Resonant tunnelling leakage in planar metal–oxide–metal nanojunctions

The leakage–current in planar nanojunctions, usually employed to realize molecular field-effect devices, is investigated. Resonances are observed on p-doped substrates when the voltage drop between drain and gate electrodes is around 1.1 V. These resonances are related to resonant tunneling via impurity atoms and are otherwise not observed on n-type substrates.     

Synthesis and processing of ceramic–metal composites by reactive metal penetration

Molten aluminum reduces and penetrates silicate ceramics to produce a metal–ceramic composite which yields an Al₂O₃ skeleton infiltrated with a solidified Al–Si alloy. Penetration experiments have been used to study the influence of p(O₂), temperature and substrate composition on penetration kinetics and composite microstructure. The limiting kinetic step for Al penetration is the chemical reaction between Al and the ceramic. For dense substrates the maximum reaction rates are observed between 1000–1200°C and are independent of p(O₂). For porous substrates it is necessary to reach a critical temperature or p(O₂), before infiltration starts. Increasing the Si concentration in the molten Al results in the reduction of the reaction rates.     

Synthesis of nanoparticles composed of silver and copper for metal–metal bonding

A metal–metal bonding technique is described that uses nanoparticles composed of silver and copper. Colloid solutions of nanoparticles with an Ag content of 0–100?mol% were prepared by simultaneous reduction of Ag⁺ and Cu²⁺ using hydrazine with polyvinylpyrrolidone and citric acid as stabilisers. The nanoparticles ranged in size from 34 to 149?nm depending on the Ag content. Copper discs were strongly bonded at 400°C for 5?min under 1.2?MPa pressure in hydrogen gas; the maximum shear strength was as high as 23.9?MPa. The dependence of shear strength on the Ag content was explained by a mismatch between the d-spacings of Cu metal and Ag metal.     

Dual wavelength demultiplexer based on metal–insulator–metal plasmonic circular ring resonators

Abstract

In this paper, we investigated a plasmonic demultiplexer structure based on Metal–Insulator–Metal (MIM) waveguides and circular ring resonators. In order to achieve the structure of demultiplexer, two improved ring resonators have been used, which input and outputs MIM waveguides coupled by the ring resonators. To improve the transmission efficiency, a reflector was introduced at the right end of the input and output waveguides. By substituting the ring core with dielectric, the possibility of tuning the resonance wavelength of the proposed structure is illustrated, and the effect of various parameters such as radius and refractive index in transmission efficiency is studied in detail. This is useful for the design of integrated circuits in which it is not possible to extend the dimension of the ring resonator to attain a longer resonance wavelength. Transmission efficiency and quality factor of the single ring are 84% and 110, respectively. The simulation results using finite difference time domain method shows that in the proposed demultiplexer, which is composed of two rings with different core refractive indexes, the average power efficiency, bandwidth for each output channel, and the mean value of crosstalk are estimated 80%, 17 nm, and ?26.95 dB, respectively. It is revealed that the significant features of the device are high transmission efficiency, low crosstalk, high-quality factor, and tunability for desired wavelengths. Therefore, the proposed structure has the potential to be applied in plasmonic integrated circuits.     

Nanostructures bilayer ZnO/MgO dielectrics for metal–insulator–metal capacitor applications

Bilayer ZnO/MgO dielectrics for metal–insulator–metal (MIM) capacitor application were successfully deposited using simple chemical technique which is sol–gel spin coating method with different annealing temperatures. Important criteria in determining good dielectric layer have been investigated which include structural, electrical and dielectric properties. Cubic-like grain was observed for films annealed at 400 and 425 °C which enhance the carrier density and polarization that resulted in high k value produced. Bilayer film annealed at 475 °C improved in small surface roughness (17.629 nm), minimum leakage current density (~10^?8 A cm^?2) and high resistivity (3.14 × 10⁵ Ω cm). Dielectric constant, k was varied with frequency and k value was found to be 5.09 at 10 kHz. The results obtained in this study indicated that film annealed at temperature of 475 °C is suitable to be used as dielectrics for MIM capacitor application.     

Transition metal oxides – Thermoelectric properties

Transition metal oxides (TMOs) are a fascinating class of materials due to their wide ranging electronic, chemical and mechanical properties. Additionally, they are gaining increasing attention for their thermoelectric (TE) properties due to their high temperature stability, tunable electronic and phonon transport properties and well established synthesis techniques. In this article, we review TE TMOs at cryogenic, ambient and high temperatures. An overview of strategies used for morphological, compositing and stoichiometric tuning of their key TE parameters is presented. This article also provides an outlook on the current and future prospects of implementing TMOs for a wide range of TE applications.     

Special features of the interface between glass–metal coatings of superhard materials powders and metal matrices

The main results of the investigation of special features of the formation of the interface between the glass coating on the diamond and cBN powders with metals, that are bonds of grinding tools are described and generalized. It has been shown that the mutual diffusion occurring in the contact zone results in the increase of the adhesion at the interphase boundary, which ensures a strong fastening of a metal coating on a glass aggregate and the glass aggregate itself in a metal bond.     

Graphene-reinforced metal matrix nanocomposites – a review

The research works of graphene-reinforced metal matrix composites will be summarised in this paper. Comparatively, much less research works have been undertaken in this field. Graphene has been thought to be an ideal reinforcement material for composites due to its unique two-dimensional structure and outstanding physical and mechanical properties. It is expected to yield structural materials with high specific strength or functional materials with exciting thermal and electrical characteristics. This paper will introduce all kinds of graphene-reinforced metal matrix composites that have been studied. The microstructure and mechanical properties, processing techniques, graphene dispersion, strengthening mechanisms, interfacial reactions between graphene and the metal matrix and future research works in this field will be discussed.     

Assembled nanoparticle films with crown ether–metal ion “sandwiches” as sensing mechanisms for metal ions

Specialized nanoparticles known as monolayer-protected clusters (MPCs) were affixed with metal selective crown ether (CE) functional groups and assembled into novel thin films to form potential metal ion sensing materials. Films of MPCs modified with potassium specific 15-crown-5 ligands (CE-MPCs) were successfully assembled using both dithiol linkages and ester-coupling reactions. Film responses to potassium are observed spectroscopically as the manifestation of changing interparticle spacing within a film in the presence and absence of potassium. Growth dynamics, film structure, and metal response are examined. Additionally, the important role of flexibility, especially in the interconnectivity of the CE-MPCs within the film and between the CE groups themselves, is experimentally identified.

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Processing of Nb–Cu metal matrix composites

Abstract

During the development of new processing routes for Nb₃Sn superconductor, factors influencing the workability of two-phase metallic composites have been investigated. The ease with which such composites can be fabricated depends strongly on the relative hardnesses of the phases. Production of a regular, uniform filamentary structure is promoted by low hardness ratios in the initial composite.

MST/547     

Interface-dominated mechanical behavior in advanced metal matrix composites

Metal matrix composites(MMCs)incorporate a reinforcing or functional secondary phase into a metal matrix to achieve specific properties.Of the parameters which may affect the mechanical behavior of MMCs,the structure and properties of the reinforcement/matrix interface play a crucial role.This article reviews recent developments in measuring the interfacial properties in advanced MMCs,with an emphasis on the use of micro-/nano-mechanical testing approaches.It is shown that,with the novel in situ and ex situ experimental capability,researchers can now obtain some of the critical interfacial properties as well as the effects of reinforcement/matrix interfaces on the composites’deformation and failure mechanisms that were unattainable previously by conventional methodologies.Moreover,the micro-/nano-mechanical testing platform allows for both fundamental and applied research on the composites’mechanical performance under service conditions,which is considered a promising and emerging research direction.     

Polarization at metal–biomolecular interfaces in solution

Metal surfaces in contact with water, surfactants and biopolymers experience attractive polarization owing to induced charges. This fundamental physical interaction complements stronger epitaxial and covalent surface interactions and remains difficult to measure experimentally. We present a first step to quantify polarization on even gold (Au) surfaces in contact with water and with aqueous solutions of peptides of different charge state (A3 and Flg-Na3) by molecular dynamics simulation in all-atomic resolution and a posteriori computation of the image potential. Attractive polarization scales with the magnitude of atomic charges and with the length of multi-poles in the aqueous phase such as the distance between cationic and anionic groups. The polarization energy per surface area is similar on aqueous Au {1 1 1} and Au {1 0 0} interfaces of approximately −50 mJ m⁻² and decreases to −70 mJ m⁻² in the presence of charged peptides. In molecular terms, the polarization energy corresponds to −2.3 and −0.1 kJ mol⁻¹ for water in the first and second molecular layers on the metal surface, and to between −40 and 0 kJ mol⁻¹ for individual amino acids in the peptides depending on the charge state, multi-pole length and proximity to the surface. The net contribution of polarization to peptide adsorption on the metal surface is determined by the balance between polarization by the peptide and loss of polarization by replaced surface-bound water. On metal surfaces with significant epitaxial attraction of peptides such as Au {1 1 1}, polarization contributes only 10–20% to total adsorption related to similar polarity of water and of amino acids. On metal surfaces with weak epitaxial attraction of peptides such as Au {1 0 0}, polarization is a major contribution to adsorption, especially for charged peptides (−80 kJ mol⁻¹ for peptide Flg-Na₃). A remaining water interlayer between the metal surface and the peptide then reduces losses in polarization energy by replaced surface-bound water. Computed polarization energies are sensitive to the precise location of the image plane (within tenths of Angstroms near the jellium edge). The computational method can be extended to complex nanometre and micrometer-size surface topologies.     

Preparation of γ-alumina precursors for metal reinforcement

In the metal matrix composite field, both fine (<0.5 µm) and coarse, crystalline, calcined aluminas with narrow or broad particle size distributions, are being used as reinforcement phase. The effect was studied of the preparation method of fine boehmite (-AlOOH), precursor of the -Al₂O₃, on the product morphology. The material was produced by heating three kinds of hydrothermal precursors at different pH, and for 2 h at 200°C, using constant stirring. Under the conditions investigated (i.e., 0.12 mol/dm³ of Al(OH)₃ and only diluted NaOH and HNO₃ solutions used to adjust the pH of slurry), the pH of hydrothermal slurry influenced the product morphology; in contrast, the three different hydrothermal precursors, namely dry aluminum hydroxide gel, fresh aluminum hydroxide precipitate and gibbsite reagent powders, had only a little effect on the product morphology. The dehydration/transformation mechanism from Al(OH)₃ to -AlOOH is believed to be dissolution/reprecipitation rather than a direct dehydration.     

Mechanical behaviour of metal–matrix composite deposits

The electroplating technique is used for producing thin sheets of copper- or nickel-based composites containing different volume fractions of -alumina dispersions. The microhardness and tensile behaviour of such composites, in both the as-deposited and the annealed state, are characterized. The strengthening mechanism of electroplated composites is found to be a combination of Orowan-type strengthening and the Hall–Petch effect.     

Tunable narrow band filter based on a surface plasmon polaritons Bragg grating with a metal–insulator–metal waveguide

A tunable narrow band filter based on a Bragg grating with surface plasmon polaritons is developed and investigated numerically by using the finite-difference time-domain method. A defect state with narrow transmission peak (about 15?nm) is shown to appear in the bandgap by introduction of a defect into the Bragg grating, which can thus be used as filtering device. We also show that double-channel filtering can be realized by introducing two defects into the Bragg grating. The resonant wavelengths in the bandgap are related to the position of defects and the refractive index of the insulator. Our results may provide useful information in the design of tunable narrow band filters in nano-circuits.     

Pressure infiltration processes to synthesize metal matrix composites – A review of metal matrix composites,the technology and process simulation

Metal matrix composites (MMCs) acquire their improved physical and mechanical properties through the careful reinforcement of their matrices by a variety of light but strong and stable reinforcement materials. The pressure infiltration process (PIP) is one of the most important techniques used for making MMCs with a high reinforcement content in which a molten metal or alloy is injected and solidified in a mold packed with continuous or discontinuous reinforcement materials. Several factors affect the quality of MMCs made by this process. These include, but are not limited to, the reinforcement type, preform geometry, applied pressure and pressure control, as well as the transport phenomena of the molten metal. This paper presents a review of the various aspects of MMCs, the process in terms of the technological details, the latest developments in the reinforcement materials used and the simulation models developed for pressure infiltration manufacturing of MMCs.     

Alatiacts of Selected Aiticles on metal Published in China

89A0001 Internal Friction Associated withMartensitic Transformation of As-cast Mn-CuAlloys Internal friction of martensitictransformation of as-cast Mn-Cu alloys with90%Mn was studied. Results show that the peaktemperature of the stable peak (T=0) at lowfrequencies is independent of the measuringfrequency, but the peak height decreases withincreasing frequency. It is, therefore, notof a static hysteresis mechanism. The peakheight is dependent on T and f at a constantheating or cooling rate, but it does not showa linear relationship with T, 1/f or T/f. Thepeak height is independent of the strain amplitudein the yange (A_ε: 1× 10~(-5)--1×10~(-4)). Consequentlythe low frequency internal friction of martensitictransformation is not only a volume effect,but also a surface effect connected with coherentboundaries. XIE Cunyi, WEN Yiting and ZHU     

Post-impact fatigue damage growth in fiber–metal laminates

Fiber–metal laminates (FMLs) are a family of hybrid materials currently being considered for use in airframe structural applications. Post-impact fatigue strength tests were carried out on several varieties of GLAss REinforced (GLARE) aluminum laminates. The panels were impacted in a drop weight impact tower located at the Institute for Aerospace Research of the National Research Council of Canada. Observations made by other researchers that the internal impact damage in FMLs is confined to the immediate impact site were confirmed. The impacted specimens were cycled in tension–tension fatigue until failure. Cracks developed along side the dent and also at the edges of the gauge section of the specimen. Aluminum baseline specimens had significantly lower fatigue lives than the FML specimens. The stress-state surrounding the dent is complicated and contributed to unusual fatigue crack initiation behavior in some GLARE variants.     

Mechanical properties of nanocomposite metal–ceramic thin films

Thin film composites consisting of metallic nanocrystals embedded in an insulating host have been synthesized using alternating-target pulsed laser deposition of Ni and Al₂O₃ on silicon (100) substrate. The evaluation of structural quality of the thin film composites using high resolution transmission electron microscopy and scanning transmission electron microscopy with atomic number contrast has revealed the formation of a biphase system with thermodynamically driven segregation of Ni and alumina during pulsed laser deposition. The best hardness values of the thin film composites, measured using nanoindentation techniques, were found to be 20–30% larger than pure alumina films fabricated under identical conditions. Fracture toughness measurements of the composite showed slight toughening due to embedding of Ni nanoparticles.