Copper preoxidation effect on initial growth stages and individual graphene domains using ethanol precursor in chemical vapor deposition
Andrea Gnisci1*, Giuliana Faggio1, Giacomo Messina1
Theodoros Dikonimos2, Andrea Capasso3, Francesco Buonocore2, Nicola Lisi2
1* DIIES Dept., University “Mediterranea” of Reggio Calabria, 89122 Reggio Calabria, Italy,
2 ENEA, DTE PCU IPSE, Casaccia Research Centre, Via Anguillarese 301, 00123 Rome, Italy
3 Istituto Italiano di Tecnologia Graphene Labs, Via Morego 30, Genova 16163, Italy
Ethanol is an attractive precursor for the growth of graphene in replacement of methane because its operation it’s safer and cheaper. Its growth kinetic is faster than methane and it leads to the formation of continuous carbonaceous films in seconds rather than minutes [1-3]. As a consequence, individually nucleated graphene islands could not be observed before their coalescence into continuous films, and were not reported in literature until recently. However, hexagonal single-crystals of graphene with a size in the mm range had been grown by ethanol-CVD inside sealed copper “enclosures” [4, 5], where the copper surface was not directly exposed to the process gases.
By decreasing the ethanol flow (2 SCCM of 0.5% Ethanol in Ar) and reducing the process pressure (0.5-1torr), it was possible to observe graphene grains before they merged into the continuous film also on copper foils directly exposed to the precursor flow. Optical, electron and atomic force microscopy (AFM) and Raman spectroscopy were used to investigate the graphene domains on Cu and after their transfer on Si/SiO2 substrates.
We characterize aligned graphene domains growth on Cu(100) for different growth time and evaluate the effects of substrate pre-oxidation on nucleation density and graphene quality. The transfer of small graphene domains on the Si/SiO2 surface was successfully performed by using cyclododecane (C12H24) as supporting material during the Cu etching . Raman and AFM showed that graphene domains were predominantly single-layer, with regular shape and very low defect density and revealed that the presence of oxidized copper is effective in retarding the nucleation, by effectively limiting the available catalytic surface. Such results indicate that ethanol in very small concentrations, has the potential to replace methane, leading to the highly efficient growth of high quality, large domain graphene.
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