Selective epitaxial growth of graphene on SiC

We present an innovative method of selective epitaxial growth of few layers graphene (FLG) on a pre-patterned SiC substrate. The methods involves, successively, the sputtering of a thin AlN layer on top of a mono-crystalline SiC substrate and, then, patterning it with e-beam lithography (EBL) and wet etching. The sublimation of few atomic layers of Si from the SiC substrate occurs only through the selectively etched AlN layer. The presence of the Raman G-band at ~1582 cm-1 in the AlN-free areas is used to validate the concept, it gives absolute evidence of the selective FLG growth.Comment: comments: 3 pages, reference 3 replace

Growth of monolayer graphene on 8deg off-axis 4H-SiC (000-1) substrates with application to quantum transport devices

Using high temperature annealing conditions with a graphite cap covering the C-face of an 8deg off-axis 4H-SiC sample, large and homogeneous single epitaxial graphene layers have been grown. Raman spectroscopy shows evidence of the almost free-standing character of these monolayer graphene sheets, which was confirmed by magneto-transport measurements. We find a moderate p-type doping, high carrier mobility and half integer Quantum Hall effect typical of high quality graphene samples. This opens the way to a fully compatible integration of graphene with SiC devices on the wafers that constitute the standard in today's SiC industry.Comment: 11 pages, 4 figures , Submitted in AP

Method for analysis of heavy sulphur compounds using gas chromatography with flame photometric detection

A method for analysis of heavy sulphur compounds in wines, based on gas chromatography (GC) with flame photometric detection, is reported. Wine samples preparation includes a dichloromethane liquid–liquid extraction followed by concentration under a nitrogen atmosphere. The extracted fraction was also analysed by GC–mass spectrometry. The method enables high recovery of sulphur compounds in wine and satisfies the requirements of repeatability and sensitivity. Applications of the method to red, white and Port wines are reported

Early stage formation of graphene on the C-face of 6H-SiC

An investigation of the early stage formation of graphene on the C-face of 6H-SiC is presented. We show that the sublimation of few atomic layers of Si out of the SiC substrate is not homogeneous. In good agreement with the results of theoretical calculations it starts from defective sites, mainly dislocations that define nearly circular flakes, which have a pyramidal, volcano-like, shape with a center chimney where the original defect was located. At higher temperatures, complete conversion occurs but, again, it is not homogeneous. Within the sample surface the intensity of the Raman G and 2D bands, evidences non-homogeneous thickness.Comment: 12 pages, 3 figure

Nonequilibrium Luminescence At The E0+Δ0 Gap In Gaas With Si-δ Doping

We studied the light scattering spectra of three molecular beam epitaxy GaAs samples with Si-δ doping. A broad feature appears in these spectra which is similar to that attributed by other authors to resonant Raman scattering by electronic intersubband transitions. By studying the dependence of this emission on exciting laser photon energy we believe that this line is really produced by nonequilibrium luminescence at the E0+Δ 0 gap.71115619562

Investigation of Long Monolayer Graphene Ribbons grown on Graphite Capped 6H-SiC (000-1)

We present an investigation of large, isolated, graphene ribbons grown on the C-face of on-axis semi-insulating 6H-SiC wafers. Using a graphite cap to cover the SiC sample, we modify the desorption of the Si species during the Si sublimation process. This results in a better control of the growth kinetics, yielding very long (about 300 microns long, 5 microns wide), homogeneous monolayer graphene ribbons. These ribbons fully occupy unusually large terraces on the step bunched SiC surface, as shown by AFM, optical microscopy and SEM. Raman spectrometry indicates that the thermal stress has been partially relaxed by wrinkles formation, visible in AFM images. In addition, we show that despite the low optical absorption of graphene, optical differential transmission can be successfully used to prove the monolayer character of the ribbons

Self-consistency in Theories with a Minimal Length

The aim of this paper is to clarify the relation between three different approaches of theories with a minimal length scale: A modification of the Lorentz-group in the 'Deformed Special Relativity', theories with a 'Generalized Uncertainty Principle' and those with 'Modified Dispersion Relations'. It is shown that the first two are equivalent, how they can be translated into each other, and how the third can be obtained from them. An adequate theory with a minimal length scale requires all three features to be present.Comment: typos corrected, published with new title following referee's advic