Icicle growth of δ-Bi2O3 tips deposited on sapphire substrate by means of the carbothermal method

We investigated the icicle growth of the δ-Bi2O3 tips on a sapphire (0001) substrate deposited by the carbothermal method. All of the δ-Bi2O3 tips grew straight and were perpendicular to the substrate. The diameter of the top of the tips is approximately 120 nm, and the upper side of the tips consists of a tetrahedron structure. The tetrahedron structure can be interpreted by observing the same planar form with the (111) plane, which consists of the (11-1), (1-11) and (-111) planes. We found that the angle of contact between the droplet and the substrate was crucial in the formation of the Bi2O3 tips, suggesting that the surface energy of a substrate may play a role in the icicle growth of Bi2O3.