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Abstract: Graphene is a basic building block for carbon materials of all dimensionalities and exhibits many unique electronic properties. But, for future applications of graphene, further tuning its electronic band structure is necessary. Recently, it has been demonstrated that graphene can react with atomic hydrogen, which transforms this zero-band-gap semimetal into an insulator [[17] Elias et al., Science 323 (2009) 610]. Here we investigate the electronic and vibrational properties of graphene sheets with H in various configurations by means of first-principles calculations based on density-function theory. It is found that the hydrogenation not only effectively modulates the band gap of graphene but also leads to the band gap transition from direct to indirect. Meanwhile, the emerging of the sp3 type bonds induced by the hydrogenation may introduce some new vibrational modes in graphene, which play a key role in determining the spectra signatures of the resulting graphene derivatives. Our results provide a satisfactory explanation for the experimentally observed changes of the Raman spectra in graphene during the hydrogenation. [Copyright &y& Elsevier]

Abstract: We have investigated the electronic and magnetic properties of the room temperature ferromagnetic diluted magnetic semiconductor (DMS) (Zn,Cr)Te with density functional calculations. The electronic and magnetic properties of (Zn,Cr)Te are very similar with those of the typical DMS (Ga,Mn)As. The stronger ionicity of ZnTe plays a key role in the electronic and magnetic properties of (Zn,Cr)Te. [Copyright &y& Elsevier]

Abstract: Using first-principles methods, we have investigated structural and electronic properties of substitutional arsenic donor (AsHg), mercury vacancies (V Hg), and their complexes in arsenic doping of HgCdTe. The role of V Hg in arsenic activation has also been discussed. Counterintuitively, we find that AsHg and V Hg is a single donor and a single acceptor, respectively. The unpaired electron of AsHg makes it act as a nucleation center, driving arsenic interstitials into clusters, which is predicted as a potential candidate for arsenic deactivation. V Hg, exhibiting comparable formation energy with the AsHg donor as well as a shallow acceptor level, is a dominant compensating acceptor in as-grown materials. Coulomb interaction allows AsHg to bind at most one or two V Hg. The resulting complexes behave as compensating acceptors at low temperature. The model outlined for carrier compensation in arsenic-doped HgCdTe contacts well with experimental observations in arsenic activation. [Copyright &y& Elsevier]