Effects of chemical fluctuations on microstructures and properties of multiferroic BiFeO3 thin films

BiFeO3 films have been grown on SrTiO3 (001) substrates by pulsed laser deposition. It was found that oxygen partial pressure is crucial to phase purity, surface morphology, and surface chemistry. Single-phase BFO films were obtained at 1 Pa O-2, while Bi2O3 appeared in the films deposited at 0.01 Pa as confirmed by x-ray diffractions. It was revealed that Fe2+ and metallic Bi exist in the films fabricated at 0.01 Pa by x-ray photoelectron spectroscopy investigation. Owing to Fe2+ in the samples deposited at 0.01 Pa, the saturation magnetization is much larger than the ones fabricated at 1 Pa. A well-saturated ferroelectric hysteresis loop with a polarization of 23.6 mu C/cm(2) was observed in the single-phase samples. In contrast, the films deposited at 0.01 Pa exhibited poor ferroelectric properties.