Graphene CVD growth on copper and nickel: role of hydrogen in kinetics and structure

Abstract

Understanding the chemical vapor deposition (CVD) kinetics of graphene growth is important for advancing graphene processing and achieving better control of graphene thickness and properties. In the perspective of improving large area graphene quality, we have investigated in real-time the CVD kinetics using CH(4)-H(2) precursors on both polycrystalline copper and nickel. We highlighted the role of hydrogen in differentiating the growth kinetics and thickness of graphene on copper and nickel. Specifically, the growth kinetics and mechanism is framed in the competitive dissociative chemisorption of H(2) and dehydrogenating chemisorption of CH(4), and in the competition of the in-diffusion of carbon and hydrogen, being hydrogen in-diffusion faster in copper than nickel, while carbon diffusion is faster in nickel than copper. It is shown that hydrogen acts as an inhibitor for the CH(4) dehydrogenation on copper, contributing to suppress deposition onto the copper substrate, and degrades quality of graphene. Additionally, the evidence of the role of hydrogen in forming C-H out of plane defects in CVD graphene on Cu is also provided. Conversely, resurfacing recombination of hydrogen aids CH(4) decomposition in the case of Ni. Understanding better and providing other elements to the kinetics of graphene growth is helpful to define the optimal CH(4)/H(2) ratio, which ultimately can contribute to improve graphene layer thickness uniformity even on polycrystalline substrates.

Radiation-mode optical microscopy on the growth of graphene

“…Optical measurements can be performed under high temperature and high pressure conditions in which graphene grows on Cu. As an example of the optical measurements on the graphene growth, in situ Raman mapping on Ni and ellipsometry on Ni and Cu were reported to observe the graphene growth in real time so far 18,22 . However, the microscopic optical observation has not been reported on the CVD growth on Cu.…”

“…If the CVD process is observed in real time, it helps the optimization of parameters and the elucidation of the growth mechanism. To date, the real-time observations of the growth of graphene have been performed in ultra-high vacuum or low-pressure (o20 Pa) conditions on various metal substrates by scanning tunnelling microscopy, scanning transmission electron microscopy, low-energy electron microscopy, in situ Raman spectroscopy, environmental scanning electron microscopy (SEM) and so on [13][14][15][16][17][18][19][20][21][22] . From the viewpoint of scalable production of graphene, however, the combination of CH 4 gas and Cu substrate is considered the most promising, which requires the source gases with relatively high pressure from several Pa to atmospheric pressure [23][24][25][26][27][28][29] .…”

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

“…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.…”

Communication: Surface-to-bulk diffusion of isolated versus interacting C atoms in Ni(111) and Cu(111) substrates: A first principle investigation

“…10 The common understanding is that the extremely low solubility of C in Cu confines the active C species to the surface resulting in monolayer graphene, while the high solubility of C in Ni results in C segregation and precipitation to form multilayer graphene. 11 This argument has been used to explain why the CVD growth of graphene on Cu is self-limiting and will be independent of both the substrate thickness and the growth time, since the formation of monolayer graphene prevents further dissociation of methane. 12 It also correctly predicts that the number of graphene layers on Ni can be controlled by limiting the carbon content in bulk Ni.…”