Direct observation of localized surface plasmon field enhancement by Kelvin probe force microscopy.
Direct observation of localized surface plasmon field enhancement by Kelvin probe force microscopy.
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DOI：
10.1038/lsa.2017.38
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发表时间：
2017-08
期刊：
影响因子：
--
通讯作者：
Li ZM
中科院分区：
文献类型：
--
作者：
Li DB;Sun XJ;Jia YP;Stockman MI;Paudel HP;Song H;Jiang H;Li ZM
表面等离子体激元（SP）是存在于金属纳米结构中的基本激发态。在过去的几年中，通过SP增强效应，光电器件的性能得到了很大的提高。在我们以前的工作中，GaN紫外探测器的响应度增加了30倍以上时，使用银纳米粒子。然而，由于缺乏实验证据，SP增强效应的物理机制尚未明确建立。为了揭示这种增强的物理起源，开尔文探针力显微镜（KPFM）被用来观察在GaN外延层上的Ag纳米颗粒附近的SP诱导的表面电位降低。在紫外光照射下，由SP引起的局部场增强迫使光生电子漂移接近Ag纳米颗粒，导致GaN外延层上Ag纳米颗粒周围的表面电势降低。对于直径约为200 nm的孤立Ag纳米颗粒，SP局域场的分布位于Ag纳米颗粒边界的60 nm内。对于银纳米颗粒的二聚体，纳米颗粒之间的局部场增强是最强的。本文给出的结果为局域场增强提供了直接的实验证据。这些结果不仅解释了使用Ag纳米颗粒观察到的GaN探测器的高性能，而且还揭示了光电器件中SP增强的物理机制，这将有助于我们进一步理解和改善未来基于SP的光电器件的性能。
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.
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