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Large local lattice expansion in graphene adlayers grown on copper
Chen, Chaoyu,Avila, José,Arezki, Hakim,Nguyen, Van Luan,Shen, Jiahong,Mucha-Kruczyń,ski, Marcin,Yao, Fei,Boutchich, Mohamed,Chen, Yue,Lee, Young Hee,Asensio, Maria C. Nature Publishing Group UK 2018 NATURE MATERIALS Vol.17 No.5
<P>Variations of the lattice parameter can significantly change the properties of a material, and, in particular, its electronic behaviour. In the case of graphene, however, variations of the lattice constant with respect to graphite have been limited to less than 2.5% due to its well-established high in-plane stiffness. Here, through systematic electronic and lattice structure studies, we report regions where the lattice constant of graphene monolayers grown on copper by chemical vapour deposition increases up to similar to 7.5% of its relaxed value. Density functional theory calculations confirm that this expanded phase is energetically metastable and driven by the enhanced interaction between the substrate and the graphene adlayer. We also prove that this phase possesses distinctive chemical and electronic properties. The inherent phase complexity of graphene grown on copper foils revealed in this study may inspire the investigation of possible metastable phases in other seemingly simple heterostructure systems.</P>
Moiré band model and band gaps of graphene on hexagonal boron nitride
Jung, Jeil,Laksono, Evan,DaSilva, Ashley M.,MacDonald, Allan H.,Mucha-Kruczyń,ski, Marcin,Adam, Shaffique American Physical Society 2017 Physical Review B Vol.96 No.8
<P>Nearly aligned graphene on hexagonal boron nitride (G/BN) can be accurately modeled by a Dirac Hamiltonian perturbed by smoothly varying moire pattern pseudospin fields. Here, we present the moire-band model of G/BN for arbitrary small twist angles under a framework that combines symmetry considerations with input from ab initio calculations. Our analysis of the band gaps at the primary and secondary Dirac points highlights the role of inversion symmetry breaking contributions of the moire patterns, leading to primary Dirac point gaps when the moire strains give rise to a finite average mass, and to secondary gaps when the moire pseudospin components are mixed appropriately. The pseudomagnetic strain fields, which can reach values of up to similar to 40 T near symmetry points in the moire cell stem almost entirely from virtual hopping and dominate over the contributions arising from bond length distortions due to the moire strains.</P>
Retraction Note: Large local lattice expansion in graphene adlayers grown on copper
Chen, Chaoyu,Avila, José,Arezki, Hakim,Nguyen, Van Luan,Shen, Jiahong,Mucha-Kruczyń,ski, Marcin,Yao, Fei,Boutchich, Mohamed,Chen, Yue,Lee, Young Hee,Asensio, Maria C. Springer Science and Business Media LLC 2018 NATURE MATERIALS Vol.17 No.11