| AVS 62nd International Symposium & Exhibition | |
| Nanometer-scale Science and Technology | Monday Sessions |
| Session NS+AS+SP-MoA |
| Session: | Optical Spectroscopy at the Nanoscale |
| Presenter: | Wei Bao, UC Berkeley |
| Authors: | W. Bao, UC Berkeley N. Borys, Lawrence Berkeley National Lab C. Ko, UC Berkeley J. Suh, UC Berkeley W. Fan, UC Berkeley A. Thron, Lawrence Berkeley National Lab Y. Zhang, UC Berkeley A. Buyanin, UC Berkeley J. Zhang, Lawrence Berkeley National Lab S. Cabrini, Lawrence Berkeley National Lab P. Ashby, Lawrence Berkeley National Lab A. Weber-Bargioni, Lawrence Berkeley National Lab S. Tongay, Arizona State University S. Aloni, Lawrence Berkeley National Lab D. Ogletree, Lawrence Berkeley National Lab J. Wu, UC Berkeley M.B. Salmeron, Lawrence Berkeley Lab, UC Berkeley P. Schuck, Lawrence Berkeley National Lab |
| Correspondent: | Click to Email |
With their remarkable electrical and optical properties, two dimensional (2D) monolayer transition metal dichalcogenide (ML-TMDC) semiconductors are ideal building blocks for atomically thin, flexible optoelectronic devices. Yet their performance falls far below theoretical expectations, particularly for critical factors such as carrier mobility and quantum yield. Overcoming these problems requires a fundamental understanding of the optoelectronic properties of these materials at the nanoscale, which is best obtained with optical microscopy and spectroscopy tools with spatial resolution below the diffraction limit. Here, we use the recently-developed “Campanile” nano-optical probe1 to spectroscopically image for the first time key optoelectronic properties in ML-MoS2 with deeply sub-wavelength resolution – i.e., at a resolution commensurate with characteristic distances such as the exciton diffusion length. We find that synthetic ML-MoS2 is composed of two distinct optoelectronic regions: a locally-ordered but mesoscopically heterogeneous interior, where photoluminescence (PL) intensity correlates with the local ratio of the exciton and trion populations, and an unexpected edge region ~300 nm wide of energetically disordered states. In addition, we directly visualize the spatially-varying optical properties of inter- and intra- flake grain boundaries and quantify the characteristic length over which they quench excitons. Complimentary Nano-Auger elemental analysis reveals that the optically “defective” grain boundary and edge regions are sulfur-deficient. The nanoscale structure-property relationships established here have broad implications for the development of atomically thin transistors, quantum optical components, photodetectors and light-emitting devices based on high-quality ML-TMDCs.
1 Bao, W. Mapping local charge recombination heterogeneity by multidimensional nanospectroscopic imaging. , 1317-1321 (2012).