We use laser-scanning nonlinear imaging microscopy in atomically thin transition metal dichalcogenides (TMDs) to reveal information on the crystalline orientation distribution, within the 2D lattice. In particular, we perform polarization-resolved second-harmonic generation (PSHG) imaging in a stationary, raster-scanned chemical vapor deposition (CVD)-grown WS2 flake, in order to obtain with high precision a spatially resolved map of the orientation of its main crystallographic axis (armchair orientation). By fitting the experimental PSHG images of sub-micron resolution into a generalized nonlinear model, we are able to determine the armchair orientation for every pixel of the image of the 2D material, with further improved resolution. This pixel-wise mapping of the armchair orientation of 2D WS2 allows us to distinguish between different domains, reveal fine structure, and estimate the crystal orientation variability, which can be used as a unique crystal quality marker over large areas. The necessity and superiority of a polarization-resolved analysis over intensity-only measurements is experimentally demonstrated, while the advantages of PSHG over other techniques are analysed and discussed.
Imaging the crystal orientation of 2D transition metal dichalcogenides using polarization-resolved second-harmonic generation
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GMM acknowledges financial support from the Stavros Niarchos Foundation within the framework of the project ARCHERS (‘Advancing Young Re-searchers’ Human Capital in Cutting Edge Technologies in the Preservation of Cultural Heritage and the Tackling of Societal Challenges’). This research has been co-financed by the European Union and Greek national funds through the Operational Program Competitiveness, Entrepreneurship and Innovation, under the call European R & T Cooperation-Grant Act of Hellenic Institutions that have successfully participated in Joint Calls for Proposals of European Networks ERA NETS (National project code: GRAPH-EYE T8ΕΡΑ2-00009 and European code: 26632, FLAGERA).
引用本文： Maragkakis G M, Psilodimitrakopoulos S, Mouchliadis L, Paradisanos I, Lemonis A et al. Imaging the crystal orientation of 2D transition metal dichalcogenides using polarization-resolved second-harmonic generation. Opto-Electron Adv 2, 190026 (2019).
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