- 學位論文
以聚焦微波電漿束合成超微細鑽石奈米結構在光電及生醫植入元件上之應用
Synthesis of Ultra-Fine Diamond Nanostructures by Using Focused Microwave Plasma Jets for Applications in Optoelectronic and Bioimplantable Devices
摘要
鑽石擁有極其優異的材料特性，被認為具有極高的應用潛力，但是一般化學氣相沉積所合成的微米晶鑽石(Microcrystalline diamond, MCD)膜，因其表面粗糙、高合成溫度及不易摻雜形成正或負型半導體等問題存在，所以限制了鑽石膜於工業上之應用。為了提升鑽石於多功能性(如光電與生醫)元件上之實際應用，合成晶粒尺寸為奈米/超奈米等級之鑽石膜(Nanocrystalline/ultrananocrystalline diamond, NCD/UNCD)，被視為最佳解決方法之一。本研究發展出一獨特的聚焦微波電漿束(Focused microwave plasma jet)技術用以改善UNCD薄膜之合成並完成UNCD薄膜之成長、改質、特徵及其功能性(光電及植入式生醫)元件應用之探討。研究結果顯示使用微波電漿束化學氣相沉積(Microwave plasma jet chemical vapor deposition, MPJCVD) 可有效促進UNCD薄膜之初始成核與成長。此製程所合成之UNCD薄膜具有的特性與典型的微波氬氣(Ar-rich)電漿成長之UNCD薄膜十分相同，但卻可在較低的Ar氣濃度(90%)、溫度(460 ℃)、工作壓力(35 Torr)及微波功率(700 W)下以更快的沉積速率 (315 nm/h)成長更平滑之UNCD薄膜。研究中將MPJCVD製程之Ar氣濃度、合成壓力、甲烷(CH4)濃度及氮氣(N2)濃度對於UNCD薄膜之合成與特性之影響進行系統性地探討，並進一步提出其可能的成長機制了解其成長條件-結構-特性之關聯。 在UNCD薄膜之功能性元件應用方面，研究中完成其製作成紫外光感測器與植入式生醫元件的可行性之探討。研究結果指出UNCD薄膜搭配金膜指狀電極所製備之紫外光感測器在紫外光輻射照度 (10-4-10-2 W/cm-2) 改變下展現出明顯的電流值變化(10-103 times)，並具備良好的時間響應性能與穩定的再現性。體外細胞(Human osteosarcoma cell line MG63)培養證實UNCD薄膜具有較類鑽碳(Diamond-like carbon, DLC)薄膜及矽基板更佳的生物相容性與生物體內穩定性，大有希望應用於植入式生醫元件之封裝。UNCD薄膜之生物相容性可經由摻雜氮(nitrogen doping)而明顯地提升，然而，生物惰性卻會因UNCD薄膜摻氮導致的結構鬆散與較低的附著度而下降。 MPJCVD合成之UNCD薄膜已被證實具有極高潛力應用於開發多功能性元件，因此我們進一步探討低維度鑽石奈米結構之MPJCVD合成、特形及應用。本研究成功地直接以MPJCVD完成鑽石奈米粒子(Diamond nanoparticles, DNPs)、頂端披附上DLC奈米點的直立矽奈米柱 (DLC nanodots-coated Si nanopillars)及直立且高細長比鑽石奈米線(Diamond nanowires, DNWs)之製作。DNPs之合成乃藉由拉長MPJCVD製程之工作距離至15 mm，導至奈米鑽石同質氣相成核與成長被優先地發生，待其於氣相中成長或團聚至一定大小(~100 nm)與重量進而掉落於基板上形成均勻尺寸之DNPs。DLC nanodots-coated Si nanopillars之製備是藉由Focused microwave plasma jet直接於矽基板上同時增強蝕刻與合成之技術所完成。 MPJCVD製程所合成之DLC nanodots直接做為直立Si nanopillars結構化之蝕刻遮罩。直立且高細長比之DNWs伴隨著奈米鑽石及石磨複合薄膜被證實具備極佳的電子場發射特性，作為場發射源可展現出極低的起始電場(3.2 V/μm)與高的電流密度。此外，由DNWs試片中抽取出之單一根鑽石奈米線的特性分析證實DNWs仍保有與一般鑽石相同的電絕緣特性，然而，其結構卻同時可展現出新穎的可撓性(bended ~87.5°)特徵。
並列摘要
The unique combination of excellent physical and chemical properties makes diamond a potential material candidate for applications in the fabrication of multifunctional devices. However, the rough surface morphology, high-temperature synthesis, and difficult P- and N-type doping of typical microcrystalline diamond (MCD) films grown from chemical vapour deposition (CVD) methods restricted the practical applications of diamond. One way of synthesizing nanocrystalline/ultrananocrystalline diamond (NCD/UNCD) films is regarded as the effective method for resolving those restrictions. The grain size of UNCD films is less than 10 nm, therefore the effect of diamond facet characteristics on their applications can be greatly decreased. The study describes a new CVD technique underlying the improved synthesis of UNCD films from focused microwave plasma jets and completes investigations of the growth, modification, characterization, and function applications in the optoelectronic and bioimplantable devices of the synthesized UNCD films. The research results demonstrated that the nucleation and growth of UNCD films could be really improved by using the microwave plasma jet chemical vapor deposition (MPJCVD). The MPJCVD yields smoother UNCD films identical to thoses produced with Ar-1%CH4 chemistry by microwave plasma chemical vapor deposition (MPCVD), but using relatively low Ar introduction (90%), low temperature (460 ℃), low pressure (35 Torr), and low microwave power (700 W) during synthesis with higher deposition rate (315 nm/h). The effects of Ar concentration, deposition pressure, CH4 concentration, and N2 concentration on UNCD film synthesis from the MPJCVD were systematically investigated. The poteintial synthesis mechanisms were proposed to understand the relationships between the deposition conditions, structures, and properties of the films. The fabrication of UNCD films-based UV photodetector and in vitro cell (Human osteosarcoma cell line MG63) cultivation experiments have been performed for investigation on functional device applications of UNCD films grown by MPJCVD. The results indicated that the device made of UNCD films combined with Au interdigital finger (IDF) electrodes exhibited obvious changes (10-103 times) in current under a range of UV irradiances (10-4-10-2 W/cm-2) with fast response and stable reproducibility. In vitro MG63 cell culture study demonstrated that UNCD-based films are better than diamond-like carbon (DLC)-based films and Si substrates for promoting the cell attachment and the stability within human body. The UNCD films are promising for the the fabrication and encapsulation of in vivo devices without induced immune response in the human body. In this study, we further investigated the MPJCVD synthesis, characterization, and application of low-dimension diamond nanostructures. The MPJCVD has been successfully developed to direct fabrication diamond nanoparticles (DNPs), DLC nanodots-coated Si nanopillar arrays, and vertical diamond nanowires (DNWs) with uitra-high aspect ratio. The DNPs synthesis was induced by preferentially homogeneous nucleation and growth of nanodiamonds in the vapor during synthesis with a prolonged plasma jet working distance of 15 mm. The nanodiamonds were grew and aggregated until to achieve a specific size with sufficient weight in the plasma jet for further landing on Si substrates coated with UNCD films. DLC nanodots-coated Si nanopillars were directly structured fom Si substrates via a specific fabrication scheme under focused microwave H2-4%CH4 plasma jet simultaneously enhanced etching and growth technique. The DLC nanodots in-situ synthesized from seeding sites on treated Si substrates, which serve as masks during the simultaneous etching process. The vertical DNWs grown accompanying nanodiamond-graphite-amorphous carbon films have been demonstrated to possess marvellous EFE properties with a low turn-on field (E0) of around 3.2 V/μm and a high current density. Moreover, the one-dimension nanowire extracted from the sample of hybrid DNWs which has been demonstrated to keep the electrically insulating property of buck diamond, but exhibited a novel flexibility (bended ~87.5°) in mechanical properties. These experimental finding provided some thinking to associated with the process of nanodiamond related materials for further controlling and obtaining the required diamond nanostructures.