Graphene-enhanced Raman spectroscopy of thymine adsorbed on single-layer graphene

Nanoscale Research Letters, Apr 2015

Graphene-enhanced Raman scattering (GERS) spectra and coherent anti-Stokes Raman scattering (CARS) of thymine molecules adsorbed on a single-layer graphene were studied. The enhancement factor was shown to depend on the molecular groups of thymine. In the GERS spectra of thymine, the main bands are shifted with respect to those for molecules adsorbed on a glass surface, indicating charge transfer for thymine on graphene. The probable mechanism of the GERS enhancement is discussed. CARS spectra are in accord with the GERS results, which indicates similar benefit from the chemical enhancement.

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Graphene-enhanced Raman spectroscopy of thymine adsorbed on single-layer graphene

Fesenko et al. Nanoscale Research Letters Graphene-enhanced Raman spectroscopy of thymine adsorbed on single-layer graphene Olena Fesenko 0 Galyna Dovbeshko 0 Andrej Dementjev 2 Renata Karpicz 2 Tommi Kaplas 1 Yuri Svirko 1 0 Institute of Physics, National Academy of Sciences of Ukraine , 46 Nauki Ave., Kyiv 03680 , Ukraine 1 Institute of Photonics, University of Eastern Finland , Yliopistokatu 7, Joensuu FI-80101 , Finland 2 Center for Physical Sciences and Technology, Institute of Physics , A. Gostauto 11, Vilnius LT-01108 , Lithuania Graphene-enhanced Raman scattering (GERS) spectra and coherent anti-Stokes Raman scattering (CARS) of thymine molecules adsorbed on a single-layer graphene were studied. The enhancement factor was shown to depend on the molecular groups of thymine. In the GERS spectra of thymine, the main bands are shifted with respect to those for molecules adsorbed on a glass surface, indicating charge transfer for thymine on graphene. The probable mechanism of the GERS enhancement is discussed. CARS spectra are in accord with the GERS results, which indicates similar benefit from the chemical enhancement. Single-layer graphene; Thymine; Surface-enhanced Raman spectroscopy (SERS); Graphene-enhanced Raman scattering (GERS); Coherent anti-Stokes Raman scattering (CARS); Graphene-enhanced coherent anti-Stokes Raman scattering (GECARS) - Background Surface-enhanced Raman spectroscopy (SERS) has become an efficient technique that enables detection and study of an extremely small amount of biochemical materials and single-molecule detection [1-4]. SERS is based on the enhancement of the local optical field by several orders of magnitude in the vicinity of a rough metal surface or metal island film due to excitation of the collective oscillations of conduction electrons at the metal surface (surface plasmons). However, investigation of the biological and biochemical species often requires substrates of higher chemical inertness. Such substrates can be based in particular on carbon allotropes, e.g., on graphene or carbon nanotubes. But in graphitic materials, the surface plasmon resonance is found in the THz range [5,6], i.e., plasmon-based local field enhancement can hardly be employed in optical spectroscopy with such carbon-based substrates. Nevertheless, it has been recently demonstrated [7-10] that the Raman signal of molecules deposited on graphene and graphene oxides is enhanced by several orders of magnitude, which is likely to be caused by the so-called chemical mechanism [11], i.e., chemical interaction of deposited molecules and carbon atoms of the substrate. This phenomenon is called graphene-enhanced Raman scattering (GERS) [12] and may become important for spectroscopy of certain biological and biochemical species. In particular, we have recently reported the enhancement for Raman and coherent anti-Stokes Raman scattering of thymine adsorbed on graphene oxide [10]. In the present paper, we report on a comparative study of the surface-enhanced Raman scattering and surfaceenhanced coherent anti-Stokes Raman scattering for thymine (Thy) adsorbed on graphene layers. Samples In the Raman and coherent anti-Stokes Raman scattering (CARS) measurements, we use aqueous 1 mg/ml and 10 g/ml solutions of commercially available thymine (SigmaAldrich, St. Louis, MO, USA). The samples for optical experiments were prepared by depositing a drop of Thy solution on graphene-on-silica or glass substrates, respectively. The average surface density of Thy after water evaporation was either 200 ng/cm2 or 20 g/cm2. The graphene-on-silica substrates were fabricated by depositing a graphene sheet on fused silica. Single-layer graphene was prepared by using chemical vapor deposition (CVD) of graphene on a copper foil described elsewhere [13,14]. Before the start of the graphitization process, the copper substrate was annealed for 1 h at a temperature of 1,000C in 15-mbar hydrogen atmosphere. After the annealing, the CVD chamber was pumped down and filled with 1:1 H2:CH4 gas mixture for 10 min (15 mbar). Because of the self-limiting graphene growth on a copper substrate, almost single-layer graphene [15] was deposited on both surfaces of the copper foil. The templated graphene growth was suppressed by short hydrogen etching at a temperature of 1,000C and pressure of 50 mbar [16]. After the etching, the CVD chamber was cooled down to room temperature in hydrogen atmosphere (15 mbar). The graphene deposited on the backside of the copper was etched away in harsh oxygen plasma (100 W/20 sccm/2 min). The graphene sheet was spin coated by a 1-m-thick polymethyl methacrylate (PMMA) layer, and then the copper foil was removed by wet etching in FeCl3. The remaining PMMA/graphene stack was rinsed in deionized water for 30 min and then placed on a silica substrate in such a way that the graphene was facing the silica. In order to relax internal stress in the stack, another PMMA layer was deposited on top of the e (...truncated)


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Olena Fesenko, Galyna Dovbeshko, Andrej Dementjev, Renata Karpicz, Tommi Kaplas, Yuri Svirko. Graphene-enhanced Raman spectroscopy of thymine adsorbed on single-layer graphene, Nanoscale Research Letters, 2015, pp. 163, Volume 10, Issue 1, DOI: 10.1186/s11671-015-0869-4