Showing papers by "K. S. Novoselov published in 2006"
TL;DR: This work shows that graphene's electronic structure is captured in its Raman spectrum that clearly evolves with the number of layers, and allows unambiguous, high-throughput, nondestructive identification of graphene layers, which is critically lacking in this emerging research area.
Abstract: Graphene is the two-dimensional building block for carbon allotropes of every other dimensionality We show that its electronic structure is captured in its Raman spectrum that clearly evolves with the number of layers The D peak second order changes in shape, width, and position for an increasing number of layers, reflecting the change in the electron bands via a double resonant Raman process The G peak slightly down-shifts This allows unambiguous, high-throughput, nondestructive identification of graphene layers, which is critically lacking in this emerging research area
13,474 citations
TL;DR: In this paper, it was shown that micrometre-size sensors made from graphene are capable of detecting individual events when a gas molecule attaches to or detaches from graphenes surface.
Abstract: The ultimate aspiration of any detection method is to achieve such a level of sensitivity that individual quanta of a measured value can be resolved. In the case of chemical sensors, the quantum is one atom or molecule. Such resolution has so far been beyond the reach of any detection technique, including solid-state gas sensors hailed for their exceptional sensitivity. The fundamental reason limiting the resolution of such sensors is fluctuations due to thermal motion of charges and defects which lead to intrinsic noise exceeding the sought-after signal from individual molecules, usually by many orders of magnitude. Here we show that micrometre-size sensors made from graphene are capable of detecting individual events when a gas molecule attaches to or detaches from graphenes surface. The adsorbed molecules change the local carrier concentration in graphene one by one electron, which leads to step-like changes in resistance. The achieved sensitivity is due to the fact that graphene is an exceptionally low-noise material electronically, which makes it a promising candidate not only for chemical detectors but also for other applications where local probes sensitive to external charge, magnetic field or mechanical strain are required.
5,510 citations
TL;DR: In this paper, it was shown that the Klein paradox can be tested in a conceptually simple condensed-matter experiment using electrostatic barriers in single and bi-layer graphene, showing that quantum tunnelling in these materials becomes highly anisotropic, qualitatively different from the case of normal, non-relativistic electrons.
Abstract: The so-called Klein paradox—unimpeded penetration of relativistic particles through high and wide potential barriers—is one of the most exotic and counterintuitive consequences of quantum electrodynamics. The phenomenon is discussed in many contexts in particle, nuclear and astro-physics but direct tests of the Klein paradox using elementary particles have so far proved impossible. Here we show that the effect can be tested in a conceptually simple condensed-matter experiment using electrostatic barriers in single- and bi-layer graphene. Owing to the chiral nature of their quasiparticles, quantum tunnelling in these materials becomes highly anisotropic, qualitatively different from the case of normal, non-relativistic electrons. Massless Dirac fermions in graphene allow a close realization of Klein’s gedanken experiment, whereas massive chiral fermions in bilayer graphene offer an interesting complementary system that elucidates the basic physics involved.
3,402 citations
08 May 2006
TL;DR: In this article, a spin valve effect was observed in planar graphite, where the applied field is swept between +450 G and -450 G. This was the first observation of spin valve effects in graphite.
Abstract: Graphene is a name given to an atomic layer of carbon atoms densely packed into a benzene-ring structure with a nearest-neighbour distance of ~1.4Aring. This theoretical material is widely used in the description of the crystal structure and properties of graphite, large fullerenes and carbon nanotubes. As a first approximation, graphite is made of graphene layers relatively loosely stacked on top of each other with a fairly large interlayer distance of ~3.4Aring . Carbon nanotubes are usually thought of as graphene layers rolled into hollow cylinders. Graphene films are made by repeated peeling of small (mm-sized) mesas of highly-oriented pyrolytic graphite (HOPG). The exfoliation continues until flakes that are nearly invisible in an optical microscope are obtained. A simple spin valve structure has been fabricated from such films using electron beam lithography. This is based on a symmetrical electrode structure and relies on imperfections in the two ferromagnetic electrodes to give different switching fields for each electrode. Despite this highly non-optimised structure we observed a 10% change in resistance at 300 K as the applied field is swept between +450 G and -450 G. The 10% change in resistance is much larger than can be attributed to MR effects in the individual permalloy electrodes (2.5% maximum), giving confidence that it is due to the spin valve effect with the graphene acting as the non-magnetic conductor. Although spin valve effects have been observed in carbon nanotubes this is the first observation of this effect in planar graphene.
7 citations
Posted Content•
12 Apr 2006
TL;DR: In this article, the so-called Klein paradox was tested in a conceptually simple condensed-matter experiment by using electrostatic barriers in single-and bi-layer graphene, showing that quantum tunneling in these materials becomes highly anisotropic, qualitatively different from the case of normal, nonrelativistic electrons.
Abstract: The so-called Klein paradox - unimpeded penetration of relativistic particles through high and wide potential barriers - is one of the most exotic and counterintuitive consequences of quantum electrodynamics (QED). The phenomenon is discussed in many contexts in particle, nuclear and astro- physics but direct tests of the Klein paradox using elementary particles have so far proved impossible. Here we show that the effect can be tested in a conceptually simple condensed-matter experiment by using electrostatic barriers in single- and bi-layer graphene. Due to the chiral nature of their quasiparticles, quantum tunneling in these materials becomes highly anisotropic, qualitatively different from the case of normal, nonrelativistic electrons. Massless Dirac fermions in graphene allow a close realization of Klein's gedanken experiment whereas massive chiral fermions in bilayer graphene offer an interesting complementary system that elucidates the basic physics involved.
2 citations