Spontaneous Nucleation and Growth of Graphene Flakes on Copper Foil in the Absence of External Carbon Precursor in Chemical Vapor Deposition

Abstract

In this work, we uncover a mechanism initiating spontaneous nucleation of graphene flakes on copper foil during the annealing phase of chemical vapor deposition (CVD) process. We demonstrate that the carbon in the bulk of copper foil is the source of nucleation. Although carbon solubility in a pure copper bulk is very low, excess carbon can be embedded inside the copper foil during the foil production process. Using time-of-flight secondary ion mass spectrometry, we measured the distribution profile of carbon atoms inside the copper foils and its variation by thermal annealing. We also studied the role of hydrogen in the segregation of carbon from the bulk to the surface of copper during annealing by scanning electron microscopy and Raman analysis. We found that carbon atoms diffuse out from the copper foil and accumulate on its surface during annealing in the presence of hydrogen. Consequently, graphene crystals can be nucleated and grown while “any external” carbon precursor was entirely avoided. To our knowledge, this is the first time that such growth has been demonstrated to take place. We believe that this finding brings a new insight into the initial nucleation of graphene in the CVD process and helps to achieve reproducible growth recipes.

On the Dynamics of Intrinsic Carbon in Copper during the Annealing Phase of Chemical Vapor Deposition Growth of Graphene

“…This is because in P-6 the depleted carbon from below 10 nm depth is accumulated close to its surface (above 10 nm). However, contrary to the results of annealing at 6 mbar H 2 , or below, 34 the concentration of carbon near the surface is decreased after annealing at 17 mbar or above H 2 pressure. Accordingly, the crossing of carbon profiles does not happen for either P-17 or P-60.…”

“…The comparison of untreated Cu and the samples annealed in 6 mbar (P-6), 17 mbar (P-17), and 60 mbar (P-60) clearly demonstrates enhancement of carbon depletion below the surface of the Cu foil with increase of the hydrogen pressure. Data of untreated and P-60 is re-plotted from ref (34).…”

“…34 We have also observed that the H 2 partial pressure during the annealing of the Cu foil has a major effect on the structure of the carbon film; at H 2 pressures as low as 1.4 mbar, spontaneous nucleation of graphene is favored, but when the pressure was increased to 6 mbar predominantly disordered graphitic film (DGF) formation has occurred on the surface. 34…”

“…4,19,27−29 Likewise, whereas most of the studies on nucleation and growth of GFs were focused on the role of an external carbon source, either in the form of precursor or contamination, 10,11,14,23,30−33 only very recently has the role of carbon inside the foil in the nucleation of GFs been revealed. 19,28,34…”

Adlayer‐Free Large‐Area Single Crystal Graphene Grown on a Cu(111) Foil

“…In addition to the decomposition of methane, the carbon that is already present inside the Cu foil at the growth temperature needs to be considered. A recent paper says that such carbon can form graphene flakes (islands) on a Cu foil surface by diffusing out without any external carbon sources . However, our growth results using 13 CH 4 gas suggest that the graphene film (including adlayers) is entirely grown from the methane gas.…”