Nanostructure of the nanopores in anodic aluminum oxide films used as template to fabricate Ag nanowires
- PDF / 1,310,211 Bytes
- 6 Pages / 584.957 x 782.986 pts Page_size
- 2 Downloads / 269 Views
Well-ordered nanoporous anodic aluminum oxide (AAO) templates have been prepared on aluminum substrates by a two-step anodization process. A voltage-controlled branching method was successfully used to thin the barrier layer of the AAO template. The nanostructures of the pores, the branched subpores, and the barrier layer in the AAO template were studied in association with the anodization process and barrier layer thinning methods. Results demonstrate the voltage-controlled branching method is a facile and effective way to thin the barrier layer. Uniform silver nanowires can be easily fabricated using alternating current (ac) electrodeposition into the pores of AAO after redressing the barrier layer. I. INTRODUCTION
In recent years, ordered nanoporous anodic aluminum oxide (AAO) has become a popular versatile template for the fabrications of nanoscale materials, such as ordered arrays of nanorods,1,2 nanowires,3,4 and nanotubes.5–7 It is well known that porous AAO templates can be prepared with a normal electrochemical method by anodizing high-purity aluminum foils at certain anodic bias in various electrolytes. By 1995, Masuda and Fukuda8 found highly ordered AAO templates could be easily obtained by a two-step anodization process, the pore size, pore density, and the thickness of the AAO template can be controlled by changing their anodization conditions.9 Compared to other porous templates that are self-assembled by surfactants and polymers, AAO is an ideal template because it consists of highly aligned nanopores with uniform shape and size.10,11 However, to use such an AAO template to fabricate nanomaterials by the electrodeposition method, these pores array in the template should be in electronic conduct. However, in the anodization process, with the growth of porous oxide film on aluminum substrate to form AAO template, one thick barrier film also forms as a semispherical oxide layer on the bottom of the pore,12 as illustrated in Fig. 1. This thick barrier layer is completely resistive, thus it is not possible to deposit metal inside the pores directly by electrochemical method.13 Usually, there are two methods to improve this shortcoming caused by the barrier layer; one is to detach the AAO template from the a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0206 J. Mater. Res., Vol. 24, No. 5, May 2009
aluminum substrate and subsequently remove the barrier layer by a chemical etching process.14 Before electrodepositon, one metal layer is coated on one side of the freestanding AAO template and serves as a contact between template and electrolyte. The metal layer should be thick enough for handling. This method is best for materials longer than several hundred nanometers because the thin membranes needed for short nanomaterials are difficult to detach from the aluminum substrate intact. Another method is to thin the barrier layer at the bottom of the pores in the AAO template and provide a more preferential site for the metal to nucleate. The AAO template still re
Data Loading...
