Fabrication of Sequential Nanostripes by Controlled Electrodeposition
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Fabrication of Sequential Nanostripes by Controlled Electrodeposition M. Mikhaylova, D. K. Kim, M. Toprak and M. Muhammed Materials Chemistry Division, Royal Institute of Technology, SE 10044, Stockholm, Sweden ABSTRACT Au nanowires and sequential metal nanostripes were prepared by AC pulse electrodeposition in anodic alumina membrane (AAM). Due to the high toxicity of cyanide-based electrolytes, which commonly used for electrodeposition of noble metals, new types of Au electroplating solution has been introduced. Electroplating solutions of noble metals Au, Ag and Pt were alternately used for nanostripes fabrication. The AAM was prepared by a two-step electrochemical anodization process in oxalic acid. The pore size was controlled by varying anodizing voltage and current density. The AAM was investigated by SEM and AFM. The results show hexagonally ordered channels with a pore diameter 50 nm. The morphology and composition of nanowires and nanostripes were examined by TEM and optical microscopes, which show uniformly, ordered Au nanowires with a length about 250 nm and a diameter about 50 nm. AuAg-Au-Pt-Au sequential nanostripes have a length about 3.5 µm and diameter 50 nm has been successfully prepared. INTRODUCTION The perspective method for the fabrication of nano-objects such as nanowires, nanodots, and nanocylinders with a uniform size distribution and shape is using the template with homogeneous structure based on highly self-ordered anodic alumina membrane (AAM). The use of AAM as a template has been attracted due to its ease way of preparation and relatively low cost of production [1,2]. Polycarbonate membrane has been attempted to synthesize nanoobjects, but the pore structure of the polycarbonate membrane is not sufficient enough to construct homogeneous nano-objects due to its irregular channel structure [3]. The selforganization of long-range pores with different diameter and length and rather good heat resistance are the some of the advantages of AAM comparing to polycarbonate membrane film. Generally aqueous solution of sulphuric, phosphoric and oxalic acids are used as electrolyte solutions for anodization process to produce the AAM with different pore structures [4, 5]. Moreover, the pore size can be controlled by changing the anodization conditions. The existence of thin barrier layer on AAM has to be noted as one of the disadvantage for the further application as a template. There are some procedures, which have been reported to remove this barrier layer without destroying the membrane channel. Usually, the AAM was immersed in H2SO4 layer at high temperatures to decrease the thickness of barrier layer [6]. Another technique to eliminate this barrier layer is to etching the AAM with phosphoric acid and bromine [7, 8]. Recently, gelatine procedure was successfully introduced for the same purpose. The gelatine sol was penetrated into the channels of AAM in a special cell and the barrier layer was dissolved in NaOH solution after cooling to room temperature [9]. Electrodeposition is one of th
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