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

Abstract

In this work, ferroelectricity is identified in nanocrystalline BiFeO3 (BFO) thin films prepared by low-temperature 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 °C) consist of BFO nanocrystals embedded in an amorphous matrix. Postannealing at 650 °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 nanocrystals. Finally, a band gap of 2.7 eV was measured by spectroscopic ellipsometry. This study opens broad possibilities toward ferroelectric oxides on 3D substrates and also for the development of new ferroelectric perovskites prepared at low temperature.

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

“…The spectra for iron reveal that Fe 3+ is the predominant species. Similar results are observed for other ALD‐grown BFO films . Whereas for Bi and Fe no significant changes in the peak position or shape occur, the scenario is different for oxygen and carbon.…”

“…Ferroelectric switching was probed on different grains and two representative hysteretic loops for the phase and the amplitude are displayed in Figures b and c, respectively. In general, the hysteresis loops measured for the grains located higher on the surface appear very symmetric and similar to those observed in ALD‐grown epitaxial BFO films (red in Figures b,c) . However, for lower‐lying grains, an asymmetric PFM response is observed (black in Figures b,c), which might be due to the clamping effect from the proximity to the neighboring grains.…”

“…Although ALD is primarily used for the growth of binary oxide films and coatings, in the last years the integration of epitaxial perovskite thin films on semiconductor substrates has been reported, making this synthesis method appealing for large‐scale deposition of complex functional oxides such as ferroelectric BaTiO 3 or BFO . The synthesis of ferroelectrically switchable BFO utilizing ALD was demonstrated for both epitaxial and polycrystalline films . Direct evidence of ferroelectricity with a remnant polarization of ≈2 μC cm −2 was first reported for a 10‐nm‐thick film grown on a LaNiO 3 (001)/SiO 2 /Si(001) substrate .…”

“…[15] The synthesis of ferroelectrically switchable BFO utilizing ALD was demonstrated for both epitaxial andp olycrystalline films. [16][17][18][19][20][21][22][23][24][25] Direct evidenceo ff erroelectricity with ar emnant polarization of % 2 mCcm À2 was first reported for a1 0-nm-thick film grown on aL aNiO 3 (001)/SiO 2 /Si(001) substrate. [19] Recently, an approach, where alterings tacks of Fe 2 O 3 and Bi 2 O 3 weredeposited, proved to provide ah igh control over the cation ratio and, hence,o ver the ferroelectric and magnetic properties of the resultingp olycrystalline BFO thin films.…”

Correlation between electrospinning parameters and magnetic properties of BiFeO3 nanofibers

“…It has been widely studied due to its potential use for information storage applications [2,3] and low band gap; thus, its ferroelectric [4][5][6][7], ferromagnetic [8][9][10][11] and photovoltaic [12][13][14] properties have been analyzed. The BiFeO 3 perovskite is particularly interesting because having ferroelectric and ferromagnetic properties, it can display magneto-electric coupling, that is, the capacity to control electrical polarization by application of a magnetic field and control magnetism by the application of an electric field [3,15].…”