Pressure-controlled preparation of nanocrystalline complex oxides using pulsed-laser ablation at room temperature

Nanocrystalline thin films of complex oxides such as BaTiO3 and LaFeO3 were prepared by pulsed laser ablation without substrate heating. Targets under various Ar pressures were irradiated using an ArF excimer laser. The off-axis configuration of targets and substrates was used to synthesize the films. The crystallinity and chemical composition of the deposited films were strongly dependent on the processing Ar gas pressure. In case of BaTiO3, the film deposited at 10 Pa was a single phase of BaTiO3 with a crystallite size around 7.2 nm. With increasing Ar pressure to 200 Pa, XRD peaks of BaTiO3 as well as BaCO3 were observed. The by-products could be due to reaction with carbon dioxide in air after taking the sample out of the chamber. For LaFeO3, the films deposited under 50 to 200 Pa had a single phase with a crystallite size below 10 nm. When the Ar pressure exceeded 100 Pa, the crystallite size tended to decrease for both BaTiO3 and LaFeO3, which could be due to formation of aggregated nanoparticles. Below 10 Pa, oxygen deficiency was observed. Over 50 Pa, the atomic concentration of all the constituent elements was almost constant, especially the [Ba]/[Ti] and [La]/[Fe] ratios, which were nearly unity.