Ab initio simulations of the kinetic properties of the hydrogen monomer on graphene

The understanding of the kinetic properties of hydrogen (isotopes) adatoms on graphene is important in many fields. The kinetic properties of hydrogen-isotope (H, D and T) monomers were simulated using a composite method consisting of density functional theory, density functional perturbation theory and harmonic transition state theory. The kinetic changes of the magnetic property and the aromatic $\pi$ bond of the hydrogenated graphene during the desorption and diffusion of the hydrogen monomer was discussed. The vibrational zero-point energy corrections in the activation energies were found to be significant, ranging from 0.072 to 0.205 eV. The results obtained from quantum-mechanically modified harmonic transition state theory were compared with the ones obtained from classical-limit harmonic transition state theory over a wide temperature range. The phonon spectra of hydrogenated graphene were used to closely explain the (reversed) isotope effects in the prefactor, activation energy and jump frequency of the hydrogen monomer. The kinetic properties of the hydrogen-isotope monomers were simulated under conditions of annealing for 10 minutes and of heating at a constant rate (1.0 K/s). The isotope effect was observed; that is, a hydrogen monomer of lower mass is desorbed and diffuses more easily (with lower activation energies). The results presented herein are very similar to other reported experimental observations. This study of the kinetic properties of the hydrogen monomer and many other involved implicit mechanisms provides a better understanding of the interaction between hydrogen and graphene.Comment: Accepted by J. Phys. Chem.

Gauge fields and curvature in graphene

The low energy excitations of graphene can be described by a massless Dirac equation in two spacial dimensions. Curved graphene is proposed to be described by coupling the Dirac equation to the corresponding curved space. This covariant formalism gives rise to an effective hamiltonian with various extra terms. Some of them can be put in direct correspondence with more standard tight binding or elasticity models while others are more difficult to grasp in standard condensed matter approaches. We discuss this issue, propose models for singular and regular curvature and describe the physical consequences of the various proposals.Comment: Proceedings of the International Conference on Theoretical Physics: Dubna-Nano2008 to be published online in Journal of Physics: Conference serie

The influence of size effect on the electronic and elastic properties of diamond films with nanometer thickness

The atomic structure and physical properties of few-layered oriented diamond nanocrystals (diamanes), covered by hydrogen atoms from both sides are studied using electronic band structure calculations. It was shown that energy stability linear increases upon increasing of the thickness of proposed structures. All 2D carbon films display direct dielectric band gaps with nonlinear quantum confinement response upon the thickness. Elastic properties of diamanes reveal complex dependence upon increasing of the number of layers. All theoretical results were compared with available experimental data.Comment: 16 pages, 5 figures, 3 table

Plasma lipids are altered in Gaucher disease: Biochemical markers to evaluate therapeutic intervention

Enzyme replacement therapy has been in clinical practice for the non-neuronopathic form of Gaucher disease for 15 years. However, the wide phenotypic variability in this disorder poses challenges to clinicians to assess patient severity and disease progression in order to effectively manage patients. Once therapy is initiated, methods to monitor the complex biochemical changes associated with the disease, and the response of these changes to therapy, are required in order to tailor therapy regimens to individual patients. We have evaluated the suitability of plasma sphingolipids and phospholipids as biochemical markers of disease burden and the efficacy of therapy to reduce that burden. Over 60 lipid species were measured using electrospray ionization-tandem mass spectrometry in plasma from controls and Gaucher patients, pre- and post-therapy. Glucosylceramide, molecular species of phosphatidylglycerol and G(M3) ganglioside were elevated in Gaucher disease, whereas species of ceramide, dihexosylceramide and sphingomyelin were decreased. Multivariate analysis enabled us to calculate the combined response of these lipids to therapy in Gaucher patients and correlate them with patient severity. Plasma lipids are proposed to be useful biomarkers for Gaucher disease.Peter J. Meikle, Philip D. Whitfield, Tina Rozaklis, David Blacklock, Stephen Duplock, Deborah Elstein, Ari Zimran, Eugen Mengel, Paul Cannell, John J. Hopwood and Maria Fullerhttp://www.elsevier.com/wps/find/journaldescription.cws_home/622796/description#descriptio

Chemical functionalization of graphene with defects

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