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A large area nanogap electrode fabrication method combinig conventional lithography patterning with the of focused ion beam (FIB) is presented. Lithography and a lift-off process were used to pattern 50 nm thick platinum pads having an area of 300 μm × 300 μm. A range of 30-300 nm wide nanogaps (length from 300 μm to 10 mm ) were then etched using an FIB of Ga+ at an acceleration voltage of 30 kV at various beam currents. An investigation of Ga+ beam current ranging between 1-50 pA was undertaken to optimise the process for the current fabrication method. In this study, we used Monte Carlo simulation to calculate the damage depth in various materials by the Ga+. Calculation of the recoil cascades of the substrate atoms are also presented. The nanogap electrodes fabricated in this study were found to have empty gap resistances exceeding several hundred MΩ. A comparison of the gap length versus electrical resistance on glass substrates is presented. The results thus outline some important issues in low-conductance measurements. The proposed nanogap fabrication method can be extended to various sensor applications, such as chemical sensing, that employ the nanogap platform. This method may be used as a prototype technique for large-scale fabrication due to its simple, fast and reliable features.
The metal-catalyst-free growth of carbon nanotubes (CNTs) using chemical vapor deposition and the application in field-effect transistors (FETs) is presented. The CNT growth process used a 3-nm-thick Ge layer on SiO2 that was subsequently annealed to produce Ge nanoparticles. Raman measurements show the presence of radial breathing mode (RBM) peaks and the absence of the disorder induced D-band, indicating single walled CNTs (SWNTs) with a low defect density. The synthesized CNTs are used to fabricate CNTFETs and the best device has a state-of-the-art on/off current ratio of 3×108 and a steep sub-threshold slope of 110 mV/decade.
A point source outbreak of haemorrhagic colitis due to Escherichia coli O 157. H7 producing verocytotoxin (VT), took place following a christening party in Birmingham in June 1987. Twenty-six people were affected, six were admitted to hospital and one developed haemolytic uraemic syndrome: there were no deaths. VT + E. coli O 157. H7 was isolated from 13 (57%) of 23 faecal specimens from affected people and from 3 (9%) of 33 specimens from asymptomatic people. Free VT was detected in the faeces of one further asymptomatic person. Illness was associated with eating turkey-roll sandwiches (P < 0·001) suggesting that cold meats might be an important source of infection.
Previous findings on older adults' awareness of community support services (CSSs) have been inconsistent and marred by acquiescence or over-claiming bias. To address this issue, this study used a series of 12 vignettes to describe common situations faced by older adults for which CSSs might be appropriate. In telephone interviews, 1,152 adults aged 50 years and over were read a series of vignettes and asked if they were able to identify a community organization or agency that they may turn to in that situation. They were also asked about their most important sources of information about CSSs. The findings show that, using a vignette methodology, awareness of CSSs is much lower than previously thought. The most important sources of information about CSSs included information and referral sources, the telephone book, doctors' offices, and word of mouth.
The microbiological implications of using a small-scale bucket-style washer are reported forchicken eggs. On average, the bucket washerreduced the total bacterial numbers on the surface of eggs under manufacturer-recommended conditions from 5.36 log CFU egg-1 to 2.82 log CFU egg-1. No evidence of enhanced bacterial contamination of the egg contents was found when microbiological examination was undertaken a few hours afterwashing. When washing visibly soiled free-range eggs, there was a tendency forthe wash-waterto become dirty afteronly a few batches of eggs had been washed. Washing in dirty water could increase the numbers of bacteria on the surfaces of those shells which were visibly clean before washing. These additional shell-surface bacteria however, were not detected in the egg contents (n=1032), when analyses were undertaken 1–2 hours after washing. In contrast, when washed eggs were stored for2 weeks at 15°C, we found that bacterial numbers in the egg contents were elevated when compared with unwashed controls. To determine if cool washing temperatures could cause water to taken up by egg contents, eggs were warmed to 37°C, 30°C, 25°C or 20°C and were submerged in aqueous protein stain at 15°C forup to 7 minutes. We did not observe take up of the stain solution unless its temperature was 15°C cooler than the egg contents and the eggs were immersed forat least 3 minutes.
Extended abstract of a paper presented at the Pre-Meeting Congress: Materials Research in an Aberration-Free Environment, at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, July 31 and August 1, 2004.
Fe, Co, and Ni magnetic nanoparticles have been characterized
using energy-selected imaging in a high-resolution transmission
electron microscope. The samples comprised Fe/FeOx
and Co/CoOx nanoparticles synthesized by inert gas
evaporation and a Ni/C nano-composite prepared by a sonochemical method.
All of the particles examined were found to be between 5 and
30 nm in size, with the Fe and Co crystals coated in 5–10
nm of metal oxide layer and the Ni metallic crystallites embedded
in an amorphous carbon spherical matrix.
We report the current-voltage characteristics of gold nanoparticle – biopolymer networks at room temperature. Above a threshold voltage the current-voltage relationship is almost linear. From the current-voltage scaling above threshold we argue that one-dimensional regions of the network dominate the transport. Periodic features in the conductance are found in many samples. Both the threshold voltage and the conductance features occur at voltages much greater than expected for the capacitance of the nanoparticles. Possible explanations for the structure are considered.
A wet chemical approach to preparing one- and two-dimensional arrays of gold nanoparticles assembled onto a polypeptide (poly-L-lysine) scaffold layer is reported. The electrical properties of biopolymer templated and nontemplated gold nanoparticle samples are compared. The electrical response of nontemplated samples is unstable, likely due to nanoparticle mobility. Biopolymer templating provides a simple, chemical method to immobilize the particles and is found to stabilize the electrical response (Coulomb blockade) of the array. A striking feature of the electrical properties is that the electron transport properties are dominated by transport through one-dimensional chains within the sample. Structural studies by AFM and XPS support the transport findings and provide evidence for the formation of one-dimensional assemblies within the arrays.
On water agar, hyphae of many fungi are attracted to viable
pollen grains of Pinus nigra. Hyphae of 41 of 157 species
tested could penetrate the pollen grains, ramify within the interior
and consume the contents. It is proposed that pollen serves as a
supplementary seasonal source of nutrients, particularly nitrogen, for
litter- and wood-decaying members of the Basidiomycota.
Ni/Ti multilayered thin films can be efficient neutron guides and are therefore of great interest in neutron optics. Ni/Ti and NiC/Ti multilayers with various layer thicknesses were fabricated by magnetron sputtering and characterized by high resolution transmission electron microscopy (TEM). The TEM studies, performed on cross-sectional specimens, revealed that both kinds of layers were textured and snowed coherence in the growth direction. The presence of a 2 nra thick amorphous zone at the Ni/Ti interface in the carbon free thin films was also confirmed. On the contrary, sharp interfaces were obtained in NiC/Ti multilayers. The fine structure of the different layers will also be reported.
New bismuth alkoxide and oxo-alkoxide complexes have been prepared from the salt metathesis reaction of NaOR with BiCl3. When R = CH(CF3)2, the product is [Bi(μ- OR)(OR)2(THF)]2 Similar work with R = C6F5 has not yielded a simple alkoxide, but complexes of formulation NaBi3(μ3-O)(OR)8(THF), NaBi4((μ3-O)2(OR)9(THF)2, Na2Bi4(μ3- O)2(OR)10 and Bi6(μ3 -OR)(μ3 -O)4[μ3-OBi(OR)4]3 have been observed. The reaction of BiPh3 with HOC6F5, however, did produce the desired alkoxide which has been characterized as [Bi(OR)2(μ-OR)(toluene)]2 and [Bi(OR)2(μ-OR)(toluene)[2.2 toluene. The reaction of this alkoxide with NaOC6F5 led to the production of Bi6(ν3--O)2 (μ4-O)(OR)12 and NaBi3(μ3- O)(OR)8(THF)3. Reaction of BiPh3 with HOC6F5 in THF led to the formation of Bi6(μ3-OR)(μ3-O)4[μ3-OBi(OR)4]3 (THiF)2. Surprisingly the reaction of BiEt3 and HOR (R = C6F5 or Ph) displaced only one Et group to give [Et2Bi(μ-OR)]∞ which exist as infinite chain polymers with alternating Bi-O-Bi backbones. These spiral chains form chiral helices in the crystal lattice.
Fluorite-related structures of mixed uranium oxides (Uy,M1-y)O2−x, where M = Ce, Sc, Y, have been studied using High Resolution Electron Microscopy (HREM). Ordered domains have, been observed directly in crystallites of urania-ceria solid solution. Preliminary investigations of urania-yttria also show evidence for the presence of ordered domains. A possible model for the structure of these regions is suggested.
The nature of disorder produced by low energy Ar+ and I+ ions (and atoms) in the III–V compound semiconductors InP and InSb, and in the II–VI semiconductors CdTe, ZnS and ZnSe has been studied in detail by conventional and high resolution transmission electron microscopy. It is demonstrated that for Ar+ ion bombardment the disorder in the III–V compounds comprises segregated indium islands which accumulate on the machined surfaces, while for the II–VI compounds the disorder consists of dense arrays (∼1011 cm−2) of small dislocation loops near to each bombarded surface. When Ar+ ions or Ar atoms are used for thin specimen preparation by milling prior to electron microscopy, the disorder produced gives contrast which seriously obscures images and so complicates their interpretation. This problem concerning the presence of artifactual defects can be greatly reduced or even eliminated by the use of reactive I+ ion milling for the final thinning of specimens.
Nuclear magnetic resonance (NMR) imaging of hydrogen in body water and fat is proving valuable in clinical investigation of the brain. An introduction to the technique and to the biological significance of the images is presented here. The ‘multi-parameter’ nature of these images is stressed, and the individual parameters described. NMR imaging may well be of value in investigating the pathology of organic and functional psychoses.