Published in Journal of Physical Chemistry C 117, 18919 (2013).

Graphene Nucleation Density on Copper: Fundamental Role of Background Pressure

Ivan Vlassiouk,1 Sergei Smirnov,2 Murari Regmi,1 Sumedh P. Surwade,1 Nishtha Srivastava,3 Randall Feenstra,3 Gyula Eres,1 Chad Parish,1 Nick Lavrik,1 Panos Datskos,1 Sheng Dai,1 and Pasquale Fulvio1
1Oak Ridge National Laboratory, Oak Ridge, TN
2Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, NM
3Department of Physics, Carnegie Mellon University, Pittsburgh, PA

Abstract

In this paper we discuss the effect of background pressure and synthesis temperature on the graphene crystal sizes in chemical vapor deposition (CVD) on copper catalyst. For the first time, we quantitatively demonstrate a fundamental role of the background pressure and provide the activation energy for graphene nucleation in atmospheric pressure CVD (9 eV), which is substantially higher than for the low pressure CVD (4 eV). We attribute the difference to a greater importance of copper sublimation in the low pressure CVD, where severe copper evaporation likely dictates the desorption rate of active carbon from the surface. At atmospheric pressure, where copper evaporation is suppressed, the activation energy is assigned to the desorption energy of carbon clusters instead. The highest possible temperature, close to the melting point of copper, should be used for large single crystal graphene synthesis. Using these conditions, we have synthesized graphene single crystals with sizes over 0.5 mm. Single crystal nature of synthesized graphene was confirmed by low energy electron diffraction. We also demonstrate that CVD of graphene at temperatures below 1000 °C shows higher nucleation density on (111) than on (100) and (101) copper surfaces but there is no identifiable preference at higher temperatures.

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