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Orientation of luminescent excitons in layered nanomaterials

Nature Nanotechnology volume 8, pages 271–276 (2013)Cite this article

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Abstract

In nanomaterials, optical anisotropies reveal a fundamental relationship between structural and optical properties1,2,3,4,5,6. Directional optical properties can be exploited to enhance the performance of optoelectronic devices7,8,9, optomechanical actuators10 and metamaterials11. In layered materials, optical anisotropies may result from in-plane and out-of-plane dipoles associated with intra- and interlayer excitations, respectively. Here, we resolve the orientation of luminescent excitons and isolate photoluminescence signatures arising from distinct intra- and interlayer optical transitions. Combining analytical calculations with energy- and momentum-resolved spectroscopy, we distinguish between in-plane and out-of-plane oriented excitons in materials with weak or strong interlayer coupling—MoS2 and 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA), respectively. We demonstrate that photoluminescence from MoS2 mono-, bi- and trilayers originates solely from in-plane excitons, whereas PTCDA supports distinct in-plane and out-of-plane exciton species with different spectra, dipole strengths and temporal dynamics. The insights provided by this work are important for understanding fundamental excitonic properties in nanomaterials and designing optical systems that efficiently excite and collect light from exciton species with different orientations.

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Figure 1: Theory of IP and OP dipole emission.
Figure 2: Exciton orientation in mono-, bi- and trilayer MoS2.
Figure 3: Morphology and exciton orientations in a PTCDA thin film.
Figure 4: Fit-independent method for isolating different exciton orientations.
Figure 5: Comparison of charge-transfer exciton and excimer dynamics.

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Acknowledgements

The authors thank S. Cueff, C. Dodson, T.F. Heinz, M. Jiang, J.A. Kash, J.A. Kurvits, D. Li, K.F. Mak, T.H. Taminiau and J.T. Yardley for helpful discussions. Support for R.Z. and S.K., travel for J.A.S., and the optical experiments were provided by the Air Force Office of Scientific Research (PECASE award no. FA-9550-10-1-0026), the National Science Foundation (CAREER award no. EECS-0846466, MRSEC award no. DMR-0520651) and the Nanoelectronic Research Initiative of the Semiconductor Research Corporation. J.A.S., T.S., S.Y. and I.K. were supported as part of the Center for Re-Defining Photovoltaic Efficiency through Molecule Scale Control, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences (award no. DE-SC0001085). K.H. and J.S. were supported by the National Science Foundation (DMR-0907477). GIXD measurements were carried out at beamline 11-3 at the Stanford Synchrotron Radiation Light Source, SLAC National Accelerator Laboratory, a national user facility operated by Stanford University on behalf of the US Department of Energy, Office of Basic Energy Sciences. NEXAFS measurements were carried out at beamline U7A at the National Synchrotron Light Source, Brookhaven National Laboratory, which is supported by the US Department of Energy, Office of Basic Energy Sciences (contract no. DE-AC02-98CH10886).

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Authors and Affiliations

  1. School of Engineering, Brown University, Providence, 02912, Rhode Island, USA

    Jon A. Schuller, Sinan Karaveli & Rashid Zia

  2. Energy Frontier Research Center, Columbia University, New York, 10027, New York, USA

    Jon A. Schuller, Theanne Schiros, Shyuan Yang & Ioannis Kymissis

  3. Department of Electrical and Computer Engineering, University of California, Santa Barbara, 93106, California, USA

    Jon A. Schuller

  4. Department of Physics, Case Western Reserve University, Cleveland, 44106, Ohio, USA

    Keliang He & Jie Shan

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Contributions

J.A.S., S.K. and R.Z. designed and performed the optical experiments. T.S. performed and analysed GIXD and NEXAFS measurements. K.H. and J.S. fabricated the MoS2 samples. S.Y. and I.K. fabricated the PTCDA samples. J.A.S., S.K. and R.Z. analysed the data and implemented the theoretical model. All authors provided detailed feedback on the results and helped write the manuscript.

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Correspondence to Jon A. Schuller or Rashid Zia.

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Schuller, J., Karaveli, S., Schiros, T. et al. Orientation of luminescent excitons in layered nanomaterials. Nature Nanotech 8, 271–276 (2013). https://doi.org/10.1038/nnano.2013.20

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