Layer-by-layer assembly of ultrathin composite films from micron-sized graphite oxide sheets and polycations

Unilamellar colloids of graphite oxide (GO) were prepared from natural grap hite and were grown as monolayer and multilayer thin films on cationic surf aces by electrostatic self-assembly. The multilayer films were grown by alt ernate adsorption of anionic GO sheets and cationic poly(allylamine hydroch loride) (PAH). The monolayer films consisted of 11-14 Angstrom thick GO she ets, with lateral dimensions between 150 nm and 9 mu m. Silicon substrates primed with amine monolayers gave partial GO monolayers, but surfaces prime d with Al13O4-(OH)(24)(H2O)(12)(7+) ions gave densely tiled films that cove red approximately 90% of the surface. When alkaline GO colloids were used, the monolayer assembly process selected the largest sheets (from 900 nm to 9 mu m) from the suspension. In this case, many of the flexible sheets appe ared folded in AFM images. Multilayer (GO/PAH)(n) films were invariably thi cker than expected from the individual thicknesses of the sheets and the po lymer monolayers, and this behavior is also attributed to folding of the sh eets. Multilayer (GO/PAH), and (GO/polyaniline)(n) films grown between indi um-tin oxide and Pt electrodes show diodelike behavior, and higher currents are observed with the conductive polyaniline-containing films. The resisit ivity of these films is decreased, as expected, by partial reduction of GO to carbon.