Graphene synthesis and characterization

All graphene was grown using standard literature methods on 25 μm thick Cu foils, as indicated in the main text. Prior to G, Cu substrates were annealed at T = 1000 oC in an H2 environment for ~1 hour. CH4 was then introduced for 10 minutes in order to synthesize graphene, after which the reactor was cooled to room temperature. This anneal was not performed for G growths (except for the sample shown in Fig. 1b right, which was annealed for 10 minutes at 1000 oC in order to ensure removal the induced copper oxide). Figure S1a below shows Raman spectra of various graphene growths. As noted in the main text, the n-doped graphene exhibits an additional D’ peak due to substitutional dopants. The G growths show a slight enhancement of the D and G peaks, likely due to a small amount of amorphous carbon left from the patterning process. S1b and c show DF-TEM images of samples grown using the successful orders as indicated in the table below. We have found that performing the G synthesis in a lower reactive environment (“Slow” growth) does not yield well connected films, as stated in the main text.