Ajuste do gap em grafeno bi-camada do...

Tunable band gap in AB-stacked bilayer graphene.

Graphene is a two-dimensional carbon material that takes the form of a planar lattice of sp2 bonded atoms. Since the monolayer graphene was isolated in 2004, ultrathin carbon systems have attracted tremendous attention[1]. The properties of electrons in graphene are fundamentally different from those deriving from the Schrodinger equation. In particular the quantum Hall effect is quantized with integer plus half values[2,3] and can even be observed at room temperature[4]. Monolayer graphene has a vanishing Fermi point at the Brillouin-zone corner and low-energy quasiparticles with a linear spectrum , which obey a massless Dirac equation.

The electronic bandgap is an intrinsic property of semiconductors and insulators that determines their transport and optical properties. A tunable bandgap (as such, it has a central role in modern device physics and technology and governs the operation of semiconductor devices) would be highly desirable because it would allow great flexibility in design and optimization of devices such as p–n junctions, transistors, photodiodes and lasers. In particular if it could be tuned by applying a variable external electric field.

Bilayer graphene has an entirely different (and equally interesting) band structure. Most notably, the inversion symmetric AB-stacked (Bernal) bilayer graphene is a zero-bandgap semiconductor in its pristine form. But a non-zero bandgap can be induced by breaking the inversion symmetric of the two layers. Indeed, a bandgap has been observed in a one-side chemically doped epitaxial graphene bilayer. In our work, we added potassium atoms close to one-side to induce the symmetry breaking. Also, we studied the valence band  structure of a bilayer of graphene and demonstrated that through selective control of the carrier concentration in the graphene layers, one can easily tune the band structure near the Dirac crossing.

[1] A. H. Castro Neto, F. Guinea, N. M. R. Peres, K. S. Novoselov, and A. K. Geim, Rev. Mod. Phys. 81, 109 (2009).

[2] Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Katsnelson, M. I.; Grigorieva, I. V.; Dubonos, S. V.; Firsov, A. A. Nature 2005, 438, 197–200.

[3] Zhang, Y.; Tan, Y. W.; Stormer, H. L.; Kim, P. Nature 2005, 438, 201–204.

[4] Novoselov, K. S.; Jiang, Z.; Zhang, Y.; Morozov, S. V.; Stormer, H. L.; Zeitler, U.; Maan, J. C.; Boebinger, G. S.; Kim, P.; Geim, A. K. Science 2007, 315, 1379–1379.