates for the deposition of Al shells by subsequent sputtering. The advantage of such a core/shell NW structure is that CuO and Al are uniformly mixed at the nanoscale. The onset temperatures of the exothermic reaction of the core/shell NWs were similar to those of nanoparticle (NP)-based thermites in terms of magnitude, insensitivity to equivalence ratios and sensitivity to heating rates. Moreover, the core/shell NW thermites, compared to NP-based thermites, exhibit greatly improved mixing uniformity and reduced activation energy for the thermite reaction.     

CuO/Al2O3、CuO/CeO2-Al2O3和CuO/La2O3-Al2O3催化剂中CuO物种被CO氧化的比较

用浸渍法制备了CuO/Al2O3 (Cu/Al)、CuO/CeO2- Al2O3 (Cu/CeAl)和CuO/La2O3-Al2O3(Cu/LaAl)催化剂. 通过原位XRD、Raman和H2-TPR方法， 对催化剂中的CuO物种以及CuO-Al2O3的固-固相反应进行了表征. 结果表明，对于Cu/Al催化剂，CuAl2O4存在于CuO与Al2O3层之间，CuO以高分散和晶相两种相态存在于催化剂的表层；对于Cu/CeAl催化剂，除了少量高分散和晶相的CuO存在于表层外，大部分CuO迁移到了CeO2的内层，     

A multi-step reaction model for ignition of fully-dense Al-CuO nanocomposite powders

A multi-step reaction model is developed to describe heterogeneous processes occurring upon heating of an Al-CuO nanocomposite material prepared by arrested reactive milling. The reaction model couples a previously derived Cabrera-Mott oxidation mechanism describing initial, low temperature processes and an aluminium oxidation model including formation of different alumina polymorphs at increased film thicknesses and higher temperatures. The reaction model is tuned using traces measured by differential scanning calorimetry. Ignition is studied for thin powder layers and individual particles using respectively the heated filament (heating rates of 10³–10⁴ K s^?1) and laser ignition (heating rate ～10⁶ K s^?1) experiments. The developed heterogeneous reaction model predicts a sharp temperature increase, which can be associated with ignition when the laser power approaches the experimental ignition threshold. In experiments, particles ignited by the laser beam are observed to explode, indicating a substantial gas release accompanying ignition. For the heated filament experiments, the model predicts exothermic reactions at the temperatures, at which ignition is observed experimentally; however, strong thermal contact between the metal filament and powder prevents the model from predicting the thermal runaway. It is suggested that oxygen gas release from decomposing CuO, as observed from particles exploding upon ignition in the laser beam, disrupts the thermal contact of the powder and filament; this phenomenon must be included in the filament ignition model to enable prediction of the temperature runaway.     

First-principles calculations for the elastic properties of Ni-base model superalloys: Ni/Ni3Al multilayers

A model system consisting of Ni[001](100)/Ni3Al[001](100) multi-layers are studied using the density functional theory in order to explore the elastic properties of single crystal Ni-based superalloys. Simulation results are consistent with the experimental observation that rafted Ni-base superalloys virtually possess a cubic symmetry. The convergence of the elastic properties with respect to the thickness of the multilayers are tested by a series of multilayers from 2γ′+2γ to 10γ′+10γ atomic layers. The elastic properties are found to vary little with the increase of the multilayer’s thickness. A Ni/Ni3Al multilayer with 10γ′+10γ atomic layers (3.54 nm) can be used to simulate the mechanical properties of Ni-base model superalloys. Our calculated elastic constants, bulk modulus, orientation-dependent shear modulus and Young’s modulus, as well as the Zener anisotropy factor are all compatible with the measured results of Ni-base model superalloys R1 and the advanced commercial superalloys TMS-26, CMSX-4 at a low temperature. The mechanical properties as a function of the γ′ phase volume fraction are calculated by varying the proportion of the γ and γ′ phase in the multilayers. Besides, the mechanical properties of two-phase Ni/Ni3Al multilayer can be well predicted by the Voigt-Reuss-Hill rule of mixtures.     

Structure evolution and mechanical properties enhancement of Al/AlN multilayer

A set of Al/AlN multilayers with various modulation periods were prepared using DC magnetron sputtering method. Low angle X-ray diffraction (LAXRD) was used to analyze the layered structure of multilayers. The phase structure of the films was investigated with grazing angle X-ray diffraction (GAXRD). LAXRD results indicate that well-defined multilayer modulation structures are formed for the relatively larger modulation periods. However, the loss of mutilayered structure is detected in the multilayer with low modulation period. A very wide amorphous peak is observed in multilayer with modulation period of 4 nm. The multilayers show obvious crystallization at larger modulation periods, however, the diffraction peaks are much wider than the Al single layer because of the interruption of the continuous columnar grain growth by alternating deposition processes. Nanoindentation experiments were performed to study the mechanical properties as a function of multilayer modulation period. It is found that the hardness of the multilayers is greater than the hardness calculated from rule of mixtures. With the modulation periods adjusted, the multilayers are even harder than its hard component (AlN). A maximum hardness of 24.9 GPa, about 1.9 times larger than its hard component (AlN) and 3.7 times larger than the hardness calculated from the rule of mixtures, is found at the multilayer with modulation period of 16 nm. The wear test results show that the multilayers possess lower and stable friction coefficient, and superior wear properties.     

Al/ZnO/Al薄膜的结构与磁性分析

采用直流磁控溅射的方法制备了Al/ZnO/Al纳米薄膜,并对薄膜分别在真空及空气中进行退火处理.利用X射线衍射仪(XRD)和物理性能测量仪(PPMS)分别对薄膜样品的结构和磁性进行了表征.XRD分析表明,不同的退火氛围对薄膜的微结构有着很大的影响.采用了一种新的修正方法对磁测量结果进行修正,计算了基底拟合误差的最大值,并对修正后样品的磁性进行了分析.结果显示,室温铁磁性可能与Al和ZnO基体之间发生的电荷转移以及在不同退火氛围下Al在ZnO晶格中的地位变化有关. 关键词： Al/ZnO/Al薄膜 铁磁性 磁性表征     

ZnO/CuO 核壳结构纳米线光致发光性能 与CuO壳层厚度的关系

通过分别生长核层与壳层制备出了ZnO/CuO核壳结构的纳米线。形貌和结构分析表明,ZnO核为单晶纳米线而CuO则以多晶形式覆盖在核层表面上。光致发光(PL)研究表明,ZnO纳米线PL强度随CuO壳层厚度的变化而变化。当壳层比较薄时ZnO的PL强度增大,这主要是由于CuO壳层对ZnO核层的修饰减少了表面态,而当壳层厚度增加到一定程度时,ZnO的PL强度不再变化,这主要是由于在核壳结构中形成了type-I型结构的原因。我们对这一现象做了详细的讨论。     

Structure and mechanical properties of Al/AlN multilayer with different AlN layer thickness

Nanometer scale Al/AlN multilayers have been prepared by dc magnetron sputtering technique with a columnar target. A set of Al/AlN multilayers with the Al layer thickness of 2.9 nm and the AlN layer thickness variation from 1.13 to 6.81 nm were determined. Low angle X-ray diffraction (LAXRD) was used to analyze the layered structure of multilayers. The phase structure of the coatings was investigated with grazing angle XRD (GAXRD). Mechanical properties of these multilayers were thoroughly studied using a nanoindentation and ball-on-disk micro-tribometer. It was found that the multilayer hardness and reduced modulus showed no strong dependence on the AlN layer thickness. Al2.9 nm/AlN1.13 nm multilayer had more excellent tribological properties than single layers and other proportion multilayers with a lowest friction coefficient of 0.15. And the tribological properties of all the multilayers are superior to the AlN single layer.     

Structural and magnetic properties of RF sputtered FePt/Fe multilayers

Series of [FePt(4min)/Fe(t_Fe)]₁₀ multilayers have been prepared by RF magnetron sputtering and post-annealing in order to optimize their magnetic properties by structural designs. The structure, surface morphology, composition and magnetic properties of the deposited films have been characterized by X-ray diffractometer (XRD), Rutherford backscattering (RBS), scanning electron microscope (SEM), energy dispersive X-ray spectroscope (EDX) and vibrating sample magnetometer (VSM). It is found that after annealing at temperatures above 500 °C, FePt phase undergoes a phase transition from disordered FCC to ordered FCT structure, and becomes a hard magnetic phase. X-ray diffraction studies on the series of [FePt/Fe]_n multilayer with varying Fe layer thickness annealed at 500 and 600 °C show that lattice constants change with Fe layer thickness and annealing temperature. Both lattice constants a and c are smaller than those of standard ones, and lattice constant a decreases as Fe layer deposition time increases. Only a slight increase in grain size was observed as Fe layer decreased in samples annealed at 500 °C. However, the increase in grain size is large in samples annealed at 600 °C. The coercivities of [FePt/Fe]_n multilayers decrease with Fe layer deposition time, and the energy product (BH)_max reaches a maximum in the samples with Fe layer deposition time of 3 min. Comparison of magnetic properties with structure showed an almost linear relationship between the lattice constant a and the coercivities of the FePt phase.     

Fabrication of Al/AlOx/Al Josephson junctions and superconducting quantum circuits by shadow evaporation and a dynamic oxidation process

Besides serving as promising candidates for realizing quantum computing,superconducting quantum circuits are one of a few macroscopic physical systems in which fundamental quantum phenomena can be directly demonstrated and tested,giving rise to a vast field of intensive research work both theoretically and experimentally.In this paper we report our work on the fabrication of superconducting quantum circuits,starting from its building blocks:Al/AlOx /Al Josephson junctions.By using electron beam lithography patterning and shadow evaporation,we have fabricated aluminum Josephson junctions with a controllable critical current density(jc) and wide range of junction sizes from 0.01 μm2 up to 1 μm2.We have carried out systematical studies on the oxidation process in fabricating Al/AlOx/Al Josephson junctions suitable for superconducting flux qubits.Furthermore,we have also fabricated superconducting quantum circuits such as superconducting flux qubits and charge-flux qubits.     

Thermal stability and reaction properties of passivated Al/CuO nano-thermite

Thermal stability and reaction properties of Al-CuO system, a mixture of 50-200 nm aluminum nanoparticles passivated by nitrocellulose and 12 nm copper (II) oxide, were investigated with microstructure characterization, differential thermal analysis (DTA), and thermogravimetric analysis (TGA). Transmission electron microscopy observation confirmed that the passivation coating successfully hinders the oxidization. TGA revealed that the passivation shell does not influence the ignition temperature of the thermite reaction. Reaction chemistry of the nano-thermite was elucidated by heating the composite both in inert ambient and vacuum. It was found that the thermite reaction composes of three continuing steps: At 570 °C, Al is oxidized into Al₂O₃ by reacting with CuO, which forms Cu₂O and produces a significant amount of heat. Subsequently two endothermic reactions occur. Starting at 800 °C, alumina reacts with Cu₂O and forms CuAlO₂. Above this temperature CuAlO₂ will decompose and eventually produce alumina, Cu, and O₂ at 1000 °C. Since the nano-thermite reaction pathway differs greatly from bulk thermite reactions, these results are important to develop a nano-thermite platform that can be used for a novel low cost, low temperature, and copper based microjoining and advance IC packaging.     

Fabrication of CuO/T-ZnOw nanocomposites using photo-deposition and their photocatalytic property

CuO/tetrapod-like ZnO whisker (T-ZnOw) nanocomposites were successfully synthesized using a simple photo-deposition method. Some nanocomposites exhibit remarkably improved photocatalytic property, while the extents of the improvements vary with different Cu/Zn molar ratios and polyethylene glycol (PEG) concentrations. Moreover, it is found that excessively high Cu/Zn molar ratio or PEG concentration would reduce the photocatalytic property of the nanocomposites. A direct relationship between the morphology and the photocatalytic property of CuO/T-ZnOw was established and then analyzed by discussing the photocatalytic mechanism of the CuO/T-ZnOw nanocomposites.     

微型平面复合薄膜电爆炸开关的设计和研究

开关技术是影响爆炸箔起爆系统可靠作用、微型化、低能化、集成化的关键技术。电爆炸平面开关是利用强脉冲电流使触发极金属桥箔发生电爆炸,产生高温高压等离子体,使爆炸桥区两侧的电极导通。基于微加工技术,采用Al/CuO复合薄膜材料作为触发电极,设计制造了微型平面复合薄膜电爆炸开关。采用扫描电子显微镜、差示扫描量热法和光谱谱线测温研究了触发极Al/CuO复合薄膜的形貌、反应性和电爆炸等离子体温度,通过放电电流测试研究了开关性能。结果表明,在主回路电压2000 V时,开关输出电流峰值约为1938 A,上升时间390 ns,性能优于仅以铜薄膜为触发电极的电爆炸平面开关。     

Effects of thermal annealing on structural and magnetic properties of thin Pt/Cr/Co multilayers

Thermal stability of thin Pt/Cr/Co multilayers and the subsequent changes in their structural, magnetic, and magneto-optical properties are reported. We observe CoCrPt ternary alloy phase formation due to annealing at temperatures about 773 K, which is accompanied by enhancement in the coercivity value. In addition, 360° domain wall superimposed on a monodomain like background has been observed in the pristine multilayer, which changes into a multidomain upon annealing at 873 K.     

Surface and interfacial structural characterization of MBE grown Si/Ge multilayers

Si/Ge multilayer structures have been grown by solid source molecular beam epitaxy (MBE) on Si (1 1 1) and (1 0 0) substrates and were characterized by high-resolution X-ray diffraction (XRD), atomic force microscopy (AFM), high-depth-resolution secondary ion mass spectroscopy (SIMS) and cross-section high-resolution transmission electron microscopy (HRTEM). A reasonably good agreement has been obtained for layer thickness, interfacial structure and diffusion between SIMS and HRTEM measurements. Epitaxial growth and crystalline nature of the individual layer have been probed using cross-sectional HRTEM and XRD measurements. Surface and interface morphological studies by AFM and HRTEM show island-like growth of both Si and Ge nanostructures.     

Annealing studies of Ti/Al multilayer film by slow positron beam

Single detector and coincidence Doppler broadening (CDB) spectroscopy measurements using slow positron beam were carried out to study as-deposited and annealed Ti/Al multilayer films. The changes of the film structure and defects in each layer by heat treatment have been investigated through the analysis of Doppler broadening lineshape variation. The coincidence Doppler broadening measurements revealed that Ti is the dominant diffusion species during the alloying process of Ti/Al by high temperature annealing. These results highlight the potential of slow positron beam in characterizing the vacancy-type defects evolution and mechanism of interlayer diffusion in Ti/Al multilayer film.     

CoFe/TiZr多层膜材料界面结构与性能的极化中子反射研究

利用极化中子反射技术较系统地研究了CoFe/TiZr复合多层膜材料界面结构，结果表明.1)从多层膜超镜传输特性角度考虑，等厚对层不如非等厚对层膜结构好.2)等厚对层的最佳退火温度约250℃，非等厚对层退火温度低于250℃影响不明显，等厚和非等厚对层经350℃退火后膜层变化严重.3)从布拉格峰位变化看，随着退火温度的升高，等厚对层膜的厚度先变小后变大；非等厚对层与之相反.     

CoFe/TiZr多层膜材料界面结构与性能的极化中子反射研究

利用极化中子反射技术较系统地研究了CoFe/TiZr复合多层膜材料界面结构,结果表明.1)从多层膜超镜传输特性角度考虑,等厚对层不如非等厚对层膜结构好.2)等厚对层的最佳退火温度约250℃,非等厚对层退火温度低于250℃影响不明显,等厚和非等厚对层经350℃退火后膜层变化严重.3)从布拉格峰位变化看,随着退火温度的升高,等厚对层膜的厚度先变小后变大;非等厚对层与之相反. 关键词： CoFe/TiZr多层膜 退火影响 膜层结构 极化中子反射     

Synthesis of CuO/g-C3N4 Composite with High Anti-Interference Ability for Enhanced Fenton-Like Catalysis

The combination of semiconductors and transition metal compounds for Fenton-like application has been widely reported. However, there are still some problems that can be further studied such as the optimization of metal species and in-depth research of mechanism. In this paper, using melamine and copper acetate as raw materials, a kind of composite of copper oxide and graphitic carbon nitride (CuO/g-C₃N₄) is synthesized by a facile hydrothermal method. The synthetic conditions such as type of transition metal salt and ratio of raw material are further optimized. With the presence of H₂O₂, the CuO/g-C₃N₄ composite shows exceptional broad-spectrum Fenton-like catalytic performance against the organic dyes in aqueous solution within a wide pH range, and the highest degradation rate of organic dyes can reach 99% within 10 min. After eight times of recycling, the catalytic activity of the composite can still remain more than 85%. More importantly, the CuO/g-C₃N₄ composite presented excellent anti-interference ability toward heavy metal ions and complex pollutants. Finally, the enhanced Fenton-like catalytic mechanism is illustrated in detail.     

A self-driven photodetector based on a SnS2/WS2 van der Waals heterojunction with an Al2O3 capping layer

Photodetectors based on two-dimensional (2D) materials have attracted considerable attention because of their unique properties. To further improve the performance of self-driven photodetectors based on van der Waals heterojunctions, a conductive band minimum (CBM) matched self-driven SnS₂/WS₂ van der Waals heterojunction photodetector based on a SiO₂/Si substrate has been designed. The device exhibits a positive current at zero voltage under 365 nm laser illumination. This is attributed to the built-in electric field at the interface of the SnS₂ and WS₂ layer, which will separate and transport the photogenerated carriers, even at zero bias voltage. In addition, the Al₂O₃ layer is covered by the surface of the SnS₂/WS₂ photodetector to further improve the performance, because the Al₂O₃ layer will introduce tensile stress on the surface of the 2D materials leading to a higher electron concentration and smaller effective mass of electrons in the films. This work provides an idea for the research of self-driven photodetectors based on a van der Waals heterogeneous junction.