Supporting Information
Graphene CVD at very low pressure: The impact of substrate
surface self-diffusion in domain shape
Graphene growth from liquid source
As already mentioned in the main text, in this work we grew graphene by exposing the surface of
copper foils to a constant paraffinic oil vapor background (10-3 to 10-1 mTorr) at temperatures
ranging from 850 ºC to 980 oC. This carbon precursor is a petroleum derivative composed of a
mixture of alkanes with the molecular formula CnH2n+2 in the C20 to C50 range. The major benefit
of the employment of high molecular weight liquid precursor compared to the widely used
gaseous sources, such as methane and ethylene, is the achievement of large graphene domains
(0.5 mm2) using temperatures (960 ºC) and pressures (10-3 mTorr) lower than those generally
reported in the literature.1,2 This fact can be explained in terms of the competition between
desorption and dehydrogenation of different gas phase molecules. According to Choi et al.,3 an
adsorbed molecule is most likely to desorb from the surface back to the gas phase than to
dehydrogenate if its adsorption energy is much less than the energy barrier against
dehydrogenation. As an example, the enhanced bindings calculated for C6H6 and C18H14
molecules (0.67 and 1.93 eV, respectively) should facilitate their dehydrogenation by inhibiting
their easy desorption from the metal surface. In contrast, it is more difficult for the adsorbed CH4
molecules to dehydrogenate, because their desorption barrier of 0.17 eV is one order of
magnitude smaller than the dehydrogenation barrier. Consequently, graphene growth using CH4
as the carbon source can only proceed at much higher temperatures and supersaturated gas
pressures.4,5,6 Indeed, the adoption of the liquid precursor in this work occurred mainly because it
always led to better results in terms of graphene domain size than methane at our typical
experimental conditions.
In addition, no hydrogen or other gaseous species were employed during growth and it was
found that no pretreatment of the substrate was required before the synthesis; even the usual
thermal annealing was dispensed.
Figure S1 - Hillock formation during graphene growth at 980 ºC on Cu(311). (Ptotal= 8x10-6 Torr)
Figure S2 SEM image of graphene domains at different stages (T = 950oC). Due to large deviations in nucleation
time, various phases of growth can be observed in the same sample. The scale bar in the inset is 200 nm.
Figure S3 - Schematic view of the proposed growth model. Ds is the surface diffusion tensor, τs is the life time of an
atom in a state of mobile adsorption, 𝑲 is the kinectic coefficient which give a measure of how ease adatoms coming
from the lower terrace can stick to the growing edge.
References
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