| Abstract: | 本研究將奈米碳管(Carbon Nanotubes，CNTs)作成懸浮液，為了將奈米碳管優異的電學特性表現在巨觀環境下，利用真空過濾製作成奈米碳管紙(Buckypaper，BP)。為了調控其電學參數，參考文獻中奈米碳管改變載子形態的方法(P-type or N-type)。在作成奈米碳管紙之前，將碳管退火，溫度分別在200℃、400℃、600℃、800℃，維持時間為10分鐘。此外，將巴克紙經過電漿處理分別在氬氣、氧氣與氮氣250mtorr條件下，藉此改變碳、氧、氮之間的原子成分與sp2、sp3鍵結比例。在電性量測部分，利用低溫四點電阻率量測，觀察不同溫度下巴克紙和經過加工改質處理的BP，而後樣品再利用Van der pauw方法進行霍爾量測，觀察在不同改質條件下，載子濃度及遷移率的變化 。參考在奈米碳管的文獻上得知，在不同真空度下有不同的電學特性，甚至有氣體吸附的現象，勢必對電學特性有所影響，因此探討在不同氣體氣壓下，並在通入氣體前，加熱和未加熱樣品，觀測電阻率前後的變化。研究結果發現，碳管退火在200℃時，巴克紙的電學特性不會有太大的變化，當退火溫度達400℃時，巴克紙的電阻率比起未處理的巴克紙，有下降的趨勢；當退火溫度達800℃，電阻率則會大幅的上升。此外，經過電漿處理的巴克紙以及經過氬氣與氧氣電漿處理過的巴克紙，電阻率明顯提升；而在氮氣條件下的電漿處理，電阻率則下降。霍爾量測結果顯示，其未處理的奈米碳管紙，載子濃度約為1024 (cm-3)且為P-type。經過碳管退火800℃與氬氣、氧氣和氮氣電漿處理後的巴克紙，在一定時間內為N-type，載子遷移率約為10-4 (cm2/vs)。較低的遷移率原因是，巴克紙的結構並非長程有序的晶格，載子傳輸時必須跨越碳管之間的位能障。此外，N-type的巴克紙在大氣下，以及氧氣與水氣等雜質的作用下，又會逐漸轉變回P-type。在不同氣體和氣壓下，電阻率的量測，在低真空度時，電阻率隨真空度成反比，而在高真空度下則相反。在不同氣體氣壓下，電阻率與氬氣、氧氣與氮氣的氣壓成正比，但在真空下經過加熱後，由於雜質或水氣的去除，電阻率與氣壓轉變為反比，氣壓在10Torr後趨勢又有了變化，其中巴克紙在氧氣下，電阻率的變化更為明顯。儘管N-type的奈米碳管紙在大氣下並不穩定，而且精確的濃度調控也是個問題，但已經找到方法將P-type的奈米碳管紙轉換成N-type，讓BP更有機會得以應用在電子元件上。
In this study, in order to utlize the electircal characteristic of a single CNT, we filtrate the suspension of CNTs and make it as sheet-like bulk material, called random buckypaper (RBP). The aim is to control the electrical properties. Before filtrate the suspension of CNTs, CNTs annealing was done at 200℃,400℃,600℃ and800℃ for 10 min. In addition, RBP was functionalized with RF plasma in Ar, O2 and N2 atmosphere (250 mTorr) under a power of 10W for 15 min, to increase the C, N, O elemental composition and C-O, C-N ratio. In order to compare electrical properties of each sample, we use four-point- measurement to measure resistivity, and then use Van Der Pauw method to measure carrier concentration and mobility. The resistivity is changed in different vacuum and gas. Before flow the gas, we heated or unheated the sample to discuss the resistance change.As the annealed sample, annealing temperature rises before 600℃, the resistivity decreased. When annealing temperature at 800℃, the resistivity increased. In addition, after plasma treatment buckypaper sample at Argon and Oxygen condition caused resistivity increase. In nitrogen plasma treatment condition, the resistivity decreased. After annealed 800℃ and argon, oxygen and nitrogen plasma treatment buckypaper. By hall-measurement result, Carrier concentration changeto N-type. Mobility is about 10-4 (cm2/vs). The mobility is lower than others material because of amorphous structure. Besides, N-type buckypaper storage in air, because of oxygen and water vapor, will turn back to P-type. We measure resistivity in different vacuum degree and gas. Vacuum degree increased, then the resistivity decrease. After heating the sample, the trend has changed. Resistivityhas more significant change in oxygen. The N-type sample is not stable in air.The exact concentration of is also a problem, but have found ways to P-typebuckypaper into N-type. Make BP more opportunity to be applied in electronic devices. |
