金屬氧化物奈米線的合成技術及其在奈米發電機之應用

Techniques for Synthesis of Metal Oxide Nanowires and Applications to the Nanogenerator

許乃鋒(Nai-Feng Hsu)

指導教授 ： 章明

中原大學/工學院/機械工程研究所/博士(2011年)

https://doi.org/10.6840/cycu201100503

摘要

本研究結合熱氧化法與氣固法，開發了一套快速合成金屬氧化物奈米線的技術，並已成功生長α-Fe2O3 和 Fe3O4奈米線在鐵鎳合金基板上，及生長ZnO奈米線陣列於鋅基板上。此方法首先將已浸泡過草酸溶液的鐵鎳合金基板及鋅基板，放置於石英管中，使其在空氣中熱氧化形成氧化層，隨後利用氣固法，當基板繼續在真空的石英管中加溫至預設溫度後，通入Ar氣20分鐘，藉由擴散的氣體使得金屬氧化物奈米線可成長在氧化層上。本研究所生成的奈米線，其直徑可維持在200 nm以下，長度可高達10 μm，且合成時間只需1.5小時。結合capillarity model 和resident time theorem可解析奈米線的生長機制，藉由vibrating sample magnetometry (VSM)可證明生長的α-Fe2O3 和 Fe3O4奈米線為高磁性材料，此外，由Raman scattering 和 PL spectrum的分析，可觀察出生長的ZnO奈米線，擁有良好的結晶品質，只有少量的氧缺陷存在奈米線表面。
在氧化鐵奈米線合成過程中，本研究透過實驗方式探討草酸對生長晶相轉換的影響。研究顯示，未浸泡過草酸溶液的鐵鎳合金基板，利用氧化輔助氣固法所生成的氧化鐵奈米線為α-Fe2O3晶相，當合金片事先浸泡在低濃度的草酸溶液中作為基板，則少數的奈米線將轉而生長成為Fe3O4晶相，隨著草酸濃度的增加，Fe3O4奈米線的生長數量亦隨之增加，直到草酸濃度至0.75 mol/L時呈現飽和現象，其大部分的氧化鐵奈米線晶相轉為Fe3O4。其次當合金片浸泡過草酸溶液在高流量的情況下，Fe3O4奈米線會有團聚生長成塊狀的現象，且隨著草酸濃度增加團聚狀況會加劇。本實驗亦曾改變合金浸泡草酸的時間，但並沒有明顯的發現產物與濃度對浸泡時間改變的關聯性。
此外，本研究亦藉由奈米操作系統，在掃描電子顯微鏡內部執行奈米線拉伸實驗，探討Fe3O4奈米線的機械性質。實驗結果得到Fe3O4奈米線的楊氏係數、降伏應力及破裂應力分別為23.8 ± 3.8 GP、428 ± 55 MPa 和 1.10 ± 0.29 GPa。應變範圍在5% 到11%之間，顯示Fe3O4奈米線擁有極佳的延展性。
最後，本研究整合應用生長於基板上的磁性奈米線及氧化鋅奈米線，完成一雛型奈米發電機系統的設計，其利用磁力控制磁性奈米線基板產生反覆震盪，藉以彎曲氧化鋅奈米線，結合磁電效應及氧化鋅奈米線的壓電效應，在Br(magnetic flux density)為400 mT的磁力作用下，於1.5cm×3cm的面積(包含3.5cm2的封裝面積及1cm2壓電面積)可達接近52 μA的電流量，此系統已具備點亮LED燈泡的能力，有機會開發成為一種綠色能源。

關鍵字

ZnO奈米線 ； 壓電效應 ； 氧化輔助氣固法 ； Fe3O4奈米線 ； 機械性質 ； α-Fe2O3奈米線

並列摘要

Oxide assisted vapor-solid (VS) process has been used for rapid crystal growth of α-Fe2O3 and Fe3O4 nanowires (NWs) on Fe:Ni (1:1) alloy substrate, and of ZnO NWs array on Zn substrate. Oxide layers have been created initially on the Fe:Ni (1:1) substrate or Zn substrate by heating it inside the quartz tube of a single tube furnace in air. The substrate is Fe:Ni (1:1) alloy or Zn piece prior immersed in solution of oxalic acid. Raise the temperature of the quartz tube to prior set temperature in vacuum and flow argon (Ar) for 20 mins. Introduction of Ar carrier gas in the step can help the axis grow NWs on the oxide layer. In the process, the grown NWs diameters can maintain below 200 nm with lengths reaching to 10 μm and the entire synthesis of NWs can be completed within 1.5 hrs. Capillarity model and resident time theorem have been combined to analyze the nanowire growth process. Vibrating sample magnetometry (VSM) study show that α-Fe2O3 and Fe3O4 NWs are high magnetic materials. Additionally, the grown ZnO NWs are proved there is good crystal quality with few oxygen vacancies on the surface by the Raman scattering and PL spectrum.
In this work, an experimental method applied to discuss influence of oxalic acid for the crystalline phase of iron oxide NWs. Experimental results indicate that grown NWs are α-Fe2O3 crystalline as Fe:Ni (1:1) alloy is immersed in water. However, as Fe:Ni (1:1) alloy is prior immersed in a solution of oxalic acid with low concentration, few NWs grew to become Fe3O4. The saturated state of Fe3O4 NWs is achieved as the oxalic acid concentration reaches 0.75 mol/L, and grown NWs mainly are Fe3O4 crystalline phase in the concentration. Further, some of the Fe3O4 NWs aggregate to appear particles in extremely gas flux as Fe:Ni (1:1) alloy is prior immersed in a solution of oxalic acid, and these particles combine to form bulk as raising oxalic acid concentration to 0.75 mol/L. Furthermore, there are not obviously varieties for grown products as varied dripping time at various oxalic acid concentrations.
Moreover, mechanical properties of Fe3O4 nanowires are investigated by a nano-tensile testing technique using a custom-made nanomanipulator inside the SEM. The modulus of elasticity, yield stress and fracture stress of Fe3O4 NWs are estimated to be 23.8 ± 3.8 GPa, 428 ± 55 MPa and 1.10 ± 0.29 GPa, respectively. Strain range at breaking of NWs is obtained 5% to 11%. The results indicate that the Fe3O4 NWs have highly malleable and stretching properties.
Eventually, a system of nanogenerator can be developed by integral magnetic NWs and ZnO NWs of growth on substrates. In this system, magnetic substrate with growth magnetic NWs bend ZnO NWs by repeatedly vibration to stimulate a PZ effect and magnetic-induce-current under an extra magnetic field. The results discovered that there is a high output current approximately 52 μA/1.5cm×3cm (the area 1.5cm×3cm is including package area 3.5cm2 and piezoelectric area 1cm2) under Br (magnetic flux density) is 400 mT. This system has possessed ability to alight LED, which may be developed to become green energy in the future.

並列關鍵字

Mechanical properties ； Oxide assisted vapor-solid ； Piezoelectric effect ； ZnO NWs ； α-Fe2O3 NWs ； Fe3O4 NWs

參考文獻

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