In the past few years, attention has been focused on the research field of one-dimensional nanostructural materials, both because of their fundamental importance and because of the wide range of potential applications in nanodevices.[1±12] Many attempts have been made to fabricate onedimensional nanostructure materials utilizing a variety of nanofabrication techniques and crystal growth methods. [1,5,6,13±20] However, it is still a challenge to synthesize an aligned and well-distributed single-crystal nanowire array. Electrochemical synthesis using a template is one of the most efficient methods for the growth of nanowires because the growth occurs almost exclusively in the direction normal to the substrate surface. [20] In addition, anodic aluminum oxide possesses uniform and nearly parallel porous structures; hence they have been used as an ideal template to produce cylindrical nanowires with a narrow diameter distribution. As CdS is one of the most important II±VI group semiconductors, having vital applications in solar cells and optoelectronic and electronic devices, the AC electrodeposition of CdS nanowires in porous anodic aluminum oxide (AAO) templates has been investigated.[21±23]However, structural studies have demonstrated that large numbers of stacking faults and twinned segments are present in these nanowires. [23] Recently, an aligned CdS singlecrystal nanowire array has been produced using DC electrolysis in AAO templates from a dimethylsulfoxide (DMSO) solution containing cadmium chloride and elemental sulfur.[24] Here we report a new electrochemical process to prepare CdS single-crystal nanowires using electrochemically induced deposition [25] in the pores of an AAO template from an acidic chemical bath containing cadmium chloride and thioacetamide (TAA). The details of the growth of the AAO templates, the deposition of the CdS, and the characterization of the nanowires can be found in the Experimental section. Figure 1a shows a typical transmission electron microscopy (TEM) image of CdS nanowires prepared by electrochemically induced deposition in the AAO template with pore diameters of about 90 nm. It can be seen that the diameter of the nanowires is about 90 nm, which corresponds to the diameter of the pores of the template used. The lengths of the nanowires range from 3 to 5 mm after deposition for 8 h. Figure 1b shows a TEM image of the nanowires deposited in the template with pore diameters of about 20 nm; the uniform diameters of about 20 nm and smooth surfaces are clearly visible. After deposition for 8 h, the length of the nanowire is up to 10 mm, which is 2±3 times as long as the nanowires deposited in a template with pore diameters of 90 nm under the same deposition conditions. This experimental result indicates that the growth rate of the nanowire increases with decreasing pore size of the AAO template.The chemical composition of the nanowires was determined using X-ray energy dispersion analysis (EDAX) and Raman spectroscopy. The EDAX spectrum shown in Figure 2a reveals that the nano...