Metal-catalyzed graphitization in Ni-C alloys and amorphous-C/Ni bilayers
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Metal-catalyzed graphitization in Ni-C alloys and amorphous-C/Ni bilayers Katherine L. Saenger, Christian Lavoie, Roy Carruthers, Ageeth A. Bol, Timothy J. Mcardle, Jack O. Chu, James C. Tsang, and Alfred Grill IBM Semiconductor Research and Development Center Research Division, T. J. Watson Research Center, Yorktown Heights, NY 10598 ABSTRACT Metal-catalyzed graphitization from vapor phase sources of carbon is now an established technique for producing few-layer graphene, a candidate material of interest for post-silicon electronics. Here we describe two alternative metal-catalyzed graphene formation processes utilizing solid phase sources of carbon. In the first, carbon is introduced as part of a cosputtered Ni-C alloy; in the second, carbon is introduced as one of the layers in an amorphous carbon (a-C)/Ni bilayer stack. We examine the quality and characteristics of the resulting graphene as a function of starting film thicknesses, Ni-C alloy composition or a-C deposition method (physical or chemical vapor deposition), and annealing conditions. We then discuss some of the competing processes playing a role in graphitic carbon formation and review recent evidence showing that the graphitic carbon in the a-C/Ni system initially forms by a metal-induced crystallization mechanism (analogous to what is seen with Al-induced crystallization of amorphous Si) rather than by the dissolution-upon-heating/precipitation-upon-cooling mechanism seen when graphene is grown by metal-catalyzed chemical vapor deposition methods. INTRODUCTION Few-layer graphene has attracted intense interest as a possible material for post-silicon electronic devices due to its high mobility, two-dimensional structure, and tunable band gap [1-3]. Methods for forming graphene such as mechanical exfoliation from graphite [3] and decomposition of single-crystal SiC [4] are not readily scalable to the wafer-scale dimensions that are expected to be required for semiconductor manufacturing. One potentially scalable method is metal-catalyzed chemical vapor deposition (CVD), in which graphene is formed on a metallic template layer exposed to a carbon-containing gas at elevated temperature (900-1000 o C). Several groups have shown that it is possible to grow few-layer graphene on Ni and transfer it to insulating substrate layers [2,5,6]. We have been investigating alternative metal-catalyzed graphene formation processes utilizing solid-phase sources of carbon. In a first approach, shown in Fig. 1A, the carbon is introduced as a component of a Ni-C alloy film; in a second, the carbon is introduced as a layer in an amorphous carbon (a-C)/Ni bilayer stack [7,8], as shown in Fig. 1B. It was hoped that these approaches might provide films of quality comparable to those achieved by CVD, but with better control over film thickness (since the carbon supply is fixed and finite. In this work, we examine the quality and characteristics of the graphene produced with these two methods as a function of starting film thicknesses, Ni-C alloy composition or a-C deposition met
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