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.

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.

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.

A Ge/Si heterostructure nanowire-based double quantum dot with integrated charge sensor

One proposal for a solid-state-based quantum bit (qubit) is to control coupled electron spins on adjacent semiconductor quantum dots. Most experiments have focused on quantum dots made from III-V semiconductors; however, the coherence of electron spins in these materials is limited by hyperfine interactions with nuclear spins. Ge/Si core/shell nanowires seem ideally suited to overcome this limitation, because the most abundant nuclei in Ge and Si have spin zero and the nanowires can be chemically synthesized defect-free with tunable properties. Here, we present a double quantum dot based on Ge/Si nanowires in which we can completely control the coupling between the dots and to the leads. We also demonstrate that charge on the double dot can be detected by coupling it capacitively to an adjacent nanowire quantum dot. The double quantum dot and integrated charge sensor serve as an essential building block to form a solid-state qubit free of nuclear spin.

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.

Electrically excited infrared emission from InN nanowire transistors

We report electrically excited infrared emission from a single InN nanowire transistor. We report on: (1) the generation of IR emission by impact excitation of carriers under a high electrical field, (2) the size of the fundamental band gap of InN NW by measuring its emission spectra, (3) the observation of interband and conduction-band to conduction-band hot-carrier emission, and the carrier relaxation rate, and finally, (4) we present evidence that suggests that the electron accumulation layer at the InN NW surface forms a surface plasmon that couples to and enhances radiative electron-hole pair recombination.

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.

Ethanol and hydrogen sensors based on ZnO nanoparticles and nanowires

Hydrogen sensing characteristics of thick films of nanoparticles of ZnO and 3% Mn or Co doped ZnO with and without impregnation of 1% Pt have been investigated over a wide concentration range. The sensor characteristics of the Pt impregnated ZnO and 3% Mn or Co-doped ZnO nanoparticles are found to be excellent with the sensitivity reaching values in the 1000-1500 range for 1000 ppm of H2 at 125 degrees C or lower. The sensitivity is quite high even for 10 ppm of H2. The response and recovery times are generally less than 10 s in the region of high sensitivity. These films exhibit very good sensing characteristics for ethanol, the sensitivity being well above 2000 at 50 degrees C for 1000 ppm of vapour. Nanowires of Pt-impregnated ZnO also exhibit satisfactory sensing characteristics, but the values of the sensitivity are somewhat lower. Humidity has negligible effect on the performance of these sensors.

Growth of high-density titanium silicide nanowires in a single direction on a silicon surface

Understanding the growth mechanisms of nanowires is essential for their successful implementation in advanced devices applications. In situ ultrahigh-vacuum transmission electron microscopy has been applied to elucidate the interaction mechanisms of titanium disilicide nanowires (TiSi2 NWs) on Si(111) substrate. Two phenomena were observed: merging of the two NWs in the same direction, and collapse of one NW on a competing NW in a different direction when they meet at the ends. On the other hand, as one NW encounters the midsection of the other NW in a different direction, it recedes in favor of bulging of the other NW at the midsection. Since crystallographically the nanowires are favored to grow on Si(110) only in the [1 -1 0] direction, this crucial information has been fruitfully exploited to focus on the growth of a high density of long and high-aspect-ratio Ti silicide NWs parallel to the surface on Si(110) in a single direction. The achievement in growth of high-density NWs in a single direction represents a significant advance in realizing the vast potential for applications of silicide NWs in nanoelectronics devices.

Epitaxial growth of silicon nanowires using an aluminium catalyst

Silicon nanowires have been identified as important components for future electronic and sensor nanodevices. So far gold has dominated as the catalyst for growing Si nanowires via the vapour-liquid-solid (VLS) mechanism. Unfortunately, gold traps electrons and holes in Si and poses a serious contamination problem for Si complementary metal oxide semiconductor (CMOS) processing. Although there are some reports on the use of non-gold catalysts for Si nanowire growth, either the growth requires high temperatures and/or the catalysts are not compatible with CMOS requirements. From a technological standpoint, a much more attractive catalyst material would be aluminium, as it is a standard metal in Si process lines. Here we report for the first time the epitaxial growth of Al-catalysed Si nanowires and suggest that growth proceeds via a vapour-solid-solid (VSS) rather than a VLS mechanism. It is also found that the tapering of the nanowires can be strongly reduced by lowering the growth temperature.

Linker-free directed assembly of high-performance integrated devices based on nanotubes and nanowires

Advanced electronic devices based on carbon nanotubes (NTs) and various types of nanowires (NWs) could have a role in next-generation semiconductor architectures. However, the lack of a general fabrication method has held back the development of these devices for practical applications. Here we report an assembly strategy for devices based on NTs and NWs. Inert surface molecular patterns were used to direct the adsorption and alignment of NTs and NWs on bare surfaces to form device structures without the use of linker molecules. Substrate bias further enhanced the amount of NT and NW adsorption. Significantly, as all the processing steps can be performed with conventional microfabrication facilities, our method is readily accessible to the present semiconductor industry. We use this method to demonstrate large-scale assembly of NT- and NW-based integrated devices and their applications. We also provide extensive analysis regarding the reliability of the method.

Versatile method for manipulating and contacting nanowires

We present a simple, non-lithographic method for electrically connecting nanowires with electrodes on planar as well as non-planar microsystems. A rigid nanowire is used as a local shadow mask during deposition of metal contacts, which we use to contact structures of widely different conductances: Multiwalled carbon nanotubes, para-hexaphenylene nanofibers, as well as indium arsenide and indium phosphide nanowires. Finally we demonstrate how the method can be extended to different electrode materials on each side of the electrode gap, as well as for investigation of the electromechanical properties of a nanowire integrated in a cantilever.

Silicon p-FETs from ultrahigh density nanowire arrays

Statistical numbers of field-effect transistors (FETs) were fabricated from a circuit of 17-nm-wide, 34-nm-pitch Si nanowires boron doped at a level of 10(18) cm-3. Top-gated 4-microm-wide Si nanowire p-FETs yielded low off-currents (approximately 10(-12) A), high on/off ratios (10(5)-10(6)), good on current values (30 microA/microm), high mobilities (approximately 100 cm2/V-s), and low subthreshold swing values (approximately 80 mV/decade between 10(-12) and 10(-10) A increasing to 200 mV/decade between 10(-10)-10(-8) A).

A generalized description of the elastic properties of nanowires

We report a model of nanowire (NW) mechanics that describes force vs displacement curves over the entire elastic range for diverse wire systems. Due to the clamped-wire measurement configuration, the force response in the linear elastic regime can be linear or nonlinear, depending on the system and the wire displacement. For Au NWs the response is essentially linear since yielding occurs prior to the onset of the inherent nonlinearity, while for Si NWs the force response is highly nonlinear, followed by brittle fracture. Since the method describes the entire range of elastic deformation, it unequivocally identifies the yield points in both of these materials.

Controlling the electronic interaction between a molecular wire and its atomic scale contacting pad

We report a quantitative study on the electronic interaction between a molecular wire and its atomic scale metallic contacting pad. A so-called "reactive Lander" molecule is manipulated using a low-temperature scanning tunneling microscope to form a planar one-end electronic contact. The increase of the STM contrast at the junction location is discussed by means of the electronic interaction between the contacting group of the molecular wire and the end atoms of the nanopad.

Molecular electronics on silicon: an ultrahigh vacuum scanning tunneling microscopy study

An ultrahigh vacuum scanning tunneling microscope (STM) was employed as a tool to characterize two distinct molecular electronic strategies on the Si(100) surface. Initially, the self-directed growth of one-dimensional styrene molecular chains on hydrogen-passivated Si(100) was investigated. High-resolution empty states imaging of these styrene nanostructures confirms alignment of phenyl groups along the chain. However, attempts at STM charge transport measurements were limited by tip induced desorption of styrene molecules. Consequently, an alternative oxygen radical chemistry was also investigated. In particular, the chemical adsorption of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) onto clean Si(100) leads to the formation of an exceptionally stable silicon-oxygen bond that can withstand high bias charge transport measurements up to +/- 5 volts. Direct charge transport measurements through individual TEMPO molecules on degenerately n-type doped Si(100) reveal room temperature negative differential resistance behavior for negative sample biases exceeding - 3 volts.

Importance of addressing National Electrical Code violations that result in unusual exposure to 60 Hz magnetic fields

We evaluated wiring in multifamily developments containing National Electrical Code(R) (NEC(R)) violations as a source of unusual exposure to 60 Hz magnetic fields. Two methods were used in this evaluation: measurement and modeling. We measured the building wiring as a source of magnetic fields in six multifamily developments in Michigan. In this small sample, building wiring proved to be an important source of exposure in four of the six cases. In all four cases with exposure from building wiring, one or more NEC violations were involved. To supplement our measurement efforts, we used computer modeling to compare magnetic field exposure due to building wiring with magnetic field exposure from external power lines. Our calculations showed that where the building wiring has a NEC violation leading to net current loops, the exposure due to wiring is likely to be more important than that from external power lines. Our results support the results obtained in a recent study of the exposure of Californian K-12 students to magnetic fields, where building wiring with one or more NEC violation was found to be the single most important exposure source. If 60 Hz magnetic fields are important to avoid, then improved enforcement of the NEC, as required by law, is perhaps the single most important mitigation policy to adopt. Bioelectromagnetics 25:102-106, 2004.

Development of electronic textiles for U.S. military protective clothing systems

The focus of this paper is on the development of a wearable electronic network that provides data and power transport. A materials and manufacturing survey was conducted to determine the best performing and most durable materials to withstand the rigors of textile manufacturing and potential military use. Narrow woven technology was selected as the most appropriate manufacturing method. A working wearable narrow fabric version of the Universal Serial Bus (USB) was successfully developed and fabricated as well as related wearable connectors. Military products developed include a personal area network and body borne antenna.

Synthesis, Electronic Properties, and Applications of Indium Oxide Nanowires

Single-crystalline indium oxide nanowires were synthesized using a laser ablation method and characterized using various techniques. Precise control over the nanowire diameter down to 10 nm was achieved by using monodisperse gold clusters as the catalytic nanoparticles. In addition, field effect transistors with on/off ratios as high as 10(4) were fabricated based on these nanowires. Detailed electronic measurements confirmed that our nanowires were n-type semiconductors with thermal emission as the dominating transport mechanism, as revealed by temperature-dependent measurements. Furthermore, we studied the chemical sensing properties of our In(2)O(3) nanowire transistors at room temperature. Upon exposure to a small amount of NO(2) or NH(3), the nanowire transistors showed a decrease in conductance of up to five or six orders of magnitude, in addition to substantial shifts in the threshold gate voltage. Our devices exhibit significantly improved chemical sensing performance compared to existing solid-state sensors in many aspects, such as the sensitivity, the selectivity, the response time and the lowest detectable concentrations. We have also demonstrated the use of UV light as a "gas cleanser" for In(2)O(3) nanowire chemical sensors, leading to a recovery time as short as 80 seconds.

Role of the wireless thermologger system in the management of the autoclave unequipped with sensor ports

Recently, the wireless thermologger system was developed. It consists of a wireless logger and the attached computer system. The wireless logger has a wireless structure and can be placed anywhere in the sterilizer chamber for thermometry. In the present study, thermal evaluations were performed twice using the wireless thermologger system in the sterilizer chamber of the prevacuum autoclave unequipped with sensor ports when it failed to pass the Bowie-Dick test and underwent mechanical repairs. Thermometry was performed when the Bowie-Dick test cycle was operated. The heat up time was measured in the range of 120.0-134.0 degrees C. The F0 value was calculated with the reference temperature at 121.0 degrees C and Z value at 10 degrees C when the sterilization temperature was over 120.0 degrees C. The first thermal evaluation was performed after three air-leaking points were repaired along with the replacement of the vacuum pump and the thermosensor. It revealed that the heat-up time was 4 min and 42 s and the F0 value was 137.5. After the temperature control systems were adjusted using the process calibrator in the prevacuum autoclave, the second thermal evaluation revealed that the heat up time was 2 mins 1 s and the F0 value was 102.7. The present study suggests that the wireless thermologger system is useful in the management of the autoclave unequipped with sensor ports when it undergoes mechanical repairs.

Surface-stress-induced phase transformation in metal nanowires

Several researchers have demonstrated, through experiments and analysis, that the structure and properties of nanometre-scale materials can be quite different to those of bulk materials due to the effect of surfaces. Here we use atomistic simulations to study a surface-stress-induced phase transformation in gold nanowires. The emergence of the transformation is controlled by wire size, initial orientation, boundary conditions, temperature and initial cross-sectional shape. For a <100> initial crystal orientation and wire cross-sectional area below 4 nm(2), surface stresses alone cause gold nanowires to transform from a face-centred-cubic structure to a body-centred-tetragonal structure. The transformation occurs roughly when the compressive stress caused by tensile surface-stress components in the length direction exceeds the compressive stress required to transform bulk gold to its higher energy metastable crystal structure.

Study of high- and low-current-configuration homes from the 1988 Denver Childhood Cancer Study

An epidemiological study conducted by Savitz et al. reported that residential wire codes were more strongly associated with childhood cancer than were measured magnetic fields, a peculiar result because wire codes were originally developed to be a surrogate for residential magnetic fields. The primary purpose of the study reported here, known as the Back to Denver (BTD) study, was to obtain data to help in the interpretation of the original results of Savitz et al. The BTD study included 81 homes that had been occupied by case and control subjects of Savitz et al., stratified by wire code as follows: 18 high current configuration (HCC) case homes; 20 HCC control homes; 20 low current configuration (LCC) case homes; and 23 LCC control homes. Analysis of new data acquired in these homes led to the following previously unpublished conclusions. The home-averaged (i.e., mean of fields measured in subjects' bedrooms, family/living rooms, and rooms where meals normally eaten) spot 60 Hz, 180 Hz, and harmonic (i.e., 60-420 Hz) magnetic fields were associated with wire codes. The 180 Hz and harmonic components, but not the 60 Hz component, were associated with case/control status. Measured static magnetic fields were only weakly correlated (rapproximately 0.2) between rooms in homes. The BTD data provide little support for, but are too sparse to definitively test, the 1995 resonance hypothesis proposed by Bowman et al. Case and control homes had similar concentrations of copper in their tap water. Copper concentration was not associated with wire codes nor with the level of electric current carried by a home's water pipe. These results of the BTD study suggest that future case/control studies investigating power frequency magnetic fields might wish to include measurements of 180 Hz or harmonic magnetic fields in order to examine their associations (if any) with disease status.

Nanotubes of boron nitride filled with molybdenum clusters

Carbon nanotubes are known to be metallic or semiconducting, depending on their helicity and diameter. However, boron nitride (BN) nanotubes are the only nanotubular product known to date that are predicted to have stable insulating properties that are independent of their atomic structure and morphology. Thus, the BN tube has attracted prime attention as an advanced nanoinsulating shield for all types of encapsulated conducting material, i.e., metal wires, clusters, etc. However, so far there have been no successes in controlled one-dimensional filling of BN nanotubes with conductive material. We report the first experimental results on the synthesis, high-resolution transmission electron microscopy, energy dispersion X-ray analysis, and electron energy loss spectroscopy of BN nanotubes that are filled with Mo clusters over their entire length. This was accomplished by means of two-step thermochemical treatment of chemically vapor-deposited C nanotubes with B2O3, CuO, and MoO3 oxides in a flowing N2 atmosphere. The first examples of BN nanotubes filled with molybdenum clusters are reported and the formation of the first nanocable (approximately 10 nm in length), consisting of a conductive metal core and an insulating BN nanotubular shield is demonstrated.

Rate of occurrence of transient magnetic field events in U.S. residences

Recent interest in the transient magnetic field events produced by electrical switching events in residential and occupational environments has been kindled by the possibility that these fields may explain observed associations between childhood cancer and wire codes. This paper reports the results of a study in which the rate of occurrence of magnetic field events with 2-200 kHz frequency content were measured over 24 h or longer periods in 156 U.S. residences. A dual-channel meter was developed for the study that, during 20 s contiguous intervals of time, counted the number of events with peak 2-200 kHz magnetic fields exceeding thresholds of 3. 3 nT and 33 nT. Transient activity exhibited a distinct diurnal rhythm similar to that followed by power frequency magnetic fields in residences. Homes that were electrically grounded to a conductive water system that extended into the street and beyond, had higher levels of 33 nT channel transient activity. Homes located in rural surroundings had less 33 nT transient activity than homes in suburban/urban areas. Finally, while transient activity was perhaps somewhat elevated in homes with OLCC, OHCC, and VHCC wire codes relative to homes with underground (UG) and VLCC codes, the elevation was the smallest in VHCC and the largest in OLCC homes. This result does not provide much support for the hypothesis that transient magnetic fields are the underlying exposure that explains the associations, observed in several epidemiologic studies, between childhood cancer and residence in homes with VHCC, but not OLCC and OHCC, wire codes.