利用氧化鋁膜為模板製備自組裝奈米結構於矽基材之研究

Abstract

本研究利用陽極氧化鋁薄膜作為模板輔助成長奈米碳管與氧化鋅奈米柱之規則陣列並探討其電子場效發射性質。具有規則排列奈米孔洞的陽極氧化鋁模板利用熱阻絲蒸鍍鋁膜之兩階段陽極氧化鋁處理所得，本研究在陽極氧化鋁與矽基材間鍍上一層鎳薄膜當作成長碳管的金屬觸媒，再以此為模板進行以乙烯與氫氣為製程氣體的熱化學氣相沉積法來合成奈米碳管，而奈米碳管將成長於陽極氧化鋁薄膜的奈米孔洞內。奈米碳管的成長受到奈米孔洞的限制，而具有較佳的垂直準直性。電子場效發射量測顯示以陽極氧化鋁輔助成長的奈米碳管陣列具有優異的場發射性質，歸因於其均勻的尺寸分佈、較佳的準直性等特性。此方式能有足夠的反應物產生高擴散率，不但促進碳氫反應物的裂解也較容易蝕刻反應所產生之副產物非晶質碳。得到奈米碳管成長之活化能為0.55 eV。我們相信利用高氫含量將有助於氣-液-固與固相擴散機制，也相對降低成長溫度。 高度規則排列的氧化鉭奈米點陣列可直接由鋁與氮化鉭薄膜之陽極氧化鋁處理獲得。氮化鉭薄膜之陽極氧化被侷限於首先形成之陽極氧化鋁奈米孔洞內，因而得到奈米尺度的柱狀氧化鉭陣列。奈米點之排列與形狀能直接的複製陽極氧化鋁模板之奈米孔洞，且奈米點之尺寸可藉由調整陽極處理之參數準確的控制。 我們利用陽極氧化鋁模板與原子層化學氣相沉積在矽基材上製備出高品質且自我組織之氧化鋅奈米柱，此方式不需要任何催化劑或觸媒層並在低溫下。由光激發光圖譜結果發現在480 nm位置具有一個藍/綠可見光。氧化鋅奈米柱場發射性質量測結果得到較低的起始電場。如此優異之場發射性質乃由於每根氧化鋅奈米柱皆垂直排列於矽基材。此方式提供一個較佳的控制方法對於製作大尺寸面積自我排列氧化鋅奈米柱，這將可以應用於許多重要的奈米技術上。

In this study, anodic aluminum oxide film was used as a template to grow carbon nanotubes (CNTs), Ta2O5 nanodots and ZnO nanorod arrays. AAO nanopore templates are obtained by Al film with a two-step anodization process. Between the AAO film and Si substrate, a Ni thin film was coated as a metal catalyst for growing CNTs. Regular arrays of CNTs grown by C2H4 and H2, which are gaseous reactants in thermal chemical vapor deposition process. The growth of CNTs was limited by nanoproes, and it possessed a better verticality. These CNT array exhibited excellent field emission characteristics. This approach enables sufficient reactants with high diffusivity, promotes dissociation of hydrocarbon reactants, as well as facilitates etching of amorphous carbon by-products. In addition, the activation energy for CNT growth on blank Si substrates was determined to be 0.55 eV. We believe that high hydrogen content is beneficial to the VLS and SPD processes, which leads to relatively reduced growth temperature. Highly ordered nanodot arrays of Ta2O5 can be obtained directly from AAO process of Al and TaN films. Anodization of Ta2O5 films was restricted into the prior formed AAO nanopores, and thus, Ta2O5 nanorods were fabricated. Arrangement and shape of nanodots were able to duplicate nanopores of AAO template. Also, the scale of nanodots was controllable precisely by tuning the parameters in the anodization process. High-quality self-aligned ZnO nanorods have been prepared on a Si substrate using the AAO template and ALD process on Si substrates without any catalyst or seed layer at temperature as low as 250 oC. Results from photoluminescence spectrum indicated that a blue/green luminescence was located around 480 nm. Field-emission measurements on the ZnO nanorods showed a low turn-on field emission. The observed excellent field-emission quality may be attributed to the fact that every nanorod was perpendicular to the Si substrate. This approach provides a well-controlled method for fabricating large-scale self-aligned ZnO nanorods for many important applications in the field of nanotechnology.