摘要
自從1980年之後，藉由微製造技術製作微型感測器和致動器已經廣泛地發展，由於它們具有高靈敏度以及快速反應，因此成為了往後研究的重點。近年，由於奈米碳管（CNTs）具有獨特的電性和優異的機械性能，因此非常適合作為奈米感測器，與微米感測器相較之下有更好的性能。然而，組裝奈米碳管的感測器一直是一種挑戰。為了實現這目標，最近介電泳（Dielectrophoresis, DEP）已被證明利用微電極來產生非均勻電場，可以操縱細胞之微米等級物質，以及可操作像是奈米碳管之奈米級粒子。但是介電泳(DEP)技術需要黃光製程來製作微金屬電極，並且介電泳力操作的區域被限制在電極附近。而光介電泳(Optically-induced dielectrophoresis, ODEP)可取代傳統介電泳技術，照射在光導材料(amorphous silicon,非晶矽)上的圖形可產生虛擬電極進而產生介電泳力，因此消除微粒子只能被操作在電極周圍的限制。在本實驗中，已發展出使用光介電泳技術來操作奈米碳管以及製作奈米碳管基底感測器，特別的是，使用光介電泳力來收集溶於酒精中的奈米碳管，隨後排列成線在兩端金電極之間，由於碳管與電極之間有電性接觸，所以可用於往後感測器之應用。使用光介電泳力收集好碳管後，等待酒精揮發後奈米碳管即可被固定在金電極之間，由於奈米碳管的電阻特性是隨著溫度上升而下降，因此可以應用於溫度感測器與熱膜風速計。此光介電泳力技術提供有效收集奈米碳管以及快速製作感測器，將會是非常有潛力的技術來發展平行收集奈米碳管基底之感測應用。

關鍵字:奈米碳管、介電泳、光介電泳、非晶矽、光導材料、熱膜感測器。

Abstract
Since their initial developments in the late 1980s, miniaturized sensors and actuators produced via microfabrication techniques have demonstrated compact footprint, high sensitivity, fast response time, and have thus garnered signification research attention. More recently, carbon nanotubes (CNTs) has been extensively explored for a variety of applications due to its unique electrical and exceptional mechanical properties, making it an excellent candidate as nano-scale sensors that promise to deliver even greater performances than micro-scale sensors. The assembly of CNTs into sensors, however, has been a challenge. Recently, dielectrophoresis (DEP), which utilizes micro-scale electrodes to generate non-uniform electric, has demonstrated its ability in manipulating micro-scale objects such as cells and even nano-scale objects such as CNTs. The DEP method, however, requires micro-scale metal electrodes that must be microfabricated in specialized facilities. Furthermore, DEP-based manipulation is restricted to the vicinity of the electrode. As an alternative to the traditional DEP method, optically-induced dielectrophoresis (ODEP) uses optical images illuminated on a photoconductive material (amorphous silicon in this study) as virtual electrodes to generate the DEP force, and therefore obviates microfabricated electrodes and is capable of particle manipulation without location restrictions. In this study, a new method that utilizes ODEP to manipulate CNTs, assemble CNT networks, and fabricate CNT-based nanosensors was demonstrated. Specifically, CNTs dissolved in ethanol were collected and concentrated by ODEP forces and aligned between a pair of metal electrodes that only served as electrical contacts for downstream sensor applications. After ethanol evaporated, CNTs became immobilized between the electrode pair. Because the resistivity of this CNTs assembly decreased as a function of increasing temperature, it was then applied as a temperature sensor and a hot-film anemometer, which could detect changes in wind speed. Offering efficient CNTs collection and ready-to-use sensor fabrication, this ODEP-based approach presents a promising method for the development the parallel assembly of CNT-based sensing applications.


Keywords: Carbon nanotubes, dielectrophoresis, optically-induced dielectrophoresis, amorphous silicon, photoconductive material, hot-film anemometer

Abstract I

摘要 III

致謝 ……………………………………………………………………………………………………………V

Table of contents............................................................................................................................... VIII

List of table………………..…………………………………………………………………………….. XI

List of Figures XIIII

Abbreviation XXIIII

Nomenclatures …………………………………………………………………………………….XXIIIII

Chapter 1 Introduction 1

1.1 MEMS and microfluidic technology 1

1.2 Carbon nanotubes (CNTs) 2

1.3 Dielectrophoresis (DEP) for application 3

1.4 Optically-induced dielectrophoresis (ODEP) system and application 5

1.5 Temperature sensor 6

1.6 Hot-film sensor 8

1.7 Motivation and objectives 11

Chapter 2 Operating principle and design 17

2.1 Amorphous silicon as a photoconductive material 17

2.2 Working principle of the DEP force 18

2.3 Working principle of the ODEP force 20

2.4Working principle of the temperature sensor 21

2.5 Working principle of the hot-film sensor 22

Chapter 3 Materials and Methods 27

3.1 Experimental overview 27

3.2 ODEP chip fabrication 28

3.3 ODEP experimental apparatus 29

3.4 ODEP-assisted CNT assembly 31

3.5 Characterization of current-voltage response of CNT nanosensor 34

3.6 Characterization of temperature coefficient of resistance of CNT nanosensor 35

3.7 Operation of CNT nanosensor as temperature Sensor 35

3.8 Operation of CNT nanosensor as hot-film anemometer 36

Chapter 4 Results and Discussion 45

4.1 ODEP-assisted CNT assembly 45

4.2 Current-Voltage (I-V) measurements 49

4.3 Frequency response of the sensor 51

4.4 Temperature coefficient of resistance of CNT nanosensor 52

4.5 Performance of CNT-based temperature sensor 52

4.6 Performance of CNT-based hot-film anemometer 53

Chapter 5 Conclusions and Future Work 67

Conclusions 67

Future work 68

References 70

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