Impact On The Electronic Structure Of Graphene Pd, Ag Deposition

Graphene is a new two-dimensional material, with unique electrical properties such as high carrier intensity and mobility at ambient temperature, half-integer quantum Hall effect and room temperature quantum Hall effect. Graphene has promising perspective in nano-electronic devices and novel gas sensors. However, pristine graphene is a zero gap metal and insensitive to hydrogen. Generally reseachers use Pt and Pd doping to induce hydrogen selectivity of graphene-based gas sensor.In our work E-beam Evaporation was applied to deposite Pd and Ag nanolayers on graphene. With a35mA E-beam flux, Pd layers with thickness of1nm and12nm were deposited on graphenes on copper foil. SEM and XPS were used to characterize the Pd nanolayers on graphene. The results show that with the same depositing E-beam flux,1nm Pd formed dispersive nanoparticles on surface and readily to be oxidized in ambience, while12nm Pd formed a compact, more stable layer. Using depth profile we find that from sample surface to the bulk, the layer’s composition is:amorphous carbon on surface, Pd metal layer, interface between Pd and Cu and the Cu bulk. At the interface of Pd and Cu some carbon exists, mainly sp2hybridized. Raman spectra analysis show that after1nm Pd depostion, the D peak intensity was greatly increased and became the main peak, which were ascribed to the induction of dislocations in graphene as the EBE depositon of Pd with residual energy. The G and2D Pesks downshifted, indicated that the Pd deposition have induced strain in graphene. So the better configuration for depositing Ag, Pd on graphene should adopted lowest residual energy of evaporated atoms thus the minimun depositing rate, and both the thicknesses of deposited Pd and Ag layers were assigned to3nm.The study of Raman spectra of pristine and deposited graphene focused on the position and intensities of graphene D peak, G peak and2D peak. Compared with pristine graphene, the Raman spectra of graphene with3nm Pd or Ag deposited show broadening of G and2D peaks, implies the surface structure of graphene had been changed. The greatly broadening D peak of3nm Ag sample revealed that before transfering graphene to SiO2/Si substrate the surface had already been some absorbed carbon atoms. There is no obvious peak shift in G and2D peaks observed, thus ambiguous doping effect is not comparable with the effect of stress. The Ag deposited sample gains an intensity15times as high as the pristine graphene, which is attributed to the Surface Enhanced Raman Scattering (SERS).For further examination of doping effect during Pd, Ag deposition on graphene, Hall Effect tests were conducted on pristine graphen,3nm Pd and Ag deposited graphene with insulate SiO2substrates. The results reveals that the3nm Pd deposition is n-doping, meanwhile a charge transfer from Pd to graphene occurred and the carrier type changed to n-type (the pristine graphene is p-type); the Ag deposited sample shows no change in carrier type, but a remarkable decrease in carrier density, which may result from the n-doping of Ag deposition, or the deposition causes damage to graphene lattice that also lead to the raise of resistivity.