Graphene: Materially Better Carbon
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Michael S. Fuhrer, Chun Ning Lau, and Allan H. MacDonald Abstract Graphene, a single atom–thick plane of carbon atoms arranged in a honeycomb lattice, has captivated the attention of physicists, materials scientists, and engineers alike over the five years following its experimental isolation. Graphene is a fundamentally new type of electronic material whose electrons are strictly confined to a two-dimensional plane and exhibit properties akin to those of ultrarelativistic particles. Graphene’s two-dimensional form suggests compatibility with conventional wafer processing technology. Extraordinary physical properties, including exceedingly high charge carrier mobility, current-carrying capacity, mechanical strength, and thermal conductivity, make it an enticing candidate for new electronic technologies both within and beyond complementary metal oxide semiconductors (CMOS). Immediate graphene applications include high-speed analog electronics and highly conductive, flexible, transparent thin films for displays and optoelectronics. Currently, much graphene research is focused on generating and tuning a bandgap and on novel device structures that exploit graphene’s extraordinary electrical, optical, and mechanical properties.
Introduction Graphene, a single atom–thick plane of carbon atoms arranged in a honeycomb lattice, is the conceptual building block for many carbon allotropes, from threedimensional graphite (a stack of graphene sheets), to one-dimensional carbon nanotubes (seamless graphene cylinders, see articles by Avouris and Martel and Liu and Hersam in this issue), to zero-dimensional buckyballs (closed graphitic cages). Until recently, this purely two-dimensional form of carbon existed only within three-dimensional graphite or tightly bound to another solid surface. Surface scientists had long been familiar with the latter appearance of graphene, or “monolayer graphite,” as an undesirable impurity layer on metal or semiconductor surfaces.1 However, the presence of a metal surface or of strong interactions between the host surface and monolayer graphite made electronic transport experiments difficult or impossible in most cases, and monolayer graphite remained an obscure curiosity. In a seminal paper in 2004, Andre Geim and Kostya Novoselov at Manchester University reported that graphene could be obtained by simply rubbing a piece of crystalline graphite against almost any smooth
surface, a process referred to as mechanical exfoliation.2,3 After exfoliating graphene on thin silicon dioxide over silicon, they found that single graphene layers could be readily identified in an optical microscope, and that they display strong field-effect transistor (FET) behavior, with silicon acting as the gate. Soon Geim and Novoselov, and simultaneously Philip Kim at Columbia University, demonstrated the quantum Hall effect in mechanically exfoliated graphene.4,5 The observation of the anomalous half-integer quantization of the Hall conductance6 provided convincing proof of the massless chiral nature of charge carriers in
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