奈米矽針及奈米碳管的生長、分析及應用

Abstract

在這個論文裡面，我們探討了奈米結構材料的幾個不同面向。這些一維或多維的奈米材料，具有微觀級- 原子或分子尺度下令人驚奇的特性。他們潛藏的應用價值以及對未來能源元件類的可能衝擊代表著其無限的價值性。這個論文中，包含著對這些奈米材料的一般討論，並且含有針對以下三個重點的加強研究： 1. 藉由電場輔助化學氣相沉積法合成單層奈米碳管薄膜 這個主題中包含著奈米碳管生長的研究討論。電場輔助化學氣相沉積法被成功用來生長奈米碳管薄膜。在生長的過程中，透過外加的強電場，催化溶液被分散並注入高溫爐中的高溫區(攝氏950-1100 度)。在最佳的生長條件下，如此生長的奈米碳管被發現幾乎均為單層的奈米碳管，並且只含有非常少許的雜質。生長時高溫爐的溫度主宰著所生長的奈米碳管長度及直徑，而奈米碳管沉積的位置會受其長度及生長的位置所影響。上述的行為，最後由透過考慮高溫爐中作用在奈米碳管的各種力學來成功的完全解釋。這個研究成果提供一種分離奈米碳管的方法，並因此富有將其應用在奈米碳管的電子元件上的潛能。 2. 獨立的奈米碳管共振視窗拉曼分析 利用由電場輔助化學氣相沉積法所生長的獨立分離碳管，透過藉由拉曼光譜的分析，去討論不同對掌性奈米碳管的物理性質的不同。獨立分離的單層奈米碳管被拿來檢測其分別的拉曼光譜在廣泛的不同連續波長雷射下的行為。這個實驗的結果被使用來觀察一整個(2n+m)碳管家族的RBM共振視窗。奈米碳管的對掌角對共振視窗寬度的影響亦被發現比其直徑的影響力還大。並且拉曼D-band的強度也被發現和其對掌角有很大的關係。最後，由分析的結果，本論文建議缺陷的散射是激發電子釋放回到基態的主因，進而主導著共振視窗寬度的大小。 3. 氧化鋅/奈米矽針在發光二極體元件上的應用 這部份主要是針是奈米材料在發光二極體元件上的應用所做的研究。這裡將會介紹ㄧ個由矽當基板的奈米p-n陣列來當材料的一個電致發光元件。元件的規模透過單一步驟的乾蝕刻過程，可以完美達到一整個晶元(wafer)大小的規模，並且這個製程是可以和目前半導體科技的製程相容的。接著透過雷射剥離沉積法，一層氧化鋅被鍍在奈米矽針陣列上面。所鍍的氧化鋅的高品質，經由很宰的陰極發光光譜峰寬，以及在拉曼光譜中，多重聲子(高達4階)的發現而被確認。此奈米針元件氧化鋅/矽的啟動電壓被發現只有2.4伏特，相當只有同材料薄膜的1/2。此外，此氧化鋅/奈米矽針二極體發光元件的設計亦被證實可成功的由電致發光。在光電材料的整合上，這個研究成果開展了矽基底在高效率LEDs上應用的可能性，並且富有和目前大規模矽晶片整合技術相容的可能性。

In this thesis several aspects of nanostructured materials are investigated. These materials, defined by having one or more dimensions at the nanometer scale, have exciting properties that link them to the microscopic realm of atoms and molecules. At the same time their application has and will have a gigantic impact on our future in fields as diverse as energy harvesting and health. A broad perspective on these materials by describing several fields of intensive current research will be given in this thesis and the emphasis will be put on three issues: 1. Synthesis of Single-walled carbon nanotubes thin films via Electrostatic spray-assisted chemical vapor deposition In this topic, a detailed study on growth of carbon nanotubes (CNTs) will be presented. Electrostatic-spray assisted chemical vapor deposition is described as a way to directly deposit single-walled nanotube (SWNT) thin films on a substrate. Through a strong electrical field, the catalyst solution was finely dispersed and injected into the heated reaction zone (950-1100 °C) during the growth. It was also found that under optimized growth conditions, the deposited materials were almost exclusively SWNTs and only contain small amounts of impurities. The growths at different temperatures result in nanotubes of different morphology and length. The location of the SWNTs’ deposition is found to be affected by the nanotube length and the growth temperature and this behavior is explained by considering different forces acting on the floating nanotubes inside the furnace. These results could provide a route of sorting floating SWNTs for electronics applications. 2. Analysis of Raman resonance windows of individual single-walled carbon nanotubes The single walled carbon nanotubes grown by the previously described ESACVD process, were investigated by Raman spectroscopy on the individual nanotube level to extract differences in the physical properties for different chirality nanotubes. Raman spectra of isolated SWNTs were obtained for a wide range of laser excitation energies to study the resonance window of the Raman RBM feature for members of (2n+m) families. A chiral angle (θ) dependence of the resonance window width (Γ) was observed that is much stronger than the diameter dependence. A strong correlation between the θ dependence in Γ and the D-band intensity was observed. The analysis in this thesis suggests that defect scattering could be an important source of electron relaxation affecting the resonance window width. 3. Application of ZnO/Si-nanotips as Light Emitting Diodes. This research represents the application part of the nanostructured material study in this thesis. A new and general approach to achieving efficient electrically-driven light emission from a Si-based nano p-n junction array will be introduced. By a single-step self-masked dry etching process, a wafer-scale array of p-type silicon nanotips were formed, which is compatible with current semiconductor technologies. On top of the silicon nanotip array, a layer of n-type ZnO film was deposited by pulsed laser deposition. The excellent quality of the ZnO film is characterized by both the narrow linewidth in cathodoluminescence spectra and the appearance of multi-phonon Raman spectra up to the 4th order. The turn-on voltage of our ZnO/Si nanotip array is found to be only ~2.4 V, which is 2 times smaller than its thin film counterpart. Moreover, electroluminescence (EL) from the ZnO/Si nanotips array light emitting diode (LED) has been demonstrated. The results shown in this research could open up new possibilities to integrate silicon-based optoelectronic devices, such as highly efficient LEDs, compatible with standard Si ultra-large-scale integrated technology.