Nano Focus
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ith the 2010 Nobel Prize awarded to K.S. Novoselov and A.K. Geim, for their study of graphene, a perspective by P. Avouris, at the IBM T. J. Watson Research Center, published in the November 10th issue of Nano Letters (DOI: 10.1021/ nl102824h; p.4285) on graphene’s electronic and photonic properties and devices is particularly timely. Extensive research has resulted from Novoselov and Geim’s work, reflected in the atypical short amount of time between discovery and award. As an ideal two-dimensional system with single atom thickness and noninteracting π and π* states, graphene possesses striking properties that not only enable validation of physical theory but also appear to make possible a variety of new materials for electronics and photonics applications. Although graphene shares many electrical properties with carbon nanotubes (CNTs), Avouris said that, from a practical, device point of view, the biggest difference is dimensionality; CNT’s many different chiralities prevent it from being a well-defined starting material unlike graphene, whose planar geometry is suitable for the highly advanced techniques already in place in the semiconductor industry. For energies appropriate for electron transport, Avouris said that graphene’s
Nano Focus Ultrafast pump-probe measurement of electron spin relaxation of single atoms
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magnetic atom on a surface can exchange energy and angular momentum with its environment, giving it excited spin states of finite lifetime. Measuring the relaxation of these atomic states is potentially useful for quantum information processing, but achieving sufficient resolution in both space and time is a challenge.
hexagonal honeycomb lattice, with two atoms per unit cell, leads to a band structure represented by two cones that touch at and are symmetric about the Dirac energy (see figure). This demonstrates that graphene has zero bandgap, and that electrons and electron holes have the same properties. Another unusual property is that the density of states increases linearly with energy. Avouris summarized the outstanding transport properties of graphene, for example, in the ballistic regime, carriers exhibit a Fermi velocity of about 106 m/s with forbidden backscattering from long-range interactions resulting in elastic mean-free paths on the order of 100 nm. Avouris discussed the challenges of using graphene in field-effect transistors due to its lack of a bandgap and made a persuasive case that graphene is an ideal material for radio frequency analog electronic devices. Current devices and approaches to fabrication problems were also presented. Methods for opening a bandgap in graphene were summarized, including cutting graphene into strips in order to reduce its dimensionality, and applying a strong electric field to graphene bilayers. Avouris said that the combination of high light transmission and high conductivity should make graphene an excellent conductive electrode for solar cells, flat panel displays, touch screens, and organic light-emitting diodes but additional progress in pro
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