MBE Growth of BiFeO₃ in Bi-oxides Adsorption Regimes

Growing phase pure BFO films by MBE, larger Bi flux is provided due to its volatility. With oxidizing agents, Fe flux will determine the speed of the deposition and excess in bismuth oxide phases desorbed from the film. The phase purity is supposed to be controlled by this desorption. However, stoichiometric BFO was obtained even at temperature lower than suggested narrow region of phase diagram. We investigated growth of BFO under bismuth oxide adsorption regime. The cumulative deposition was madeup to 40 unit cells. Two separate schemes are used. First, in each deposition step, the sample was pre- and post-soaked with Bi-O for 30 sec. In situ x-ray diffraction measurements along (00L) show good interference fringes which match with the film thickness. As the deposition proceeded to thicker films, additional broad feature appeared around L = 0.5. This may indicate a few layers of β-Bi2O3. In the second scheme, pre- or postsoaking was skipped. Sharp interference fringes develop with time. From 7 u.c. thick films, there is a sign of the second phase. The irregularity of the interference fringes are more visible for 20 and 40 u.c. unit cell. This second phase may be a super-tetragonal phase of BFO with c/a = 1.2.