Substrate grain size and orientation of Cu and Cu-Ni foils used for the growth of graphene films

Abstract

Graphene growth on Cu foils by catalytic decomposition of methane forms predominantly single-layer graphene films due to the low solubility of carbon in Cu. On the other hand, graphene growth on Cu-Ni foils can result in the controlled growth of few-layer graphene films because of the higher solubility of carbon in Ni. One of the key issues for the use of graphene grown by chemical vapor deposition for device applications is the influence of defects on the transport properties of the graphene. For instance, growth on metal foil substrates is expected to result in multidomain graphene growth because of the presence of grains within the foil that exhibit a variety of surface terminations. Therefore, the size and orientation of the grains within the metal foil should influence the defect density of the graphene. For this reason, we have studied the effect of total anneal time and temperature on the orientation and size of grains within Cu foils and Cu-Ni alloy foils with a nominal concentration of 90/10 by weight. The graphene growth procedure involves preannealing the foil in a H(2) background followed by the graphene growth in a CH(4)/H(2) atmosphere. Measurements of the substrate grain size have been performed with optical microscopy and scanning electron microscopy. These results show typical lateral dimensions ranging from a few millimeters up to approximately a centimeter for Cu foils annealed at 1030 degrees C for 35 min and from tens of microns up to a few hundred microns for the 90/10 Cu-Ni foils annealed at 1050 degrees C for times ranging from 45 to 90 min. The smaller grains within the Cu-Ni foils are attributed to the higher melting point of the Cu-Ni alloy. The crystallographic orientation within each substrate grain was studied with electron backscatter diffraction, and shows that the preferred orientation for the Cu foil is primarily toward the (100) surface plane. For the 90/10 Cu-Ni foils, the orientation of the surface of the grains is initially toward the (110) plane and shifts into an orientation midway between the (100) and (111) planes as the anneal time is increased.