Surface-enhanced Raman spectroscopy is a valuable tool for inspection of trace concentrations of various molecules; hence, this method has a great potential for characterization of functionalised graphene. However, to make this method a reliable analytical tool, the influence of the metal-graphene interactions on Raman spectra of the graphene must be understood. Here, the surface-enhanced Raman spectra of exfoliated single-layer graphene covered with gold or silver thin layers were studied. The metal-graphene interactions resulted in the broadening of the G mode and the 2D mode of graphene. A change of the 2D mode dispersion was also observed. The effects were found to be weaker for the silver layer; however, the Raman signal enhancement of the graphene features was found to be significantly stronger in case of the silver layer. Various scenarios of the observed effects are discussed: graphene-plasmon interaction, charge transfer between the metal and graphene, and selective enhancement at the lattice and topographic defects. Copyright © 2017 John Wiley & Sons, Ltd.Keywords: charge transfer; graphene; graphene-plasmon interaction; metal-graphene interaction; SERS IntroductionMetals such as gold and silver are known to strongly enhance the Raman signal of pristine graphene. [1,2] In particular, the approach is extremely important for the chemically functionalized graphene samples because it allows to identify the functional groups on the graphene surface. [3] However, it is also known that graphene may strongly interact with the metals, and this interaction is also mirrored in the Raman spectra. [4] Consequently, it is important to follow these effects.Raman spectra of a pristine graphene typically consist of the G mode, which appears at about 1,580 cm −1 , and the 2D mode, which is significantly dispersive and its wavenumber increases with the laser excitation energy. The dispersion comes from the slope of the Dirac cone; therefore, changes in the dispersion reflect changes in the electronic structure of the graphene. [5,6] In case that structural imperfections are present in a graphene sample, one can also observe the defect scattering related D and D' modes at around 1,350 and 1,620 cm −1 , respectively. As reported by several authors previously, the enhancement of a particular Raman mode of graphene depends on the excitation energy of the laser and plasmonic characteristics of the metallic structure in contact with the graphene, and consequently, the enhancement factors for the D, D', G, and 2D modes can be very different. [7,8] Moreover, not only the kind of metal but also the shape, dimensions, and mutual geometry of the metallic structure and graphene are of utmost importance.In a typical experiment, the enhancement of the Raman signal can be achieved by deposition of a thin layer of silver or gold or their nanoparticles over the graphene. This geometry, however, reduces intensity of the incoming light, and also, the scattered light is partly absorbed by the metal. Another option is to intercalate metal un...

Single layer graphene (SLG) and two-dimensional (2-D) plasmonic Ag nanoparticle arrays assembled by chemisorption of ethanethiol (ET) molecules (AgNPs-ET) were employed as components of two types of hybrid systems designed for surface-enhanced Raman scattering (SERS) spectral probing of SLG localized in the vicinity of plasmonic NPs. Both hybrids were characterized by optical microscopy, transmission electron microscopy (TEM), surface plasmon extinction (SPE), and SERS microRaman spectral measurements at four excitation wavelengths spanning the 445-780 nm range. SERS spectral probing of the glass/SLG/AgNPs-ET hybrid prepared by overdeposition of SLG on glass by the array of ET-modified Ag NPs has shown that the chemisorbed ET acts as an efficient molecular spacer between SLG and Ag NPs surface which, in turn, enabled to obtain SERS spectra of SLG unperturbed by doping or strain. TEM imaging and SERS spectral probing of the second hybrid prepared by overdeposition of AgNPs-ET array on glass by SLG revealed removal of the adsorbed ET molecules and annealing of Ag NPs during the SLG deposition. The characteristics of the resulting glass/AgNPs/SLG hybrid system, namely (i) broad distribution of the annealed Ag NPs sizes and shapes, (ii) SPE curve covering the overall visible spectral region, (iii) absence of the ET spectral bands in SERS spectra, and (iv) fairly uniform SERS enhancement of the G and 2D mode of SLG in the 532-780 nm range in the straight sample geometry indicate that this hybrid can provide a suitable platform for investigation of the excitation wavelength dependence of combined SERS/GERS (graphene-enhanced Raman scattering) enhancement experienced by various molecular species brought into contact with SLG in this hybrid. Finally, weak optical effects attributed to increased reflectivity of SLG in the near field of Ag NPs arrays have been observed in the excitation wavelength dependence of the SERS spectra of both types of hybrid systems.

Hybrid systems constituted by plasmonic nanostructures and single-layer graphene (SLG) as well as their employment as platforms for surface-enhanced Raman scattering (SERS) of the molecular species have recently become a subject of interest. By contrast, only a few studies were targeted specifically on the combination of SERS with graphene-enhanced Raman scattering (GERS) of aromatic molecules. In this paper, we have investigated the mechanisms of combined SERS + GERS by micro-Raman spectral mapping of the hybrid system constituted by annealed Ag nanoparticles (NPs) on the glass substrate overdeposited first by SLG and, subsequently, by a monolayer (ML) of free-base phthalocyanine (H 2 Pc) molecules, as well as of glass/SLG/ H 2 Pc(ML) and of graphite/H 2 Pc(ML) reference systems. Raman mapping was performed at multiple excitation wavelengths spanning the 532−830 nm range and was complemented by surface plasmon extinction and transmission electron microscopy images of the Ag NP platform. Observation of SERS + GERS in the aforementioned hybrid system was established by the determination of GERS, SERS, and SERS + GERS enhancement factors. By construction and the mutual comparison of GERS + SERS and GERS excitation profiles of H 2 Pc vibrational modes, operation of two mechanisms of GERS additively with the electromagnetic SERS enhancement in SERS + GERS of H 2 Pc in the glass/Ag NPs/SLG/H 2 Pc(ML) hybrid system has been ascertained. Finally, achievement of the same level of the weak negative doping of SLG by Ag NPs in the probed hybrid system and by glass in the reference system has been established as a necessary condition for the proper evaluation of mechanisms of combined SERS and GERS, and evidence for the fulfillment of this condition in the hybrid systems reported here was provided.

The effect of the amount of sp3 defects in graphene on the graphene enhanced Raman scattering (GERS) is studied using gradual fluorination of chemical vapour deposition grown graphene covering the Rhodamine 6G molecules. While upon a mild fluorination the GERS effect is preserved, the GERS enhancement disappears in case of a strong fluorination. After partial removal of the fluorine from the strongly fluorinated graphene by water vapor treatment, the GERS effect is restored.

We report electrochromism of M-MOF-74 (M=Mg, Mn, Co or Zn), a honeycomb nano-framework in which hexagonally packed one-dimensional<br>arrays of metal cations are coordinated with 2,5-Dihydroxyterephthalic acid linker. Raman spectroscopy upon electrochemical doping combined with density functional theory calculations reveals redox reactions of the linker while the metal cations stay divalent as<br>probed by X-ray photoemission spectroscopy. Excellent adhesion of the MOFs to glass allows synthesis of quality thin films to be implemented into electrochromic devices that exhibit promising colour contrast and durability.