Control and Characterization of Individual Grains and Grain Boundaries in Graphene Grown by Chemical Vapor Deposition

The strong interest in graphene has motivated the scalable production of high quality graphene and graphene devices. Since large-scale graphene films synthesized to date are typically polycrystalline, it is important to characterize and control grain boundaries, generally believed to degrade graphene quality. Here we study single-crystal graphene grains synthesized by ambient CVD on polycrystalline Cu, and show how individual boundaries between coalescing grains affect graphene's electronic properties. The graphene grains show no definite epitaxial relationship with the Cu substrate, and can cross Cu grain boundaries. The edges of these grains are found to be predominantly parallel to zigzag directions. We show that grain boundaries give a significant Raman "D" peak, impede electrical transport, and induce prominent weak localization indicative of intervalley scattering in graphene. Finally, we demonstrate an approach using pre-patterned growth seeds to control graphene nucleation, opening a route towards scalable fabrication of single-crystal graphene devices without grain boundaries.Comment: New version with additional data. Accepted by Nature Material

Mechanisms, functions and ecology of colour vision in the honeybee.

notes: PMCID: PMC4035557types: Journal Article© The Author(s) 2014.This is an open access article that is freely available in ORE or from Springerlink.com. Please cite the published version available at: http://link.springer.com/article/10.1007%2Fs00359-014-0915-1Research in the honeybee has laid the foundations for our understanding of insect colour vision. The trichromatic colour vision of honeybees shares fundamental properties with primate and human colour perception, such as colour constancy, colour opponency, segregation of colour and brightness coding. Laborious efforts to reconstruct the colour vision pathway in the honeybee have provided detailed descriptions of neural connectivity and the properties of photoreceptors and interneurons in the optic lobes of the bee brain. The modelling of colour perception advanced with the establishment of colour discrimination models that were based on experimental data, the Colour-Opponent Coding and Receptor Noise-Limited models, which are important tools for the quantitative assessment of bee colour vision and colour-guided behaviours. Major insights into the visual ecology of bees have been gained combining behavioural experiments and quantitative modelling, and asking how bee vision has influenced the evolution of flower colours and patterns. Recently research has focussed on the discrimination and categorisation of coloured patterns, colourful scenes and various other groupings of coloured stimuli, highlighting the bees' behavioural flexibility. The identification of perceptual mechanisms remains of fundamental importance for the interpretation of their learning strategies and performance in diverse experimental tasks.Biotechnology and Biological Sciences Research Council (BBSRC

Direct observations of grain boundary phenomena during indentation of Al and Al-Mg thin films

The deformation behaviour of Al and Al-Mg thin films has been studied with the unique experimental approach of in-situ nanoindentation in a transmission electron microscope. This paper concentrates on the role of solute Mg additions in the transfer of plasticity across grain boundaries. The investigated Al alloys were deposited onto a Si substrate as thin films with a thickness of 200-300 nm and Mg concentrations of 0, 1.1, 1.8, 2.6 and 5.0 wt% Mg. The results show that in the Al-Mg alloys, the solutes effectively pin high-angle grain boundaries, while in pure Al considerable grain boundary motion is observed at room temperature. The mobility of low-angle grain boundaries is however not affected by the presence of Mg. In addition, Mg was observed to affect dislocation dynamics in the matrix.</p

Direct observations of grain boundary phenomena during indentation of Al and Al-Mg thin films

The deformation behaviour of Al and Al-Mg thin films has been studied with the unique experimental approach of in-situ nanoindentation in a transmission electron microscope. This paper concentrates on the role of solute Mg additions in the transfer of plasticity across grain boundaries. The investigated Al alloys were deposited onto a Si substrate as thin films with a thickness of 200-300 nm and Mg concentrations of 0, 1.1, 1.8, 2.6 and 5.0 wt% Mg. The results show that in the Al-Mg alloys, the solutes effectively pin high-angle grain boundaries, while in pure Al considerable grain boundary motion is observed at room temperature. The mobility of low-angle grain boundaries is however not affected by the presence of Mg. In addition, Mg was observed to affect dislocation dynamics in the matrix

Is the Recent Decrease in Airborne Ambrosia Pollen in the Milan Area Due to the Accidental Introduction of the Ragweed Leaf Beetle Ophraella Communa?

This study aims to determine whether a significant decrease in airborne concentrations of Ambrosia pollen witnessed in the north-west of the Province of Milan in Northern Italy could be explained by environmental factors such as meteorology, or whether there is evidence to support the hypothesis that the decrease was related to the presence of large numbers of the oligophagous Ophraella communa leaf beetles that are used as a biological control agent against Ambrosia in other parts of the world. Airborne concentrations of Ambrosia, Cannabaceae and Urticaceae pollen data (2000–2013) were examined for trends over time and correlated with meteorological data. The amount of Ambrosia pollen recorded annually during the main flowering period of Ambrosia (August–September) was entered into linear regression models with meteorological data in order to determine whether the amount of airborne Ambrosia pollen recorded in 2013 was lower than would normally be expected based on the prevailing weather conditions. There were a number of significant correlations between concentrations of airborne Ambrosia, Cannabaceae and Urticaceae pollen, as well as between airborne pollen concentrations and daily and monthly meteorological data. The linear regression models greatly overestimated the amount of airborne Ambrosia pollen in 2013. The results of the regression analysis support the hypothesis that the observed decrease in airborne Ambrosia pollen may indeed be related to the presence of large numbers of O. communa in the Milan area, as the drastic decrease in airborne Ambrosia pollen in 2013 cannot be explained by meteorology alone