In order to address this issue, researchers at the Hefei University of Technology have fabricated a new form of oxide nanotubes, namely flute-like MgO nanotubes by thermal evaporation with the assistance of a low melting point metal.

In contrast to conventional nanotubes with intact walls, the flute-like MgO nanotubes possess a unique porous structure. Namely, a series of equidistant holes running along the side wall.

The fabrication process can be described as follows: the growth was initiated by evaporating Mg3N2 and Ga2O3 powder at elevated temperature, and then gallium and MgO were generated due to the chemical reaction between Mg and Ga2O3 vapor at the deposition region. The small liquid Ga droplets were encapsulated by a MgO solid shell. With the reactions continuing, more and more liquid Ga filled into the MgO vessel, directing the growth of MgO nanotubes along a one-dimensional direction.

Until now, MgO nanotubes with intact walls were obtained. A trick for the growth of flute-like MgO nanotubes is to control the evaporation sources and make Ga2O3 exhaust first. Thus, at the final stage of the reaction, the generated Ga was too little to sustain the growth of the MgO nanotubes and as a result the liquid Ga columns would be fully encapsulated by the MgO hard shells.

Since the thermal expansion of liquid Ga became considerable with increasing temperature, this caused the intact MgO nanotubes to rupture at the two tips as well as at weak points within the thin side walls. As soon as the holes were generated, liquid Ga began to evaporate out of the nanotubes and left the empty flute-like MgO nanotubes behind.

The researchers presented their work in Nanotechnology.