- 學位論文
以微波輔助法在矽基板及針尖上成長奈米碳管的研究
Studies of Microwave Eenhanced growth of Carbon Nanotubes Synthesized on Si Wafers and Scanning Probes
摘要
在本篇論文中，我們分別在矽基板及針尖上成長奈米碳管，兩者都是利用導入的微波能量產生高熱能，以達到裂解甲烷的目的。 首先，我們選用旋鍍法將含有鐵的有機鹽(C7H17COO)3Fe 鍍在矽基板上，然後使用可吸收微波能量的材料碳化矽(SiC)來均勻加熱矽基板，從而熱裂解甲烷(CH4)以進行奈米碳管的成長。我們先試著去抓取最佳的基板溫度，接著，在同基板溫度(~1000℃)，不同時間的依變下，我們觀察到製得奈米碳管的直徑與成長時間呈現正相關的特性。隨著成長時間的增加，長成的奈米碳管將催化劑(鐵)消化殆盡後，仍不斷沈積的碳粒掩蓋了長成的奈米碳管，因而觀察到奈米碳管埋在碳粒的底部。製得的奈米碳管的TEM、SEM及場發射特性一一被量測出，在起始電場~0.55 有量到奈米碳管場發射特性，且在6 電場下有3 的電流密度。 其次，我們取鎢針或鐵針當基材，在鎢針尖上沾含鐵有機鹽(C7H17COO)3Fe後，再用250℃退火30min.，我們發現直接成長奈米碳管於鎢針時，具有低微波瓦數(30W-50W)，低碳源(~5%)，低成長時間(~5min.)的特性，因而大大降低製作的成本，甚至，我們發現改用鐵針當基材後，不需沾催化劑便可長成碳奈管，因而縮短製作時間。製得的奈米碳管也以TEM、SEM來觀測。我們也發現在實驗過程中加入氮氣，成長的奈米碳管具有竹節狀(bamboo)的結構。最後測量出奈米碳管的針尖場發射。
並列摘要
In this thesis, we grew carbon nanotubes (CNTs) on silicon substrate and metal tips respectively, in both case, microwave was introduced for the gathering of heat, and there upon results in the pyrolysis of methane. First, using the method of spin-coating, organic salt (C7H17COO)3Fe was first deposited on our Si-substrate, then a modified chemical vapor deposition (CVD) process, which utilizes a susceptor (SiC) to absorb the microwave and to self-generate the heat, and thereon results in localized dissociation of the CH4 gases was used to grow carbon nanotubes on the Si (Fe) substrate. Optimal substrate temperature ( ~1000 0C) was chosen to conduct the measurement of the time-dependent CNTs characteristics. We found that the diameter of the CNTs increases as the deposition time increased. After the catalyst Fe had being used up by the as-grown CNTs as time passed by, the still growing carbon nanoparticles covered on top of the as-grown CNTs, and therefore, the CNTs were embedded under the nanoparticles as observed from our SEM graphs. The field emission properties of our CNTs were measured with a very low turned-on field (E0~0.55 ), but also a very low emission current density (Jc~3 ) at 6.0 applied field. Next,tungsten and iron tips are used as our substrates. Tungsten tips dipped with organic salt(C7H17COO)3Fe was annealed at 250 ℃ for 30 min. before put into the chamber. We found that, low microwave power (30-50W), low carbon source(~5%), low growth time (~5min.) characterized the growth of CNTs on the tungsten tip. We ever found that, using iron tip without the dip of orgnic catalyst still enables us to grow CNTs. Finally,the introduction of N2 during the growth process often results in the CNTs with bamboo-like structure as revealed from the TEM micrographs.