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PublicationsCategoriesFeatured paper: Electronic StructureTunable Excitons in Biased Bilayer Graphene
Cheol-Hwan Park and Steven G. Louie
Nano Lett., 2010, 10 (2), pp 426–431 Recent measurements have shown that a continuously tunable bandgap of up to 250 meV can be generated in biased bilayer graphene [Y. Zhang et al., Nature 459, 820 (2009)], opening up pathway for possible graphene-based nanoelectronic and nanophotonic devices operating at room temperature. Here, we show that the optical response of this system is dominated by bound excitons. The main feature of the optical absorbance spectrum is determined by a single symmetric peak arising from excitons, a profile that is markedly different from that of an interband transition picture. Under laboratory conditions, the binding energy of the excitons may be tuned with the external bias going from zero to several tens of meV’s. These novel strong excitonic behaviors result from a peculiar, effective “one-dimensional” joint density of states and a continuously-tunable bandgap in biased bilayer graphene. Moreover, we show that the electronic structure (level degeneracy, optical selection rules, etc.) of the bound excitons in a biased bilayer graphene is markedly different from that of a two-dimensional hydrogen atom because of the pseudospin physics. Featured paper: CVD growthWafer-Scale Synthesis and Transfer of Graphene FilmsNano Lett., 2010, 10 (2), pp 490–493
Youngbin Lee, Sukang Bae, Houk Jang, Sukjae Jang, Shou-En Zhu, Sung Hyun Sim, Young Il Song, Byung Hee Hong and Jong-Hyun Ahn
Featured paper: Mechanical PropertiesTunable Excitons in Biased Bilayer Graphene
Constanze Metzger, Sebastian Rmi, Mengkun Liu, Silvia V. Kusminskiy, Antonio H. Castro Neto, Anna K. Swan and Bennett B. Goldberg
Nano Lett., 2010, 10 (1), pp 6–10 Measurements on graphene exfoliated over a substrate prepatterned with shallow depressions demonstrate that graphene does not remain free-standing but instead adheres to the substrate despite the induced biaxial strain. The strain is homogeneous over the depression bottom as determined by Raman measurements. We find higher Raman shifts and Grneisen parameters of the phonons underlying the G and 2D bands under biaxial strain than previously reported. Interference modeling is used to determine the vertical position of the graphene and to calculate the optimum dielectric substrate stack for maximum Raman signal.
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