以Co2NiO4 和CoPdO2為觸媒利用微波電漿輔助化學氣相沉積法合成含合金之碳奈米結構

Abstract

為著做為絕緣的合金奈米線的可能應用，本實驗計畫使用合金氧化物為觸媒，研究充填合金在碳奈米結構中的可能性和他們的成長機制。使用微波電漿化學氣相沉積法，在矽晶片上合成含有合金的奈米結構，以Co2NiO4和CoPdO2合金氧化物為觸媒，甲烷和氮氣為來源 氣體。純金屬(Co、Ni和Pd)的鍍膜使用物理氣相沉積法，沉積在Si 晶片上。沉積後的基材放置在大氣爐中做氧化處理形成合金氧化物。 鍍有合金氧化膜的基材，使用氫電漿前處理使觸媒形成奈米島狀形貌，用以合成奈米結構。這合金氧化物合成奈米結構，以AFM、SEM、 TEM、XRD、EPMA、EDX、Raman和J-V量測分析其特性。 結果顯示使用CoPdO2觸媒可合成充填金屬的奈米結構，而Co2NiO4觸媒則沒發現可以形成充填合金的奈米結構。在這裡CoPdO2合成之奈米結構為端部成長(tip growth)之碳奈米管或奈米顆粒。而以Co2NiO4觸媒合成之奈米結構為(base growth)之碳奈米管。結果也指出形成奈米結構的關鍵參數有觸媒原料、氫電漿前處理時間和沉積溫度。氫電漿前處理時間之作用實質上是延長奈米島狀觸媒的聚集效應。所以較長的處理時間有助於形成較大的島狀觸媒，以利形成充填合金的碳奈米管。沉積溫度的作用基本上是相似於氫電漿前處理時間的作用。在較高的沉積溫度有助於提高觸媒的流動性而可被毛細作用力充填進入管中。 在場發射性質方面，結果顯示充填合金的碳奈米管沒有場發射的 現象。沒有充填合金的碳奈米管起始電壓為4.8 V/μm(定義在電流密度為1 μA/cm2下)。另外值得注意的一點是在目前的條件下，並沒有發現竹節狀碳奈米管的出現，雖然在文獻報導上加入氮氣是合成竹節狀碳奈米管的主要因素。

ABSTRACT For potential applications as the insulated alloy nano-wires, this work was planning to examine the feasibility of filling the alloy in carbon nanostructures using alloy oxides as catalysts and to study their growth mechanisms. The alloy-contained carbon nanostructures were synthesized on Si wafer by microwave plasma chemical vapor deposition (MPCVD) using CH4 and N2 as source gases and alloy oxides (Co2NiO4 and CoPdO2) as catalysts. The pure metal coatings (Co, Ni and Pd) on Si wafers were prepared by physical vapor deposition. The coated substrates were followed by oxidation in air furnace to form alloy oxides coatings. The alloy oxide-coated substrates were then pretreated in hydrogen plasma atmosphere to become nano-islands to act as catalysts for nanostructure growth. The alloy oxide-assisted nanostructures were characterized by AFM, SEM, TEM, XRD, EPMA, EDX, Raman spectroscopy and field emission J-V measurement. The results show that the alloy-filled carbon nanostructures can be obtained by using CoPdO2 as the catalyst instead of Co2NiO4. Where the CoPdO2-assisted nanostructures are tip-growth CNTs or nano-particles, and the Co2NiO4–assisted nanostructures are base-growth CNTs. The results also indicate that the key parameters governing the nanostructures are catalyst materials, hydrogen plasma pretreatment time and deposition temperature. Effect of hydrogen plasma pretreatment time is essentially to prolong the agglomeration effect on the nano-islands of catalyst. Therefore, longer pretreatment time favors a larger island size to form alloy-filled CNTs. Effect of deposition temperature is basically similar to effect of hydrogen plasma pretreatment time. A high deposition temperature favors a higher fluidity of catalyst to fill into the tubes by capillary force. On field emission properties, the results show that the alloy-filled CNTs have no significant field emission. The turn-on voltage of the CNTs without filling alloy is about 4.8 V/□m defined at current density of 1 □A/cm2. It is also interesting to note that there are no bamboo-like CNTs in the present conditions, though the presence of N were often reported to be the main parameter to form bamboo-like CNTs.