Tuning the surface morphology of self-assembled graphene-like thin films through pH variation

Graphene-like (GL) layers were prepared through a two steps oxidation/reduction method starting from a high surface carbon black, and pH of the GL layers in water suspension was varied. The effect of pH of such suspension on the morphology of self-assembled GL films has been studied. Zeta potentials of the water suspensions were measured to estimate the stability of the suspension at several pH values and to select the samples for deeper investigation by atomic force microscopy (AFM). AFM measurements on four different samples are then described and discussed. The reported results show how the surface roughness and morphology are affected by the pH in the preparation process: in particular, the lowest pH sample exhibits a granular surface, while at higher pH more regular morphologies are produced, with interesting observations as concerns the thickness of some surface features. The observations are interpreted in terms of the forces acting in water suspension and of the role of hydrophobic or hydrophilic behaviors. The results demonstrate the possibility to tune the surface properties of GL films by simply acting on the pH of the suspension during the fabrication, and help to understand the microscopic physical mechanisms involved in the film assembly. (C) 2015 Elsevier B.V. All rights reserved.