Thermal diffusivity of nonfractal and fractal nickel nanowires

The potential of using nanometallic wires inside a matrix as new generation of thermal interface material led us to study the thermal diffusivity of nickel nanowires embedded inside porous alumina template. Thermal diffusivity measurements using a laser flash method showed size dependence for nickel nanowires inside nanochannel alumina (NCA) templates having nominal pore diameters of 200, 100, and 20 nm. Nickel nanowires embedded inside these templates showed decreasing diffusivity values of 10.7x10(-6), 8.5x10(-6), and 6.5x10(-6) m(2) s(-1) at 300 K with decreasing wire diameter when deposited at 40 degrees C. Nanowires fabricated at 60 degrees C showed similar decreasing diffusivity with wire diameter, and a further 42%-48% reduction was observed when compared to 40 degrees C samples. The modified effective medium theory (MEMT) was employed to evaluate the experimental thermal diffusivity. Calculations based on MEMT resulted in mean thermal conductivities of 70.7 and 36.2 W m(-1) K(-1) for nickel nanowires fabricated at 40 and 60 degrees C respectively. These values are similar to 20% and 60% lower than the thermal conductivity value of bulk nickel. A strong grain size dependence of thermal diffusivity in the nanowires was observed. It is believed that the decrease in diffusivity in lower temperature wires is associated with defects/dislocations in large single crystals and reduction in wire diameters according to pore diameters of NCA. Whereas in higher temperature wires, the drastic reduction in diffusivity is believed to arise from self-similar fractal morphology composed of nanogranules, close to the dimension of electron mean free path

The Impact of Surfactant Sodium Dodecyl Sulfate on the Microstructure and Thermoelectric Properties of p-type (Sb1-xBix)2Te3 Electrodeposited Films

This work reports on the synthesis of p-type (Sb1-xBix)2Te3 thin films using pulsed electrodeposition with and without the presence of an anionic surfactant, sodium dodecyl sulfate (SDS). The effect of SDS on the morphology of the films was investigated, and it was found that films with SDS in the electrolyte were smooth and denser as compared to the films without SDS. Post-deposition annealing of the films resulted in preferential crystal orientation. The Seebeck coefficient showed an improvement of 49% for the films deposited with SDS, which improved the overall power factor of the films by 143%

Characterizing stress in ultrathin silicon wafers

The aim of this letter is to calculate the mechanical grinding induced bow and stress in ultrathin silicon wafers. The reverse leakage current of a p-n junction diode fabricated on a 4 in. silicon wafer was measured for wafers thinned to various thicknesses. A correlation with the residual stress was obtained through band gap narrowing effect. The analytical results were compared with experimental bow measurements using a laser profiler. The bow in 50 mu m thick wafer was found to be less than 2 mm using the current grinding process. (c) 2006 American Institute of Physics. (DOI:10.1063/1.2336212

Ultra-long metal nanowire arrays on solid substrate with strong bonding

Ultra-long metal nanowire arrays with large circular area up to 25 mm in diameter were obtained by direct electrodeposition on metalized Si and glass substrates via a template-based method. Nanowires with uniform length up to 30 μm were obtained. Combining this deposition process with lithography technology, micrometre-sized patterned metal nanowire array pads were successfully fabricated on a glass substrate. Good adhesion between the patterned nanowire array pads and the substrate was confirmed using scanning acoustic microscopy characterization. A pull-off tensile test showed strong bonding between the nanowires and the substrate. Conducting atomic force microscopy (C-AFM) measurements showed that approximately 95% of the nanowires were electrically connected with the substrate, demonstrating its viability to use as high-density interconnect

Ultra-fast rate capability of a symmetric supercapacitor with a hierarchical Co3O4 nanowire/nanoflower hybrid structure in non-aqueous electrolyte

A free standing Co3O4 nanowire/nanoflower hybrid structure on flexible carbon fibre cloth (CFC) was designed via a facile hydrothermal approach followed by thermal treatment in air. The Co3O4 hybrid structure on CFC showed interesting electrochemical performance in both alkaline and organic electrolytes when used as electrodes for symmetric supercapacitors. Compared to conventional alkaline electrolytes, the fabricated symmetric cell in organic electrolyte has delivered a high rate and cyclic performance. A supercapacitor made from this hierarchical hybrid architecture showed a maximum specific capacitance of 4.8 mF cm-2 at a constant density of 3 mA cm-2 in organic electrolyte. In terms of energy and power, the symmetric supercapacitor conveyed an energy density of 4.2 mW h cm-3 with a power density of 1260 mW cm-3. Also, the device exhibited reasonable tolerance for mechanical deformation under bended conditions demonstrating the flexibility of the materials. The impressive electrochemical activity is mainly attributed to their high surface area (60.3 m2 g-1) resulting from their nano/mesoporous structure; reasonable electrical conductivity resulted from binder-free and intimate metal oxide/substrate integration and superior flexibility of the carbon fibre cloth. Thereby, it was concluded that the direct growth of the Co3O4 nanostructure on CFC is a promising electrode for the advanced flexible energy storage devices regardless of the electrolyte

Fabrication of micro-thermoelectric devices for power generation and the thermal management of photonic devices

This work demonstrates and discusses the fabrication of cross-plane configured micro thermoelectric devices for the power generation and thermal management of the photonic devices. The device is fabricated using a cost-effective electrodeposition technique on the silicon wafer with 210 pairs of the electrodeposited p-type BiTe and n-type CuTe pillars. The complete device is fabricated using the flip-chip bonding technique. Our focus in this work is on the challenges in the device fabrication and the solutions employed to overcome the obstacles thereby successfully fabricating the micro thermoelectric device

Silver nanowire array-polymer composite as thermal interface material

Silver nanowire arrays embedded inside polycarbonate templates are investigated as a viable thermal interface material for electronic cooling applications. The composite shows an average thermal diffusivity value of 1.89x10(-5) m(2) s(-1), which resulted in an intrinsic thermal conductivity of 30.3 W m(-1) K(-1). The nanowires' protrusion from the film surface enables it to conform to the surface roughness to make a better thermal contact. This resulted in a 61% reduction in thermal impedance when compared with blank polymer. An similar to 30 nm Au film on the top of the composite was found to act as a heat spreader, reducing the thermal impedance further by 35%. A contact impedance model was employed to compare the contact impedance of aligned silver nanowire-polymer composites with that of aligned carbon nanotubes, which showed that the Young's modulus of the composite is the defining factor in the overall thermal impedance of these composites

Supercapattery based on binder-free Co3 (PO4)2·8H2O multilayer nano/microflakes on nickel foam

A binder-free cobalt phosphate hydrate (Co3(PO4)2·8H2O) multilayer nano/microflake structure is synthesized on nickel foam (NF) via a facile hydrothermal process. Four different concentrations (2.5, 5, 10, and 20 mM) of Co2+ and PO4–3 were used to obtain different mass loading of cobalt phosphate on the nickel foam. The Co3(PO4)2·8H2O modified NF electrode (2.5 mM) shows a maximum specific capacity of 868.3 C g–1 (capacitance of 1578.7 F g–1) at a current density of 5 mA cm–2 and remains as high as 566.3 C g–1 (1029.5 F g–1) at 50 mA cm–2 in 1 M NaOH. A supercapattery assembled using Co3(PO4)2·8H2O/NF as the positive electrode and activated carbon/NF as the negative electrode delivers a gravimetric capacitance of 111.2 F g–1 (volumetric capacitance of 4.44 F cm–3). Furthermore, the device offers a high specific energy of 29.29 Wh kg–1 (energy density of 1.17 mWh cm–3) and a specific power of 4687 W kg–1 (power density of 187.5 mW cm–3)