Interface properties of Ag and Au/graphene heterostructures studied by micro-Raman spectroscopy

Entani, Shiro; Sakai, Seiji; Matsumoto, Yoshihiro; Naramoto, Hiroshi*; Hao, T.; Maeda, Yoshihito

We have studied the influence of the interface formation of graphene with noble metals (Ag and Au) on its vibrational properties by using confocal micro-Raman spectroscopy. The interactions at the metal/graphene interface are investigated by comparing the results from two different regions, the heterostructure and pristine graphene regions, with and without noble metals on the same graphene sheet. In Ag/graphene, the Raman signal intensity was increased by the surface enhanced Raman scattering process, and the enhanced signals are found to be composed of the broadened D and G peak components emitted from the Ag/graphene interface. The precise evaluation of graphene-layer-number-dependence of the D and G bands revealed that the disordered graphitic carbons were adhered on the glass substrate during the sample preparation by the micromechanical cleavage method. In the 2D band, no obvious peak shift induced by the heterostructure formation was observed in Ag/graphene, whereas a large shift (more than 15 cm) was observed at Au/single layer graphene. This is considered to be due to the difference in the amount of the doped carriers in graphene between two heterostructures.