Spatial-Temporal Imaging of Anisotropic Photocarrier Dynamics in Black Phosphorus

Bolin Liao; Huan Zhao; Ebrahim Najafi; Xiaodong Yan; He Tian; Jesse Tice; Austin J. Minnich; Han Wang; Ahmed H. Zewail

doi:10.1021/acs.nanolett.7b00897

Spatial-Temporal Imaging of Anisotropic Photocarrier Dynamics in Black Phosphorus

Bolin Liao, Huan Zhao, Ebrahim Najafi, Xiaodong Yan, He Tian, Jesse Tice, Austin J. Minnich, Han Wang, Ahmed H. Zewail

Research output: Contribution to journal › Article › peer-review

64 Scopus citations

Abstract

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.

Original language	English
Pages (from-to)	3675-3680
Number of pages	6
Journal	Nano Letters
Volume	17
Issue number	6
DOIs	https://doi.org/10.1021/acs.nanolett.7b00897
State	Published - Jun 14 2017
Externally published	Yes

Funding

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.

Keywords

Black phosphorus
anisotropy
hot carrier dynamics
ultrafast electron microscopy

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10.1021/acs.nanolett.7b00897

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title = "Spatial-Temporal Imaging of Anisotropic Photocarrier Dynamics in Black Phosphorus",

abstract = "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.",

keywords = "Black phosphorus, anisotropy, hot carrier dynamics, ultrafast electron microscopy",

author = "Bolin Liao and Huan Zhao and Ebrahim Najafi and Xiaodong Yan and He Tian and Jesse Tice and Minnich, {Austin J.} and Han Wang and Zewail, {Ahmed H.}",

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T1 - Spatial-Temporal Imaging of Anisotropic Photocarrier Dynamics in Black Phosphorus

AU - Liao, Bolin

AU - Zhao, Huan

AU - Najafi, Ebrahim

AU - Yan, Xiaodong

AU - Tian, He

AU - Tice, Jesse

AU - Minnich, Austin J.

AU - Wang, Han

AU - Zewail, Ahmed H.

PY - 2017/6/14

Y1 - 2017/6/14

N2 - 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.

AB - 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.

KW - Black phosphorus

KW - anisotropy

KW - hot carrier dynamics

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Spatial-Temporal Imaging of Anisotropic Photocarrier Dynamics in Black Phosphorus

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