Previous studies have shown that monolayer graphene films can be grown on Cu substrates by the catalytic decomposition of methane molecules.[1-5] The solubility of carbon in Cu is negligible at the growth temperatures typically used for graphene growth. This results in the formation of films that self-terminate at a monolayer coverage since there is very little (if any) carbon in the sub-surface region that can precipitate to the graphene overlayer during the cooling phase. Indeed, our prior work suggests that the growth is entirely surface mediated with no contribution from segregation of carbon from the bulk.[2] In an attempt to enhance the catalytic activity of the surface and to grow multilayer graphene rather than solely monolayer graphene, use of a commercial 70%-30% Cu-Ni alloy foil (which also has some Fe and Mn present) has been investigated. Growth was performed in a home-made, cold-wall, chemical vapor deposition (CVD) system [6] at a growth temperature of 1000 ° C (as measured with a pyrometer through a quartz window) with pure CH4 at a pressure of 8 Torr. To determine the surface alloy composition during the different phases of growth, X-ray photoelectron spectroscopy (XPS) measurements have been performed on the Cu-Ni foil before anneal, after anneal in H2, and after growth of graphene in a CH4 environment. XPS measurements were made at both normal emission, and at an exit angle of 50° to enhance the surface sensitivity. Before anneal, the measurements indicate that the surface is Ni-rich and heavily oxidized. After annealing in H2, only a small amount of oxide remained, and the alloy fraction of the surface region was 21% Ni. This indicates that the outermost layer of atoms is probably Cu, but further study is indicated. Growth of the graphene overlayer resulted in an increase of the Ni composition of the surface region to 28%, with only trace amounts of oxygen present. Low energy electron diffraction (LEED) measurements of the foils showed only diffuse background for the Cu-Ni foils before anneal and after anneal in H2. The LEED measurements of the foil after graphene growth showed diffraction spots and ring structures at 70 eV, which are attributed to the formation of multidomain graphene. Support from the Office of Naval Research is appreciated.

[1] X. S. Li, et al., Science 324, 1312 (2009).

[2] X. S. Li, et al., Nano Letters 9, 4268 (2009).

[3] X. S. Li, et al., Nano Letters 9, 4359 (2009).

[4] X. S. Li, et al., ECS Transactions 19, 41 (2009).

[5] W. Cai, et al., Nano Letters (in-press).

[6] W. Cai, et al., Nano Research 2, 851 (2009).