제목 [5/16][colloquium] Tip Enhanced Nano Raman Scattering Imaging of 2-D Nanomaterials
작성자 물리학과홈피 등록일 2017-05-10 오후 3:32:22 조회수 198
추천 0 비추천 0
날짜 : 5월 16일
시간 : 오후 4시 30분
장소 : R404
연사 :  정문석 교수님 ( 성균관대학교 에너지과학과 )
제목 : Tip Enhanced Nano Raman Scattering Imaging of 2-D Nanomaterials
Recently, 2 dimensional(2D) nanomaterials such as graphene, boron nitride, and layered transition-metal dichalcogenide (TMdC) materials with the chemical structure MX2 (M = Mo, W, Ti, V, Ta, Hf, Pt and X = S, Se, Te) have attracted considerable interest in the fundamental sciences and applications. In this presentation, nano spectroscopy analysis of 2D nanomaterials with Tip enhanced Raman scattering (TERS) will be provided. TERS is a unique tool for investigating Raman scattering mapping with nanometer spatial resolution beyond optical diffraction limit. Using representative tips fabricated under the optimal etching condition, we demonstrate the TERS experiment of tungsten disulfide (WS2) monolayer grown by a chemical vapor deposition method with a spatial resolution of ~40 nm. Monolayer WS2 has been especially known for its high photoluminescence(PL) quantum yield, which is greater than that of monolayer MoS2. However, the conventional PL and Raman spectroscopy have a limit to analyze nanoscale structures such as local disorders, grain boundaries, dopants, and edges which affect to the optical properties of WS2. Here, we conduct systematic studies to investigate monolayer WS2 by using TERS. As measuring monolayer WS2 on a gold foil, PL background can be quenched by a charge transfer. We also measure the surface morphology of WS2 by a scanning tunneling microscope and scanning electron microscope to compare with TERS images. Moreover, we identify that grain boundaries in chemical vapor deposition grown large area graphene possess a twisted bilayer structure, as determined from correlated analysis of topography, near-field scattering, and multispectral TERS imaging with ~18 nm spatial resolution. In addition, we determine the misorientation angle of the bilayer grain boundaries from a detailed quantitative analysis of the phonon scattering properties associated with the modified electronic structure at the K-point of the Brillouin zone. We also investigate the distinct Raman characteristics of other defects such as wrinkles and nucleation sites, which are strongly correlated with nanoscopic structural curvature effects and atomic scale carbon hybridization. This work not only reveals the detailed properties of the defects in large area graphene at the nanoscale regime, but also demonstrates the potential of correlated analysis of multispectral TERS imaging as generally applicable to a wide range of two-dimensional materials.
1. Hyun Jeong, & M. S. Jeong* et al. “Semiconductor-Insulator-Semiconductor Diode Consisting of Monolayer MoS2, h-BN, and GaN Heterostructure“, ACS Nano 9 (10), 10032 (2015).
2. Hyun Jeong, & M.S. Jeong* et al. “Metal-Insulator-Semiconductor Diode Consisting of Two-Dimensional Nanomaterials“, Nano Letters 16 (3), 1858-1862 (2016).
3. Hye Min Oh, & M. S. Jeong* et al. "Photochemical Reaction in Monolayer MoS2 via Correlated Photoluminescence, Raman Spectroscopy and Atomic Force Microscopy", ACS Nano, 10(5) 5230 (2016)
4. Hye Min Oh & M.S. Jeong* et al. “Modulating electronic properties of monolayer MoS2 via electron withdrawing functional groups of Graphene oxide”, ACS Nano, 10(11), 10446 (2016)
5. Kyoung-Duck Park & M.S. Jeong* et al “Probing Bilayer Grain Boundaries in Large Area Graphene with Tip-Enhanced Raman Spectroscopy”, Advanced Materials, 29, 1603601(2017)

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