Experimental and DFT high pressure study of fluorinated graphite (C2F)(n).

XPS+EQUIPE-VIDE+LCSInternational audienceWe studied the high pressure behavior of poly(dicarbon monofluoride) (C2F)n up to 37 GPa both theoretically, within the first-principle framework of the density functional theory, taking into account van der Waals corrections to the total energy, and experimentally, combining in situ Raman spectroscopy, XRD and X-ray photoelectron spectroscopy (XPS) measurements. The (C2F)n structure has a complex mixed sp2 sp3 character where graphene layers are intercalated among sp3 carbon hybridized structural domains. We observed three phase transitions in the high pressure range explored. The first transition is observed around 12 GPa and is dominated by strain effects. Above 16 GPa the intercalated graphene layers corrugate and change from the sp2 to sp3 hybridization state. Above 25–27 GPa the new pressure-induced phase becomes unstable. We find that, by varying applied pressure or by changing the hybridization due to the fluorination of graphite, the band structure of (C2F)n can be modified, resulting in valence and conduction bands touching at the K point, as in graphene, thus turning (C2F)n into a semimetal. This could provide a new pathway to reversibly engineer the band structure and conductivity for applications in high energy density batteries

Performance of τ\tau-lepton reconstruction and identification in CMS

The performance of tau-lepton reconstruction and identification algorithms is studied using a data sample of proton-proton collisions at sqrt(s)=7 TeV, corresponding to an integrated luminosity of 36 inverse picobarns collected with the CMS detector at the LHC. The tau leptons that decay into one or three charged hadrons, zero or more short-lived neutral hadrons, and a neutrino are identified using final-state particles reconstructed in the CMS tracker and electromagnetic calorimeter. The reconstruction efficiency of the algorithms is measured using tau leptons produced in Z-boson decays. The tau-lepton misidentification rates for jets and electrons are determined