在微觀尺度下,科學家常常想研究各種材料的特性,但若尺度達到數百奈 米時,受限於其光學限制,便無法再用肉眼觀察,於是各種研究方法便應運而 生。表面電漿與拉曼光譜學便是其中兩種重要的方法。當金屬微結構於外加電 場下,被驅策的頻率位於共振結構時,能產生局域性場增強,而此場增強即可 用於微弱訊號的量測,如超穎材料或氧化物薄膜。
利用此特性,我們便可用於拉曼光譜的進階量測。如菱長晶相之鐵酸鉍薄 膜長在鈦酸鍶基板上,基板訊號過強導致鐵酸鉍薄膜訊號微弱,表面增強拉曼 便是我們用來改善這項問題的方法。藉由奈米尺度的金結構,局域表面電漿共 振可經由雷射激發,並提高拉曼散射的機率,進而使鐵酸鉍薄膜的訊號增強。
於本實驗中,利用於鐵酸鉍薄膜上塗布光阻 PMMA,並使用原子力顯微鏡 於表面上作刻劃不同圖樣,再配合電子束蒸鍍機於樣品上蒸鍍金,利用丙酮舉 離後即可得到奈米尺度的金奈米結構。透過波長 532 nm 的綠光雷射與 633 nm 的紅光雷射,可量測拉曼增強,同時討論不同形狀、方向與入射偏振光之拉曼 訊號增強與散射波長。
實驗結果顯示,不同大小的奈米金結構,可以得到不同效果的增強,尤其 又以方框的拉曼增強較微為顯著,且雷射偏振方向垂直開口方向時,可以有較 明顯的增強,但增強的程度也與排列緊密度有關,礙於技術限制,最精細只能 做出 300x300 nm 的開口方框,如果日後的技術能控制的更加精準,則更可能 製作出具有強增強的結構。

In this study, we used nano lithography to fabricate gold nano patterns on BiFeO3 thin film grown on SrTiO3. The thickness of BiFeO3 thin film is about 100 nm. Due to the strong Raman signal of thick SrTiO3, Raman signals of BiFeO3 are too weak to detect and analyze. In order to enhance the signal, we fabricated several shapes of gold nano structures via atomic force microscopy on thin BiFeO3 film. The main mechanism is from the excitation of surface plasma. We excited localized surface plasma resonance with two kinds of laser sources, red and green. When we chose red one, the structure which was smaller and had more tips could have stronger enhanced signal because of the stronger enhanced electric field, enhancement factor(EF) was counted as well. In the end, we found the 300x300 nm spilt square rings with 200 nm space between had strongest enhancement, the strongest EF is 1000 times more than that of the original signal, due to the higher density of rings and more tips under the laser spot. As a conclusion, we can use this structure to enhance Raman signal of BiFeO3 thin film.

參考文獻
【1】Gene H. Haertling, J. Am. Ceram Soc. 82, 4 797 (1999).
【2】E. Erenstein, N.D. Mathur and J.F.Scott, Nature 442, 17 (2006).
【3】T. Zhao, A. Scholl, et al. , App. Phys. Lett. 90, 123104 (2007).
【4】A. Moores, F. Goettmannb, New J. Chem. , 30, 1121 (2006).
【5】邱國斌、蔡定平,金屬表面電漿共振, 物理雙月刊(廿八卷二期)(2006)
【6】A. Moores, F. Goettmannb, New J. Chem. , 30, 1123 (2006).
【7】U. Kreibig and M. Vollmer, “Optical Properties of Metal Clusters”, Springer
(1995).
【8】 Marcos M. Alvarez, Joseph T. Khoury et al, J. Phys. Chem. B, 101, 3706
(1997).
【9】Marcos M. Alvarez, Joseph T. Khoury et al, J. Phys. Chem. B, 101, 3706 (1997).
【10】Thearith Ung, Luis M. Liz-Marza ́n et al, J. Phys. Chem. B, 105, 3441
(2001).
【11】Georgeta C. Lica, Brian S. Zelakiewicz et al, J. Phys. Chem. B, 108, 19896
(2004).
【12】Craig F. Bohren, Donald R. Huffman, “Absorption and scattering of light
by small particles”, Wiley (1998).
【13】F. Gonella and P. Mazzoldi, “Handbook of Nanostructured Materials and
Nanotechnology”, Elsevier (2000).
【14】Audrey Moores, Fre ́de ́ric Goettmannb, New J. Chem. , 30, 1121 (2006).
【15】U. Kreibig and M. Vollmer, “Optical Properties of Metal Clusters”, Springer
(1995).
【16】程光煦, 拉曼 布里淵散射(第二版), 科學出版社(2007)
【17】Ewen Smith, Geoffrey Dent, Modern Raman Spectroscopy– A Practical
Approach (2005).
【18】Y. G. Sun and Y. N. Xia, Anal. Chem., 74, 5297 (2002).
【19】K. Kneipp, H. Kneipp et al, Chem. Rev., 99, 2957 (1999).
【20】Zhilin Yang, Javier Aizpurua and Hongxing Xu , J.Raman Spectrosc., 40,
1343 (2009).
【21】 Jan W. Slot and Hans J. Geuze, Eur. J. Cell Biol., 38, 87 (1985).
【22】Andreas Otto, “Surface-Enhanced Raman scattering: classical and chemical
origins”, Springer (1984).
【23】Manuel Cardona and Gernot Güntherodt, “Light Scattering in solids IV—
Electronic, Scattering Spin Effects, SERS and Morphic Effects”, (1984).
【24】Alan Campion and Patanjali Kambhampati, Chem. Soc. Rev, 27, 241 (1998)
【25】C.Y.Liu, M.M.Dvoynenkoetal, Appl.Phys.Lett.,96,033109(2010).
【26】W. Eerenstein, N. D. Mathur et al, Nature, 442, 759 (2006).
【27】I. Sosnowska, W. Schäfer et al, Appl. Phys. A 74, S1040 (2002).
【28】ManojK.Singhetal.,PRB72,132101(2005).
【29】 P. R. West, S. Ishii, G. V. Naik, N. K. Emani, V. M. Shalaev, and A. , Boltasseve,"Searching for better plasmonic materials," Laser & Photonics Reviews, vol. 4, 795, (2010).
【30】W.Yue et al, Sensors and Actuators B, 171 (2012).
【31】W Yue et al, J.Phys. Chem. C 117, 21908 (2013).
【32】 黃. 郭清癸, 牟中原, “金屬奈米粒子的製造,” 物理雙月刊, vol. 廿三卷 六
期, 614 (2001).
【33】曾賢德, “金奈米粒子的表面電漿共振特性:耦合、應用與樣品製作,” 73 物
理雙月刊, vol. 卅二卷二期, 126, (2010).
【34】Z.Q.Cheng, F. Nan et al, Nanoscale1463 (2015).
【35】P. Ndokoye a, X. Li et al , J of Colloid and Interface Science 462,341(2016).
【36】E. C. Le Ru, E. Blackie, J. Phys. Chem. C , 111, 13794 (2007).