| Porous anodic aluminum oxide (AAO) templates have got a widerange of applications owing to their simple preparation, easy controlof nanopores and chemical stability. In this paper, a series of AAOtemplates were first prepared by using the two-step anodizationprocess, and then Fe, Ni nanowire and nanotube arrays wereelectrochemically deposited into these AAO templates. The structureand morphology of the nanomaterials were analyzed by x-raydiffraction (XRD), transmission electron microscopy(TEM) andscanning electron microscopy (SEM). The magnetic measurementswere performed using vibrating sample magnetometer (VSM).Conclusions presented in this paper can be summarized as follows:(1) A series of ordered AAO templates were obtained in sulfuricacid, oxalic acid and phosphoric acid, respectively. We studied theimpact of oxidation voltage, electrolyte temperature, oxidation timeand pore widening time on the morphology of the membranes. It isfound that diameter of the AAO templates prepared in sulfuric acid electrolyte is less than 30 nm. When oxalic acid used as electrolyte,and the oxidation voltage is 30-80 V, we can obtain AAO templateswith diameter of several tens nanometers. When phosphoric acidused as electrolyte, and the oxidation voltage is 100-200 V, we canobtain AAO templates with diameter of several hundred nanometers.No matter what kinds of acid used as the electrolyte we can have thefollowing rules within a certain range: the diameter of AAO templatesincreases with increasing oxidation voltage and pore widening time.By extending the secondary oxidation time we can increase thethickness of the template. Through a series of experiments, we havegot some experimental conditions for the preparation of a templatewith specific size, which can be used for the next preparation ofone-dimensional nanomaterials.(2) A series of Fe nanowire arrays were prepared byelectrochemical deposition method in the through hole templates. Wehad studied the impact of pore diameter size and oxidation voltage onFe nanowire’morphology and magnetic properties.The results showthat the Fe nanowires are polycrystal with (111) and (211) diffractionpeaks, and the diameter of the nanowires is consistent with the porediameter of the AAO templates. The coercivity is higher when the fieldis applied parallel to the axis of the nanowires than that when the fieldis perpendicular to the axis. In addition, the nanowires aspect ratio decreases with the increase of the template diameter, which willdecrease the shape anisotropy. Therefore, the coercivity andremanence decrease accordingly. Both length and morphology of thenanowires are strongly influenced by the oxidation voltage. When theoxidation voltage is -1.1V, Fe nanowires show a very smooth surfaceand long length, and have a maximum coercivity. Consequently, themagnetic property of nanowires is strongly inflenced not only by theaspect ratio but also by the morphology.(3) Ni nanowires and nanotubes were obtained by electrochemicaldeposition method. The results show that Ni nanowires have a verysmooth surface and large aspect ratio. The coercivity is higher whenthe field is applied parallel to the axis of the nanowires than that whenthe field is perpendicular to the axis. The Ni nanotubes have smoothouter wall, thin tube wall and uniform wall thickness. The coercivity inthe parallel direction of the nanotubes is larger when compared tothat in the perpendicular direction, and the easy magnetizationdirection is oriented along the nanotubes axis bacause the shapeanisotropy occupied a dominant position. The different magneticproperties of Ni nanotubes and nanowires may be due to thedifference of their morphology. |
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