Nanowires alumina

Alumina nanotubes have been prepared by the anodic oxidation of aluminum [41] the resulting tubes have one-dimensional channels with uniform diameters of 5nm and lengths of 50-100 nm. An alumina membrane with a highly ordered nanohole array in 50-100 nm diameter has also been synthesized by long-period anodization thus these local alumina nanotubes have been tried as a template for metal nanowire formation. 

Figure 6(a) shows a SEM image of bismuth nanowires embedded in an anodic alumina template after pressure injection. The pore diameter of the template was about 42 nm, and the maximum pressure and temperature applied for the injection process were about 310 bar and 325°C, respectively. A small amount of copper was introduced into hquid bismuth to enhance its injection the copper atoms should be segregated from bismuth during solidification because they have zero solubihty in solid bismuth. Upon solidification, the copper flakes were brought to the top surface of Bi due to their... 

Fig. 6. (a) SEM image of the bottom surface of an anodic alumina template filled with bismuth. The pore diameter is 42 nm. (b) TEM micrograph of the cross section of a 65-nm bismuth nanowire array (Zhang et al., 1999). 

The smallest diameter attained for bismuth nanowires by the pressure injection method was about 13 nm, using a pressure of approximately 0.3 kbar (Zhang et al., 1999). Finer nanowires might be fabricated by increasing injection pressures (Huber et al., 2000), but it remains to be seen if the anodic alumina templates would retain their structural integrity under those high pressures. 

In contrast to nanowires synthesized by the pressure injection method, nanowires derived electrochemically are typically polycrystalline with no preferred crystal orientation. However, some exceptions occur. For example, polycrystalline CdS nanowires fabricated by ac electrodeposition in anodic alumina were shown to have a preferred wire growth orientation along the c axis (Routkevitch et al., 1996). Recently, Xu et al. (2000a, 2000b) prepared... 

For nanowires embedded in an insulating matrix with a large band gap (e.g., alumina or mica), electrons are well confined within the wires. Thus, to a good approximation, the electron wavefunction, [Pg.186]

Black, M. R., Lin, Y.-M., Dresselhaus, M. S., Tachibama, M., Fang, S., Rabin, O., Ragot, F., Eklund, P. C., and Dunn, B., Measuring the dielectric properties of nanostructures using optical reflection and transmission bismuth nanowires in porous alumina. MRS Symp. Proc. 581, 623 (2000). 

An exhaustive study has been carried out recently on the synthesis of BN nanotubes and nanowires by various CVD techniques.17 The methods examined include heating boric acid with activated carbon, multi-walled carbon nanotubes, catalytic iron particles or a mixture of activated carbon and iron particles, in the presence of ammonia. With activated carbon, BN nanowires are obtained as the primary product. However, with multi-walled carbon tubes, high yields of pure BN nanotubes are obtained as the major product. BN nanotubes with different structures were obtained on heating boric acid and iron particles in the presence of NH3. Aligned BN nanotubes are obtained when aligned multi-walled nanotubes are used as the templates (Fig. 40). Prior to this report, alignment of BN nanotubes was achieved by the synthesis of the BN nanotubule composites in the pores of the anodic alumina oxide, by the decomposition of 2,4,6-trichloroborazine at 750 °C.116 Attempts had been made earlier to align BN nanotubes by... 

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