以陽極氧化鋁製作鈷奈米結構材料之研究

Abstract

由於奈米材料具有特殊的性質，近年來對於奈米材料的研究和應用已引起廣泛的注意。而在目前科技研究領域中，如何控制奈米材料的尺寸、形狀及規則性是重要的課題。 本研究利用奈米多孔性的陽極氧化鋁薄膜做為模板，以交流電鍍或脈衝電鍍法的方式，成功製備出具有高規則性的鈷奈米材料陣列。為了增加AAO的導電性，實驗中採取兩種方法，一是以降電壓的方式來減少阻障層的厚度，另一種方法則是不讓鋁膜完全氧化，留下約200nm厚度的鋁膜做為導電層。進一步藉由改變擴孔時間來控制鈷的尺寸大小，改變電鍍時間則可得到不同長度的Co奈米材料，再以氫氧化鈉移除AAO模板。 實驗結果顯示，電鍍製備的Co為多晶材料，其磁化方向與晶體結構有關，在較小孔洞尺寸的模板中可得到以hcp (002)結構為主的Co，對單一Co奈米材料量測到的磁力影像為全暗或全亮，表示方向垂直於試片表面，平行於hcp [002]方向；反之，在具有較大孔洞尺寸的模板中則得到hcp和fcc混合的Co奈米材料，其磁化方向平行於試片表面，對單一Co奈米材料而言，磁力影像是由亮暗成對的區域所組成。

Due to many interesting properties of nanostructured material, studies and applications of nanomaterials have attracted much attention in recent years. How to control the size, shape and arrangement of nanostructured materials is a key issue in current research. Highly ordered cobalt nanorod arrays are successfully electrodeposited using the nanoporous anodic aluminum oxide as the template. We use two methods to increase the conductivity of the AAO template. In one method, the thickness of the barrier layer is first decreased by lowering the anodization voltage. The other method uses the unanodized aluminum as the conductive layer. The size of cobalt nanomaterial is controlled by changing the pore widening time. We can obtain various cobalt nanorods of various height by changing the electrodeposition time. Finally, the AAO template is removed by NaOH. The study shows that polycrystalline cobalt naorods are electrodeposited. The magnetic moment is related to the crystal structure. The structure of cobalt nanorod prepared with the template of smaller pore size is mainly hcp(002). The magnetic force microscopy (MFM) pattern of every cobalt nanorod is either completely bright or completely dark. The magnetic moment of the cobalt nanorod is perpendicular to the sample surface and parallel to the hcp [002] direction. On the other hand, the structure of cobalt nanorod prepared with the template of larger pore size is hcp (002) and fcc (200). The magnetic moment of the cobalt nanorod is parallel to the sample surface. The MFM pattern of every cobalt nanorod consists of one bright and one dark contrast regions.