Atom-Dependent Edge-Enhanced Second-Harmonic Generation on MoS2 Monolayers

• Published in: Nano letters Vol. 18; no. 2; pp. 793 - 797
• Main Authors: Lin, Kuang-I, Ho, Yen-Hung, Liu, Shu-Bai, Ciou, Jian-Jhih, Huang, Bo-Ting, Chen, Christopher, Chang, Han-Ching, Tu, Chien-Liang, Chen, Chang-Hsiao
• Format: Journal Article
• Language: English
• Published: American Chemical Society 14.02.2018
• Subjects: edge termination; edge states; second-harmonic generation; MoS2; 2D materials; density functional theory
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/acs.nanolett.7b04006

Edge morphology and lattice orientation of single-crystal molybdenum disulfide (MoS2) monolayers, a transition metal dichalcogenide (TMD), possessing a triangular shape with different edges grown by chemical vapor deposition are characterized by atomic force microscopy and transmission electron microscopy. Multiphoton laser scanning microscopy is utilized to study one-dimensional atomic edges of MoS2 monolayers with localized midgap electronic states, which result in greatly enhanced optical second-harmonic generation (SHG). Microscopic S-zigzag edge and S–Mo Klein edge (bare Mo atoms protruding from a S-zigzag edge) terminations and the edge-atom dependent resonance energies can therefore be deduced based on SHG images. Theoretical calculations based on density functional theory clearly explain the lower energy of the S-zigzag edge states compared to the corresponding S–Mo Klein edge states. Characterization of the atomic-scale variation of edge-enhanced SHG is a step forward in this full-optical and high-yield technique of atomic-layer TMDs.