單一金奈米線電阻式化學感測器

A Resistive-Type Chemical Sensor Based on a Single Gold Nanowire

林欣瑜(Hsin-Yu Lin)

指導教授 ： 林鶴南

國立清華大學/工學院/材料科學工程學系/博士(2009年)

https://doi.org/10.6843/NTHU.2009.00784

摘要

In recent years, metal nanowires have great potential for optical, electrical sensing due to their high surface to volume ratio and higher sensitivity. A convenient method for the fabrication of metal nanowires by a combination of atomic force microscopy (AFM) nanomachining on a thin polymer resist, metal deposition and lift-off is presented on the basis of their advantages of ease of operation, applicability on insulating substrates. For sensing applications, a single metal nanowire connected with metal electrodes fabricated by a combination of atomic force microscopy nanomachining and conventional photolithography is reported and confirmed by a linear current-voltage relationship.
A single Au nanowire connected with Ti electrodes is first created and used as a resistive-type chemical sensor due to the better conductivity and higher biocompatibility. The chemical sensing capability is demonstrated by the selective binding of alkanethiolate molecules onto a single Au nanowire connected with Ti or Au electrodes and the subsequent resistance increase due to increased surface scattering after chemical adsorption.
It is found that the resistance increases by around 9% after the complete coverage of either octadecanethiol (ODT) or dodecanethiol (DDT) molecules onto a 20 nm thick Au nanowire with Ti electrodes. The relationships between the resistance increase and the alkanethiol concentration for the two types of alkanethiolate
molecules are obtained. A theoretical explanation has also been derived and explains the obtained relationships with satisfaction.
On the other hand, the resistance increases after the complete coverage of DDT molecules onto a 20 nm thick Au nanowire between Au electrodes is found to be around 11%, which is slightly larger than the previous 9% increase. It has been confirmed that the contact resistance between an Au nanowire and a Ti electrode (~ 180 Ω) is much larger that between an Au nanowire and an Au electrode (~ a few Ω). It can therefore be known that the contact resistance experiences a smaller resistance increase (3%) than the Au nanowire after the adsorption of alkanethiols.
Furthermore, a real-time measurement to monitor the relationship between the resistance increase and the time is also obtained for the investigation of the adsorption kinetics. It is found that the resistance reaches the saturation value during the shorter time as immersing in higher concentration and the value is in a good agreement with the experimental data before.

關鍵字

金奈米線 ； 電阻式化學感測器 ； 原子力顯微術奈米加工技術 ； 光學微影術 ； 自組裝分子

並列摘要

近年來，由於金屬奈米線具有較高的表面積對體積比，高靈敏度，使其不管
是在光學、電性感測應用上具有相當大的潛力且受到廣大的重視。本文即利用
原子力顯微術奈米加工技術(atomic force microscopy nanomachining)在單層阻劑
上刻畫出奈米凹槽，經由鍍膜、去阻劑製程得到寬度40 nm 到100 nm 的金屬奈
米線，其優點在於製作簡單且不需使用導電基板。為了將此奈米線應用在感測
上， 本文則結合了原子力顯微術奈米加工技術(atomic force microscopy
nanomachining)及光學微影技術(photolithography)，將單根金屬奈米線(single gold
nanowire)跨接在金屬電極兩端得到一元件，並量測得到線性的電流與電壓曲線。
由於金奈米線具有良好的導電性及較高的生物相容性，本文製作單根金奈米
線跨接鈦金屬電極兩端作為電阻式化學感測器(resistive-type chemical sensor)，其
感測原理是因自組裝分子(self-assembled monolayer, SAM)會與金奈米線形成化
學鍵結，使其電阻值會因導電電子在傳輸過程中與表面的散射效應增加而上
升，並以此作為感測依據。文中使用兩種不同溶液，十八烷硫醇 (octadecanethiol,
ODT) 及十二烷硫醇分子 (dodecanethiol, DDT)，分別與金奈米線做化學吸附反
應，實驗結果發現當奈米線表面完全吸附上硫醇分子時，電阻值增加率皆達到
約9%。也推導出電阻改變率與硫醇濃度的理論關係式，發現與實驗結果相當符
合。
為了得知接觸電阻(contact resistance)對於感測的影響，製作了單根金奈米線
跨接在金電極兩端作為感測元件，並對十二烷硫醇分子 (dodecanethiol, DDT)溶
液做吸附反應，實驗結果發現當奈米線完全吸附上硫醇分子時，其電阻增加率
為11%。由此結果，再對接觸電阻值作吸附反應前後的電阻值增加率計算，已
知金奈米線對鈦電極的接觸電阻值約為180 Ω，而對金電極的接觸電阻值極小忽
略不計，可得知金奈米線與鈦電極間的接觸電阻值會貢獻一部分的電阻值增加
率大約3%。除此之外，為了得知分子吸附的動力學，本文設計了一即時量測的
系統，得到了電阻值對時間的關係圖，發現濃度高時，分子吸附達到飽和所需
的時間較短，且電阻值上升達到飽和的值跟非即時量測的實驗結果相當符合。

並列關鍵字

gold nanowires ； resistive-type chemical sensor ； atomic force microscopy nanomachining ； photolithography ； self-assembled monolayer

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