Tunable Enhancement of Raman Scattering in Graphene‐Nanoparticle Hybrids

Abstract

The realization of graphene‐gold‐nanoparticle (G‐AuNP) hybrids is presented here through a versatile electrochemical approach, which allows the continuous tuning of the size and density of the particles obtainable on the graphene surface. Raman scattering from graphene, which is significantly enhanced in such hybrids, is systematically investigated as a function of the size and density of particles at the same location. In agreement with theory, it is shown that the Raman enhancement is tunable by varying predominantly the density of the nanoparticles. Furthermore, it is observed that the increase in Raman cross‐section and the strength of Raman enhancement varies as a function of the frequency of the vibrational mode, which may be correlated with the plasmonic fingerprint of the deposited AuNPs. In addition to this electromagnetic enhancement, support is found for a chemical contribution through the occurrence of charge transfer from the AuNPs onto graphene. Finally, G‐AuNP hybrids can be efficiently utilized as SERS substrates for the detection of specifically bound non‐resonant molecules, whose vibrational modes can be unambiguously identified. With the possibility to tune the degree of Raman enhancement, this is a platform to design and engineer SERS substrates to optimize the detection of trace levels of analyte molecules.

Strongly enhanced Raman scattering of graphene by a single gold nanorod

“…5,21 Moreover, once the metallic nanostructures were fabricated, the plasmonic nanostructures were fixed, and their optical properties were seldom tuned. 12 Here, we show that a simple well defined system, i.e., a single gold nanorod (AuNR) and monolayer graphene hybrids, is helpful in understanding the basics of SERS. 22 And, the plasmonic resonance of the metallic nanostructures can be tuned in situ with photothermal reshaping method to investigate SERS of graphene elaborately.…”

“…[6][7][8][9] Most SERS-active systems studied to date are based on ensemble and random nanostructures. [10][11][12][13][14][15][16][17][18][19][20] For instance, different metallic nanostructures have been prepared by nanofabrication or wetchemical synthesis, and the nanostructures were deposited on graphene or were covered by graphene. Only a few reports talk about the interaction of a single plasmonic nanostructure with the graphene.…”

“…28 All these results confirm that the background signal of the AuNR-graphene hybrids comes from the light emission of the AuNRs. 12 Besides the photoluminescence background, the strongly enhanced Raman signal of graphene is observed and scattering (dots) spectra of the same AuNR-graphene hybrids before (red) and after (green) photothermal reshaping. The Raman spectrum of graphene without AuNRs is shown (black line) for comparison.…”

“…5 Here, we choose the 2D mode of the graphene to characterize the Raman enhancement factor because of the less photoluminescence background compared to the G mode. 5,12 The Raman intensity of the graphene is enhanced about 2.3-fold by a single AuNR before photothermal reshaping compared to that on silica. Then, we use the photothermal method to change the AuNRs' shape and tune their LSPR band, which could also change the separation between the AuNRs and the graphene.…”

Surface‐enhanced Raman spectra on graphene

“…Thus, many groups focused on in-deep understanding of the effect inspecting various scenarios. [2,13] For example, Sun et al proposed that a large SERS enhancement is a joint effect of the charge transfer and electromagnetic coupling, which is closely correlated with the near-field plasmon coupling of Ag nanoparticles in contact with the graphene bilayer. [14] He et al studied the Raman signal enhancement using Au nanorods [15] and concluded that when the resonant wavelength of the Au nanorods matches well with excitation laser wavelength, the Raman enhancement factor is highest up to 1,000-fold.…”