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Issue 18, 2016
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Probing the size dependence on the optical modes of anatase nanoplatelets using STEM-EELS

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Abstract

Anatase titania nanoplatelets with predominantly exposed {001} facets have been reported to have enhanced catalytic properties in comparison with bulk anatase. To understand their unusual behaviour, it is essential to fully characterize their electronic and optical properties at the nanometer scale. One way of assessing these fundamental properties is to study the dielectric function. Valence electron energy-loss spectroscopy (EELS) performed using a scanning transmission electron microscope (STEM) is the only analytical method that can probe the complex dielectric function with both high energy (<100 meV) and high spatial (<1 nm) resolution. By correlating experimental STEM-EELS data with simulations based on semi-classical dielectric theory, the dielectric response of thin (<5 nm) anatase nanoplatelets was found to be largely dominated by characteristic (optical) surface modes, which are linked to surface plasmon modes of anatase. For platelets less than 10 nm thick, the frequency of these optical modes varies according to their thickness. This unique optical behaviour prompts the enhancement of light absorption in the ultraviolet regime. Finally, the effect of finite size on the dielectric signal is gradually lost by stacking consistently two or more platelets in a specific crystal orientation, and eventually suppressed for large stacks of platelets.

Graphical abstract: Probing the size dependence on the optical modes of anatase nanoplatelets using STEM-EELS

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Publication details

The article was received on 29 Dec 2015, accepted on 07 Apr 2016 and first published on 08 Apr 2016


Article type: Paper
DOI: 10.1039/C5NR09264G
Citation: Nanoscale, 2016,8, 9727-9735
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    Probing the size dependence on the optical modes of anatase nanoplatelets using STEM-EELS

    E. Liberti, R. Menzel, M. S. P. Shaffer and D. W. McComb, Nanoscale, 2016, 8, 9727
    DOI: 10.1039/C5NR09264G

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