Electrically tunable bandgap observed in ABC-trilayer graphene
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Electrically tunable bandgap observed in ABC-trilayer graphene
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raphene’s hexagonal honeycomb lattice leads to a band structure that can be represented by two cones that touch at and are symmetric about the Dirac energy. Single-layer graphene therefore has a zero bandgap and the electrons and electron holes have the same properties. With no bandgap, however, it is difficult to control the electrical conductivity of graphene and opening of a tunable bandgap would represent a significant step forward in exploiting graphene in electronic and photonic applications. One approach to achieving a bandgap is through the use of materials consisting of crystallographically stacked layers of graphene. While a bandgap has been induced in AB-stacked bilayer graphene through application of a perpendicular electric field, this does not occur in typical trilayer graphene, which exhibits ABA, or Bernal stacking, due to its mirror symmetry (see Figure 1a). The recently discovered rhombohedral trilayer graphene, which has ABC stacking (see Figure 1b), has, however, been predicted to exhibit an induced bandgap. Now, T.F. Heinz and co-researchers from Columbia University along with E. Capelluti from the Institute for Complex Systems, Italy, and Instituto de Ciencia de Materiales de Madrid,
rived in this work provides a guide to identifying the active sites needed for the formation of complex metal hydrides for hydrogen storage applications. In addition, these studies show that, in place of expensive and less available noble metals, an inexpensive and abundant metal such as aluminum can be turned into an active catalyst by selectively placing Ti atoms on the surface, thus enabling activation of molecular hydrogen and facilitating CO and hydrogen removal at low tempera-
tures. Furthermore, even though high concentrations of CO can block the Ti sites, thereby inhibiting catalytic activity toward hydrogen activation, the active sites show a promising tolerance to low contamination levels of CO in H2. Lower desorption temperatures occur under these conditions, which frees up the active sites. This work provides the first direct evidence that Al doped with Ti can carry out the essential first step of molecular hydrogen activation. Jean Njoroge
Spain, have used b a theory and experiment to demonstrate bandgaps as large as 120 meV in ABCtrilayer graphene. As reported in the September 25 online edition of Nature Physics (DOI: 10.1038/ A3 B3 A3 B3 d c nphys2102), the A2 B2 A2 B2 researchers invesA1 B1 A1 B1 tigated graphene trilayer samples Figure 1. Crystal structures are shown for (a) ABA and (b) ABC trifrom exfoliated kish layer graphene. The yellow and green atoms represent the A and B sublattices of the graphene honeycomb structure, respectively. graphite (a nearly Tight-binding diagrams are shown for (c) ABA and (d) ABC trilayer ideal crystal pregraphene. Effective interlayer coupling vanishes at the K-point, cipitated from molso that the yellow atoms become non-bonding monomers. The blue atoms then form a trimer in the ABA trilayer,
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