The Parameter Space of Graphene Chemical Vapor Deposition on Polycrystalline Cu

Abstract

A systematic study on the parameter space of graphene CVD on polycrystalline Cu foils is presented, aiming at a more fundamental process rationale in particular regarding the choice of carbon precursor and mitigation of Cu sublimation. CH 4 as precursor requires H 2 dilution and temperatures ≥1000°C to keep the Cu surface reduced and yield a high quality, complete monolayer graphene coverage. The H 2 atmosphere etches as-grown graphene, hence maintaining a balanced CH 4 /H 2 ratio is critical. Such balance is more easily achieved at low pressure conditions, at which however Cu sublimation reaches deleterious levels. In contrast, C 6 H 6 as precursor requires no reactive diluent and consistently gives similar graphene quality at 100-150°C lower temperatures. The lower process temperature and more robust processing conditions allow the problem of Cu sublimation to be effectively addressed. Graphene formation is not inherently self-limited to a monolayer for any of the precursors. Rather, the higher the supplied carbon chemical potential the higher the likelihood of film inhomogeneity and primary and secondary multilayer graphene nucleation. For the latter, domain boundaries of the inherently polycrystalline CVD graphene offer pathways for a continued carbon supply to the catalyst. Graphene formation is significantly affected by the Cu crystallography, i.e. the evolution of microstructure and texture of the catalyst template form an integral part of the CVD process.

Detection of graphene domains and defects using liquid crystals

“…Although LC alignment is known to rely on the p-stacking interactions between Gr. and LC molecules 17,18,26 , this effect does not explain the preference of one easy axis over the other two. Further study is needed to understand the origin of LC alignment on Gr.…”

A dilute Cu(Ni) alloy for synthesis of large-area Bernal stacked bilayer graphene using atmospheric pressure chemical vapour deposition

“…For instance, in low-pressure CVD, annealing at high temperatures !1000 C leads to a significant increase in the rate of Cu sublimation. 32 However, in atmospheric pressure CVD at the same annealing temperatures (i.e., !1000 C), the rate of Cu sublimation is expected to decrease significantly. In fact, at higher pressures, the sublimation of Cu is suppressed.…”

“…Nonetheless, H 2 effects in CVD graphene growth have positive effects. For instance, the effect of H 2 in CVD graphene growth was viewed as a co-catalyst in the formation of active surface bound carbon species required for graphene growth 32,35,36 and etches away the weak carbon-carbon bonds (graphene edges) for the growth of bilayer or multilayer graphene. 33,37 The effects of H 2 are expected to be the same for graphene films obtained on both Cu and Cu(0.46 at.…”

Chemical vapour deposition of freestanding sub-60 nm graphene gyroids

“…Hence the temperature instabilities of sub-micron unit cell structures can be similarly addressed for metals that in those respects show a similar behaviour to Ni, 37 such as Co, 43 or for metals, that require higher growth temperatures but have lower self-diffusivities, such as Pt. [44][45][46] For metals, such as Cu, that require higher temperatures for graphene growth and have high self-diffusivities (3 orders of magnitude higher for Cu than Ni at 900 °C), 47,48 successfully applying our approach may be more challenging. Nonetheless there are further avenues to increase template stability for instance by plasma precoating.…”