Characterization and nanopatterning of organically functionalized graphene with ultrahigh vacuum scanning tunneling micr
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aphene is a two-dimensional atomic layer of sp2-bonded carbon in a honeycomb lattice.1–3 Seminal work exploring its unusual physics in 2004 Spurred substantial research activity, revealing exceptional properties for graphene, including high carrier mobilities,4,5 mechanical strength,6 optical transparency,7 and thermal conductivity.8 While this combination of properties suggests great promise for graphene in electronic applications, its lack of a bandgap and chemical inertness present challenges that need to be addressed before graphene is widely employed in integrated circuits.9,10 Surface functionalization of graphene is a potential solution, as chemical methods can modulate the band structure, tune doping levels, and provide tailored chemical reactivity that can seed the deposition and growth of other materials (e.g., dielectrics and metals) with precisely controlled interfaces. Many of the initial efforts to functionalize graphene have drawn from previously known chemistries involving graphite,
fullerenes, and carbon nanotubes. While these forms of carbon have been extensively studied and offer many promising directions for the chemical functionalization of graphene,11–13 several important differences exist between graphene and other carbon allotropes that can influence its chemical reactivity. For example, in contrast to graphite, suspended graphene has both surfaces available for reaction, while supported graphene can be structurally and/or electronically influenced by the underlying substrate. In addition, graphene lacks the high curvature of fullerenes and carbon nanotubes, which tends to reduce its chemical reactivity. For these reasons, graphene surface functionalization presents unique challenges and opportunities that make it a fertile area of materials research. As a two-dimensional material that is compatible with traditional planar fabrication techniques, lithographic patterning of graphene is also being pursued as a method for engineering its electronic properties.14 In particular, researchers are actively
Qing Hua Wang, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; [email protected] Mark C. Hersam, Materials Science and Engineering, Northwestern University, Evanston, IL 60208-3108 USA; [email protected] DOI: 10.1557/mrs.2011.134
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MRS BULLETIN • VOLUME 36 • JULY 2011 • www.mrs.org/bulletin
© 2011 Materials Research Society
CHARACTERIZATION AND NANOPATTERNING OF ORGANICALLY FUNCTIONALIZED GRAPHENE WITH STM
exploring nanolithography as a method for creating semiconducting graphene nanoribbons (GNRs) with an electronic bandgap inversely proportional to width.15,16 While GNRs have been produced by lithographic14,17 or chemical methods,18–20 the development of reliable methods for producing high yields of GNRs with a controlled bandgap remains an open challenge. Furthermore, since the electronic properties of a GNR depend sensitively on the geometry and passivation of its edges,21 lithographic and/or chemical strategies require improved precision at or near the atomic scale
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