石墨烯與光子晶體共振腔結構之表面電漿探討及其在生醫感測的應用

Abstract

近年來，光學感測器對於生醫相關檢測的應用逐漸受到重視，其快速、便利及其非破壞性的檢測方式是其一大優勢，此外，觀察物質的光學特性也為檢測提供了另一個判斷的依據，特別是藉由侷限表面電漿能量的奈米結構更是在生醫感測的領域被廣為應用。本論文以有限元素法針對光子晶體結構結合石墨烯的表面電漿的光學感測器進行設計與應用。所設計的感測器類型為擁有高度電可調性的混合電漿生物感測器，可用於辨識中紅外波段範圍內的蛋白質分子指紋。此類型元件設計由一個光子能隙結構和一個以缺陷形成的共振腔組成，以此將電漿能量限制在共振腔內，實現光與分析物之間的強交互作用，而單層的石墨烯佈置於腔體結構中，除了能夠增強表面電漿的效應之外，也提供了元件的電性可調能力，藉由在腔體中填滿欲分析之物質以進行感測。此外，也藉由不同材料特性的搭配及石墨烯所佈置的範圍作了兩種設計，文中也針對此兩種不同設計的結果深入探討。設計的元件具有很高的等效靈敏度，而等效靈敏度的定義為在將分析物添加到腔體中時共振頻率偏移對應於等效折射率所變化之比例，而等效折射率是同時考慮到腔體結構和分析物的光學特性所影響的參數，不同於其他感測器只考慮了物質折射率變化，為本文的特點之一。而此類型元件另一個優點就是透過向石墨烯施加不同的偏壓來實現廣範圍的電可調性，以此可以調整腔體的等效折射率來提高針對非預設目標分析物的靈敏度。此類型元件的結構概念是依據光子理論所設計，並可透過由下而上的生長的薄膜製程及蝕刻技術來完成元件的製作，此研究結果預期對於微奈米尺度生物樣品的識別和紅外光學感測器是有益的。In recent years, optical sensors have been valued gradually for the applications in biosensing. The high speed, convenient and non-destructive detection methods are the primary advantages of optical sensors. Besides, we can also have another basis for judgement by observing the optical properties of matters. Especially, nanostructures with localized surface plasmonic resonance have increasingly been used in the field of biosensing. In this study, we designed a type of structures combined photonic crystal and graphene as an optical sensor based on surface plasmon by using finite element method. This type of sensors are highly tunable hybrid plasmonic biosensors, and they can be used to identify the fingerprints of protein in infrared range. This type of design consisted a photonic band gap structure and a defect as a cavity to confine plasmonic energy in it for enhancing the interaction between light and matters. A single layer graphene is placed in cavity structure, not only enhance the effect of surface plasmon but provide the electrical tunability to the sensor and we can detect analysis by filling it in the cavity. Besides, we also proposed two design of structures by changing the materials used and the region size of graphene placed.The designed component has a very high effective sensitivity, and the effective sensitivity is defined as the ratio of the shift with the change of the effective refractive index after adding the analyte to the cavity. The effective sensitivity is the parameter which considers the effect of the cavity structure and the optical properties of the analyte. Another advantage of this kind of component is that it can achieve a wide-range electrical tunability by applying different voltage bias to graphene, then we can adjust the effective refractive index of cavity to promote the sensitivity to non-default analytes. This kind of component is based on the photonic crystal theory, and the prototype can fabricated by bottom-up and lithography fabrication. We expect the results of the study will benefit the development of the nanoscale biosensing and infrared sensors.