Formation of BiFeO₃ from a Binary Oxide Superlattice Grown by Atomic Layer Deposition

Abstract

We report on the growth of polycrystalline BiFeO thin films on SiO /Si(001) and Pt(111) substrates by atomic layer deposition using the precursors ferrocene, triphenyl-bismuth, and ozone. By growing alternating layers of Fe O and Bi O , we employ a superlattice approach and demonstrate an efficient control of the cation stoichiometry. The superlattice decay and the resulting formation of polycrystalline BiFeO films are studied by in situ X-ray diffraction, in situ X-ray photoelectron spectroscopy, and transmission electron microscopy. No intermediate ternary phases are formed and BiFeO crystallization is initiated in the Bi O layers at 450 °C following the diffusion-driven intermixing of the cations. Our study of the BiFeO formation provides an insight into the complex interplay between microstructural evolution, grain growth, and bismuth oxide evaporation, with implications for optimization of ferroelectric properties.

Toward a Low-Temperature Route for Epitaxial Integration of BiFeO3 on Si

“…This strategy is different from previous investigations on the formation and films due to minimized diffusion requirements and suppressing the formation of larger Bi 2 O 3 regions, which were found to be partially crystallized at a deposition temperature of 290 °C. 29 At the initial stage of the in situ TEM annealing process, the as-deposited BiFeO 3 film on the (001)-oriented SrTiO 3 /Si substrate was heated up to 250 °C, which is 30 °C above the deposition temperature. Although the majority of the BiFeO 3 layer remained in the amorphous state, a thin crystalline layer of the ALD-grown BiFeO 3 film at the interphase to the SrTiO 3 layer was already present (Figure 1).…”

“…This observation is consistent with our previous study of the crystallization behavior of BFO from Bi 2 O 3 −Fe 2 O 3 superlattices, where most of the several-nanometer-thick layers of Bi 2 O 3 were already crystalline after the deposition, whereas the Fe 2 O 3 layers remained amorphous. 29 Subsequent heating was performed at a rate of 5 °C/min up to 300 °C. The ordering in the semicrystalline sublayer improved toward the (001) orientation imposed by the substrate.…”

Complementary SEM-AFM of Swelling Bi-Fe-O Film on HOPG Substrate

“…In Equation (8), the area of the layer ∆S is 0.65 µm 2 and the calculated excess of potential energy ∆E is 4,2 fJ. The observed phenomena were reversible when the "bubbles" maintained their ellipsoid shape.…”

“…Substituting location a Figure 6b, the surface tension σ is equal to 6.4 mN/m. Based on the available data, one can also calculate other parameters, for example, the change in potential energy of the surface molecules by Equation (8):…”

“…The destruction of this feature can be achieved by both the replacement of bismuth ions by isovalent cations and the preparation of thin films [4][5][6]. Atomic layer deposition (ALD) was reported to be a reliable method for BFO deposition on silicon oxide/platinum (from Ferrocene (Fe(Cp) 2 ) and Bi-triphenyl (Bi(ph) 3 ) precursors) [7,8], on zinc oxide (from Bismuth (III) 2,3-dimethyl-2-butoxide and iron (III) tert-butoxide precursors) [9], silicon (from β-diketonate, tris (2,2,6,6-tetramethyl-3,5-heptanedionato) iron(III) (Fe(TMHD) 3 ) and Bi(TMHD) 3 precursors) [10] and strontium titanate (from Bi(thd) 3 and Fe(thd) 3 precursors) [11]. Besides the variation in precursors, ALD methods for BFO differ by the combination of cycles [12,13], possible plasma enhancement of the deposition [14], different temperatures of the process [15] and post-treatment [16].…”