Size-controlled synthesis and gas sensing application of tungsten oxide nanostructures produced by arc discharge

Several different synthetic methods have been developed to fabricate tungsten oxide (WO(3)) nanostructures, but most of them require exotic reagents or are unsuitable for mass production. In this paper, we present a systematic investigation demonstrating that arc discharge is a fast and inexpensive synthesis method which can be used to produce high quality tungsten oxide nanostructures for NO(2) gas sensing measurements. The as-synthesized WO(3) nanostructures are characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), finger-print Raman spectroscopy and proton induced x-ray emission (PIXE). The analysis shows that spheroidal-shaped monoclinic WO(3) crystal nanostructures were produced with an average diameter of 30 nm (range 10-100 nm) at an arc discharge current of 110 A and 300 Torr oxygen partial pressure. It is found that the morphology is controlled by the arc discharge parameters of current and oxygen partial pressure, e.g. a high arc discharge current combined with a low oxygen partial pressure results in small WO(3) nanostructures with improved conductivity. Sensors produced from the WO(3) nanostructures show a strong response to NO(2) gas at 325 °C. The ability to tune the morphology of the WO(3) nanostructures makes this method ideal for the fabrication of gas sensing materials.

Modulation of field emission properties of znO nanorods during arc discharge

Zinc oxide (ZnO) nanorods have been synthesized via the arc discharge method. Different oxygen partial pressures were applied in the arc discharge chamber to modulate the field emission properties of the as-synthesized ZnO nanorods. Scanning electron microscopy (SEM) was carried out to analyze the morphology of the ZnO nanorods. The ion beam analysis technique of proton induced X-ray emission (PIXE) was performed to probe the impurities in ZnO nanorods. SEM images clearly revealed the formation of randomly oriented ZnO nanorods with diameters between 10-50 nm. It was found that the morphology and the electrical properties of the ZnO nanorods were dependent on the oxygen partial pressure during arc discharge. In addition enhanced UV-sensitive photoconductivity was found for ZnO nanorods synthesized at high oxygen partial pressure during arc discharge. The field emission properties of the nanorods were studied. The turn-on field, which is defined at a current density of 10 microA cm(-2), was about 3 V microm(-1) for ZnO nanorods synthesized at 99% oxygen partial pressure during arc discharge. The turn-on field for ZnO nanorods increased with the decrease of oxygen partial pressure during arc discharge. The simplicity of the synthesis route coupled with the modulation of field emission properties due to the arc discharge method make the ZnO nanorods a promising candidate for a low cost and compact cold cathode material.

An estimate of amyotrophic lateral sclerosis heritability using twin data

BACKGROUND

Causative gene mutations have been identified in about 2% of those with amyotrophic lateral sclerosis (ALS), often, but not always, when there is a strong family history. There is an assumption that there is a genetic component to all ALS, but genome-wide association studies have yet to produce a robustly replicated result. A definitive estimate of ALS heritability is therefore required to determine whether ongoing efforts to find susceptibility genes are worth while.

METHODS

The authors performed two twin studies, one population- and one clinic-based. The authors used structural equation modelling to perform a meta-analysis of data from these studies and an existing twin study to estimate ALS heritability, and identified 171 twin pairs in which at least one twin had ALS.

RESULTS AND DISCUSSION

Five monozygotic twin pairs were concordant-affected, and 44 discordant-affected. No dizygotic twin pairs were concordant-affected, and 122 discordant-affected. The heritability of sporadic ALS was estimated as 0.61 (0.38 to 0.78) with the unshared environmental component 0.39 (0.22 to 0.62). ALS has a high heritability, and efforts to find causative genes should continue.

Promising thermoelectric properties of commercial PEDOT:PSS materials and their bi2Te3 powder composites

Newly commercialized PEDOT:PSS products CLEVIOS PH1000 and FE-T, among the most conducting of polymers, show unexpectedly higher Seebeck coefficients than older CLEVIOS P products that were studied by other groups in the past, leading to promising thermoelectric (TE) power factors around 47 μW/m K(2) and 30 μW/m K(2) respectively. By incorporating both n and p type Bi(2)Te(3) ball milled powders into these PEDOT:PSS products, power factor enhancements for both p and n polymer composite materials are achieved. The contact resistance between Bi(2)Te(3) and PEDOT is identified as the limiting factor for further TE property improvement. These composites can be used for all-solution-processed TE devices on flexible substrates as a new fabrication option.

Electron beam annealing of Fe+ implanted Si nanostructures

Silicon nanostructures (nanowhiskers) have been formed at surface densities approximately 10(9) cm-2 by electron beam annealing (EBA) prior to the implantation of 7 keV Fe+ ions to fluences from 1 x 10(13) - 4 x 10(15) Fe+ cm(-2). A second EBA step is then applied to relieve implantation-induced stresses. RBS analysis shows that the implanted Fe remains close to the surface. AFM characterisations of the implanted nanowhiskers before and after the final EBA step are summarised in graphs of height versus surface density. In a striking result it is shown that the nanowhiskers not only survive processing but also grow significantly. For example, at the highest fluence of 4 x 10(15) Fe+ cm(-2), the average height more than doubles: the increases are from 5.0 nm to 6.5 nm under implantation and from 6.5 nm to 11.8 nm under EBA. In addition there is a significant increase in surface density from an initial value of 1.6 x 10(9) cm(-2) to 4.3 x 10(9) cm(-2). These results highlight the feasibility of doping Si surface nanostructures with magnetic ions to fabricate Si devices for spin-dependent enhanced field emission.