Invited Paper 2D+MI+NS-MoA1
Observing the Mechanisms of Graphene Growth during Chemical Vapor Deposition: Routes to Controlling Layer Number and Domain Size

Monday, October 22, 2018, 1:20 pm, Room 201B

Chemical vapor deposition (CVD) on polycrystalline metal foils has emerged as the most economic and versatile means for producing 2D materials over large areas,¹ and directly integrating them with other device materials to achieve new functionality.² To tailor these materials to specific applications, a detailed understanding of the underlying growth mechanisms is required such that parameters such as domain size, defect density, and layer number can be precisely controlled. However, the elevated temperatures and reactive gas environments involved in growth make direct observation challenging, whilst ex situ measurements are often ambiguous.

Here we apply environmental scanning electron microscopy (ESEM) and ambient pressure X-ray photoelectron spectroscopy (APXPS) to directly observe graphene growth under realistic CVD conditions on polycrystalline Pt foils.³ This reveals a variety of processes involved in graphene formation including isothermal growth by direct hydrocarbon dissociation, isothermal dissolution into the catalyst bulk, and precipitation on cooling. The balance of these processes, and thus growth outcome, is shown to depends critically on the distribution of carbon close to the catalyst surface, which is in turn is intimately linked to the processing profile.We thereby develop a growth model for graphene CVD that considers precursor dissociation, mass-transport, attachment to the edge of growing graphene domains.⁴ This is shown to generally applicable to several transition metal catalysts,⁵ and serves as a general framework for understanding and optimizing the growth of 2D materials on polycrystalline catalysts.

We thus demonstrate that the CVD process can be rationally designed to yield different desired growth outcomes from the same polycrystalline starting catalyst, including uniform SLG with large domain sizes (>100 μm), large isolated BLG domains (>50 μm), and uniform BLG. Our result show that through targeted operando experiments the influence of key process parameters can be established, enabling precise control over 2D material growth including domain sizes and layer number.

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3. R. S. Weatherupet al. Nano Lett. 16, 6196–6206 (2016).

4. R. S. Weatherupet al. ACS Nano 6, 9996–10003 (2012).

5. A. Cabrero-Vilatela et al. Nanoscale 8, 2149–2158 (2016).