Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology, 335 Gwahangno, Yuseong-gu, Daejeon 305-701, Republic of Korea.
ACS Nano. 2010 Dec 28;4(12):7175-84. doi: 10.1021/nn1017507. Epub 2010 Nov 22.
Plasmonics allow localization of an electromagnetic (EM) field into nanoscale "hotspots", a feature that is of technological significance due to potential applications related to spectroscopic sensing and nanofocusing. In relation to this, many researchers have sought to fabricate metallic nanostructures with sharp edges, as they provide much higher EM field enhancement compared with rounded structures. However, a fabrication method satisfying stringent requirements for the efficient EM field enhancement including three-dimensionality, vertical orientation, large-area fabrication, and tunability of structural features, which are of practical importance for efficient plasmonic light enhancement at hotspots, has yet to be achieved. Herein, we fabricate large-area, vertically aligned three-dimensional plasmonic tip (i.e., nanofunnel) arrays with unprecedented flexibility in the control of the structural features by directional photofluidization lithography. Using this approach, the structural features of nanofunnel tips including the sharpness, shape, and orientation were precisely controlled in a scalable and deterministic manner. The effects of the structural features of the nanofunnel on the EM field enhancement were systematically investigated and analyzed, and the optimum tip features for maximum EM field enhancement were thereupon identified. The suggested nanofabrication technique and resulting structures will be of practical importance in spectroscopic and nanophotonic applications.
等离子体激元能够将电磁场局域到纳米级的“热点”中，由于与光谱传感和纳米聚焦相关的潜在应用，这一特性具有重要的技术意义。在这方面，许多研究人员试图制造具有锐利边缘的金属纳米结构，因为它们与圆形结构相比，能够提供更高的电磁场增强。然而，一种能够满足包括三维性、垂直取向、大面积制造和结构特征可调性在内的高效电磁场增强的严格要求的制造方法，对于在热点处实现有效的等离子体光增强仍然没有实现。在此，我们通过定向光流光刻技术制造了大面积、垂直排列的三维等离子体尖端（即纳米漏斗）阵列，在控制结构特征方面具有前所未有的灵活性。通过这种方法，可以以可扩展和确定的方式精确控制纳米漏斗尖端的结构特征，包括锐度、形状和取向。系统地研究和分析了纳米漏斗的结构特征对电磁场增强的影响，从而确定了实现最大电磁场增强的最佳尖端特征。所提出的纳米制造技术和得到的结构将在光谱学和纳米光子学应用中具有实际意义。
