Fe nanowires in nanoporous alumina: Geometric effect versus influence of pore walls

Fe nanowires were fabricated by electrodeposition into nanoporous alumina templates grown in sulfuric and oxalic acid by a pulse electrodeposition. A 42 nm diameter Fe nano wire grown in sulfuric anodized pores is essentially a single-crystalline object that grows preferentially so as to align its (110) axis along the long axis of the pore. Its coercivity is 1654 Oe and a squareness of 0.66 for axially aligned magnetic fields. For an Fe nanowire grown in oxalic anodized pores, both (110) and (200) diffraction peaks are observed, suggesting a polycrystalline object. Its coercivity and squareness are reduced to 1120 Oe and 0.47, respectively. Increasing pore diameter results in improved crystallinity for the nanowires deposited in the oxalic templates. However, their coercivities and squareness are reduced because of the decreased aspect ratio and hence shape anisotropy. We ascribe the differing crystallinity observed for nanowires grown in the two sets of templates to differences in the material properties of the barrier layer and the pore wall, where metal nucleates in the electrodeposition process likely brought about by the incorporation of anions out of the electrolyte.close262

Multiple Nanowire Species Synthesized on a Single Chip by Selectively Addressable Horizontal Nanochannels

The synthesis of horizontal porous anodic alumina (PAA) structures with individually addressable channel systems is demonstrated. This was achieved by developing a multicontact design of aluminum finger structures (two to five contacts) on silicon wafers. These aluminum contacts were electrically isolated from each other, allowing the individual anodization of each contact at different conditions. This way it is possible to synthesize different pore diameters, pore densities, and channel lengths on a single chip. Scanning electron microscopy (SEM) characterization revealed that the neighboring contacts are not significantly altered during the anodization procedure. After successful barrier-layer thinning, the individual finger structures of each contact were filled by electrodeposition and thermal chemical vapor deposition. The resulting metal (Au, Cu, Ni, Co) and semiconductor (Te, Si) nanowires embedded within the porous anodic alumina mold were characterized by SEM and energy dispersive X-ray measurements. The multicontact fabrication results open a new route toward complex nanoelectronic and sensing applications