Abstract
The mechanism by which Cu catalyst pretreatments control graphene nucleation density in scalable chemical vapor deposition (CVD) is systematically explored. The intrinsic and extrinsic carbon contamination in the Cu foil is identified by time-of-flight secondary ion mass spectrometry as a major factor influencing graphene nucleation and growth. By selectively oxidizing the backside of the Cu foil prior to graphene growth, a drastic reduction of the graphene nucleation density by 6 orders of magnitude can be obtained. This approach decouples surface roughness effects and at the same time allows us to trace the scavenging effect of oxygen on deleterious carbon impurities as it permeates through the Cu bulk. Parallels to well-known processes in Cu metallurgy are discussed. We also put into context the relative effectiveness and underlying mechanisms of the most widely used Cu pretreatments, including wet etching and electropolishing, allowing a rationalization of current literature and determination of the relevant parameter space for graphene growth. Taking into account the wider CVD growth parameter space, guidelines are discussed for high-throughput manufacturing of “electronic-quality” monolayer graphene films with domain size exceeding 1 mm, suitable for emerging industrial applications, such as electronics and photonics.
Highlights
Scalable, controlled crystal growth of graphene and related 2D materials is the foremost challenge and enabling factor for any technology exploiting their unique properties
For graphene growth on such polycrystalline Cu foils, it has been established that under most Chemical vapor deposition (CVD) conditions graphene does not preferentially nucleate at the Cu grain boundaries, neither do the lateral grain dimensions of the Cu surface limit the size of graphene domains.[18−20] The ever increasing body of literature on graphene nucleation control on polycrystalline Cu foils indicates that foil pretreatment is of paramount importance, whereby two main lines of treatment have emerged: surface etching/electropolishing[21−23] and the addition of oxygen.[14,19,24−26] It is widely demonstrated that graphene typically nucleates heterogeneously at defects, surface steps, and impurities on the Cu surface,[21,23,27] while the rationale for both treatment methods is eliminating or passivating these nucleation sites
A similar level of graphene nucleation density (GND) reduction can be achieved by depositing a cleaner film of Cu on top of the Cu foil, which buries/dilutes the initially present carbon impurities
Summary
Scalable, controlled crystal growth of graphene and related 2D materials is the foremost challenge and enabling factor for any technology exploiting their unique properties. Given the complexity of polycrystalline Cu surfaces combined with the highly dynamic nature of the Cu surface at elevated temperatures during CVD and the limited understanding of the graphene growth process, the causality and detailed effects of the various pretreatments remain largely unclear. While rolling striations in commercial Cu foils are well documented to cause an increased
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