Abstract
本篇論文對於「自組裝單晶氧化銅奈米線（CuO nanowires）」提出一種新的合成方式，利用此一方法，可將氧化銅奈米線成長於鍍有銅基多層金屬膜（Cu-based multilayer）之二氧化矽/矽基板（SiO2/Si-substrate）的表面，有利於未來相關元件之製造與應用。實施此技術之關鍵，是使用無電鍍鈷磷化鎢（electroless CoWP）薄膜做為一種奈米篩（nanofilter），用以催化氧化銅奈米線於低溫空氣鍛燒製程（400 C, 1 atm）中合成；此種無電鍍鈷磷化鎢薄膜，常被用來作為一種銅的擴散阻隔層。 氧化銅奈米線合成條件之最佳化，是經過一系列實驗設計與基礎研究所達到的；其中，特別針對鈷磷化鎢薄膜的催化效應、製程時間效應、溫度效應，以及製程氣體壓力效應做探討。具有單斜晶（monoclinic）結晶性之單晶氧化銅奈米線，可藉由120分鐘之低溫空氣鍛燒（400 C, 1 atm）成功的被合成出來（奈米線直徑：10 - 50 nm、長度：~7 um、密度：~109 NWs/cm2）。 本研究中，使用場發射掃描式電子顯微鏡（FESEM）、原子力顯微鏡（AFM）、X光繞射儀（XRD），以及穿透式電子顯微鏡（TEM），針對氧化銅奈米線與鈷磷化鎢薄膜表面之物理性質進行分析；另一方面，更探討氧化銅奈米線之電性質與場發射特性。經由電性量測發現，本研究所合成之氧化銅奈米線呈現電阻特性，並具有比先前之研究報導相對低的電阻率（resistivity），約在10 - 60 ohm cm之間。場發射特性量測也指出，此氧化銅奈米線具有低的啟動電場（turn-on field）約為4.5 V/um，以及高的場增強因子（field enhancement factor）約為1400。此外，本論文也探討以鈷磷化鎢奈米篩催化合成氧化銅奈米線的成長機制，更嘗試提出一種成長機制模型，提供未來各種奈米線合成研究之參考。 This thesis presents a new approach to synthesize self-aligned, uniform, and single-crystal cupric oxide nanowires (CuO NWs) on Cu-based multilayer on SiO2/Si for future device fabrication. The key is to introduce electroless cobalt tungsten phosphide (CoWP), which is normally used as a Cu diffusion barrier, as the nanofilter to catalyze CuO-nanowire synthesis simply by the calcination at 400 C in air (1 atm). The CuO-nanowire syntheses were optimized by series of fundamental investigation and experimental designs, especially on the catalytic effect of CoWP, growth time, growth temperature, and process pressure. The single-crystal monoclinic CuO nanowires synthesized exhibit a diameter of 10 - 50 nm, the length up to 7 um, a density of 109 NWs/cm2, and an average growth rate of 50 nm/min, for the samples calcined for 120 min. The physical properties of CuO nanowires and CoWP capping layer were analyzed by field-emission scanning electron microscope (FESEM), atomic force microscope (AFM), X-ray diffractometer (XRD), and transmission electron microscope (TEM) equipped with an energy dispersive spectrometer (EDS). In addition, the electrical and field-emission (FE) properties were also measured and discussed in this work. The individual as-synthesized CuO nanowire exhibits ohmic behavior with a resistivity of 10 - 60 ohm cm, which is relatively lower than those reported. From the measured field-emission properties of CuO nanowires on SiO2/Si-substrate, a low turn-on field of 4.5 V/um and high field enhancement factor of about 1400 have been achieved. Besides, based on the results of FESEM, AFM, cross-sectional TEM, and XRD analyses, the possible catalytic growth mechanism of CuO nanowires was also discussed. The vapor-solid (VS) mechanism is most likely responsible for the CuO-nanowire synthesis of this work. The model of growth mechanism for CuO-nanowire synthesis catalyzed by CoWP nanofilter has also been proposed in this study.