Fabrication of metal nanoparticles-graphene nanocomposites and study of the charge transfer effect

Composites fabricated by metal nanoparticles supported on graphene sheets are promising for many technological applications ranging from sensing, energy production and storage, catalysis to electronics and optoelectronics. This is due to the benefits offered by the properties of both components. In particular, charge transfer effects at graphene-nanoparticles interface are the basis for the operation of several devices. Here we present an approach to fabricate hybrid composites consisting of graphene-noble metal nanoparticles. Mono- and bimetallic platinum and palladium nanoparticles are produced by laser ablation in a liquid environment and their morphology is characterized by transmission electron microscopy. In addition, in order to fabricate low-dimensional hybrid composites, the nanoparticles are loaded on graphene layer by spin coating of colloidal solutions and the density of the nanoparticles on graphene was evaluated by scanning electron microscopy. The nanoparticles-graphene charge transfer was studied by employing Raman spectroscopy and conductive atomic force microscopy. In particular, the degree of the G and 2D Raman peak shifts (evidenced by the Raman Spectroscopy measurements) and the characteristics of the current-voltage curves (evidenced by conductive atomic force microscopy) allowed inferring an n-type doping effect of the metal nanoparticles on the graphene properties, i. e. electrons transfer from the nanoparticles to the graphene layers. A combined analysis of these results allow us to demonstrate that the chemical composition of the metal nanoparticles is a key parameter in determining the charge transfer phenomenon in low-dimensional systems.