Influence of Lattice Distortion Induced by a Vicinal SrTiO₃(001) Substrate in Single-Domain BiFeO₃ Thin Films Prepared by Radio Frequency Planar Magnetron Sputtering

Abstract

Single-domain BFO thin films are prepared on a SrRuO3-buffered SrTiO3 (STO) (001) substrate by RF planar magnetron sputtering. A domain structure is controlled by vicinal direction of the STO substrate. The BFO thin films on vicinal STO along <110> show single-domain structure without any domain walls. To confirm the influence of epitaxial strain on lattice distortion and ferroelectricity, single-domain BFO thin films with thicknesses ranging from 10–1000 nm are prepared. Synchrotron X-ray diffraction reveals that lattice relaxation and step bunching occur in the thickness range of 50–200 nm. The BFO films with thicknesses over 300 nm are almost free from the influence of the epitaxial strain induced by (001)-oriented substrates. The remanent polarization P r is almost constant at about 60 µC/cm2. However, P r slightly increases in the BFO films with thicknesses less than 200 nm. Even the 100-nm-thick BFO film show fully saturated D–E hysteresis at RT, and the P r is 65 µC/cm2.

Impact of film thickness on the external quantum efficiency of bulk photovoltaic effects in Mn-doped BiFeO3 thin films

“…In addition, surface roughness was found not to increase with increases in the BFMO film thickness. These results are in good agreement with prior work concerning the step-flow growth of BFO thin films on vicinal STO substrates 41). Single domain films were required to assess the BPVE associated with these BFMO thin films because the BPVE is greatly affected by the crystal direction.For this reason, both vertical and lateral PFM images of the BFMO thin films were acquired.…”

“…These results are in good agreement with prior work concerning the step-flow growth of BFO thin films on vicinal STO substrates. 41) Single domain films were required to assess the BPVE associated with these BFMO thin films because the BPVE is greatly affected by the crystal direction. In theory, the current density (J) generated by the BPVE can be expressed as 21)…”

“…The vicinal angle of the STO (001) was 4°along the 〈110〉 STO direction, so that each BFMO thin film was a single domain based on limiting variations in the in-plane orientation using the step edges of the STO surface. [37][38][39][40][41] Prior to growing the SRO bottom electrode layer, a Ti-O terminated STO surface was obtained by etching the substrate with a buffered solution of HF for 5 s, followed by annealing at 1000 °C for 60 min, to produce a well-aligned STO surface having a step-and-terrace structure. Following this, the 30 nm thick SRO layer and the BFMO thin film were grown by radio frequency (RF) planar magnetron sputtering.…”

Enhancement of photovoltage by electronic structure evolution in multiferroic Mn-doped BiFeO3 thin films

“…For preventing from charging up during SXPES and SXAS spectra, the maximum thickness is 150 nm. According to our previous study 28 , epitaxial strains of 150 nm and 1 μm thick BFO thin films can be estimated as -0.45% and − 0.30%, respectively, indicating small difference. In addition, the first principles calculations predicted that the epitaxial strains mainly cause symmetrical change of the electronic structure 36 .…”

“…Therefore, 1 µm thick BFMO thin films with various amounts of dopant (0, 0.5, 1.0, 3.0 and 10 at%) were grown on vicinal SrTiO 3 (001) (STO) substrates by conventional RF planar magnetron sputtering process. Vicinal STO substrates with the [001] STO direction inclined 4° toward [110] STO have been used for the domain engineering [25][26][27][28] of BFMO thin films. Figure 1a-c show surface atomic force microscopy (AFM), and vertical and lateral piezoresponse force microscopy (PFM) images of a Mn 1 at%-doped BFO thin film.…”