Final Report Summary - ECO-GRAPHENE (Electronic correlation in pristine and doped graphene layers)
We have investigated the distinct changes of the electronic band structure upon (1) covalent, (2) substitutional and (3) ionic functionalization. To that end we have performed functionalization of graphene on metals by (1) hydrogen, (2) nitrogen and (3) potassium. It has been shown that the relevant physics in each case is quite different. The huge charge transfer of alkali metals results in an increase of the Fermi level, and the lattice distortion induced by hydrogenation causes defect scattering and bandgap opening. Regarding substitutional doping by nitrogen impurities, it was shown that sp2 bonded nitrogen transfers charge to graphene.
We have also found a new electronic state in H-graphene that is located between the π and π * bands. For undoped H-graphene this state is energetically situated within the gap around EF and is accessible with absorption spectroscopies such as NEXAFS. In the case of n-doped H-graphene the midgap state becomes available for electrons and directly observable with ARPES since it is then situated below EF . Therefore, the H impurity band likely acts as an electron acceptor level which provides the possibility to control the electron concentration in Hgraphene via the H/C ratio. An estimation of the Mott criterion and a calculation of the typical DOS suggests that above H/C 1% and below H/C 6%, the acceptor level can form an extended impurity band.
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