Graphene–ultrasmall silver nanoparticle interactions and their effect on electronic transport and Raman enhancement

The modulation of electrical and Raman properties of ultrafine (∼4 nm) Ag nanoparticle/graphene/SiO hybrid material at low coverage is evaluated with gradual nanoparticle incorporation by the gas aggregation deposition technique. The different contributing factors, such as doping, impurity scattering or strain, are assessed. Incorporation of Ag nanoparticles produce a very efficient n-type doping of graphene (∼7.5 e per particle) maintaining a constant mobility for particle coverage below ∼0.3 monolayers. Doping efficiency is determined by the probability for nanoparticles to be deposited in contact with graphene. The Fermi level upshift is modeled within the charged impurity scattering mechanism in the whole coverage range. A crossover to the regime where impurity scattering dominates is evidenced at large particle concentration. Surface-enhanced Raman scattering is detected in graphene phonons in the limit of vanishing plasmon resonance and very low coverage (∼0.08) that correspond to ∼1500 nanoparticles at the laser spot. Small distortions of the graphene lattice (±0.012%) induced by the nanoparticles overcome the predicted changes in Raman phonons related to carrier doping and originate I/I damping. This evolution of physical properties with gradual incorporation of Ag nanoparticles is anticipated to provide valuable hints to tune the optical and electronic performance of these graphene-based hybrid systems.
This work is supported by MINECO (MAT2012-37276-C03-01) and from Comunidad de Madrid, project S2013/MIT-2740 (PHAMA_2.0-CM).