Edge Nonlinear Optics on a MoS2 Atomic Monolayer

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Science  02 May 2014:
Vol. 344, Issue 6183, pp. 488-490
DOI: 10.1126/science.1250564

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Optics On the Edge

The ability to isolate stable materials just one atom thick has provided the impetus for a new generation of thin films technologies. Often, the materials are conceptually imaged in the form of an artist's impression as single continuous layers—a single crystal sheet of atoms. Scanning probe and transmission electron microscopies reveal the reality, however, where the material resembles a patchwork quilt with polycrystals of different orientation and size separated by grain boundaries forming a mosaic. These structures play an influential role in determining the transport and optical properties of the membrane. Yin et al. (p. 488; see the Perspective by Neshev and Kivshar) demonstrate a simple microscopy technique based on the nonlinear optical response of the materials to probe and characterize atomically thin layers of MoS2. The technique should prove useful during the characterization and optimization of atomically thin membranes.


The translational symmetry breaking of a crystal at its surface may form two-dimensional (2D) electronic states. We observed one-dimensional nonlinear optical edge states of a single atomic membrane of molybdenum disulfide (MoS2), a transition metal dichalcogenide. The electronic structure changes at the edges of the 2D crystal result in strong resonant nonlinear optical susceptibilities, allowing direct optical imaging of the atomic edges and boundaries of a 2D material. Using the symmetry of the nonlinear optical responses, we developed a nonlinear optical imaging technique that allows rapid and all-optical determination of the crystal orientations of the 2D material at a large scale. Our technique provides a route toward understanding and making use of the emerging 2D materials and devices.

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