Effect of Template Materials on the Top Morphologies of Cu Nanowires
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Effect of Template Materials on the Top Morphologies of Cu Nanowires Ran-Jin Lin, Luh-Huei Wu, Ching-Hsiang Tsai and Chien-Min Sung* Electronics Research & Service Organization, Industrial Technology Research Institute, Hsinchu, 300, Taiwan, Republic of China * KINIK company, Ying-Ko, Taipei County, 239, Taiwan, Republic of China ABSTRACT An array of copper nanowires (50-110 nm in diameters) was deposited by the electrolysis of CuSO4-H2SO4 solution at room temperature using DC current. The array was created by forcing deposited copper to follow a pattern of nano tunnels. These nano tunnels were formed with two different methods: anodizing an aluminum film that coated on a silicon wafer to form nano holes within oxidized alumina, and etching the ion-tracked polycarbonate membrane. The difference in top morphologies of the Cu nanowires in these templates is very marked. The copper nano wires deposited in anodized alumina template form the separate spherical balls with diameter of about 10 µm on the surface of the alumina film, in spite of the template thickness of only 0.5 µm. In contrast, no such Cu agglomeration was formed with copper nano wires deposited in holes of polycarbonate. This variance in copper morphologies is likely due to the difference of the interface energy between Cu and anodic alumina and that of Cu and polycarbonate. INTRODUCTION In recent years, the development of one-dimensional nano-structures has received increased attention. These nano-structures have potential applications in many fields such as electronics, optics and magnetism. One of such nano-structures is the array of nano-wires that may be formed with different materials [1]. For the metal nanowires, the methods are direct evaporation through a shadow mask [2], the use of ion milling to pattern a previously deposited thin film [3], and nanochannel structure templates of anodic aluminum oxide film [4,5] and track-etched polycarbonate membrane [6,7]. Copper metal is one of the best electrical conductors. Interest applications of Cu nanowires are current leads in nanodevices and field emission devices. Large area Cu films can easily fabricated by the cheap electrochemical plating method. Therefore, the growth study of Cu nanowires is made by the electrodeposition in nanoporous membrane templates of anodic aluminum oxide film and track-etched polycarbonate membrane. The difference of surface morphologies of Cu nanowires grown from above two templates will be discussed. EXPERIMENTAL DETAILS The copper nanowires were grown by the DC electrodeposition of CuSO4-H2SO4 electrolyte at a room temperature with a nanoporous template of anodic alumina films on Si wafer and track etched polycarbonate membrane. The commercially ion track etched polycarbonate membranes (Poretics® PCTE) were used. The specific membranes had a thickness of 6 µm with a pore size of 50 nm and a pore density of 6x108 pores/cm2. Prior to electrodeposition, a gold layer (100 nm thick) was deposited on one side of the membrane. This film electrode and copper plate were
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