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Real-space imaging of transient carrier dynamics by nanoscale pump–probe microscopy

Nature Photonics volume 4, pages 869–874 (2010)Cite this article

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Abstract

Smaller and faster are key concepts underlying the progress of current nanoscience and nanotechnology. The development of a method of exploring the transient carrier dynamics in organized nanostructures with pinpoint accuracy is therefore highly desirable. Here, we present a new microscopy that enables real-space measurement of the spatial variation of ultrafast dynamics. It is a pulse-laser-combined scanning tunnelling microscopy with a novel delay-time modulation method based on a pulse-picking technique. A non-equilibrium carrier distribution is generated with ultrashort laser pulses, and its relaxation processes are observed by scanning tunnelling microscopy using a pump–probe technique. We have directly analysed the recombination of excited carriers via the gap states associated with a cobalt nanoparticle/GaAs structure in real space. Through the site dependence of the decay time on the tunnelling current injection from the scanning tunnelling microscopy tip, the hole capture rate at the gap states has been imaged on the nanoscale for the first time.

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Figure 1: Schematics of the microscopy system and its probe mechanism.
Figure 2: Carrier dynamics over a wide range of timescales measured using the developed microscopy.
Figure 3: Bulk-side and surface-side carrier decay reflected in ΔI(td).
Figure 4: Carrier recombination via cobalt nanoparticle/GaAs gap states.
Figure 5: Real-space analysis of the hole capture rate at cobalt nanoparticle/GaAs gap states.

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Acknowledgements

The authors thank Y. Hirayama of Tohoku University in Japan for stimulating discussions.

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Authors and Affiliations

  1. Institute of Applied Physics, CREST-JST, University of Tsukuba, Tsukuba, 307-8573, Japan

    Yasuhiko Terada, Shoji Yoshida, Osamu Takeuchi & Hidemi Shigekawa

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  1. Yasuhiko Terada
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  2. Shoji Yoshida
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  3. Osamu Takeuchi
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  4. Hidemi Shigekawa
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Contributions

Y.T. performed the SPPX-STM experiment and data analysis. S.Y. assisted in the SPPX-STM experiment and laser operation. O.T. provided technical and theoretical advice. H.S. organized and supervised the project and edited the paper. All authors carried out extensive analysis of the results.

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Correspondence to Hidemi Shigekawa.

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The authors declare no competing financial interests.

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Terada, Y., Yoshida, S., Takeuchi, O. et al. Real-space imaging of transient carrier dynamics by nanoscale pump–probe microscopy. Nature Photon 4, 869–874 (2010). https://doi.org/10.1038/nphoton.2010.235

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