Porous MgO film grown on sapphire by pulsed-laser deposition

A porous MgO film was grown on sapphire by pulsed-laser deposition. First, small islands of ZnO are grown, and then MgO at a high temperature and high vacuum is deposited. The shortest distance between the two pores is about 5 um. The ZnO grains are grown at the bottom of the pore. The ZnO grains at the rim of the bottom are thinner than that of the centre at the bottom, at which the grains look like thin nano-rods. It is evident that MgO would not be deposited on ZnO small islands at a high vacuum and high temperature when the substrate is sapphire. This morphology can be used for fabricating the materials in which the shortest distance between the two nanoparticles is about 5 mum. It seems that other porous materials can also be realised by this method.