Abstract
The discovery of efficient sources of terahertz radiation has been exploited in imaging applications1, and developing a nanoscale terahertz source could lead to additional applications. High-frequency mechanical vibrations of charged nanostructures can lead to radiative emission, and vibrations at frequencies of hundreds of kilohertz have been observed from a ZnO nanobelt under the influence of an alternating electric field2. Here, we observe mechanical resonance and radiative emission at ∼0.36 THz from core–shell ZnO mesocrystal microspheres excited by a continuous green-wavelength laser. We find that ∼0.016% of the incident power is converted into terahertz radiation, which corresponds to a quantum efficiency of ∼33%, making the ZnO microspheres competitive with existing terahertz-emitting materials1,3. The mechanical resonance and radiation stem from the coherent photo-induced vibration of the hexagonal ZnO nanoplates that make up the microsphere shells. The ZnO microspheres are formed by means of a nonclassical, self-organized crystallization process4,5,6, and represent a straightforward route to terahertz radiation at the nanoscale.
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Acknowledgements
This work was supported by the National Basic Research Programs of China (grants 2011CB922102, 2007CB936301, 2007CB310404), as well as the National and Jiangsu Natural Science Foundations (grants BK2008020, 60976063, 10874071). Partial support was also provided by the Hong Kong Research Grants Council (RGC) under General Research Funds (GRF) no. CityU 112608) and City University of Hong Kong (Strategic Research Grant (SRG) 7008009).
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X.L.W. designed the experimental setup, performed the experiments, analysed the data, and co-wrote the manuscript. S.J.X. analysed the data and co-wrote the manuscript. Z.L. and J.C.S. performed the experiments. J.C. and P.H.W. designed the experimental setup and analysed the data. T.H.L. plotted all the figures. P.K.C. analysed the data and co-wrote the manuscript.
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Wu, X., Xiong, S., Liu, Z. et al. Green light stimulates terahertz emission from mesocrystal microspheres. Nature Nanotech 6, 103–106 (2011). https://doi.org/10.1038/nnano.2010.264
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DOI: https://doi.org/10.1038/nnano.2010.264
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