Control of thickness uniformity and grain size in graphene films for transparent conductive electrodes

Abstract

Large-scale and transferable graphene films grown on metal substrates by chemical vapor deposition (CVD) still hold great promise for future nanotechnology. To realize the promise, one of the key issues is to further improve the quality of graphene, e.g., uniform thickness, large grain size, and low defects. Here we grow graphene films on Cu foils by CVD at ambient pressure, and study the graphene nucleation and growth processes under different concentrations of carbon precursor. On the basis of the results, we develop a two-step ambient pressure CVD process to synthesize continuous single-layer graphene films with large grain size (up to hundreds of square micrometers). Scanning electron microscopy and Raman spectroscopy characterizations confirm the film thickness and uniformity. The transferred graphene films on cover glass slips show high electrical conductivity and high optical transmittance that make them suitable as transparent conductive electrodes. The growth mechanism of CVD graphene on Cu is also discussed, and a growth model has been proposed. Our results provide important guidance toward the synthesis of high quality uniform graphene films, and could offer a great driving force for graphene based applications.

Single-step deposition of high-mobility graphene at reduced temperatures

“…7a-d and detailed in Methods and Supplementary Note 2. The average value of the FWHM of the 2D-band, which was fit to a single Lorentzian, was 28.8 cm À 1 , and the average ratio (I 2D /I G ) ¼ 2.7, both consistent with the figure of merit for monolayer graphene [15][16][17][18]20 .…”

“…6a indicates negligible defects, whereas the histogram of the 2D/G intensity ratio (I 2D / I G ) shown in Supplementary Fig. 6b reveals that the average of the (I 2D /I G ) value is B2, which agrees with the figure of merit (I 2D /I G )41 for monolayer graphene [15][16][17][18] . This notion of predominantly monolayer graphene described in this work is further corroborated by detailed studies of a PECVD-graphene sample transferred from Cu to a SiO 2 substrate, which prevents the complication of slow oxidation of the Cu substrate that could result in the 2D linewidth broadening with time due to the influence of the substrate (see Supplementary Note 2).…”

“…In contrast, spectra from the bottom side (Fig. 1k) showed that the D-band decreased and eventually vanished with increasing growth time, whereas the relative intensities of 2D and G-bands indicate the formation of monolayer graphene [15][16][17][18] , as described in Methods and Supplementary Fig. 6a,b.…”

“…7a-d, a large spatial map over an area of (160 Â 150) mm 2 revealed a mean FWHM value ¼ 28.8 cm À 1 for the 2D-band and a mean value (I 2D /I G ) ¼ 2.7, both are consistent with predominantly monolayer graphene if we use either the criterion of 2D-band FWHMo30 cm À 1 as the figure of merit for monolayer graphene on SiO 2 (ref. 20) or the criterion (I 2D /I G )41 for monolayer graphene on various substrates [15][16][17][18] .…”

Single-Layer Graphene Synthesis on a Al2O3(0001)/Cu(111) Template Using Chemical Vapor Deposition

“…To assess the growth mechanism, one has to detect first if the second graphene layer grows on top of the first layer (see Figs. 1a-1b), [30][31][32] or between the first layer and the growth substrate (see Figs. 1c-1f).…”