[Thu. 30 Nov. 2017] Prof. Sunmin Ryu/Department of Chemistry, POSTECH, Pohang, South Korea

“Surface Science of 2-Dimensional Crystals Probed by Optical Spectroscopy”

Two-dimensional crystals (2DX) represented by graphene hold substantial potentials both in fundamental research and industrial applications owing to novel electronic and optical properties enabled by dimensional confinement. In addition, their intrinsic properties are readily manipulated by chemical entities in direct contact because of their high fraction of surface atoms. To uncover and control emerging properties, my group has explored surface and interfacial science of low dimensional materials and developed optimized spectroscopic methods. In particular, Raman spectroscopy has proven to be a versatile analytical probe because of the varying spectral features for different thickness, stacking, defect density, charge density, mechanical strain, temperature, etc. Such multimodal sensitivity, however, turns into difficulty when multiple unknown variables are to be determined simultaneously. In this talk, I will explain that the effects of strain and charges in graphene can be optically separated from each other by correlation analysis of the two modes, enabling simple quantification of both. Employing the analysis, I will present our recent findings on important surface scientific problems in 2-dimension such as structural deformation caused by substrates and thermal perturbation, interfacial charge transfer, and molecular diffusion through 2DX-substrate interface.

References

1.      J. E. Lee, G. Ahn, J. Shim, Y. S. Lee, and S. Ryu,* “Optical Separation of Mechanical Strain from Charge Doping in Graphene”, Nature Commun. 3, 1024 (2012) 

2.      J. Shim, C. H. Lui, T. Y. Ko, Y.-J. Yu, P. Kim, T. F. Heinz, and S. Ryu,* “Water-Gated Charge Doping of Graphene Induced by Mica Substrates”, Nano Lett. 12, 648 (2012) 

3.      D. Lee, G. Ahn and S. Ryu,* “Two-Dimensional Water Diffusion at a Graphene-Silica Interface”, J. Am. Chem. Soc. 136, 6634 (2014)