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Growing nanowires by Electrochemical Deposition

For semiconductors, the electrochemical deposition technique was used in 1996 for fabricating arrays of CdS NWs with lengths up to 1 mm and diameters as small as 9 nm. Researchers have reported that a group of II–IV semiconductor NW arrays (CdS, CdSe, and CdTe) can be made by dc electrochemical deposition in porous AAO. Nano wires (NW) may also be grown by electrochemical deposition methods in combination with templates such as porous anodic aluminum oxide (AAO), nano-channel glass, and porous polymer films self-organized from diblock copolymers.


For the growth of nano wires, the template is attached to the cathode and subsequently brought into contact with the deposition solution. The anode is placed in the deposition solution parallel to the cathode. When an electric field is applied, cations diffuse towards and get reduced at the cathode, resulting in the growth of nanowires inside the pores of the template. After pore filling, free-standing nanowires can be obtained by dissolution of the template membrane. The length of the pores, which can be tuned by the etching process, determines the length of the NWs.


The most widely used templates for electrochemical deposition of NWs is AAO, which has been used for the fabrication of a wide range of NW materials including mainly metals, conductive polymers, and metal oxide materials, as well as multi segmented NWs.

Cylindrical nanowires

As a further step, the pores in the templates/membranes can be regularly arranged to have a cylindrical shape of a constant diameter. This is achieved by imprinting the aluminum surface prior to the anodization process with a lithographically prefabricated stamp to generate specific arrangements of pores and the resulting NWs have a narrow size distribution.


Self-organization of metal and semiconductor NWs can be made to occur by electrochemical step-edge decoration of highly-oriented pyrolytic graphite surfaces. This is a large-scale approach to fabricate supported NWs. When combined with modern nanolithography techniques, this method can be potentially extended to horizontally aligned NWs of various shapes. However, while the material produced by this technique is limited mainly to metals, a second chemical reaction of the metal NWs is needed in order to transform them into semiconductors. The key issue for semiconductor NWs fabricated by electrochemical deposition is the crystalline quality. In most cases the NWs are not epitaxially grown and hence are either amorphous or polycrystalline in structure. They consist of small crystals with an abundance of defects, which might limit their technical application, especially in optics.

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