Properties of boehmite and Al2O3 thin films prepared from boehmite nanofibres

Transparent and nanoporous self-standing films consisting of oriented boehmite nanofibres were fabricated via the self-assembly of the fibres. The film-forming ability of boehmite nanofibres was closely related to their aspect ratio, and the fibres of 100 to 5000 in aspect ratio were favourable to fabricate the films. Crystallinity and stability of boehmite fibres and the films increased with an increase in the aspect ratio of the fibres. The boehmite films were easily transformed to gamma-, theta- and alpha-Al2O3 films by calcination while keeping the original shapes of the films. Transformation temperatures to gamma-, theta- and alpha-Al2O3 films tended to rise, respectively, with the aspect ratio of the fibres forming the films. When the boehmite films were calcined at the temperatures of 300 degrees C to 800 degrees C, the obtained gamma-Al2O3 films exhibited bright bluish-white emission under the excitation of a UV lamp. The emission intensity tended to increase with a decrease in the aspect ratio of the fibres forming films.