Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014)
    Thin Films Wednesday Sessions
       Session TF-WeP

Paper TF-WeP34
Chemically Enhanced Raman Scattering of Rhodamine 6 G Molecule Adhere to Graphene, MoS2 and WSe2: Efficiency Variation determined by Pressure and Charge Transfer

Wednesday, December 10, 2014, 4:00 pm, Room Mauka

Session: Thin Films Poster Session
Presenter: Hyunmin Kim, Daegu Gyeongbuk Institute of Science and Technology, Korea
Authors: H. Kim, Daegu Gyeongbuk Institute of Science and Technology, Korea
Y. Lee, Sungkyunkwan University, Korea
S.M. Jeong, Daegu Gyeongbuk Institute of Science and Technology, Korea
J.H. Cho, Sungkyunkwan University, Korea
J.-H. Ahn, Yonsei University, Korea
Correspondent: Click to Email
Recently, graphene enhanced Raman scattering (GERS) is very popular as a method to extract chemical information from dye molecules due to its excellent quenching effect on otherwise superfluous fluorescent backgrounds. Here, we introduce a new method to enhance Raman signals of a graphene-rhodamine 6G (R6G)-graphene sandwich structure by creating a magnet-induced static pressure to maximize the chemical contact of the R6G molecules with graphene. The increase in pressure in the graphene-R6G-graphene sandwich geometry plays a crucial role in enhancing the Raman signal by approximately up to 30 times in comparison to that acquired from a R6G/graphene layered film. In addition, we found that the pressure-induced enhancement effects in the planar vibrational motion of the R6G (1200–1500 cm^-1) were more recognizable than the low wavenumber region and were almost comparable to the surface-enhanced Raman scattering signals observed from the spontaneously formed “folded” pseudo π-bonded graphene-R6G-graphene sandwich structures. The enhancement effect diminished with an increase in the number of graphene layers (on the bottom side), clearly discernible upon imaging the graphene/glass sandwiched structures placed on top of exfoliated multilayered graphene coated with R6G. We also studied the surface enhanced Raman scattering of R6G using 2-dimensional hexagonal honeycomb layers such as MoS2, Wse2 systems to compare with graphene. Thick (~10 nm) physisorbed adsorptions of R6G onto MoS2 and Wse2 nanosheets were made with soaking ~ 100 M level of aqueous R6G solution, allowing us to implement a photocurrent measurement and subsequently correlate it with Raman spectroscopy. The fluorescence quenching factor of R6G molecules coated on MoS2 and Wse2 systems was measured by approximately 100 times higher than that of solution-state R6G molecules. All results were quantitatively correlated with the amount of charge transfers obtained from phototransistor measurement, strongly suggesting that the Raman enhancement factor of molecules coated to hexagonal atomic layered systems can be predicted by photocurrent measurements. We also investigated the thickness dependence of MoS2 and Wse2 layers on the enhanced Raman signals of adsorbed R6G, showing that the enhancement effect of MoS2 systems was maximized in the single layered nanosheets, demonstrating almost a linear-scale tailoring of Raman signals with the increase of the numbers of layers, while that of Wse2 still remained substantial until the double layered nanosheets followed by a drastic decrease above them.