- 2D Crystals
Researchers from the National Physical Laboratory (the NPL) and the University of Cambridge wants to redefine the ampere, using the world's first graphene single-electron pump (SEP).
The idea is to redefine the ampere in terms of the electron charge. The SEP creates a flow of individual electrons by shutting them in a quantum dot and then emitting them one at a time at a well-defined rate. The researchers managed to produce such a pump for the first time, and this can provide the speed of electron flow - which can be used to redefine the ampere.
We discuss flat-band surface states on the (111) surface in the tight-binding model with nearest-neighbor hopping on the diamond lattice, in analogy to the flat-band edge states in graphene with a zigzag edge. The bulk band is gapless, and the gap closes along a loop. The verge of the flat-band surface states is identical with this gap-closing loop projected onto the surface Brillouin zone. When anisotropies in the hopping integrals increase, the bulk gapless points move and the distribution of the flat-band states expands in the Brillouin zone. Then when the anisotropy is sufficiently large, the surface flat bands cover the whole Brillouin zone. Because of the completely flat bands, we can construct surface-state wavefunctions which is localized in all the three directions.
Due to the predominantly surface character of graphene, it is highly suitable for functionalization with external atoms and/or molecules leading to a plethora of new and interesting phenomena. Here we show ferromagnetic properties of hydrogen-functionalized epitaxial graphene on SiC. Ferromagnetism in such a material is not directly evident as it is inherently composed of only non-magnetic constituents. Our results nevertheless show strong ferromagnetism, which cannot be explained by simple magnetic impurities. The ferromagnetism is unique to hydrogenated epitaxial graphene on SiC, where interactions with the interfacial buffer layer play a crucial role. We argue that the origin of the observed ferromagnetism is governed by electron correlation effects of the narrow Si-dangling-bond (Si-DB) states in the buffer layer exchange-coupled to localized states in the hydrogenated graphene layer. This forms a quasi-three-dimensional ferromagnet with a Curie temperature higher than 300 K.
We analyze the role of ac-driven Rashba spin-orbit coupling in monolayer graphene including a spin-dependent mass term. Using the Magnus expansion as a semi-analytical approximation scheme a full account of the quasienergie spectrum of spin states is given. We discuss the subtleties arising in correctly applying the Magnus expansion technique in order to determine the quasienergy spectrum. Comparison to the exact numerical solution gives appropriate boundaries to the validity of the Magnus expansion solution.
A single graphene layer placed between two parallel Ni(111) surfaces screens the strong attractive force and results in a significant reduction of adhesion and sliding friction. When two graphene layers are inserted, each graphene is attached to one of the metal surfaces with a significant binding and reduces the adhesion further. In the sliding motion of these surfaces the transition from stick-slip to continuous sliding is attained, whereby non-equilibrium phonon generation through sudden processes is suppressed. The adhesion and corrugation strength continues to decrease upon insertion of the third graphene layer and eventually saturates at a constant value with increasing number of graphene layers. In the absence of Ni surfaces, the corrugation strength of multilayered graphene is relatively higher and practically independent of the number of layers. Present first-principles calculations reveal the superlubricant feature of graphene layers placed between pseudomorphic Ni(111) surfaces, which is achieved through the coupling of Ni-3d and graphene-$\pi$ orbitals. The effect of graphene layers inserted between a pair of parallel Cu(111) and Al(111) surfaces are also discussed. The treatment of sliding friction under the constant loading force, by taking into account the deformations corresponding to any relative positions of sliding slabs, is the unique feature of our study.
Using First-principle calculations, substrate effect of O-terminated (rt3 x rt3) MgO (111) on graphene was investigated for spintronics application. Surprisingly, the graphene can be turned into a spin-polarized semiconductor, which implies that the totally spin-polarized current can be generated and its on/off switching can be also controlled. The origin of the spin-polarized band structure is spin-ordering due to alternative sp2-sp3 covalent bondings induced by the MgO (111) substrate. The results indicate that the tailored pattern of the chemisorption can be highly efficient or introducing totally spin-polarized current to the graphene.
Silvan Roth, Fumihiko Matsui, Thomas Greber and Jürg Osterwalder
Zengguang Cheng, Junfeng Hou, Qiaoyu Zhou, Tianyi Li, Hongbian Li, Long Yang, Kaili Jiang, Chen Wang, Yuanchang Li and Ying Fang
Hyong Seo Yoon, Juhwan Lim, Sang Uk Son, Duck-Hwan Kim, Insang Song et al.
The detection of biotin-streptavidin binding was demonstrated by the resonance frequency measurement of a simple resonance circuit using graphene oxide dielectric. The resonance frequency was decreased to the lower frequency range as biotin and streptavidin were bound to the graphene oxide film. Gra … [Appl. Phys. Lett. 102, 193701 (2013)] published Tue May 14, 2013.
I. H. Baek, K. J. Ahn, B. J. Kang, S. Bae, B. H. Hong et al.
We investigate transmission characteristics and sheet conductivity of mono- to multi-layer graphene deposited on quartz in the terahertz (THz) frequency region. The free carrier absorption and Fabry-Perot interference between graphene layers give rise to nonlinear decrease of THz transmission from 7 … [Appl. Phys. Lett. 102, 191109 (2013)] published Tue May 14, 2013.
Author(s): Kristian Berland and Per Hyldgaard
The adsorption of benzene and C60 on graphene and boron nitride is studied using density functional theory with the van der Waals density functional (vdW-DF). By comparing these systems we can systematically investigate their adsorption nature and differences between the two functional versions vdW-…
[Phys. Rev. B 87, 205421] Published Tue May 14, 2013
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