Revealing hole trapping in zinc oxide nanoparticles by time-resolved X-ray spectroscopy.
Nat Commun 2018;
9:478. [PMID:
29396396 PMCID:
PMC5797134 DOI:
10.1038/s41467-018-02870-4]
[Citation(s) in RCA: 48] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2017] [Accepted: 01/05/2018] [Indexed: 12/02/2022] Open
Abstract
Nanostructures of transition metal oxides, such as zinc oxide, have attracted considerable interest for solar-energy conversion and photocatalysis. Both applications are sensitive to the transport and trapping of photoexcited charge carriers. The probing of electron trapping has recently become possible using time-resolved element-sensitive methods, such as X-ray spectroscopy. However, valence-band-trapped holes have so far escaped observation. Herein we use X-ray absorption spectroscopy combined with a dispersive X-ray emission spectrometer to probe the charge carrier relaxation and trapping processes in zinc oxide nanoparticles after above band-gap photoexcitation. Our results, supported by simulations, demonstrate that within 80 ps, photoexcited holes are trapped at singly charged oxygen vacancies, which causes an outward displacement by ~15% of the four surrounding zinc atoms away from the doubly charged vacancy. This identification of the hole traps provides insight for future developments of transition metal oxide-based nanodevices.
Metal-oxide nanostructures are used in a range of light-driven applications, yet the fundamentals behind their properties are poorly understood. Here the authors probe photoexcited zinc oxide nanoparticles using time-resolved X-ray spectroscopy, identifying photocatalytically-active hole traps as oxygen vacancies in the lattice.
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