Growth and characterization of ceria thin films and Ce-doped γ-Al2O3 nanowires using sol-gel techniques.

γ-Al(2)O(3) is a well known catalyst support. The addition of Ce to γ-Al(2)O(3) is known to beneficially retard the phase transformation of γ-Al(2)O(3) to α-Al(2)O(3) and stabilize the γ-pore structure. In this work, Ce-doped γ-Al(2)O(3) nanowires have been prepared by a novel method employing an anodic aluminium oxide (AAO) template in a 0.01 M cerium nitrate solution, assisted by urea hydrolysis. Calcination at 500 °C for 6 h resulted in the crystallization of the Ce-doped AlOOH gel to form Ce-doped γ-Al(2)O(3) nanowires. Ce(3+) ions within the nanowires were present at a concentration of < 1 at.%. On the template surface, a nanocrystalline CeO(2) thin film was deposited with a cubic fluorite structure and a crystallite size of 6-7 nm. Characterization of the nanowires and thin films was performed using scanning electron microscopy, transmission electron microscopy, electron energy loss spectroscopy, x-ray photoelectron spectroscopy and x-ray diffraction. The nanowire formation mechanism and urea hydrolysis kinetics are discussed in terms of the pH evolution during the reaction. The Ce-doped γ-Al(2)O(3) nanowires are likely to find useful applications in catalysis and this novel method can be exploited further for doping alumina nanowires with other rare earth elements.

Fabrication of nanorods by metal evaporation inside the pores of ultra-thin porous alumina templates.

Porous alumina has attracted a great deal of attention as a template material for the growth of nanowires and nanodots. Typically, the pores have a high aspect ratio, which forbid the use of evaporation techniques for filling them, due to a pore closure effect. For this reason electrochemical methods are mainly used. However, there are materials, such as Al, which are very difficult to deposit electrochemically. In this work, the fabrication of Al nanorods by electron gun evaporation into low aspect-ratio pores of ultra-thin porous alumina templates is described. The thicknesses of the templates are in the range from 50 to 70 nm, while their pores have diameters from 20 to 40 nm, i.e. their diameter:height aspect ratios are very low, from 1:1.5 to 1:3. These properties make it possible to completely fill the pores with evaporation techniques. This method can be generalized to any target and substrate material.