Quantum Hall activation gaps in bilayer graphene

We have measured the quantum Hall activation gaps in bilayer graphene at filling factors $\nu=\pm4$ and $\nu=\pm8$ in high magnetic fields up to 30 T. We find that energy levels can be described by a 4-band relativistic hyperbolic dispersion. The Landau level width is found to contain a field independent background due to an intrinsic level broadening and a component which increases linearly with magnetic field.Comment: 4 pages, accepted version (just removed a few typos), will appear as Fast Track Communication in Solid State Commu

Global transcriptional response of Saccharomyces cerevisiae to the deletion of SDH3

<p>Abstract</p> <p>Background</p> <p>Mitochondrial respiration is an important and widely conserved cellular function in eukaryotic cells. The succinate dehydrogenase complex (Sdhp) plays an important role in respiration as it connects the mitochondrial respiratory chain to the tricarboxylic acid (TCA) cycle where it catalyzes the oxidation of succinate to fumarate. Cellular response to the Sdhp dysfunction (i.e. impaired respiration) thus has important implications not only for biotechnological applications but also for understanding cellular physiology underlying metabolic diseases such as diabetes. We therefore explored the physiological and transcriptional response of <it>Saccharomyces cerevisiae </it>to the deletion of <it>SDH3</it>, that codes for an essential subunit of the Sdhp.</p> <p>Results</p> <p>Although the Sdhp has no direct role in transcriptional regulation and the flux through the corresponding reaction under the studied conditions is very low, deletion of <it>SDH3 </it>resulted in significant changes in the expression of several genes involved in various cellular processes ranging from metabolism to the cell-cycle. By using various bioinformatics tools we explored the organization of these transcriptional changes in the metabolic and other cellular functional interaction networks.</p> <p>Conclusion</p> <p>Our results show that the transcriptional regulatory response resulting from the impaired respiratory function is linked to several different parts of the metabolism, including fatty acid and sterol metabolism.</p

Nanolithography and manipulation of graphene using an atomic force microscope

We use an atomic force microscope (AFM) to manipulate graphene films on a nanoscopic length scale. By means of local anodic oxidation with an AFM we are able to structure isolating trenches into single-layer and few-layer graphene flakes, opening the possibility of tabletop graphene based device fabrication. Trench sizes of less than 30 nm in width are attainable with this technique. Besides oxidation we also show the influence of mechanical peeling and scratching with an AFM of few layer graphene sheets placed on different substrates.Comment: 11 pages text, 5 figure

Physics in graphene & quantum rings : from mesoscopic device fabrication to measurement in high magnetic fields

New materials often lead to spectacular discoveries. A prominenent example is graphene, a single layer of carbon atoms arranged in a honeycomb lattice. This one atom thick carbon sheet has a high crystal quality and remarkable electronic properties. The charge carriers in graphene behave as massless relativistic particles enabling the study of quantum electrodynamics in a 'pencil trace'. In this thesis we look at the electronic properties of graphene in high magnetic fields. The quantum Hall effect observed in this two-dimensional (2D) system displays plateaus at half-integer values, in contrast to the integer quantum Hall effect in conventional 2D systems, and remains visible up to room temperature. This last observation is not only of major importance for the understanding of quantum phenomena but it also paves the way for high temperature applications of quantum physics in solid state materials, such as the high temperature quantum resistance metrology shown in this thesis. To fundamentally understand the origin of the half-integer quantum Hall effect we look at its temperature dependence and experimentally map out the underlying Landau level structure. The zeroth Landau level appears to be energetically very sharp compared to broad higher Landau levels and it splits into two levels at very low temperatures. Scaling experiments on the plateau-plateau transitions show details on the delocalization of charge carriers in the Landau level tails. Besides new materials, also new device geometries in existing materials can lead to new physics. We use local anodic oxidation with an atomic force microscope to create quantum rings in AlGaAs-heterostructures. In the quantum limit, at high magnetic fields, these rings show a new type of quantum oscillations which are shown to be related to the flux-quantized, discrete electronic size of the ring leading to a corresponding modulation of its two-point conductance

Valley-polarized massive charge carriers in gapped graphene

Contains fulltext : 117323.pdf (publisher's version ) (Open Access

Quanten-Hall-Effekt in Graphen

Contains fulltext : 75965.pdf (publisher's version ) (Closed access)8 p

Grafeen: een wereld van nieuwe fysica

Contains fulltext : 34734.pdf (publisher's version ) (Closed access