Effect of substrate and subphase conditions on the surface morphology of graphene oxide sheets prepared by Langmuir–Blodgett technique

Abstract

Graphene oxide (GO) sheets were transferred by Langmuir–Blodgett technique on Si and SiO2/Si substrates. The surface pressure – area isotherms of ‘amphiphilic’ GO sheets at the air–water interface are found to be highly sensitive to subphase pH, which significantly affects their hydrophilicity and the interaction between the sheets. The surface morphology of GO sheets transferred under different subphase and transfer conditions has been studied. RCA-1 (NH4OH:H2O2:H2O – 1:1:2) treatment of Si is found to be necessary for the transfer of GO sheets. The deposition on RCA-1 treated Si, is also highly sensitive to the compressibility of the Langmuir monolayer. Thus, transfer of well defined, uniformly distributed and flat GO sheets on Si is possible only in a narrow window of process parameters, namely, subphase pH, target pressure and lifting speed. In contrast, the transfer behavior and morphology of GO sheets on RCA-1 treated SiO2/Si is practically insensitive to changes in subphase pH, target pressure and lifting speed. This behavior is attributed to the uniformly strong hydrophilic character of SiO2/Si surface, compared to that of Si. The different behavior of Si surface, even after RCA-1 treatment, is attributed to its microscopic chemical and topographical inhomogeneities.