Electronic transport in single-walled carbon nanotubes, and their application as scanning probe microscopy tips

Single-walled carbon nanotubes (SWNTs) are remarkable molecules composed of a graphite sheet rolled into a seamless cylinder. With nanometer diameter, and micrometer length, their physical properties are due to a mixture of quantum and classical effects. This work investigates the electrical transport properties of these molecules, and demonstrates their application as Atomic Force Microscopy (AFM) tips. SWNTs were grown by catalysed chemical vapour deposition (cCVD), and characterized using AFM, electron microscopy and Raman spectroscopy. Electronic devices were fabricated from SWNTs grown by cCVD on Si02. Electronic transport through the SWNT devices was studied using electric force microscopy (EFM) and scanned gate microscopy (SGM). SGM was used to study the effects of defects on transport through the devices. A novel form of SGM, based on the modulation of the tip-gating potential by the oscillating tip in dynamic mode AFM, was demonstrated and shown to massively enhance the signal to noise ratio. Using EFM we directly demonstrated the transition from ballistic transport in metallic SWNT at low source-drain voltages, to diffusive transport at high-source drain voltages. EFM was also used to image the charge injection induced around a SWNT at high gate voltages, and correlate it with the observed hysteresis in the transconductance of SWNT devices. Both of these results are of fundamental importance to the future applications of SWNT electronic devices. The high bias behaviour of metallic SWNT is crucial to their proposed use as interconnects in nanoscale devices. Hysteresis in the transconductance of semiconducting SWNT devices is limiting their application as chemical and biological sensors, where environmental effects are monitored by the change in conductance of the devices. SWNTs were mounted at the apex of AFM tips, and used as high resolution scanning probe tips. Electrical transport through the SWNT-AFM tips was investigated using both liquid (Hg) and solid contacts. An efficient technique for fabricating nanowire AFM tips, using SWNT-AFM tips as templates, was also invented. The resultant nanowire tips were shown to be robust, high aspect ratio, electrical probes. Using calibration samples fabricated from SWNTs, SWNT-AFM tips were quantitatively demonstrated to increase the resolution of EFM. Under optimal conditions identical features could be distinguished down to separations as low as 15 nm, comparable to the topographic resolution

An Intelligent Fuse-box for use with Renewable Energy Sources integrated within a Domestic Environment

This paper outlines a proposal for an intelligent fuse-box that can replace existing fuse-boxes in a domestic context such that a number of renewable energy sources can easily be integrated into the domestic power supply network, without the necessity for complex islanding and network protection. The approach allows intelligent control of both the generation of power and its supply to single or groups of electrical appliances. Energy storage can be implemented in such a scheme to even out the power supplied and simplify the control scheme required, and environmental monitoring and load analysis can help in automatically controlling the supply and demand profiles for optimum electrical and economic efficiency. Simulations of typical scenarios are carried out to illustrate the concept in operation

Optimizing the Jiles-Atherton Model of Hysteresis by a genetic algorithm

Modeling magnetic components for simulation in electric circuits requires an accurate model of the hysteresis loop of the core material used. It is important that the parameters extracted for the hysteresis model be optimized across the range of operating conditions that may occur in circuit simulation. This paper shows how to extract optimal parameters for the Jiles-Atherton model of hysteresis by the genetic algorithm approach. It compares performance with the well-known simulated annealing method and demonstrates that improved results may be obtained with the genetic algorithm. It also shows that a combination of the genetic algorithm and the simulated annealing method can provide an even more accurate solution that either method on its own. A statistical analysis shows that the optimization obtained by the genetic algorithm is better on average, not just on a one-off test basis. The paper introduces and applies the concept of simultaneous optimization for major and minor hysteresis loops to ensure accurate model optimization over a wide variety of operating conditions. It proposes a modification to the Jiles-Atherton model to allow improved accuracy in the modeling of the major loop

van der Waals epitaxy of monolayer hexagonal boron nitride on copper foil : growth, crystallography and electronic band structure

We investigate the growth of hexagonal boron nitride (h-BN) on copper foil by low pressure chemical vapour deposition (LP-CVD). At low pressure, h-BN growth proceeds through the nucleation and growth of triangular islands. Comparison between the orientation of the islands and the local crystallographic orientation of the polycrystalline copper foil reveals an epitaxial relation between the copper and h-BN, even on Cu(100) and Cu(110) regions whose symmetry is not matched to the h-BN. However, the growth rate is faster and the islands more uniformly oriented on Cu(111) grains. Angle resolved photoemission spectroscopy measurements reveal a well-defined band structure for the h-BN, consistent with a band gap of 6 eV, that is decoupled from the copper surface beneath. These results indicate that, despite a weak interaction between h-BN and copper, van der Waals epitaxy defines the long range ordering of h-BN even on polycrystalline copper foils and suggest that large area, single crystal, monolayer h-BN could be readily and cheaply produced

Recycling of peroxiredoxin IV provides a novel pathway for disulphide formation in the endoplasmic reticulum

Ero1 is thought to be the only oxidase that mediates the re-oxidation of protein disulphide isomerases (PDIs) during oxidative protein folding in the ER. This study reveals that peroxiredoxin IV can also directly oxidize PDI-family members and thus act as a second source of oxidizing equivalents for disulphide-bond formation in the ER

Composition profiles of InAs–GaAs quantum dots determined by medium-energy ion scattering

The composition profile along the [001] growth direction of low-growth-rate InAs–GaAs quantum dots (QDs) has been determined using medium-energy ion scattering (MEIS). A linear profile of In concentration from 100% In at the top of the QDs to 20% at their base provides the best fit to MEIS energy spectra

Projected impacts of 21st century climate change on diapause in Calanus finmarchicus

Diapause plays a key role in the life cycle of high latitude zooplankton. During diapause animals avoid starving in winter by living in deep waters where metabolism is lower and met by lipid reserves. Global warming is therefore expected to shorten the maximum potential diapause duration by increasing metabolic rates and by reducing body size and lipid reserves. This will alter the phenology of zooplankton, impact higher trophic levels and disrupt biological carbon pumps. Here we project the impacts of climate change on the key North Atlantic copepod Calanus finmarchicus under IPCC RCP 8.5. Potential diapause duration is modelled in relation to body size and overwintering temperature. The projections show pronounced geographic variations. Potential diapause duration reduces by more than 30% in the Western Atlantic, whereas in the key overwintering centre of the Norwegian Sea it changes only marginally. Surface temperature rises, which reduce body size and lipid reserves, will have a similar impact to deep water changes on diapause in many regions. Because deep water warming lags that at the surface, animals in the Labrador Sea could offset warming impacts by diapausing in deeper waters. However, the ability to control diapause depth may be limited

One-step grafting of polymers to graphene oxide

The direct grafting of poly(N-isopropylacrylamide) to the basal plane of graphene oxide has been achieved in a single step: cleavage of the terminal thiocarbonylthio group on RAFT grown poly(N-isopropylacrylamide) reveals a reactive thiol that attacks the epoxides present across the surface of graphene oxide. The new composite material was characterised by a combination of SSNMR, FTIR, Raman, EDX, XPS, TGA and contact angle measurement; it shows enhanced thermal stability and solubility in water

Is graphene on copper doped?

Angle-resolved photoemission spectroscopy (ARPES) and X-ray photoemission spectroscopy have been used to characterise epitaxially ordered graphene grown on copper foil by low-pressure chemical vapour deposition. A short vacuum anneal to 200 °C allows observation of ordered low energy electron diffraction patterns. High quality Dirac cones are measured in ARPES with the Dirac point at the Fermi level (undoped graphene). Annealing above 300 °C produces n-type doping in the graphene with up to 350 meV shift in Fermi level, and opens a band gap of around 100 meV. Dirac cone dispersion for graphene on Cu foil after vacuum anneals (left: 200 °C, undoped; right: 500 °C, n-doped). Centre: low energy electron diffraction from graphene on Cu foil after 200 °C anneal. Data from Antares (SOLEIL)