[1] [1] P. Zijlstra, J. W. M. Chon, and M. Gu, Nature 459, 410 (2009).

[2] [2] H. Ditlbacher, B. Lamprecht, A. Leitner, and F. R. Aussenegg, Opt. Lett. 25, 563 (2000).

[3] [3] T. J. Antosiewicz, P. Wrobel, and T. Szoplik, Plasmonics 6, 11 (2011).

[4] [4] W. L. Barnes, A. Dereus, and T. W. Ebbesen, Nature 424, 824 (2003).

[5] [5] Y. Chen, R. Zheng, Y. Lu, P. Wang, and H. Ming, Chin. Opt. Lett. 9, 100605 (2011).

[6] [6] L. Zhou, F. Ding, H. Chen, W. Ding, W. Zhang, and S. Y. Chou, Anal. Chem. 84, 4489 (2012).

[7] [7] J. N. Anker, W. P. Hall, O. Lyandres, N. C. Shah, J. Zhao, and R. P. Van Duyne, Nat. Mater. 7, 442 (2008).

[8] [8] A. Y. Elezzabi, K. J. Chau, C. A. Baron, and P. Maraghechi, Opt. Express 17, 71171 (2009).

[9] [9] B. Wood, J. B. Pendry, and D. P. Tsai, Phys. Rev. B 74, 115116 (2006).

[10] [10] W. C. Liu, C. Y. Wen, K. H. Chen, W. C. Lin, and D. P. Tsai, Appl. Phys. Lett. 78, 685 (2001).

[11] [11] B. Jia, H. Shi, J. Li, Y. Fu, C. Du, and M. Gu, Appl. Phys. Lett. 94, 151912 (2009).

[12] [12] H. Gao, H. Shi, C. Wang, C. Du, X. Luo, Q. Deng, Y. Lv, X. Lin , and H. Yao, Opt. Express 13, 6815 (2005).

[13] [13] W. Yu, Y. Fu, L. Li, H. Zhang, H. Liu, Z. Lu, and Q. Sun, Plasmonics 6, 35 (2011).

[14] [14] Y. Wang, W. Srituravanich, C. Sun, and X. Zhang, Proc. SPIE 6324, 632407 (2006).

[15] [15] A. Yanai and U. Levy, Opt. Express 17, 924 (2009).

[16] [16] Z. Liu, J. M. Steele, W. Srituravanich, Y. Pikus, C. Sun, and X. Zhang, Nano Lett. 5, 1726 (2005).

[17] [17] Y. Fu, X. Zhou, and Y. Liu, Plasmonics 5, 111 (2010).

[18] [18] FDTD. Lumerical, http://www.lumerical.com.

[19] [19] Z. Liu, J. M. Steele, H. Lee, and X. Zhang, Appl. Phys. Lett. 88, 171108 (2006).

[20] [20] B. H. Cheng, Y.-C. Lan, and D. P. Tsai, Opt. Express 21, 14898 (2013).

[21] [21] Q. Zhan, Adv. Opt. Photon. 1, 1 (2009).

[22] [22] Y. Fu and X. Zhou, Plasmonics 5, 287 (2010).