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Published June 14, 2017 | Supplemental Material + Submitted + Accepted Version
Journal Article Open

Spatial-Temporal Imaging of Anisotropic Photocarrier Dynamics in Black Phosphorus


As an emerging single elemental layered material with a low symmetry in-plane crystal lattice, black phosphorus (BP) has attracted significant research interest owing to its unique electronic and optoelectronic properties, including its widely tunable bandgap, polarization-dependent photoresponse and highly anisotropic in-plane charge transport. Despite extensive study of the steady-state charge transport in BP, there has not been direct characterization and visualization of the hot carriers dynamics in BP immediately after photoexcitation, which is crucial to understanding the performance of BP-based optoelectronic devices. Here we use the newly developed scanning ultrafast electron microscopy (SUEM) to directly visualize the motion of photoexcited hot carriers on the surface of BP in both space and time. We observe highly anisotropic in-plane diffusion of hot holes with a 15 times higher diffusivity along the armchair (x-) direction than that along the zigzag (y-) direction. Our results provide direct evidence of anisotropic hot carrier transport in BP and demonstrate the capability of SUEM to resolve ultrafast hot carrier dynamics in layered two-dimensional materials.

Additional Information

© 2017 American Chemical Society. Received: March 1, 2017; Revised: May 10, 2017; Published: May 15, 2017. This work is partially supported by the National Science Foundation (DMR-0964886) and the Air Force Office of Scientific Research (FA9550-11-1-0055) in the Gordon and Betty Moore Center for Physical Biology at the California Institute of Technology. The work is also supported by the Army Research Office (W911NF-16-1-0435), the Air Force Office of Scientific Research FATE MURI program (FA9550-15-1-0514), and the Northrop Grumman Institute of Optical Nanomaterials and Nanophotonics (NG-ION2) at University of Southern California. B.L. is grateful for the financial support from the KNI Prize Postdoctoral Fellowship in Nanoscience at the Kavli Nanoscience Institute of California Institute of Technology. Author Contributions: B.L., H.Z. and H.W. conceived the project. H.Z. prepared the BP samples. H.Z. and J.T. performed the Raman characterization. B.L. and E.N. carried out the SUEM measurements. B.L., H.Z., X.Y., H.T., A.J.M., and H.W. analyzed the data. B.L., H.Z., A.J.M., and H.W. wrote the manuscript. A.H.Z. led the development of the SUEM technique and supervised the research effort during the initial stage of the project. B.L. and H.Z. contributed equally. The authors declare no competing financial interest.

Attached Files

Accepted Version - acs_2Enanolett_2E7b00897.pdf

Submitted - 1702.05835.pdf

Supplemental Material - nl7b00897_si_001.pdf


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