Large-scale chemical vapor deposition of graphene on polycrystalline nickel films: Effect of annealing conditions

Abstract

In the present study, 8-in. silicon substrates, covered with thin (200 nm) polycrystalline nickel films have been employed for the growth of graphene by chemical vapor deposition. In order to control the uniformity and coverage of the graphene, thin nickel layers were used due to their less deep grain boundary grooves and ability to store less carbon in comparison with thick nickel films (>500 nm). The preferential sites for the growth of multilayer graphene were influenced by the surface pretreatment of the polycrystalline nickel films at 1025 °C under different ambient conditions (hydrogen and vacuum). Significant differences in the surface morphologies were observed for the annealed nickel films. The growth of larger grains up to ~6 μm for the films annealed in hydrogen could be attributed to hydrogen interstitials. On the other hand, grains up to ~3 μm were extracted for the films annealed in vacuum. Graphene was grown after exposing the annealed Ni films to ethylene at 925 °C. The lower range (42–106 cm−1) of full width at half maxima of the 2D band as determined by Raman spectroscopy was obtained for the films annealed in hydrogen as compared to the ones annealed in vacuum (51–128 cm−1), indicating that the thickness uniformity of graphene was strongly influenced by the surface modifications of nickel films.