Electrical and Spectroscopic Characterizations of Ultra-Large Reduced Graphene Oxide Monolayers

Abstract

Ultra large and single-layer graphene oxide sheets (up to millimeter in lateral size) are obtained by a modified Hummers’ method, where we replace the first aggressive oxidation process with a short sonication step in H2SO4 solutions. The lateral size of obtained GO sheets can be adjusted by the sonication period: it decreases with the increasing sonication time. The thin-film electrodes made from ultra large reduced GO sheets exhibit lower sheet resistance compared with those from small-size reduced GO sheets. Moreover, the transistor devices made from these single-layer GO sheets after 800 °C thermal reduction exhibit the effective hole mobility ranged between 4 and 12 cm2/(V s). Raman spectroscopic results suggest that the enhancement in mobility at a higher-mobility regime is well explained by the graphitization of GO rather than the removal of functional groups. The ratio between the 2D and G peak areas, I(2D)/I(G), is well correlated to the effective hole mobility values in reduced GO sheets.

The extended growth of graphene oxide flakes using ethanol CVD

“…7 Despite these advantages and a substantial progress in RGO research over the years, we are still not able to produce RGO on 35 substrates with good homogeneity and conductivity for practical applications. 10 This is due to the incomplete, poor coverage and different sizes of RGO flakes on substrates; posing a challenge to working with RGO fabrication.…”

“…To grow and extend the size of RGO, a modified Hummers 10,21 method was first used to obtain Graphene Oxide (GO) sheets. Briefly, graphite flakes were pre-oxidized using concentrated H 2 SO 4 , ultra-sonicated and filtered to remove small graphite debris.…”

“…Then, the dried pre-oxidized graphite powder was added into concentrated H 2 SO 4 and KMnO 4 . Thereafter, the GO was 10 electrostatically attached to the APTES-functionalized SiO 2 substrates. The substrates, with 1-2 layers of GO on top, were placed on a holder and placed in a CVD tube furnace setup ( Figure S1).…”

“…These assignments are in agreement to previous reports. 10,25 After CVD treatment of 15 minutes (Figure 5b), the carbonyl and epoxy acid signatures In addition to C1s spectra, the C KLL spectra were also measured to compare sp 2 to sp 3 ratio in the treated samples. Figure 6 shows the spectra of the first derivative of X-ray excited C KLL between diamond, HOPG and CVD treated samples (treatment times = 15, 30, 60, 120 minutes).…”

“…Figure 6 shows the spectra of the first derivative of X-ray excited C KLL between diamond, HOPG and CVD treated samples (treatment times = 15, 30, 60, 120 minutes). The D value between 10 the maximum of the positive-going excursion and the minimum of the negative-going excursion in the derivative XAES spectra represents the energy separation. This D value conforms to linear proportionality between the graphite and diamond.…”