Femtosecond laser direct writing of metallic microstructures by photoreduction of silver nitrate in a polymer matrix.

Continuous silver microstructures were produced by three-dimensional (3-D) direct laser writing using a femtosecond-pulsed laser beam with polyvinylpyrrolidone (PVP) films containing silver ions. The lines drawn by scanning a tightly focused laser beam ranged from 200 nm to 1.7 microm. Using a sample solution of high density of silver nitrate, a continuous silver line with a resistivity of 3.48 x 10(-7) ohms m was produced. Not only 3-D microstructures such as pyramidal models but also hybrid microstructures comprising polymer and silver lines were demonstrated. The 3-D direct laser writing of metallic microstructures has potential for application to 3-D electrical wiring of electronic devices and MEMS devices.

Nonlinear-optical phase modification in dispersion-engineered Si photonic wires.

The strong dispersion and large third-order nonlinearity in Si photonic wires are intimately linked in the optical physics needed for the optical control of phase. By carefully choosing the waveguide dimensions, both linear and nonlinear optical properties of Si wires can be engineered. In this paper we provide a review of the control of phase using nonlinear-optical effects such as self-phase and cross-phase modulation in dispersion-engineered Si wires. The low threshold powers for phase-changing effects in Si-wires make them potential candidates for functional nonlinear optical devices of just a few millimeters in length.

Nonlinear optics in photonic nanowires.

We review recent research on nonlinear optical interactions in waveguides with sub-micron transverse dimensions, which are termed photonic nanowires. Such nanowaveguides, fabricated from glasses or semiconductors, provide the maximal confinement of light for index guiding structures enabling large enhancement of nonlinear interactions and group-velocity dispersion engineering. The combination of these two properties make photonic nanowires ideally suited for many nonlinear optical applications including the generation of single-cycle pulses and optical processing with sub-mW powers.

Solitons and spectral broadening in long silicon-on- insulator photonic wires.

We report measurements and numerical modeling of spectral broadening and soliton propagation regimes in silicon-on-insulator photonic wire waveguides of 3 to 4 dispersion lengths using 100fs pump pulses. We also present accurate measurements of the group index and dispersion of the photonic wire.

Generation of polarization entangled photon pairs using silicon wire waveguide.

We report the experimental generation of polarization entangled photon pairs based on spontaneous four-wave mixing in a silicon waveguide. Using a nano-scale silicon wire waveguide placed in a fiber loop, we obtained 1.5-microm band polarization entanglement with two-photon interference visibilities of >83%.

Self-transducing silicon nanowire electromechanical systems at room temperature.

Electronic readout of the motions of genuinely nanoscale mechanical devices at room temperature imposes an important challenge for the integration and application of nanoelectromechanical systems (NEMS). Here, we report the first experiments on piezoresistively transduced very high frequency Si nanowire (SiNW) resonators with on-chip electronic actuation at room temperature. We have demonstrated that, for very thin (~90 nm down to ~30 nm) SiNWs, their time-varying strain can be exploited for self-transducing the devices' resonant motions at frequencies as high as approximately 100 MHz. The strain of wire elongation, which is only second-order in doubly clamped structures, enables efficient displacement transducer because of the enhanced piezoresistance effect in these SiNWs. This intrinsically integrated transducer is uniquely suited for a class of very thin wires and beams where metallization and multilayer complex patterning on devices become impractical. The 30 nm thin SiNW NEMS offer exceptional mass sensitivities in the subzeptogram range. This demonstration makes it promising to advance toward NEMS sensors based on ultrathin and even molecular-scale SiNWs, and their monolithic integration with microelectronics on the same chip.

Electrochemical devices made from conducting nanowire networks self-assembled from amyloid fibrils and alkoxysulfonate PEDOT.

Proteins offer an almost infinite number of functions and geometries for building nanostructures. Here we have focused on amyloid fibrillar proteins as a nanowire template and shown that these fibrils can be coated with the highly conducting polymer alkoxysulfonate PEDOT through molecular self-assembly in water. Transmission electron microscopy and atomic force microscopy show that the coated fibers have a diameter around 15 nm and a length/thickness aspect ratio >1:1000 . We have further shown that networks of the conducting nanowires are electrically and electrochemically active by constructing fully functional electrochemical transistors with nanowire networks, operating at low voltages between 0 and 0.5 V.

Large anisotropy of electrical properties in layer-structured In2Se3 nanowires.

Layer-structured indium selenide (In 2Se 3) nanowires (NWs) have large anisotropy in both shape and bonding. In 2Se 3 NWs show two types of growth directions: [11-20] along the layers and [0001] perpendicular to the layers. We have developed a powerful technique combining high-resolution transmission electron microscopy (HRTEM) investigation with single NW electrical transport measurement, which allows us to correlate directly the electrical properties and structure of the same individual NWs. The NW devices were made directly on a 50 nm thick SiN x membrane TEM window for electrical measurements and HRTEM study. NWs with the [11-20] growth direction exhibit metallic behavior while the NWs grown along the [0001] direction show n-type semiconductive behavior. Excitingly, the conductivity anisotropy reaches 10 (3)-10 (6) at room temperature, which is 1-3 orders magnitude higher than the bulk ratio.

Recording electrocardiograms using 3-limb lead cables instead of the standard 4: a modification to minimize incorrect electrode placements.

The similarity between and the number of limb lead cables play an important role in the frequency of incorrect connection of limb electrodes. Hence, a modified electrocardiogram (ECG) acquisition procedure is proposed in this brief communication, whereby the left-leg (LL) and right-leg (RL) electrode cables are combined into 1 cable, referred to as combined LL/RL cable. The electrode wires in the combined LL/RL cable are connected to 2 electrodes placed on both sides of the LL. The combined LL/RL cable is unique enough (being thicker) not to be mistaken with the upper limb electrode cables. The proposed modification will not in any way influence the ECG waveforms or amplitudes, and it can be expected to substantially reduce incorrect limb electrode placements.

Flux transformers made of commercial high critical temperature superconducting wires.

We have designed flux transformers made of commercial BiSCCO tapes closed by soldering with normal metal. The magnetic field transfer function of the flux transformer was calculated as a function of the resistance of the soldered contacts. The performances of different kinds of wires were investigated for signal delocalization and gradiometry. We also estimated the noise introduced by the resistance and showed that the flux transformer can be used efficiently for weak magnetic field detection down to 1 Hz.

Complexity of MRI induced heating on metallic leads: experimental measurements of 374 configurations.

BACKGROUND: MRI induced heating on PM leads is a very complex issue. The widely varying results described in literature suggest that there are many factors that influence the degree of heating and that not always are adequately addressed by existing testing methods. METHODS: We present a wide database of experimental measurements of the heating of metallic wires and PM leads in a 1.5 T RF coil. The aim of these measurements is to systematically quantify the contribution of some potential factors involved in the MRI induced heating: the length and the geometric structure of the lead; the implant location within the body and the lead path; the shape of the phantom used to simulate the human trunk and its relative position inside the RF coil. RESULTS: We found that the several factors are the primary influence on heating at the tip. Closer locations of the leads to the edge of the phantom and to the edge of the coil produce maximum heating. The lead length is the other crucial factor, whereas the implant area does not seem to have a major role in the induced temperature increase. Also the lead structure and the geometry of the phantom revealed to be elements that can significantly modify the amount of heating. CONCLUSION: Our findings highlight the factors that have significant effects on MRI induced heating of implanted wires and leads. These factors must be taken into account by those who plan to study or model MRI heating of implants. Also our data should help those who wish to develop guidelines for defining safe medical implants for MRI patients. In addition, our database of the entire set of measurements can help those who wish to validate their numerical models of implants that may be exposed to MRI systems.

A generic approach for embedded catalyst-supported vertically aligned nanowire growth.

We demonstrate a general approach for growing vertically aligned, single-crystalline nanowires of any material on arbitrary substrates by using plasma-sputtered Au/Pd thin films as a catalyst through the vapor-liquid-solid process. The high-energy sputtered Au/Pd atoms form a reactive interface with the substrate forming nanoclusters which get embedded in the substrate, thus providing mechanical stability for vertically aligned nanowire growth. We demonstrate that our approach for vertically aligned nanowire growth is generic and can be extended to various complex substrates such as conducting indium tin oxide.

Solution-processed metal nanowire mesh transparent electrodes.

Transparent conductive electrodes are important components of thin-film solar cells, light-emitting diodes, and many display technologies. Doped metal oxides are commonly used, but their optical transparency is limited for films with a low sheet resistance. Furthermore, they are prone to cracking when deposited on flexible substrates, are costly, and require a high-temperature step for the best performance. We demonstrate solution-processed transparent electrodes consisting of random meshes of metal nanowires that exhibit an optical transparency equivalent to or better than that of metal-oxide thin films for the same sheet resistance. Organic solar cells deposited on these electrodes show a performance equivalent to that of devices based on a conventional metal-oxide transparent electrode.

Nanosecond delay with subpicosecond uncertainty.

We have combined a commercially available, variable-length coaxial delay line (trombone line) with a high-resolution linear translation system. The result is better resolution and lower uncertainty in the achievable delays than previously available. The range of delay is 0 ps to approximately 1250 ps, the bidirectional resolution is 2.0 ps, the unidirectional resolution is 0.2 ps, and the uncertainty (95% confidence interval) in the measured delay is +/-0.09 ps. Drift, temperature dependence, repeatability, linearity, and hysteresis were also examined.

InAs/InP radial nanowire heterostructures as high electron mobility devices.

Radial core/shell nanowires (NWs) represent an important class of one-dimensional (1D) systems with substantial potential for exploring fundamental materials electronic and photonic properties. Here, we report the rational design and synthesis of InAs/InP core/shell NW heterostructures with quantum-confined, high-mobility electron carriers. Transmission electron microscopy studies revealed single-crystal InAs cores with epitaxial InP shells 2-3 nm in thickness, and energy-dispersive X-ray spectroscopy analysis further confirmed the composition of the designed heterostructure. Room-temperature electrical measurements on InAs/InP NW field-effect transistors (NWFETs) showed significant improvement in the on-current and transconductance compared to InAs NWFETs fabricated in parallel, with a room-temperature electron mobility, 11,500 cm(2)/Vs, substantially higher than other synthesized 1D nanostructures. In addition, NWFET devices configured with integral high dielectric constant gate oxide and top-gate structure yielded scaled on-currents up to 3.2 mA/microm, which are larger than values reported for other n-channel FETs. The design and realization of high electron mobility InAs/InP NWs extends our toolbox of nanoscale building blocks and opens up opportunities for fundamental and applied studies of quantum coherent transport and high-speed, low-power nanoelectronic circuits.

Selective surface functionalization of silicon nanowires via nanoscale joule heating.

In this letter, we report a novel approach to selectively functionalize the surface of silicon nanowires located on silicon-based substrates. This method is based upon highly localized nanoscale Joule heating along silicon nanowires under an applied electrical bias. Numerical simulation shows that a high-temperature (>800 K) with a large thermal gradient can be achieved by applying an appropriate electrical bias across silicon nanowires. This localized heating effect can be utilized to selectively ablate a protective polymer layer from a region of the chosen silicon nanowire. The exposed surface, with proper postprocessing, becomes available for surface functionalization with chemical linker molecules, such as 3-mercaptopropyltrimethoxysilanes, while the surrounding area is still protected by the chemically inert polymer layer. This approach is successfully demonstrated on silicon nanowire arrays fabricated on SOI wafers and visualized by selective attachment of gold nanoparticles.

Sonochemical synthesis of platinum nanowires and their applications as electro-chemical actuators.

We report the sonochemical synthesis of platinum nanowires on carbon nanotube templates and their application in electrochemical actuation. The fabrication of platinum nanowires was achieved by suspending well separated single wall carbon nanotubes in isopropyl alcohol and ultra-sonically agitating the solution in the presence of dihydrogen hexachloroplatinate. The platinum nanowires were further processed into micro and macro scale free standing sheets by vacuum filtration. An electrochemical cantilever actuator was constructed using the platinum nanowire sheet which actuated under electrical bias. Displacement of '3 mm was readily achieved when the electrical potential was swept at low voltages between -2 V and 2 V at a scan rate of 200 mV/s. The actuator showed the metallic actuation characteristics instead of that from carbon nanotubes. These results show the applicability of metallic nanomaterials for actuation technologies.

The controllable syntheses and electrochemical study of 1-dimensional nanowires, 2-dimensional nanoplatelets, and 3-dimensional nanotowers of MnO2.

We report a facile hydrothermal synthetic approach to selectively produce 1-dimensional, 2-dimensional, or 3-dimensional MnO2 nanomaterials reliably and conveniently. The influences of reaction conditions on the morphology and crystallographic forms and the formation mechanism of the as-obtained MnO2 nanostructures have been studied in this work. And the materials produced by this method have excellent crystalline nature. Preliminary electrochemical study indicates that the as-prepared 2-dimensional MnO2 nanomaterials are excellent cathode materials using in lithium batteries.