Temperature dependent carrier mobility in graphene: Effect of Pd nanoparticle functionalization and hydrogenation

Abstract

The two dimensional nature of graphene, with charge carriers confined within one atomic layer thickness, causes its electrical, optical, and sensing properties to be strongly influenced by the surrounding media and functionalization layers. In this study, the effect of catalytically active Pd nanoparticle (NP) functionalization and subsequent hydrogenation on the hall mobility and carrier density of chemical vapor deposition synthesized graphene has been investigated as a function of temperature. Prior to functionalization, the mobility decreased monotonically as the temperature was reduced from 298 to 10 K, indicating coulomb scattering as the dominant scattering mechanism as expected for bilayer graphene. Similar decreasing trend with temperature was also observed after 2 nm Pd deposition, however, hydrogenation of the Pd NP led to significant enhancement in mobility from ∼2250 to 3840 cm2/V s at room temperature, which further monotonically increased to 5280 cm2/V s at 10 K. We attribute this contrasting trend in temperature dependent mobility to a switch in the dominant scattering mechanism from coulomb to surface optical (SO) phonon scattering due to higher dielectric constant and polar nature of PdHx formed upon hydrogenation of the Pd NPs.