Surface-enhanced Raman scattering of graphene caused by self-induced nanogating by GaN nanowire array

摘要

A constant height of gallium nitride (GaN) nanowires with graphene depositedon them is shown to have a strong enhancement of Raman scattering, whilstvariable height nanowires fail to give such an enhancement. Scanning electronmicroscopy reveals a smooth graphene surface which is present when the GaNnanowires are uniform, whereas graphene on nanowires with substantial heightdifferences is observed to be pierced and stretched by the uppermost nanowires.The energy shifts of the characteristic Raman bands confirms that thesedifferences in the nanowire height has a significant impact on the localgraphene strain and the carrier concentration. The images obtained by Kelvinprobe force microscopy show clearly that the carrier concentration in grapheneis modulated by the nanowire substrate and dependent on the nanowire density.Therefore, the observed surface enhanced Raman scattering for graphenedeposited on GaN nanowires of comparable height is triggered by self-inducednano-gating to the graphene. However, no clear correlation of the enhancementwith the strain or the carrier concentration of graphene was discovered.