Fabrication Of Ni And Co-Pt Nanowires Using AAO Template

The porous anodic alumina template has attracted due attention because of itsspecial characters including uniform highly oriented pores and these pores parallel toeach other. This template fabricated by anodizing the aluminum in oxalic acid,sulfuric acid or phosphate acid has different pore diameter which range from 10nm to200nm and different pore length which range from 20nm to 5μm. The diameter andlength of pores depend on the anodization conditions, generally, the higher theanodized voltage is, the larger the pore diameter of porous alumina is;the longer thetime is, the thicker the membrane is. A layer named barrier layer can be created at theinterface of oxide layer and metal during the process of oxidation, its thicknessremains constant at a given voltage and proportional to the voltage. This layer willresist the cathodic current during the course of electrodeposition because of itsinsulation. To make it easier for the cathodic current pass through this layer, we needto increase the cathodic current or dissolve both the aluminum and this layer by themethod of chemical erosion, but these two ways are not efficient. The over highcathodic current causes some hydrogen evolution, which may inhibit the process ofdeposition. Using appropriate chemical solution to move the aluminum substrate andthe barrier layer may influence the pore structure of the anodic alumina template.Therefore, it is necessary to thin the barrier layer without destroying the metalsubstrate by applying current limited anodized steps. The current limited anodizedmethod can produce a comparative thin barrier layer which owns a lower thicknessabout 10nm. This thin layer can be broken by thermal shock during electrodepositioneasily. Using this method, the metal and metallic alloy can be deposited into pores ofporous alumina membrane successfully.By anodizing aluminum in acidic electrolytes, we prepared the porous aluminamembrane successfully which owns cylindrical and uniformly sized pores. Westudied the influence of experimental condition on the pore structure and come tomany conclusions, for example, the purer the aluminum substrate is, the higherordered the pore is;the diameter of pore will increase with the growth of electrolyticconcentration and so on.In recent years, oxide nanowire arrays have become hot topic because of theirelectrical or other properties. The method of anodizing aluminum can not only beused to prepare porous alumina membrane but also can synthesize alumina nanowirearrays. We reported a convenient and inexpensive way to prepare a high yield ofalumina nanowire arrays by anodic oxidation in appropriate phosphoric solution atthe definite voltage. We use SEM to study the characteristic of alumina nanowirearrays and use XRD and EDX to reveal the structure and the component of theproducts. The research of SEM indicates that the diameter and the length of aluminananowire arrays can be controlled by applied anodizing voltage. The diameter of thealumina nanowires becomes larger with the increase of anodizing voltage, while thelength of the nanowires becomes shorter. When the voltage grows to over high value,the nanopores are obtained instead of nanowires. The results of XRD and EDXreveal that the composition of the products is alumina.The magnetic nanowire arrays have become one of the interesting investigatedclasses of materials. These nanowires have many fundamental characters andpotential applications of their properties. Particularly, the fabrication of orderedmagnetic metal nanowire arrays has attracted considerable scientific and commercialattention due to their applications in high-density magnetic recording and sensor. Weprepare Ni and Co-Pt nanowire arrays by the method of DC electrodeposition usingporous alumina thinned barrier layer. The length of the nanowires is linear withdeposition time and the diameter of the nanowires is determined by the pore diameterof the porous alumina membrane. We use the SEM, EDX and XRD to study themicrostructure and the component of the Ni nanowire arrays. The results reveal thatthe nanowire arrays are uniform, well isolated and parallel to each other and thecomposition of the fabricated products is Ni. When the orientation of appliedmagnetic field is consistent with the axis of the nanowires, the coercivity of Ninanowires is 67 Oe and this value is much enhanced compared to that of bulk Ni. Weuse the SEM to study the microstructure of Co-Pt nanowire can also obtain the sameresult: these nanowires are parallel to each other and they are uniformed. We need todo further work on the characterization of properties of these nanowires.