Surface tension driven flow forming aluminum oxide microtubes

Aluminum oxide microtubes decorated with metallic nanoparticles were produced through thermal oxidation method by using metallic aluminum microwire above its melting point, i.e., in the liquid phase. The obtained translucent aluminum oxide microtubes have 66 µm of internal diameter, with a wall thickness of ∼2 µm while the patterned Al metallic nanoparticles have diameter in the range 50-200 nm. Structural characterization indicated that the microtube wall is formed by amorphous oxide phase which coexist with crystallized metallic one. Heat treatment at T = 1050 °C leads to the crystallization into Al2O3 phase. During the fabrication process, a thin oxide layer was formed first on the molten liquid surface establishing a solid oxide tube with a liquid inner core. The formation and growth of a spherical droplet, at the microwire's end, draw the molten aluminum inner core, acting as a driving force for the liquid mass transfer movement and microtube formation. The capillary effect and surface tension driven flow effect plays an important role towards the microtube formation.