新穎磷酸硬質陽極氧化法並且應用在製備錐形孔洞模板

Abstract

陽極氧化鋁 (anodic aluminum oxide, AAO) 是具有高深寬比奈米孔道及典型規則孔洞陣列之結構，其被廣泛地運用於各式各樣功能性奈米結構，如奈米磁性存儲器，奈米傳感器，奈米光子器件，奈米能值器件以及奈米電子器件。傳統的製造氧化鋁孔陣列亦稱為軟質陽極氧化鋁 (mild anodization, MA) 需要數天的生長時間並且其生長環境條件亦有許多限制。近年來，另一種新穎方法硬質陽極氧化鋁 (hard anodization, HA) 也發展相當成功;硬質陽極氧化鋁相較於傳統的軟質陽極氧化鋁具有快速的生長速率以及更大面積規則排列的奈米孔洞。然而，由草酸硬質陽極法所製成的氧化鋁薄膜與我們所提出之磷酸硬質陽極法相比，有著因為結構性裂縫和缺陷所造成較差的機械性能。 於此研究中，我們提出一創新方法，由磷酸溶液為基質之陽極氧化過程，製備大範圍排列規則以及高成長率之氧化鋁膜。於陽極氧化鋁之成長環境中所供給電壓、電解液濃度以及溫度皆對多孔質氧化鋁結構型態造成巨大影響，都必須詳細研究討論。於多孔氧化鋁自我排列行為中，發現從施加電壓160伏特到270伏特並無需像傳統方法中實施預先陽極氧化步驟。當施加電壓從160伏特至210伏特之間其所成長孔洞之孔洞間距離大約為325奈米至390奈米與所施加的電壓呈現線性關係。然而，此線性關係於施加電壓為220伏特到270伏特卻消失，出現飽和現象，造成此現象原因為孔洞成長過程中所產生的焦耳熱累積且無法均勻散熱。於是，我們使用了新穎磷酸硬質陽極氧化鋁方法中之最佳參數(施加電壓210伏特、電解液濃度2.5%、溫度-10oC)製備出大面積且高規則排列度之圓錐狀陽極氧化鋁模板，並且透過旋轉塗層或熱壓方式皆可獲得圓錐狀聚甲基丙烯酸甲脂(PMMA)之奈米結構。除此之外，此圓錐狀聚甲基丙烯酸甲脂奈米結構經由氟化物處理後具有超疏水現象，並符合Cassie’s model具備良好自潔作用。此創新之製備多孔氧化鋁模板方法製程簡單，成本效益高，並且於不同領域之奈米技術應用也有相當大價值。

Nanoporous anodic aluminum oxide (AAO), a typically self-ordered nanopore material featuring of ordered high-aspect-ratio channels, has been widely used for the development of various functional nanostructures such as nano-magnetic memories, nanosensors, nanophotonic devices, nano-energe devices and nanoelectronic devices. The conventional fabrication of self-ordered Al2O3 pore arrays so-called mild-anodization (MA) requires several days of processing time and the self-ordering phenomenon occurs only in narrow process windows. Recently, a new attempt for AAO process, hard-anodization (HA), has successfully demonstrated. The HA process offers substantial advantages over conventional anodization processes in terms of processing time, allowing 3000% faster oxide growth with improved long-range ordering of the nanopores. However, compared with H3PO4 HA by us, AAO films obtained in suffer from poor mechanical properties because of structural cracks and defects, while uniformly sized parallel channels and irregular top surface with ‘‘pore in pore’’ structures cannot be exclusive in those using C2H2O4 HA process. In this work, we report an innovative H3PO4-based HA process for long-range ordered and high growth-rate alumina membranes. The various anodization parameters including applied voltage, electrolyte concentration, and temperature which have significant impact on the morphology of AAO will be discussed deeply. The self-ordering behavior in nanoporous AAO using H3PO4 HA process unlike conventional methods is investigated at applied voltage from 160 to 270 V without pre-anodization step. The applied voltage via the interpore distance is linearly relationship at anodization voltages from 160 to 210 V and presents an interpore distance from 325 to 390 nm. Unexpectedly, the linearly relationship will vanish and saturate from 220 to 270 V, which may result from the jour-heat accumulation supported by the chronoamperic response. By using advantages of H3PO4 HA method to fabricate taper AAO templates, we can obtain highly ordered and high-aspect-ratio taper AAO templates and then the tapered acrylic (PMMA) nanostructure can be obtained by spin coating or hot embossing. Moreover, we find that the PMMA surface with taper nanostructure coating fluoalkysliane display superhydrophobic phenomenon which can be served as a self-cleaning surface. The innovative AAO template fabrication is simple and cost-effective, and is of great value for applications in diverse areas of nanotechnology.