A 'modified' Langmuir-Blodgett technique for transfer of graphene oxide monolayer sheets on solid substrates

A 'modified' Langmuir-Blodgett (MLB) technique has been developed as a simple, low cost, energy efficient and scalable alternative to conventional Langmuir-Blodgett (LB) technique for the transfer of graphene oxide (GO) monolayer sheets from air-water interface on to solid substrates. This technique uses a simple apparatus consisting of a glass or teflon reservoir and a vertically held stationary substrate. The transfer of GO sheets from the air-water interface onto hydrophilic substrates takes place by a downward movement of the meniscus, through controlled draining of subphase. The MLB technique facilitates the transfer of well defined, uniformly distributed, morphologically flat and adherent GO sheets under a wide range of conditions, namely subphase pH in the range, 3.5-6.5, target pressure in the range, 0.5-8 mN m(-1) and meniscus speed in the range, 0.5-3 mm min(-1) on RCA-1 treated Si and SiO2/Si. Compared to LB technique, it offers a substantially larger tolerance for subphase and transfer conditions, even on 'weakly' hydrophilic (RCA-1 treated) Si substrates, as neither crumpling of GO sheets nor transfer of GO agglomerates and multilayers are observed in a wide window of operation. Subsequent chemical reduction of the MLB transferred GO sheets with hydrazine vapor followed by thermal treatment at 400 degrees C results in reduced graphene oxide (RGO) sheets, which contain similar to 70% graphitic carbon, with O/C ratio similar to 0.16 and display Raman G-mode similar to 1590 cm(-1), together with I(D)/I(G) ratio similar to 1. The electrical conductivity and field effect mobility values of RGO sheets were measured in back gated field effect geometry and are comparable to those for RGO sheets obtained by LB as well as other approaches, followed by chemical/thermal reduction. Thus the newly developed MLB technique opens a simple, versatile and scalable route to obtain device quality GO and RGO sheets on solid substrates