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Direct observation of localized surface plasmon field enhancement by Kelvin probe force microscopy

A surface plasmon (SP) is a fundamental excitation state that exists in metal nanostructures. Over the past several years, the performance of optoelectronic devices has been improved greatly via the SP enhancement effect. In our previous work, the responsivity of GaN ultraviolet detectors was increa...

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Bibliographic Details
Published in:Light, science & applications science & applications, 2017-08, Vol.6 (8), p.e17038-e17038
Main Authors: Li, Da-Bing, Sun, Xiao-Juan, Jia, Yu-Ping, Stockman, Mark I, Paudel, Hari P, Song, Hang, Jiang, Hong, Li, Zhi-Ming
Format: Article
Language:English
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Summary:A surface plasmon (SP) is a fundamental excitation state that exists in metal nanostructures. Over the past several years, the performance of optoelectronic devices has been improved greatly via the SP enhancement effect. In our previous work, the responsivity of GaN ultraviolet detectors was increased by over 30 times when using Ag nanoparticles. However, the physics of the SP enhancement effect has not been established definitely because of the lack of experimental evidence. To reveal the physical origin of this enhancement, Kelvin probe force microscopy (KPFM) was used to observe the SP-induced surface potential reduction in the vicinity of Ag nanoparticles on a GaN epilayer. Under ultraviolet illumination, the localized field enhancement induced by the SP forces the photogenerated electrons to drift close to the Ag nanoparticles, leading to a reduction of the surface potential around the Ag nanoparticles on the GaN epilayer. For an isolated Ag nanoparticle with a diameter of ~200 nm, the distribution of the SP localized field is located within 60 nm of the boundary of the Ag nanoparticle. For a dimer of Ag nanoparticles, the localized field enhancement between the nanoparticles was the strongest. The results presented here provide direct experimental proof of the localized field enhancement. These results not only explain the high performance of GaN detectors observed with the use of Ag nanoparticles but also reveal the physical mechanism of SP enhancement in optoelectronic devices, which will help us further understand and improve the performance of SP-based optoelectronic devices in the future. Surface plasmons: probing field enhancement Kelvin probe force microscopy has provided direct evidence of localized electric field enhancement due to surface plasmons. While surface plasmon enhancement is widely used to improve the performance of optoelectronic devices, the physics behind it is still not fully understood. Dabing Li of Changchun Institute of Optics, Fine Mechanics and Physics in China and co-workers illuminated silver nanoparticles on a gallium nitride layer with ultraviolet light and used Kelvin probe force microscopy—a variant of atomic force microscopy used to map the work function of a surface—to probe the properties near the nanoparticles. Their measurements revealed a drop in the surface potential near both isolated single nanoparticles and dimers—closely spaced pairs of nanoparticles. This drop indicates field enhancement and provides in
ISSN:2047-7538
2095-5545
2047-7538
DOI:10.1038/lsa.2017.38