Abstract
The chemical vapour deposition (CVD) of graphene on three polycrystalline transition metal catalysts, Co, Ni and Cu, is systematically compared and a first-order growth model is proposed which can serve as a reference to optimize graphene growth on any elemental or alloy catalyst system. Simple thermodynamic considerations of carbon solubility are insufficient to capture even basic growth behaviour on these most commonly used catalyst materials, and it is shown that kinetic aspects such as carbon permeation have to be taken into account. Key CVD process parameters are discussed in this context and the results are anticipated to be highly useful for the design of future strategies for integrated graphene manufacture.
Highlights
Chemical vapour deposition (CVD) has emerged as the dominant method to synthesise large single-crystalline domains and continuous films of “electronic-grade” graphene and other two-dimensional (2D) materials.[1,2,3,4,5] Critical to the graphene chemical vapour deposition (CVD) process is the use of a catalyst that enables low activation energy pathways for precursor dissociation, graphene nucleation, domain growth and merging
The central point is that while the catalyst’s carbon solubility presents a potential reservoir, depending on CVD conditions, this reservoir may never be filled, and the kinetics of the CVD process are critical to the growth behaviour
We thereby identify key CVD process parameters that must be adjusted to achieve the desired outcome based on consideration of the catalyst properties and the kinetics of growth
Summary
Chemical vapour deposition (CVD) has emerged as the dominant method to synthesise large single-crystalline domains and continuous films of “electronic-grade” graphene and other two-dimensional (2D) materials.[1,2,3,4,5] Critical to the graphene CVD process is the use of a catalyst that enables low activation energy pathways for precursor dissociation, graphene nucleation, domain growth and merging. The question of which catalysts can be used is of fundamental importance and a key issue for integrated graphene manufacture. We systematically compare graphene CVD on three polycrystalline transition metal catalysts, namely Co, Ni and Cu, and propose a first-order growth model that can serve as a reference to optimize growth on any elemental or alloy catalyst Roll-to-roll approaches demand reusability of the catalyst, low cost and ease of graphene removal,[6,7,8] whereas approaches without graphene transfer where the catalyst is part of the device structure or removed while the graphene stays on the target substrate demand graphene growth on a wide range of different catalyst materials at suitably benign CVD conditions.[9,10] In spite of numerous surface science studies on the atomic structure of graphene layers on different single-crystal metal surfaces,[11,12] the conditions and challenges for scalable graphene CVD are notably distinct and with a lack of basic understanding of graphene formation, catalyst selection criteria are yet to be well established.
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