Mapping Carrier Dynamics on Material Surfaces in Space and Time using Scanning Ultrafast Electron Microscopy

Abstract
Selectively capturing the ultrafast dynamics of charge carriers on materials surfaces and at interfaces is crucial to the design of solar cells and optoelectronic devices. Despite extensive research efforts over the past few decades, information and understanding about surface-dynamical processes, including carrier trapping and recombination remains extremely limited. A key challenge is to selectively map such dynamic processes, a capability that is hitherto impractical by time-resolved laser techniques, which are limited by the laser’s relatively large penetration depth and consequently they record mainly bulk information. Such surface dynamics can only be mapped in real space and time by applying four-dimensional (4D) scanning ultrafast electron microscopy (S-UEM), which records snapshots of materials surfaces with nanometer spatial and sub-picosecond temporal resolutions. In this method, the secondary electron (SE) signal emitted from the sample’s surface is extremely sensitive to the surface dynamics and is detected in real time. In several unique applications, we spatially and temporally visualize the SE energy gain and loss, the charge carrier dynamics on the surface of InGaN nanowires and CdSe single crystals and its powder film. We also provide the mechanisms for the observed dynamics, which will be the foundation for future potential applications of S-UEM to a wide range of studies on material surfaces and device interfaces.

Citation
Mapping Carrier Dynamics on Material Surfaces in Space and Time using Scanning Ultrafast Electron Microscopy 2016 The Journal of Physical Chemistry Letters

Acknowledgements
The work reported here was supported by the King Abdullah University of Science and Technology.

Publisher
American Chemical Society (ACS)

Journal
The Journal of Physical Chemistry Letters

DOI
10.1021/acs.jpclett.5b02908

PubMed ID
26911313

Additional Links
http://pubs.acs.org/doi/abs/10.1021/acs.jpclett.5b02908

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