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. - Highlights: • BiFeO₃ films have been pulsed laser deposited using various laser fluences and spot sizes. • Bi/Fe ratio and out of plane lattice parameter correlate with laser fluence. • Critical thickness for film relaxation is increased for Bi/Fe = 1. • Excellent composition and thickness uniformity are demonstrated.