Structural properties of pulsed laser deposited SnOx thin films

Nanocrystalline SnO x thin films were grown by means of pulsed laser deposition onto substrates held at relatively low temperature (470 K) and by varying the background oxygen gas pressure up to 66.7 Pa. The formation of the nanocrystalline structures in the films has been investigated in detail by using X-ray diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The results showed that, upon increasing oxygen gas pressure up to 13.3 Pa, the laser induced plasma expands forming a shock wave and it is possible to obtain almost stoichiometric films composed of nanoparticles exceeding 10 nm in size and essentially with a tetragonal rutile crystalline structure. Further increase of the oxygen pressure up to 66.7 Pa induces a worsening of the material's structural properties with a drastic reduction of the nanoparticles size down to 1 nm and the development of a large amount of an amorphous phase. The analysis of the SAED patterns shows that the unit cell shrinks along the principal crystallographic axes, due to oxygen atoms vacant sites, in agreement with the stoichiometry parameter values determined from X-ray core level photoemission spectroscopy measurements.