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Unformatted text preview: Laser-Synthesized Epitaxial Graphene Sangwon Lee, Michael F. Toney, Wonhee Ko, , ' Jason C. Randel, , ' Hee Joon Jung, Ko Munakata, Jesse Lu, Theodore H. Geballe, Malcolm R. Beasley, Robert Sinclair, Hari C. Manoharan, ' ,# and Alberto Salleo , * Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States, Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States, Department of Applied Physics, Stanford University, Stanford, California 94305, United States, ' Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States, and Department of Electrical Engineering and # Department of Physics, Stanford University, Stanford, California 94305, United States M uch exciting materials physics centered around graphene has been uncovered in only a few years since the realization that a single-layer graphene sheet is stable. 1 2 3 Control over the synthesis of this material however is still being developed and high-quality wafer- scale graphene layers cannot be reproduc- ibly fabricated. Various synthesis ap- proaches have been suggested by different research groups. 2,4 2 12 The first graphene studies were made on micromechanically exfoliated highly oriented pyrolitic graph- ite. 2 While this method produces high- quality graphene flakes, it is not suitable for scaling and industrial production. More recently, methods based on chemical vapor deposition (CVD) on a transition metal film or surface segregation of carbon out of a su- persaturated metal (Ru) film were proposed. 7 2 10,13 Using these techniques, graphene films were obtained over large ar- eas; however, since the synthesis occurs at high temperature ( ; 1000 C), the large dif- ference in the thermal expansion coeffi- cients between the materials leads upon cooling to the formation of wrinkles up to tens of nm in height in the graphene layer. Furthermore, the quality of the graphene layer is sensitive to the grain structure of the underlying metal: ultrasmooth essentially single crystalline regions in the metal films are required to obtain good quality graphene. Finally, the graphene films grown on metals must be subsequently trans- ferred to substrates suitable for the fabrica- tion of microelectronic devices. Other graphene preparation methods based on chemical synthesis 6 or unzipping of nanotubes 11,12 suffer from drawbacks such as low yield and difficulty to controllably po- sition the graphene films on a substrate. A very promising route toward the syn- thesis of well-controlled and uniform graphene films for electronic applications is thermal decomposition of SiC. By heat- ing SiC in a vacuum, Si evaporates and a layer of graphene forms, termed epitaxial graphene (EG) because of its crystallo- graphic relationship with the underlying SiC lattice....
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- Fall '08