磁光表面電漿共振檢測元件之研究

Study of Magneto-Optic Surface Plasmon Resonance Sensing Devices

李國豪(Kuo-Hao Lee)

指導教授 ： 王子建

國立臺北科技大學/電資學院/光電工程系研究所/碩士(2012年)

摘要

本論文研究四種檢測薄膜結構之磁光表面電漿共振的檢測特性，分析磁光膜層/金膜的結構、厚度比、總厚度等參數，對於檢測特性之影響，並建立實驗量測裝置，進行磁光調變的表面電漿共振檢測之量測。
所設計的檢測系統使用衰逝全反射架構，以金膜作為表面電漿激發層，藉由施加磁場於鐵磁性材料層引發磁光效應，結合表面電漿共振原理與磁光調變技術對待測溶液進行檢測。在模擬計算上，使用4×4轉移矩陣法進行計算，藉由改變各膜層位置及厚度比例，找尋最佳化的檢測膜層結構組成，以提升磁光調變表面電漿共振元件之檢測功能。計算結果顯示，由於作為磁光膜層的鐵或鈷薄膜，雖具有較強的磁光效應，但因其具有較大的複數折射率虛部，對於光的吸收也較大，在提昇檢測靈敏度時，磁光膜層與金膜的相對厚度的設計是很重要的，除此之外，由於耦合進入薄膜的衰逝場的範圍有限，如何使足夠的衰逝場與鐵磁性材料作用產生磁光效應，且能有效激發足夠的表面電漿波，金膜與磁光膜層的厚度以及其相對位置關係，將會對檢測靈敏度有很大的影響。
在檢測實驗中，以外加交流磁場作連續的磁光調變，可有效抑制雜訊，提升訊號雜訊比，精確量測磁光表面電漿共振所造成的反射率變動量。相較於傳統的表面電漿共振感測裝置，所研究的磁光調變感測裝置具有主動調變檢測訊號的功能，可有效提昇靈敏度兩倍，對於未來檢測低濃度生化分子的研究，將會帶來很大的幫助。

關鍵字

衰逝全反射 ； 表面電漿共振 ； 磁光效應 ； 磁光調變

並列摘要

This thesis studied the sensing properties with four different thin-film structure. The influence of sensing properties with magneto-optic (MO) layer/gold film structure, thickness ratio, and total thickness is discussed. Finally, the measurement setup of MO modulated surface plasmon resonance (SPR) sensing is established.
In this study, we present a MO modulated SPR sensing system in the attenuated-total-reflection (ATR) configuration, which can be used to measure the concentration of analyte. The samples composed of a sensing region with Au film and a magneto-optically active layer with ferromagnetic materials are thermally evaporated on a glass. In simulation, the 4×4 Transfer Matrix Method is used. This calculation will find optimal structure parameters, the effect of MO layer/gold position and thickness ratio are discussed. Simulation results show that sensitivity can be enhanced by optimizing the structure parameters. In this application, the result of magneto-optical (MO) enhancement signal is extremely depending on the thickness of the ferromagnetic material. Transition metals such as Fe and Co exhibit the larger image part of complex refractive index (k), so that their absorption coefficients are higher than those of Au. Therefore, the choice of ferromagnetic material thickness is extremely significant. In addition, the position of ferromagnetic material must be adjusted in order to balance optical absorption and a high degree of MO activity. The thickness and position of films is changed to optimize the sensing property.
During the sensing measurement, the alternate magnetic field as field-modulated and lock-in technique as MO signal record that can be determined by relation between the reflection intensity and refractive index change is used. In comparison with the conventional SPR sensing, that is based on changes in the optical properties at the sensing surface in passive, the MOSPR can be modulated actively by external field to improve sensing sensitivity. Finally, the sensitivity of MOSPR sensor is double enhanced compared to conventional SPR.

並列關鍵字

surface plasmon resonance ； attenuated-total-reflection ； magneto-optical

參考文獻

[13] 洪健雄，何拓利，周榮華，陳寬任，「電漿子學原理與應用」，真空科技，第二十五卷，第一期，第9-23頁，2012。

[18] 蘇書玄，李彥龍，蔡志申，「表面磁光科爾效應系統與Co/Ir(111)之磁性研究」，東海科學，第六卷，第1-15頁，2004。

[1] L. J. Davis III and M. Deutsch, “Surface plasmon based thermo-optic and temperature sensor for microfluidic thermometry,” Rev. Sci. Instrum., vol. 81, p. 114905, 2010.

[2] T.-J. Wang, C.-C. Cheng, and S.-C. Yang, “Surface plasmon resonance biosensing by electro-optically modulated attenuated total reflection,” Appl. Phys. B, vol. 103, pp. 701-706, 2011.

[3] Z. Wang, Z. Zheng, K. Wang, Y. Su, L. Liu, L. Song, Y. Bian, R. Hou, S. Li, and J. Zhu, “Sensitive voltage interrogation method using electro-optically tunable SPR sensors,” Opt. Express, vol. 19, pp. 26651-26659, 2011.