Effect of intermittent oxygen exposure on chemical vapor deposition of graphene
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Research Letter
Effect of intermittent oxygen exposure on chemical vapor deposition of graphene Selcuk Temiz, Zafer Mutlu, and Sina Shahrezaei, Materials Science and Engineering Program, University of California, Riverside, CA 92521, USA Mihrimah Ozkan, Materials Science and Engineering Program, University of California, Riverside, CA 92521, USA; Department of Electrical and Computer Engineering, University of California, Riverside, CA 92521, USA Cengiz S. Ozkan, Materials Science and Engineering Program, University of California, Riverside, CA 92521, USA; Department of Mechanical Engineering, University of California, Riverside, CA 92521, USA Address all correspondence to Cengiz S. Ozkan at [email protected] (Received 27 July 2017; accepted 26 September 2017)
Abstract Chemical vapor deposition is the most proficient method for growing graphene on copper foils due to its scalability, repeatability, and uniformity, etc. Herein, we systematically study the effect of oxygen (O2) exposure on graphene growth. We introduced O2 before and during the growth, and then studied its effects on the morphology, crystallinity, and nucleation density of graphene. We observe that introducing O2 during growth significantly improves the graphene crystallinity while pre-dosing O2 before growth reduces the graphene nucleation density. These studies suggest that intermittent O2 exposure play a significant role in graphene growth, enabling scalable production of high-quality graphene.
Introduction Graphene, as one of many stable carbon (C) allotropes, is the two-dimensional (2D) arrangement of C atoms on a hexagonal lattice structure. Even though, theoretical studies of graphene went back to 1940s,[1] the experimental work on graphene has started in 2004, by Geim and Novoselov and their discovery of isolation of single-layer graphene by using the so-called scotch tape method,[2] and number of publications both experimental and theory are getting exponentially increased since then. Graphene is an exceptional material with its unique properties such as high electrical and thermal conductivity,[3,4] excellent electronic mobility,[5,6] and mechanical strength[7] by far than any other materials. In graphene, four outer shell electrons make three σ bonds in plane and leaving one out of plane pz orbital available for electronic conduction. These σ bonds formed by the sp2 orbitals give graphene excellent mechanical and thermal properties. Graphene is around hundred times stronger than the strongest steel, and it is quite flexible. The highly mobile pz orbital electrons are located above and below the graphene sheet, and they give graphene excellent electronic properties such as Dirac-type energy dispersion, high mobility, etc. Dirac-type energy dispersion in graphene implies that electrons have zero effective mass, and lack of electronic bandgap enables ballistic carrier transport around symmetry points. Graphene can be synthesized by using different methods such as chemical vapor deposition (CVD),[8] epitaxial graphene growth on silicon carbide
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