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Friction stir back extrusion (FSBE) is a technique for lightweight metal extrusion. The frictional heat and severe plastic deformation of the process generate an equiaxed refined grain structure because of dynamic recrystallization. Previous studies proved that the fabrication of tube and wire structures is feasible. In this work, hollow cylindrical billets of 6063-T6 aluminum alloy were used as starting material. A relatively low extrusion ratio allows for a temperature and deformation gradient through the tube wall thickness to elucidate the effect of heat and temperature on the microstructure evolution during FSBE. The force and temperature were recorded during the processes. The microstructures of the extruded tubes were characterized using an optical microscope, energy-dispersive x-ray spectroscopy, electron backscatter diffraction, and hardness testing. The process reduced the grain size from 58.2 μm to 20.6 μm at the inner wall. The microhardness of the alloy was reduced from 100 to 60–75 HV because of the process thermal cycle. [ABSTRACT FROM AUTHOR]

We report on the impact of laser processing on material and device performance characteristics for integrated energy applications. A femtosecond laser was used for development of flexible and transparent supercapacitors, while a nanosecond laser was successfully exploited for high-performance Al-air battery development. A laser direct-write process enabled integration of a three-dimensional-structured micro-supercapacitor on flexible polymer substrate, exhibiting peak specific capacitance of 42.6 mF/cm2 at current density of 0.1 mA/cm2. Femtosecond laser processing was also exploited for development of a novel transparent supercapacitor on silk substrate. The MnO2-coated transparent supercapacitors exhibited high transmittance exceeding 59%. Laser processing in combination with printing technique was used for development of a novel Al-air battery. The nanosecond laser process was effective in sintering the anode printed using Al nanoparticle ink. The efficiency of the laser sintering process was reflected in good battery discharge performance. [ABSTRACT FROM AUTHOR]

Stretchable electronic sensing devices are defining the path toward wearable electronics. High-performance flexible strain sensors attached on clothing or human skin are required for potential applications in the entertainment, health monitoring, and medical care sectors. In this work, conducting copper electrodes were fabricated on polydimethylsiloxane as sensitive stretchable microsensors by integrating laser direct writing and transfer printing approaches. The copper electrode was reduced from copper salt using laser writing rather than the general approach of printing with pre-synthesized copper or copper oxide nanoparticles. An electrical resistivity of 96 μΩ cm was achieved on 40-μm-thick Cu electrodes on flexible substrates. The motion sensing functionality successfully demonstrated a high sensitivity and mechanical robustness. This in situ fabrication method leads to a path toward electronic devices on flexible substrates. [ABSTRACT FROM AUTHOR]

The effect of trace amounts of rare earth element Ce on the wettability, mechanical properties and microstructure of Ag17CuZnSn filler metal was investigated systematically by means of microstructure and spectroscopic characterizations. H62 brass and 304 stainless steel were brazed with Ag17CuZnSn-xCe filler metals. The results indicate that wettability and oxidation resistance of filler metal are remarkably improved with adding trace amount of Ce. The shear strength of brazed joint increases 29% compared to that of brazed joint without adding Ce. Moreover, it is observed that the trace amount of Ce in Ag17CuZnSn filler metal refines the brazed joint matrix microstructure. The elements diffusion is examined during the brazing process. More Ce can diffuse into the stainless steel than that of either Cu or Zn. Compared to the Cu solid solution, Fe prefers to diffuse into the Ag solid solution. When the Ce content is 0.3 wt.%, some bright and brittle Ce-bearing particles appear in the bottom of dimples which deteriorate the shear strength of brazed joint. The results of this study can stimulate the use of low-silver brazing filler metals for various applications. [ABSTRACT FROM AUTHOR]

Silver nanoparticle surface morphologies can be controlled using ultraviolet light or visible light-emitting diode (LED)-assisted photonic reduction of Ag ions in solution. Ultraviolet nanosecond laser interference lithography (LIL) is a cost-effective method for fabricating periodic structures in a polymer matrix, and in this work, we combine with photonic reduction to produce novel nanostructured substrates. Differing reduction times result in differing fringe widths and nanoparticle sizes, with nanoparticle shape gradually changing from spherical to plate-shaped with increasing (365 to 615 nm) excitation wavelengths. Such nanostructured substrates, when utilized for surface-enhanced Raman spectroscopy (SERS), realized analytical enhancement factors for naproxen of about 10 with plate-shaped nanoparticles, which was at least ten times greater than the enhancement afforded by spherical nanoparticles. A three-dimensional finite element method simulating localized surface plasmon resonance properties of these controlled silver structures demonstrated nanostructured plates effectively enhanced local electrical fields. Our results demonstrate that multi-wavelength photonic reduction integrated with LIL is an excellent means of providing sensitive substrates for SERS. [ABSTRACT FROM AUTHOR]

Potential applications for three-dimensional microstructure devices developed rapidly across numerous fields including microoptics, microfluidics, microelectromechanical systems, and biomedical devices. Benefiting from many unique fabricating advantages, internal manufacturing methods have become the dominant process for three-dimensional microstructure device manufacturing. This paper provides a brief review of the most common techniques of femtosecond laser three-dimensional internal manufacturing (3DIM). The physical mechanisms and representative experimental results of 3D manufacturing technologies based on multiphoton polymerization, laser modification, microexplosion and continuous hollow structure internal manufacturing are provided in details. The important progress in emerging applications based on the 3DIM technologies is introduced as well. [ABSTRACT FROM AUTHOR]

During the last two decades, considerable efforts have been made to explore new generations of interconnecting materials and printed lines to replace the traditionally used toxic lead-based solders in electronic packaging industries. Accordingly, development of electrically conductive adhesives (ECAs) with high electrical conductivity has become an interesting and urgent research venue in this field. Recently, the incorporation of nano-sized conductive fillers inside the conventional formulation of ECAs has drawn considerable attention as an attempt to increase their electrical conductivity. In this article, we review different types of nanofillers that have been utilized inside the conventional ECAs to improve the electrical conductivity of ECAs. We focus on the synergetic effects of silver flakes and the nanofillers on electron transportation through the electrical network; the mechanisms of electrical conductivity enhancement are discussed. Special attention is given to the surface properties of the nanofillers and their corresponding influences on the filler-filler interaction, which has direct effect on the final electrical performance of the hybrid ECAs. [ABSTRACT FROM AUTHOR]

Electrically conductive adhesives (ECAs) filled with silver nanoparticle (Ag NP)-decorated graphene were prepared and the effect of curing temperature on the electrical conductivity of the ECAs was discussed. Mono-dispersed Ag NPs with an average size of 9 nm were successfully deposited and simultaneously functionalized with mercaptopropionic acid (MPA) on graphene surface. The surface functionalization of the NPs with MPA made the decorated graphene dispersible in organic solvents, which facilitated its dispersion inside epoxy. The decorated graphene was added into conventional ECAs (consisting of silver flakes and epoxy) at concentrations close to the percolation threshold and beyond that resulting in a significant electrical conductivity improvement (especially at concentrations close to the percolation threshold). The electrical resistivity of hybrid ECAs with the decorated graphene decreased as the curing temperature increased. Curing the ECA with 1 wt% of the decorated graphene at 220 °C resulted in a highly conductive adhesive with a low electrical resistivity of 4.6 × 10 Ω cm (close to that of eutectic lead based solders). The dramatic electrical conductivity improvement of ECAs is due to the sintering between small Ag NPs on the graphene surface and silver flakes. Morphological and thermal studies showed that Ag NPs start to sinter at approximately 150 °C when the MPA layer began to decompose from their surface. The quality of filler-filler interaction was investigated by monitoring the effect of temperature on the electrical resistivity of conductive fillers 'thin-film' before their addition to epoxy. [ABSTRACT FROM AUTHOR]

We report here a simple and innovative method to prepare large-scale silver nanoparticle films based on the controlled coffee ring effect. It is demonstrated that the films can be used as surface-enhanced Raman scattering probes to detect low-concentration medicines. Silver nanoparticles with the average size about 70 nm were prepared by reduction of silver nitride. In our experiment, the coffee ring effect was controlled by tilting the substrates during the deposition of silver nanoparticle films. Silver nanoparticle films were spontaneously formed on the surface of silicon substrates at the temperatures about 50°C based on the solvent evaporation and the coffee ring effect. The microstructure of the films was investigated using the scanning electron microscope and atomic force microscope. The surface roughness of the films is found as small as 20 nm. Then, the films were exposed to aqueous solutions of medicine at different concentrations. A comparison with a Raman spectra measured with a conventional Raman spectrometer showed that the Raman signal can be detected in the solution with concentrations as low as 1 × 10 M, and the enhancement factor achieved by the silver nanoparticle film can at least reach to 1.08 × 10. Our experimental results indicate that this technique is promising in the production of large-scale silver nanoparticle films for the surface-enhanced Raman scattering. These may be utilized in biochemical and trace analytical applications. [ABSTRACT FROM AUTHOR]

A procedure for joining polyol-synthesized silver nanowires in air using current-induced Joule heat welding is reported. Using a common probe station and photolithographically patterned gold electrodes, the welding process is completed using a common semiconductor analyzer. A unique two-step procedure eliminates the dielectric barrier at the point of contact without damaging the nanowires away from the junction. This procedure is designed for metal-metal contacts where a strong dielectric intermediate layer might exist, which can occur with metals prone to oxidation or corrosion in air, or as a result of the electrode deposition process. Ohmic connections are also established in cases where there is an initial gap between two nanowires. [ABSTRACT FROM AUTHOR]

Si has been considered as one of the most attractive anode materials for Li-ion batteries (LIBs) because of its high gravimetric and volumetric capacity. Importantly, it is also abundant, cheap, and environmentally benign. In this review, we summarized the recent progress in developments of Si anode materials. First, the electrochemical reaction and failure are outlined, and then, we summarized various methods for improving the battery performance, including those of nanostructuring, alloying, forming hierarchic structures, and using suitable binders. We hope that this review can be of benefit to more intensive investigation of Si-based anode materials. [ABSTRACT FROM AUTHOR]

Ag-nanoparticle films were deposited on glass and silicon substrates by evaporation of a colloidal solution. Periodic structures were created in these Ag nanoparticle deposits by ultraviolet nanosecond laser interference lithography (LIL). We find that the periodic structure and size of Ag nanoparticles in these oriented arrays can be controlled by varying laser pulse energy as well as the number of pulses used in irradiation. The effect of these parameters on the overall morphology of these deposits is shown to be promising as a new technique for the engineering of sub-micron nanoparticle structures. Ag films with laser-induced sub-micron periodic structures were evaluated as substrates for surface-enhanced Raman spectroscopy using rhodamine B adsorbed from a 10 M solution. Enhancement factors were found to be >10 those found in conventional Raman scattering and 10 times greater than those from standard Ag-nanoparticle films. These results indicate that the LIL method has promise in the nanostructuring of Ag-nanoparticle films for ultrasensitive SERS biosensing substrates. [ABSTRACT FROM AUTHOR]

Pharmaceuticals in wastewater effluents are a current and emerging global problem and the development of cost-effective methods to facilitate their removal is needed to mitigate this issue. Advanced oxidation processes (AOPs), in particular UV/TiO, have potential for wastewater treatment. In this study, TiO anatase phase nanobelts (30-100 nm in width and 10 μm in length) have been synthesized using a high temperature hydrothermal method as a means to photocatalyze the oxidation of pharmaceutical contaminants. We have investigated a model dye (malachite green), three pharmaceuticals and personal care products-naproxen, carbamazepine, and theophylline-that are difficult to oxidize without AOP processes. TiO nanobelts were exposed to 365 nm UV illumination and the measured photocatalytic degradation rates and adsorption parameters of pharmaceuticals were explored using kinetic models. Furthermore we have determined the degree of pharmaceutical degradation as a function of solution pH, illumination time, temperature, and concentration of contaminant. In addition, the roles of active oxygen species-hydroxyl radial (OH·), positive holes (h), and hydrogen peroxide (HO)-involved were also investigated in the degradation process. These studies offer additional applications of hierarchical TiO nanobelt membranes, including those harnessing sunlight for water treatment. [ABSTRACT FROM AUTHOR]

Carbon modified TiO2 nanobelts (TiO2-C) were synthesized using a hydrothermal growth method, as a support material for palladium (Pd) nanoparticles (Pd/TiO2-C) to improve the electrocatalytic perfor mance for methanol electrooxidation by comparison to Pd nanoparticles on bare TiO2 nanobelts (Pd/TiO2) and activated carbon (Pd/AC). Cyclic voltammetry characterization was conducted with respect to saturated calomel electrode (SCE) in an alkaline methanol solution, and the results indicate that the specific activity of Pd/TiO2-C is 2.2 times that of Pd/AC and 1.5 times that of Pd/TiO2. Chronoamperometry results revealed that the TiO2-C support was comparable in stability to activated carbon, but possesses an enhanced current density for methanol oxidation at a potential of -0.2 V vs. SCE. The current study demonstrates the potential of Pd nanoparticle loaded on hierarchical TiO2-C nanobelts for electrocatalytic applications such as fuel cells and batteries. [ABSTRACT FROM AUTHOR]

Low temperature interconnection processes for lead-free packaging and flexible electronics are currently of great interest. Several studies have focused on bonding using silver nanoparticles (Ag NPs) or copper nanoparticles (Cu NPs). However, pressure assistance is generally necessary for bonding with nanomaterial pastes, which limits its industrial applications. Here, a unique method for bonding of copper wires using Ag NP and nanowire binary pastes is examined, in which joining is accomplished from 60 to 200 °C and yet without the application of pressure. Bonding is facilitated by solid state sintering of Ag nanomaterials and metallic bonding between Cu and Ag interfaces. The effects of different additions of Ag nanowires in bonded joints are studied, in which addition of 20 vol% Ag nanowires improves bonding strength after low temperature sintering by 50-80 % compared with Ag nanoparticle paste. A mechanical reinforcement effect due to introduction of Ag nanowires has been confirmed by observation of the fracture path propagation, where necking, breakage and pullout of nanowires occur on loading. This low temperature pressureless bonding technology has the potential for wide use for interconnection in lead-free microcircuits and flexible electronic packaging. [ABSTRACT FROM AUTHOR]

Low-temperature bonding by sintering of Ag nanoparticles (NPs) is a promising lead-free bonding technique used in the electronic packaging industry. In this work, we prepare Ag nanoparticle (NP) paste using both an aqueous method and a polyol method. Sintering bonding trials were then conducted using different forms of Ag NPs. The results showed that use of the aqueous-based Ag NP paste led to inhomogeneous distribution of NPs, known as the 'coffee-ring effect.' This led to low strength of fabricated joints. We investigated the influence of the coffee-ring effect and ways to depress it by changing the bonding material composition. Our results show that, when using polyol-based Ag NP paste as the bonding material, the coffee-ring effect was successfully depressed due to increased Marangoni flow. The corresponding shear strength of joints was increased significantly to 50 MPa at bonding temperature of 250°C. [ABSTRACT FROM AUTHOR]

A simple method has been proposed to prepare polymer-protected Cu-Ag mixed nanoparticles (NPs), which are suitable for use as low-temperature bonding materials. The polymer coated on the Cu-Ag mixed NPs can protect them from oxidation effectively when heated in air at temperature lower than 280°C. The low-temperature bonding process utilizing Cu-Ag mixed NPs as the bonding material is investigated. The bonding experiments show that robust joints are formed using Cu-Ag mixed NPs at 160°C in air. The shear test shows that addition of copper to silver is helpful for improving joint strength. This novel sintering-bonding technology using Cu-Ag mixed NPs as an interconnection material has potential for application in the electronics packaging industry. [ABSTRACT FROM AUTHOR]

Silver nanoparticle (NP) paste was fabricated and used to bond copper wire to copper foil at low temperatures down to 160°C. The silver NP paste was developed by increasing the concentration of 50 nm silver NP sol from 0.001 vol.% to 0.1 vol.% by centrifugation. The 0.001 vol.% silver NP sol was fabricated in water by reducing silver nitrate (AgNO) using sodium citrate dihydrate (NaCHO·2HO). The bond was formed by solid-state sintering among the individual silver NPs and solid-state bonding of these silver NPs onto both copper wire and foil. Metallurgical bonds between silver NPs and copper were confirmed by transmission electron microscopy (TEM). The silver NPs were coated with an organic shell to prevent sintering at room temperature (RT). It was found that the organic shell decomposed at 160°C, the lowest temperature at which a bond could be formed. Shear tests showed that the joint strength increased as the bonding temperature increased, due to enhanced sintering of silver NPs at higher temperatures. Unlike low-temperature soldering techniques, bonds formed by our method have been proved to withstand temperatures above the bonding temperature. [ABSTRACT FROM AUTHOR]

Single domain GdBa2Cu7-δ (Gd123) bulk superconductors were fabricated in air by top-seeding melt-texture growth. Performance of the air-processed Gd123 was successfully enhanced by addition of both BaCO3 and BaCuO2− x , which suppress the formation of Gd1+ x Ba2− x Cu3O7-δ solid solutions. The optimum doping amount ranges from 0.05 to 0.15, M BaCO3 and 0.05 to 0.1, M BaCuO2− x per molar Gd123. The distribution of the second phase particles was observed by scanning electron microscopy. A narrow band formed by Gd2BaCuO5 particle concentration appeared around the seeding zone in both a– b plane and c-growth sector in Gd123 single grain. Trapped magnetic field density reached 0.67, T for sample with 24 mm in diameter and 8, mm in thickness and a high critical current density J c up to 91,200, A/cm2 was achieved at 77, K under self-field. [ABSTRACT FROM AUTHOR]

Metallic bonding at an interface is determined by the application of heat and/or pressure. The means by which these are applied are the most critical for joining nanoscale structures. The present study considers the feasibility of room-temperature pressureless joining of copper wires using water-based silver nanowire paste. A novel mechanism of self-generated local heating within the silver nanowire paste and copper substrate system promotes the joining of silver-to-silver and silver-to-copper without any external energy input. The localized heat energy was delivered in-situ to the interfaces to promote atomic diffusion and metallic bond formation with the bulk component temperature stays near room-temperature. This local heating effect has been detected experimentally and confirmed by calculation. The joints formed at room-temperature without pressure achieve a tensile strength of 5.7 MPa and exhibit ultra-low resistivity in the range of 101.3 nOhm·m. The good conductivity of the joint is attributed to the removal of organic compounds in the paste and metallic bonding of silver-to-copper and silver-to-silver. The water-based silver nanowire paste filler material is successfully applied to various flexible substrates for room temperature bonding. The use of chemically generated local heating may become a potential method for energy in-situ delivery at micro/nanoscale. [ABSTRACT FROM AUTHOR]