Anomalously Strong Electric Near-Field Enhancements at Defect Sites on Au Nanoshells Observed by Ultrafast Scanning Photoemission Imaging Microscopy
Anomalously Strong Electric Near-Field Enhancements at Defect Sites on Au Nanoshells Observed by Ultrafast Scanning Photoemission Imaging Microscopy
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DOI：
10.1021/jp407424n
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发表时间：
2013-11-07
影响因子：
3.7
通讯作者：
Nesbitt, David J.
中科院分区：
文献类型：
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作者：
Grubisic, Andrej;Mukherjee, Shaunak;Nesbitt, David J.
用超快扫描光电子成像显微镜研究了ITO衬底上单个SiO_2核-金壳纳米粒子的多光子光电子发射。高于预期的光电发射产额(类似于10(5)倍)和对激发激光偏振方向的强烈敏感性表明，Au纳米壳层表面存在异常高的电磁场增强区域(即“热点”)。测得的光电子电流的大小与每个纳米颗粒上1-2个局域热点相一致，呈现出名义上与50-100相近的垂直杆E垂直杆/垂直杆E-0垂直杆的近场增强因子。二次电子显微镜(SEM)研究揭示了每个纳米颗粒表面的粗糙，这很可能是由于合成后的Ostwald成熟的Au壳层造成的。然而，没有发现这些特征与产生最大光电子发射率的激光偏振之间的相关性，这表明导致观察到的高电子发射率的热点比我们类似于3-5 nm的扫描电子显微镜分辨率要小。对于两个最常观察到的缺陷几何形状(即，凹凸体和针孔)的近场增强(垂直条E垂直条/垂直条E-0垂直条，类似于20)的数值电动力学模拟可以解释
Multiphoton photoelectron emission from individual SiO2 core-Au shell nanoparticles supported on an ITO substrate is studied with ultrafast scanning photoemission imaging microscopy. Higher than expected photoemission yields (similar to 10(5)-fold) and a strong sensitivity to excitation laser polarization direction indicate the presence of anomalously high electromagnetic field enhancement areas (i.e., "hot spots") on the surface of Au nanoshells. The measured magnitude of the photoelectron current is consistent with 1-2 localized hot spots on each nanoparticle exhibiting electric near-field enhancement factors of nominally vertical bar E vertical bar/vertical bar E-0 vertical bar similar to 50-100. Secondary electron microscopy (SEM) studies reveal asperities on the surface of each nanoparticle that most likely arise due to postsynthetic Ostwald ripening of the Au shell layer. However, no correlation is found between these features and the laser polarization that yields the maximum photoelectron emissivity, indicating that the hot spots responsible for the observed high electron emission rates are smaller than our SEM resolution of similar to 3-5 nm. Numerical electrodynamics simulations of near-field enhancements (vertical bar E vertical bar/vertical bar E-0 vertical bar similar to 20) for the two most commonly observed defect geometries (i.e., asperities and pinholes) can account for