Laser fluence and spot size effect on compositional and structural properties of BiFeO3 thin films grown by Pulsed Laser Deposition

We investigated the effect of laser fluence and spot size on the structure and composition of BiFeO3 (BFO) epitaxial thin films grown on SrTiO3 substrates by Pulsed Laser Deposition. X-ray diffraction shows that BFO's out of plane lattice parameter increases with the laser fluence. A coherent epitaxial film growth is observed for all tested laser fluences and spot sizes for thicknesses up to 16 nm. The critical thickness at which relaxation occurs depends either on the laser fluence or spot size. The fluence dependence of the out of plane lattice parameter is accompanied with a cationic composition variation. Bi vacancies are evidenced at lower fluences while as Bi/Fe tends towards 1 a higher relaxation critical thickness is observed. An optimum Bi/Fe ratio is obtained for a fluence of 1.72 J/cm2. This result was confirmed by wavelength-dispersive x-ray spectroscopy (WDS) scans over a 1 cm2 film. An excellent thickness and composition uniformity is attained over the entire sample area.