Tuning the electronic transport properties of graphene through functionalisation with fluorine

Engineering the electronic properties of graphene has triggered great interest for potential applications in electronics and opto-electronics. Here we demonstrate the possibility to tune the electronic transport properties of graphene monolayers and multilayers by functionalisation with fluorine. We show that by adjusting the fluorine content different electronic transport regimes can be accessed. For monolayer samples, with increasing the fluorine content, we observe a transition from electronic transport through Mott variable range hopping in two dimensions to Efros - Shklovskii variable range hopping. Multilayer fluorinated graphene with high concentration of fluorine show two-dimensional Mott variable range hopping transport, whereas CF0.28 multilayer flakes have a band gap of 0.25eV and exhibit thermally activated transport. Our experimental findings demonstrate that the ability to control the degree of functionalisation of graphene is instrumental to engineer different electronic properties in graphene materials.Comment: 6 pages, 5 figure

Properties of Phase transitions of a Higher Order

The following is a thermodynamic analysis of a III order (and some aspects of a IV order) phase transition. Such a transition can occur in a superconductor if the normal state is a diamagnet. The equation for a phase boundary in an H-T (H is the magnetic field, T, the temperature) plane is derived. by considering two possible forms of the gradient energy, it is possible to construct a field theory which describes a III or a IV order transition and permits a study of thermal fluctuations and inhomogeneous order parameters.Comment: 13 pages, revtex, no figure

Optimization of multivariate analysis for IACT stereoscopic systems

Multivariate methods have been recently introduced and successfully applied for the discrimination of signal from background in the selection of genuine very-high energy gamma-ray events with the H.E.S.S. Imaging Atmospheric Cerenkov Telescope. The complementary performance of three independent reconstruction methods developed for the H.E.S.S. data analysis, namely Hillas, model and 3D-model suggests the optimization of their combination through the application of a resulting efficient multivariate estimator. In this work the boosted decision tree method is proposed leading to a significant increase in the signal over background ratio compared to the standard approaches. The improved sensitivity is also demonstrated through a comparative analysis of a set of benchmark astrophysical sources.Comment: 10 pages, 8 figures, 3 tables, accepted for publication in Astroparticle Physic