Preparation And Characterization Of Diameter-graded And Multi-branched Nanowires

One-dimensional nanomaterials have received considerable attention over the past decade because of their novel physical and chemical properties and potential applications in future nanodevices. It is well known, however, that the property of nanomaterials is heavy dependent with its shape, so how to control the shape of nanomaterials becomes a hot topic in material research field at present. As one of the useful means in the shape control of one-dimensional nanomaterials, anodic alum -inum oxide (AAO) templates have received widely attention. In this paper, we pay considerable attention to the shape controlling of metal nanowires based on AAO templates, and then develop the template-synthesis method for fabricating nanowires with different shapes.1)We have extended the functions of the AAO template to fabricate graded and multi-branched nanochannels. The AAO template with a graded pore diameter was prepared through gradually changing the anodic voltage during an anodization in 0.3M sulfuric acid or oxalic acid. While the AAO templates with various branched pores were prepared through one- to multi-step varying the anodic voltage by a factor of 1/ 2 during an anodization of aluminum in 0.3M oxalic acid.2)Based on the templates with a graded pore diameter, several graded metal nanowires (i.e. Ag, Fe, and Bi) were achieved by electrochemical deposition. SEM and TEM were used to characterize these nanowires. The results show that these nanowires have obvious graded diameters along the nanowire direction with gradient ranging from about 12 to 31nm for Ag and Fe, and from about 11 to 55nm for Bi. Their high-resolution TEM images show that Ag nanowires and Bi nanowires have single-crystalline structure, and Fe nanowire has polycrystalline structure.3)The corresponding multi-branched Fe nanowires were achieved by electrodepositing Fe into the branched pores of the AAO template used. Selecting area electron diffraction and high-resolution TEM images show that these branched Fe nanowires have a single-crystalline stem with a body-centered cubic lattice and polycrystalline branches.