Epigraphene : epitaxial graphene on silicon carbide

This article presents a review of epitaxial graphene on silicon carbide, from fabrication to properties, put in the context of other forms of graphene.Comment: 46 pages, 322 references, 35 figures. Submitted December 201

LARCH Vogels Nationaal; een expertsysteem voor het beoordelen van de ruimtelijke samenhang en de duurzaamheid van broedvogelpopulaties in Nederland

Het model LARCH is een onderdeel van het kerninstrumentarium van het Natuurplanbureau. Het model voorspelt de kans op duurzaam voorkomen van vooral diersoorten op basis van de ruimtelijke configuratie van leefgebieden en de kwaliteit daarvan. Dit rapport beschrijft het toepasbaar maken van LARCH voor 89 broedvogelsoorten in Nederland, LARCH VOGELS NATIONAAL genaamd. Ten behoeve hiervan is een speciale begroeiingstypenkaart vervaardigd. Het model maakt deel uit van de Natuurplanner van het RIVM. De Natuurplanner integreert kennis over de effecten van de zogenoemde "ver"-thema's (verdroging, verzuring, vermesting) op planten en vegetatie(structuur). Door de uitbreiding met broedvogels kan ook de kennis over versnippering worden meegenomen

Measurements and computations on the behaviour of the insecticides azinphosmethyl and dimethoate in ditches

The unintentional pollution of surface water was studied during spraying of the insecticides azinphos-methyl and dimethoate on two fruit farms. Spray drift depended closely on the local situations at the fruit farms (windbreaks, distance from trees to ditches, paths) and on way of application.During application, the concentrations of both insecticides in water and in ditch bottoms were measured. Methods were adapted or developed for sampling, extraction, clean-up and gas-chromatography. Shortly after spraying, concentrations were several hundreds of mg m -3. The half-lives of azinphos- methyl ranged from 3 to 4 d; those for dimethoate ranged from 4 to 13 d.Water flow from and to ditch sections was estimated on both fruit farms during application. Flow through the ditch bottom was estimated as a closing item in a balance equation. All items of water balance were introduced into computation models of the behaviour of pesticides in surface water and bottom material. The set of differential equations was solved numerically after programming in the computer language CSMP III. Simulation of a trial with low discharge from a siphon-linked ditch indicated that conversion of both compounds in water was 70-90% of the material balances. Penetration into the ditch bottom was slow. During water flow through the ditches, convective transport and dispersion were predominant.Decline of azinphos-methyl and dimethoate was also measured in outdoor tank systems with a bottom layer. Fluctuations in pH and variations in light penetration influenced decline rates. Computations for the tank system indicated that conversion in the water compartment was the major item in material balance. The computed and measured masses of the insecticides in the bottom layer were less than 10% of the amount added.Conversion rates in surface water and in systems with anaerobic bottom material were measured in the laboratory at 10 and 20 °C. Conversion in water in the dark was slow, with half-lives of both compounds at about 100 d at 20 °C. The conversion rates of azinphos-methyl in anaerobic bottom material at 20 °C. was about ten times those in surface water. Copper ions were catalytic in the conversion of both insecticides in water.</p

Microscopic correlation between chemical and electronic states in epitaxial graphene on SiC(000-1)

We present energy filtered electron emission spectromicroscopy with spatial and wave-vector resolution on few layer epitaxial graphene on SiC$(000-1) grown by furnace annealing. Low energy electron microscopy shows that more than 80% of the sample is covered by 2-3 graphene layers. C1s spectromicroscopy provides an independent measurement of the graphene thickness distribution map. The work function, measured by photoelectron emission microscopy (PEEM), varies across the surface from 4.34 to 4.50eV according to both the graphene thickness and the graphene-SiC interface chemical state. At least two SiC surface chemical states (i.e., two different SiC surface structures) are present at the graphene/SiC interface. Charge transfer occurs at each graphene/SiC interface. K-space PEEM gives 3D maps of the k_|| pi - pi* band dispersion in micron scale regions show that the Dirac point shifts as a function of graphene thickness. Novel Bragg diffraction of the Dirac cones via the superlattice formed by the commensurately rotated graphene sheets is observed. The experiments underline the importance of lateral and spectroscopic resolution on the scale of future electronic devices in order to precisely characterize the transport properties and band alignments

Multi-shell gold nanowires under compression

Deformation properties of multi-wall gold nanowires under compressive loading are studied. Nanowires are simulated using a realistic many-body potential. Simulations start from cylindrical fcc(111) structures at T=0 K. After annealing cycles axial compression is applied on multi-shell nanowires for a number of radii and lengths at T=300 K. Several types of deformation are found, such as large buckling distortions and progressive crushing. Compressed nanowires are found to recover their initial lengths and radii even after severe structural deformations. However, in contrast to carbon nanotubes irreversible local atomic rearrangements occur even under small compressions.Comment: 1 gif figure, 5 ps figure

Electronic structure of epitaxial graphene grown on the C-face of SiC and its relation to the structure

International audienceThe interest in graphene stems from its unique band structure that photoemission spectroscopy can directly probe. However, the preparation method can significantly alter graphene's pristine atomic structure and in turn the photoemission spectroscopy spectra. After a short review of the observed band structure for graphene prepared by various methods, we focus on graphene grown on silicon carbide. The semiconducting single crystalline hexagonal SiC provides a substrate of various dopings, where bulk bands do not interfere with that of graphene. Large sheets of high structural quality flat graphene grow on SiC, which allows the exact same material to be used for fundamental studies and as a platform for scalable electronics. Moreover, a new graphene allotrope (multilayer epitaxial graphene) was discovered to grow on the 4H-SiC C-face by the confinement controlled sublimation method. We will focus on the electronic structure of this new graphene allotrope and its connection to its atomic structure

Highly-ordered graphene for two dimensional electronics

With expanding interest in graphene-based electronics, it is crucial that high quality graphene films be grown. Sublimation of Si from the 4H-SiC(0001) Si-terminated) surface in ultrahigh vacuum is a demonstrated method to produce epitaxial graphene sheets on a semiconductor. In this paper we show that graphene grown from the SiC$(000\bar{1})$ (C-terminated) surface are of higher quality than those previously grown on SiC(0001). Graphene grown on the C-face can have structural domain sizes more than three times larger than those grown on the Si-face while at the same time reducing SiC substrate disorder from sublimation by an order of magnitude.Comment: Submitted to Appl. Phys. Let

Electronic Cooling via Interlayer Coulomb Coupling in Multilayer Epitaxial Graphene

In van der Waals bonded or rotationally disordered multilayer stacks of two-dimensional (2D) materials, the electronic states remain tightly confined within individual 2D layers. As a result, electron-phonon interactions occur primarily within layers and interlayer electrical conductivities are low. In addition, strong covalent in-plane intralayer bonding combined with weak van der Waals interlayer bonding results in weak phonon-mediated thermal coupling between the layers. We demonstrate here, however, that Coulomb interactions between electrons in different layers of multilayer epitaxial graphene provide an important mechanism for interlayer thermal transport even though all electronic states are strongly confined within individual 2D layers. This effect is manifested in the relaxation dynamics of hot carriers in ultrafast time-resolved terahertz spectroscopy. We develop a theory of interlayer Coulomb coupling containing no free parameters that accounts for the experimentally observed trends in hot-carrier dynamics as temperature and the number of layers is varied.Comment: 54 pages, 15 figures, uses documentclass{achemso}, M.T.M. and J.R.T. contributed equally to this wor

Rational use of ¹⁸F-FDG PET/CT in patients with advanced cutaneous melanoma:A systematic review

18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) is increasingly used in patients with advanced melanoma. Immune checkpoint inhibitors and BRAF/MEK-targeted therapy have transformed the therapeutic landscape of metastatic melanoma. Consequently, a need for markers predicting (early) response to treatment and for monitoring treatment (toxicity) has arisen. This systematic review appraises the current literature evidence for rational use of 18F-FDG PET/CT scans in staging, clinical decision-making, treatment monitoring and follow-up in advanced melanoma. 18F-FDG PET/CT has high overall accuracy for detection of distant metastases and is, combined with cerebral MRI, the preferred imaging strategy for staging metastatic melanoma. In contrast, strong evidence supporting the standard use of 18F-FDG PET/CT for predicting and monitoring therapy response and toxicity is currently lacking. Essential for determining the position of 18F-FDG PET/CT during treatment course in advanced melanoma are well-designed studies with standardized scanning protocols, incorporation of clinical parameters and comparison with contrast-enhanced CT alone