银纳米结构中局域表面等离子体在电信波长下的光发射电子显微术
Photoemission electron microscopy of localized surface plasmons in silver nanostructures at telecommunication wavelengths
摘要：
我们使用中心波长为1.55微米的飞秒激光脉冲在Ag纳米结构处成像场增强。成像基于在光电发射电子显微镜（PEEM）中观察到的非线性光电发射。将图像直接与相同结构的紫外PEEM和扫描电子显微镜（SEM）成像进行比较。此外，我们已经进行了原子尺度的扫描隧道显微镜（STM）上相同类型的银纳米结构和金基板上。从单个Ag颗粒的光电子光谱测量显示出更大的贡献，从高阶光电子过程以上的功函数阈值比将预测的完全微扰模型，与最近的结果使用较短的波长一致。调查广泛的选择银纳米粒子和纳米线，场增强观察到从30%的银纳米粒子和从没有的纳米线。在PEEM实验和随后的SEM分析中均未观察到纳米结构的激光诱导损伤。通过直接比较相同纳米结构的SEM和PEEM图像，我们可以得出结论，场增强与平均纳米结构尺寸和形状无关。相反，我们建议，在观察到的场增强的变化可能源于衬底和电连接到衬底的粒子之间的楔形界面。
英文摘要：
We image the field enhancement at Ag nanostructures using femtosecond laser pulses with a center wavelength of 1.55 micrometer. Imaging is based on non-linear photoemission observed in a photoemission electron microscope (PEEM). The images are directly compared to ultra violet PEEM and scanning electron microscopy (SEM) imaging of the same structures. Further, we have carried out atomic scale scanning tunneling microscopy (STM) on the same type of Ag nanostructures and on the Au substrate. Measuring the photoelectron spectrum from individual Ag particles shows a larger contribution from higher order photoemission process above the work function threshold than would be predicted by a fully perturbative model, consistent with recent results using shorter wavelengths. Investigating a wide selection of both Ag nanoparticles and nanowires, field enhancement is observed from 30% of the Ag nanoparticles and from none of the nanowires. No laser-induced damage is observed of the nanostructures neither during the PEEM experiments nor in subsequent SEM analysis. By direct comparison of SEM and PEEM images of the same nanostructures, we can conclude that the field enhancement is independent of the average nanostructure size and shape. Instead, we propose that the variations in observed field enhancement could originate from the wedge interface between the substrate and particles electrically connected to the substrate.
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