Nanocrystalline Ferroelectric BiFeO3 Thin Films by Low-Temperature Atomic Layer Deposition

In this work, ferroelectricity is identified in nanocrystalline BiFeO3 (BFO) thin films prepared by lowtemperature atomic layer deposition. A combination of X-ray diffraction, reflection high energy electron diffraction, and scanning transmission electron microscopy analysis indicates that the as-deposited films (250 degrees C) consist of BFO nanocrystals embedded in an amorphous matrix. Postannealing at 650 degrees C for 60 min converts the sample to a crystalline film on a SrTiO3 substrate. Piezoelectric force microscopy demonstrates the existence of ferroelectricity in both as-deposited and postannealed films. The ferroelectric behavior in the as-deposited stage is attributed to the presence of nano crystals Finally, a band gap of 2.7 eV was measured by spectroscopic ellipsometry. This study opens broad possibilities toward ferroelectric substrates and also for the development of new ferroelectric oxides on 3D perovskites prepared at low temperature.