奈米碳管/碳螺旋線圈之成長、機械性質與機電元件之研究

Carbon nanotubes/nanocoils: Synthesis, mechanical properties and electromechanical devices

張能凱(Neng-Kai Chang)

指導教授 ： 張所鋐

國立臺灣大學/工學院/機械工程學研究所/博士(2008年)

https://doi.org/10.6342/NTU.2008.00165

摘要

本文主要是針對奈米碳管以及碳螺旋線圈的成長，機械性質的量測與機電方面的應用做相關的研究與討論。奈米碳管由於具有獨特的結構、電性和機械性質，吸引眾多研究人員的目光，奈米碳管如同分子般大小的一維材料，不但提供了一個理想的基礎研究平台，也可以被用在許多極具潛力的應用，例如：奈米電子元件、感測器、超強複合材料、超平面顯示器、燃料電池…等等。然而，對於製作奈米碳管元件而言，如何控制奈米碳管的方向性以及位置是一個極大的挑戰，本文利用化學與物理方式分別製作不同形態的催化劑，以化學氣相沉積法，從這些催化劑中，成長大面積平行排列單/多層奈米碳管，催化劑種類對於成長方向性排列的奈米碳管之影響將在本文中討論。
奈米碳管除了以筆直的形態呈現外，也可以三維立體的螺旋狀來表現，本文改良以往的成長技術，成功地在低價的不?袗?上成長大量的碳螺旋線圈，碳螺旋線圈佔所有碳產物之比例高達80%，本研究發現在不?袗?表面添加錫奈米粒子，同時配合適當的退火溫度，能有效地提升碳螺旋線圈的產率，本研究之結果未來可用於大量生產碳螺旋線圈。
奈米碳管的機械性質已有相當多研究進行相關的討論，也有許多量測方法相繼被開發出來，目前最為準確的方法是利用共振的原理來量測奈米碳管的彈性模數，本研究將提出一套更為精確的共振偏移法來量測奈米碳管彈性模數，本研究發現一般傳統共振法量測奈米碳管強度時會有20％的誤差，利用共振偏移法則能有效去除這項誤差。至於碳螺旋線圈的機械性質，本文是發展出一項利用側向力顯微鏡的技術對碳螺旋線圈進行壓縮與伸長測試，比較傳統的量測方法，本方法能在常溫常壓下進行，而且能精確控制碳螺旋線圈變形量小到10 奈米大到數十微米。所量出來的碳螺旋線圈機械強度也會在本文中討論。
從理論與實驗可知奈米碳管的應變規因子可高達數百以上，本文利用成長方向性排列之單層奈米碳管技術，製作出釐米長的懸空單層奈米碳管結構，再將其轉移到具有溝槽結構的可撓性基板上，製作出來的可撓性電子元件，其應變靈敏度達0.004％，應變規因子高達269，本方法所製作出來的可撓性應變感測電子元件不但具有高靈敏度、高應變規因子，還適合大量生產。
碳螺旋線圈的機電性質目前還不是很清楚，本研究首先利用介電泳動法將碳螺旋線圈平行排列在可撓性基板上，在介電泳動法中，分別調整操作電壓以及可撓性基板上的電極間距，藉此得到最佳平行排列碳螺旋線圈的條件，接下來，在機電性質量測結果中，發現碳螺旋線圈的應變規因子約在20∼50之間，其數值與多層奈米碳管相當，隨著碳螺旋線圈平行排列的數量愈多，其應變規因子也愈低，其中的原因與機制將在本文中討論。

關鍵字

奈米碳管 ； 碳螺旋線圈 ； 機械性質 ； 化學氣相沉積法 ； 可撓性 ； 應變感測器

並列摘要

This dissertation reports on the synthesis of carbon nanotubes/nanocoils, the measurement of their mechanical properties and some of their electromechanical applications. Carbon nanotubes have attracted considerable attention because of their remarkable structural, electrical and mechanical properties. They not only offer an ideal arena for fundamental research but also have great potential for various applications, including nanoelectronic devices, sensors, high-strength composite materials, flat-panel displays, hydrogen fuel cells, and others. However, for applications in nanoelectronics, controlling the locations and orientations of carbon nanotubes is extremely challenging. This work prepared several catalysts via chemical and physical methods. Large-scale aligned carbon nanotubes were synthesized using chemical vapor deposition. The effect of the catalysts on the growth of directional aligned carbon nanotubes was also discussed.
Carbon nanotubes are generally grown in straight wire-like structure. However, under specific growth conditions, carbon nanotubes can be also grown in 3D helical/spiral structures. This work demonstrates high-yield growth of carbon nanocoils on stainless steel by chemical vapor deposition. The stainless steel substrate was coated with tin acetate as the catalyst. The effects of the tin and preparative oxidation pretreatment on the morphologies of the carbon nanocoils were investigated. Tin was found to be crucial in the formation of the carbon nanocoils. A preparative oxidation temperature of 800 centigrade degree yields 80% nanocoil growth in carbon products. This synthetic approach is scalable for the mass production of carbon nanocoils.

The mechanical properties of carbon nanotubes have been extensively discussed in the literature, and various measurement methods have also been developed. The most accurate method for estimating the elastic modulus of carbon nanotubes is considered to be the resonance method. This study demonstrates a resonance shift method that is more accurate than the resonance method. It is found that the estimation of the elastic modulus of carbon nanotubes by the traditional resonance method could yield a 20% deviation, compared with the value estimated from the resonance shift method.

Theoretical and experimental studies have shown that carbon nanotubes have a gauge factor of above several hundreds. This work demonstrates an approach for fabricating high-sensitivity flexible strain sensors at room temperature. At first, the well-aligned mm-long single-walled carbon nanotube (SWCNT) was chemical vapor deposition grown on silicon. The SWCNT was then transferred from the silicon substrate to the flexible substrate and cross the pre-fabricated trench between two electrodes. To prevent shipping, the most of the mm-long SWCNT was in well contact with the electrodes to provide strong adhesion. Therefore, during the bending experiments, the suspended SWCNT exhibits effectively strained, inducing piezo-resistivity change. Experimental results reveal that the sensor achieves a high strain resolution of 0.004%. The measured piezoresistive gauge factor of the flexible sensor is 269. The demonstrated technique for fabricating flexible sensors provides the advantage of high sensitivity and high quality and is suitable for mass production.

The electromechanical properties of carbon nanocoils have not yet been properly studied. In this work, carbon nanocoils were aligned and positioned using dielectrophoresis techniques. The applied voltage and the gap between the electrodes were controlled to optimize conditions to align the carbon nanocoils between the electrodes. The electromechanical measurements indicate that the gauge factor of the carbon nanocoils was in the range 20 to 50, which is close to that of multi-walled carbon nanotubes. The gauge factor declines as the number of aligned carbon nanocoils between the electrodes increases. The mechanism was also discussed.

並列關鍵字

Carbon nanotube ； Carbon nanocoil ； Mechanical properties ； Chemical vapor deposition ； Flexible ； Strain sensor

參考文獻

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