Properties Of BiFeO3 Thin Films Research Articles

Influence of RE2O3 (Dy2O3, Yb2O3, and Lu2O3) buffer layers on the structural and ferroelectric characteristics of BiFeO3 thin films

This study investigates the impact of RE2O3 (Dy2O3, Yb2O3, and Lu2O3) buffer layers on the structural and ferroelectric properties of BiFeO3 thin films grown using a spin-coating method. BiFeO3 thin films with various RE2O3 buffer layers were analyzed using x-ray diffraction, atomic force microscopy, secondary ion mass spectrometry, and x-ray photoelectron spectroscopy to determine their crystalline structures, surface topographies, depth profiles, and chemical compositions, respectively. The RE2O3-buffered BiFeO3 film showed better electrical properties compared to the control BiFeO3 film. The buffer layer composed of Yb2O3 showed the lowest leakage current of 6.82 × 10−6 A cm−2, highest remnant polarization of 44.1 μC cm−2, and smallest coercive field of 189 kV cm−1 because of the incorporation of Yb3+ ions into the BiFeO3 film, high degree of (110) preferred orientation, high Fe3+ content, low surface roughness, reduction of Fe3+ valence fluctuation to Fe2+ ions, and decrease in oxygen vacancies. Such BiFeO3 thin films with various RE2O3 buffer layers using spin-coating method pave a pathway toward practical applications of spintronic, sensor and memory.

Electrical and structural properties of BiFeO3 thin films with four distinct buffer layers: La2O3, Pr2O3, Sm2O3, and Tm2O3

In this study, BiFeO3 thin films were fabricated using a spin-coating technique on SrRuO3/n+-Si substrates, employing four different RE2O3 (La2O3, Pr2O3, Sm2O3, and Tm2O3) buffer layers. The investigation focused on assessing the structural and ferroelectric characteristics of these films. X-ray diffraction analysis revealed a (110) preferred orientation with a perovskite-rhombohedral structure in films with RE2O3 buffer layers. Atomic force microscopy analysis indicated smooth surfaces for these layers. Secondary ion mass spectrometry demonstrated high levels of Bi ions in films with RE2O3 buffer layers, while X-ray photoelectron spectroscopy revealed a low Fe2+/Fe3+ ratio in these layers. Notably, the film with a Sm2O3 buffer layer showed a lower leakage current (2.05 × 10−6 A/cm2) and a higher remnant polarization (43.65 μC/cm2). This improvement is attributed to Sm3+ ions fostering (110) orientation, reducing surface roughness, increasing Fe3+ content, thereby minimizing oxygen vacancies, and suppressing Fe3+ to Fe2+ valence fluctuation.

Ultrafast Optically Induced Perturbation of Oxygen Octahedral Rotations in Multiferroic BiFeO3 Thin Films.

The functional properties of complex oxides, including magnetism and ferroelectricity, are closely linked to subtle structural distortions. Ultrafast optical excitations provide the means to manipulate structural features and ultimately to affect the functional properties of complex oxides with picosecond-scale precision. We report that the lattice expansion of multiferroic BiFeO3 following above-bandgap optical excitation leads to distortion of the oxygen octahedral rotation (OOR) pattern. The continuous coupling between OOR and strain was probed using time-resolved X-ray free-electron laser diffraction with femtosecond time resolution. Density functional theory calculations predict a relationship between the OOR and the elastic strain consistent with the experiment, demonstrating a route to employing this approach in a wider range of systems. Ultrafast control of the functional properties of BiFeO3 thin films is enabled by this approach because the OOR phenomena are related to ferroelectricity, and via the Fe-O-Fe bond angles, the superexchange interaction between Fe atoms.

Non-volatile memory characteristics of flexible ferroelectric field-effect transistors consisting of Sm-doped BiFeO3 thin films

This study investigates the impact of Sm doping on the structural, electrical, and functional properties of BiFeO3 (BFO) thin films. The aim is to improve their non-volatile memory characteristics for use in flexible ferroelectric field-effect transistors (FeFETs). We fabricated Sm-doped BFO (SBFO) thin films on flexible mica substrates with Sm concentrations ranging from 0 to 15 %. The FeFET device structures, which include MoS2 monolayer channels and SBFO thin films with Pt bottom electrodes, were analyzed. The SBFO thin films displayed a (111) preferential orientation due to the influence of underlying Pt electrodes. Notably, the SBFO thin film doped with a 10 % Sm concentration showed optimal enhancements, including a reduction in leakage current density and an increase in remanent polarization to 55.8 μC/cm2, compared to undoped thin film (35.5 μC/cm2). Furthermore, the thin film exhibited superior fatigue resistance for up to 1012 switching cycles and maintained stable values under significant bending stress for ferroelectric polarizations. On the other hand, SBFO thin film with 15 % Sm doping displayed relaxor antiferroelectric behavior, highlighting the importance of doping concentration. Therefore, for non-volatile memory application reliability, the FeFET device featuring a 10 % Sm-doped SBFO thin film not only enhanced the memory window but also showed superior fatigue characteristics over 1012 switching cycles, compared to its undoped counterpart. These findings demonstrate the effect of Sm doping in customizing the properties of BFO thin films for advanced, flexible non-volatile memory devices, offering a novel insight to optimize ferroelectric field-effect transistor performance.

Facile Control of Ferroelastic Domain Patterns in Multiferroic Thin Films by a Scanning Tip Bias.

BiFeO3, known as the "holy grail of all multiferroics", provides an appealing platform for exploration of multifield coupling physics and design of functional devices. Many fantastic properties of BiFeO3 are regulated by its ferroelastic domain structure. However, a facile programable control on the ferroelastic domain structure in BiFeO3 remains challenging and our understanding on the existing control strategies is also far from complete. This work reports a facile control of ferroelastic domain patterns in BiFeO3 thin films under area scanning poling by exploiting the tip bias as the control parameter. Combining scanning probe microscopy experiments and simulations, we found that BiFeO3 thin films with pristine 71° rhombohedral-phase stripe domains exhibit at least four switching pathways solely by controlling the scanning tip bias. As a result, one can readily write mesoscopic topological defects into the films without the necessity to change the tip motion. The correlation between conductance of the scanned region and the switching pathway is further investigated. Our results extend the current understanding on the domain switching kinetics and the coupled electronic transport properties in BiFeO3 thin films. The facile voltage control of ferroelastic domains should facilitate the development of configurable electronic and spintronic devices.

Reduced Leakage Current and Enhanced Photovoltaic Effect in Zn-Doped BiFeO3 Thin Films

Zn-doped BiFeO3 (BFO) thin films with compositional formula BiFe1–xZnxO3 (x = 0, 0.1, and 0.2) have been epitaxially grown on SrRuO3 buffered SrTiO3 substrates by pulsed laser deposition. The high-concentration Zn doping does not suppress the ferroelectric polarization of the BFO films, and the Zn-doped BFO thin films also show reduced leakage current and an enhanced photovoltaic effect. By optical and photoelectron spectroscopy measurements, with Zn doping, the BFO thin films show more oxygen vacancies and a structural evolution, and moreover, a blue-shift of optical bandgap and an increase of work function are demonstrated. The reduction of leakage current and the enhancement of photovoltaic effect are related to the variation of interfacial Schottky junctions and oxygen vacancies with doping. This study reveals systematic insights into the effects of Zn doping on the physical properties of BFO thin films.

Nd dopant effect on structural properties of BiFeO3 thin films and application in a negative capacitance transistor

When Nd doping in BiNdFeO (BNFO) film exceeds 10%, the two diffraction peaks (104)/(110) merge into one sharp single peak with increasing addition of Nd. It seems that a phase structural distortion can be obtained due to the substitution of Nd3+ ion for Bi3+ ion. For ferroelectric properties, among all Nd-doped (0%–20%) BiFeO3 capacitors, the BNFO capacitor with 10% Nd doping shows a higher Pr value due to a phase structural distortion and a lower leakage current. In a resistive-capacitive circuit diagram, the transient response of the voltage (V FE) across the BNFO capacitor can be measured. We demonstrate that the capacitance value is negative in the spike interval of V FE(t), with the result that the negative capacitance of BNFO with a 10% Nd doping capacitor can obviously improve the I DS–V GS characteristics of a control thin-film transistor.

Impact of laser energy on resistive switching properties of BiFeO3 thin films

In this report, BFO thin film samples were deposited using Pulsed Laser Deposition (PLD) technique by altering the PLD laser energy from 150 to 250 mJ, to study the role of laser energy on resistance switching property of pure BFO thin film. Efficient resistive switching properties are essentially required for realization of a memristor device. An appreciably high resistance ratio (∼100) between HRS i.e. high resistance state (“OFF” state) and LRS i.e. low resistance state (“ON” state) was obtained for the sample fabricated at 200 mJ PLD laser energy with a stable retention period of 106 s with reproducible endurance cycles of 108. From the study of charge transport mechanism, it has been observed that the Ohmic conduction is the dominating mechanism in the lower applied biased region while space charge limited conduction (SCLC) and Child's law are the dominating mechanisms in the higher applied biased region for all the deposited BFO thin film samples. Current study extends the application of multiferroic BFO thin films for memory devices.

The effects of Eu3+ doping on the epitaxial growth and photovoltaic properties of BiFeO3 thin films

1 Eu 3+ doping induces a phase transition from tetragonal to rhombohedral for BiFeO 3 film; 2 A decrease in coercivity and a sharp change in band gap upon Eu 3+ doping have been observed; 3 Eu 3+ can be used to tailor the photovoltaic effect of ITO/Eu x Bi 1- x FeO 3 / Ca 0.96 Ce 0.04 MnO 3 ; Nowadays, photovoltaic effect has been widely studied in various ferroelectric materials due to its applications as optoelectronic devices. In this work, with BiFeO 3 (BFO) films as the photovoltaic materials, we report the effects of Eu 3+ doping content on the phase structure, ferroelectric and optical properties of BFO films grown on Ca 0.96 Ce 0.04 MnO 3 /YAlO 3 (001) substrate. We found that a small doping level of 0.05 could induce a phase change of BFO from tetragonal to rhombohedral, due to the shrinking of the lattice upon Eu 3+ doping and the breaking of surface terrace structure induced by Ca 0.96 Ce 0.04 MnO 3 layer. This results in a sharp band gap reduction from 3.30 eV to 2.60 eV, and a decrease in the coercivity of ferroelectric polarization switching. Based on these findings, we investigate the photovoltaic effects of ITO/Eu x Bi 1- x FeO 3 /Ca 0.96 Ce 0.04 MnO 3 vertical capacitors. It is found that the short-circuit current density ( J sc ) decreases with increasing Eu 3+ doping, whereas the open-circuit voltage ( V oc ) first increases to a level of 0.1 V and then decreases with further Eu 3+ doping. This could be explained by the combined effect of Schottky-junction and depolarization field on the photovoltaic process. Our research suggests that a moderate Eu 3+ doping is helpful for enhancing the photovoltaic effect of BFO thin film devices. .

Effect of Yb-doping on structural and electrical properties of BiFeO3 thin films

In this paper, the incorporation of ytterbium into the BiFeO3 thin film was fabricated on the Pt/Ti/SiO2/Si substrates by using both dc and rf magnetron co-sputtering method at room temperature. The impact of ytterbium content on structural properties and electrical characteristics of the BiFeO3 thin films was investigated. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy techniques were applied to examine the crystal structures, elemental compositions, microstructures, and film morphologies of these thin films, respectively. The Yb-doped BiFeO3 thin film fabricated at the 11 W condition exhibited the lowest leakage current and the highest remnant polarization among these conditions. This result is attributed to the formation of a stronger BiFeO3 (202) component leading to the decrease in oxygen vacancies.

Effect of (Zn, Mn) co-doping on the structure and ferroelectric properties of BiFeO3 thin films

BiFe1-2xZnxMnxO3 (BFZMO, with x = 0–0.05) thin films were synthesized via sol–gel method. Effects of (Zn, Mn) co-doping on the structure, ferroelectric, dielectric, and optical properties of BiFeO3 (BFO) films were investigated. BFZMO thin films exhibit rhombohedral structure. Scanning electron microscopy (SEM) images indicate that co-doping leads to a decrease in grain size and number of defects. Leakage current density (4.60 × 10−6 A/cm2) of BFZMO film with x = 0.02 was found to be two orders of magnitude lower than that of pristine BFO film. Owing to decreased leakage current density, saturated P–E curves were obtained. Maximum double remnant polarization of 413.2 μC/cm2 was observed for BFZMO thin film with x = 0.02, while that for the BFO film was found to be 199.68 μC/cm2. The reason for improved ferroelectric properties is partial substitution of Fe ions with Zn and Mn ions, which resulted in a reduction in the effect of oxygen vacancy defects. In addition, co-doping was found to decrease optical bandgap of BFO film, opening several possible routes for novel applications of these (Zn, Mn) co-doped BFO thin films.

Probing polarization dynamics at specific domain configurations: Computer-vision based automated experiment in piezoresponse force microscopy

Topological defects in ferroelectric materials have attracted much attention due to the emergence of conductive, ferroic, and magnetic functionalities. However, many topological configurations dynamically evolve during the switching processes, making them a challenge to characterize via traditional techniques. Here, we implement an automated experimentation approach for the exploration of functional properties in BiFeO3 thin films. Specifically, we visualize the ferroelectric domain structures via single frequency piezoresponse force microscopy and implement a computer vision-based algorithm to discover features of interest at which spectroscopic measurements are taken. Subsequently, we employ dimensionality reduction techniques to reveal characteristic polarization behaviors at these features. This approach can be extended to other spectroscopies and modalities to probe only specific features of interest, ultimately enabling dynamical processes in ferroelectrics to be studied.

Effect of polarization rotation on the optical and photovoltaic properties of BiFeO3 thin films

Visible-light-active ferroelectric materials are gaining increasing attention due to the unique ferroelectric photovoltaic effect. To boost the light harvesting capability, vast research is devoted to band gap engineering by chemical substitutions, regardless of the side effect on ferroelectric polarization. Here, we focus on how polar order affects the optical and photovoltaic properties. Using BiFeO3 as the model system, we induce the polarization rotation by A-site La substitution, which results in continuous reduction of optical anisotropy of the samples, as revealed by the concerted optical characterizations. This further causes the decrease of angular dependence of ferroelectric photovoltaic effect on the light polarization. The results demonstrate the inner connection of the ferroelectric polarization and optical anisotropy via the lattice degree of freedom.

Photoconductivity and Photovoltaic Studies on Polycrystalline Bi1−xM′xFe1−yM″yO3−δ (M′ = K+ and Cs+; M″ = Ti4+; x = y = 0 and 0.1) Thin Films

The recent surge of interest in using all-inorganic materials like CsPbI3 for photovoltaic devices has brought significant interest in exploring the properties of BiFeO3 (BFO) by substituting Cs+ and K+ at the Bi3+ site. The aim of the present work is to study the parameters like controlling the lattice and surface oxygen vacancy (VO) defects which can significantly improve the photovoltaic device performances. Monovalent substituted and aliovalent co-substituted Bi1−xM'xFe1−yM"yO3−δ (M′ = K+ and Cs+; M" = Ti4+; x = y = 0 and 0.1) are grown on fluorine-doped tin oxide (FTO)/glass substrates by metal-organic chemical solution deposition method. Photoconductivity and photovoltaic properties of these films are studied in FTO/Bi1−xM'xFe1−yM"yO3−δ/Au capacitor configuration. Aliovalent substitution (for M' = K+ and Cs+, BK10FO and BCs10FO, respectively) at Bi3+ sites create VO in BFO thin films. Further, grain size reduction from 100 nm to 30 nm also results in the creation of surface VO defects. Tauc plot shows a reduction in the bandgap (Eg) values from 2.32 eV to 2.26 eV due to the formation of mid-bandgap VO defect states. Consequently, ferroelectric properties also get diminished. Aliovalent K+-Ti4+ co-substitution in BFO thin films brings back the Eg values to 2.3 eV, i.e., similar to pristine BFO thin films suggesting suppression of VO. This results in the revival of ferroelectric nature in aliovalent co-substituted thin films. Photoconductivity studies show two order enhancement in conductivity for BK10FO thin film devices compared to pure BFO. This enhancement is attributed to the mid-bandgap VO defect states due to aliovalent substitution. On the other hand, photoconductivity observed in BCs10FO devices is comparable with pristine BFO devices. Contrary to this, aliovalent co-substituted thin films show a decreasing trend of photoconductivity compared to M'+ substituted BFO suggesting that VO defects get suppressed due to charge compensation. Photoconductivity and photovoltaic device studies show similar behavior. BK10FO devices exhibit short circuit current density (JSC) ~0.45 µA/cm2, which is larger than that observed in BFO devices (JSC ~0.3 µA/cm2). But, BCs10FO devices show lesser JSC 0.07 µA/cm2. Open circuit voltage (VOC) observed in BFO devices is around 3 V which decreases to 0.1 V and 0.06 V for BK10FO and BCs10FO devices, respectively. This decrease in VOC is attributed to the reduction of the ferroelectric nature of the films. BFO, BK10FO, and BCs10FO devices show photovoltaic switching upon poling the films. Co-substituted thin films show a reduction in the JSC and betterment in the VOC compared to the monovalent substituted BFO thin films. This happens due to the suppression of VO defects by partial charge compensation in aliovalent co-substituted BFO films. This study explicitly brings out the role of VO on the photovoltaic and photoconductivity properties of BFO thin films.

Effects of solvents and Al doping on structure and physical properties of BiFeO3 thin films

In this study, BFO and BFAO thin films were prepared on fluorine-doped tin oxide (FTO) substrates via spin coating with two different acid solvents. One is nitric acid solution (solvent I), the other is a mixture of 2-methoxyethanol and glacial acetic acid (solvent II). The structure, morphology, elemental valence states, and ferroelectric properties of BiFeO3 (BFO) and BiFe0.96Al0.04O3 (BFAO) films were investigated. X-ray diffraction (XRD) results show that all the films are R3c structure and have no impurity phase. The SEM results show that the BFO thin film prepared by solvent II is more compact, uniform, and has low porosity. Raman spectra show that Al doping causes structural distortion. Al doping can solve the problem of porosity and increase the density of BFO thin film. Therefore, the density of BFAO-II sample is better. X-ray photoelectron spectroscopy (XPS) shows that the presence of Al reduces the oxygen vacancy content. This is beneficial to reduce the leakage current density and improve the ferroelectric properties. The leakage current density of BFAO-II sample is 10-3 A/cm2, and the double residual polarization value is 110.2 μC/cm2. Compared with BFO-II sample, it is significantly improved. In addition, Al doping can reduce the band gap of BFO films. This work will be a new idea for the further application of Al doped bismuth ferrite films.

Effects of Nd and Mn Co-dopant on the Micro Structure and Optical Properties of BiFeO3 Thin Films Elaborated by Chemical Solution Deposition (CSD)

Bismuth Ferrite (BiFeO3), Neodymium (Nd) and Manganese (Mn) (Bi1-xNdxFe1-yMnyO3) with (x, y = 0.03, 0.03; 0.03, 0.05; 0.05, 0.03; 0.05, 0.05) were prepared by Chemical Solution Deposition (CSD) method at annealing temperatures of 550 °C. The effects of addition of Nd and Mn co-dopants in the BiFeO3 on the crystal structure and optical properties are presented. The results of X-Ray Diffraction (XRD) characterization showed that the addition of Nd and Mn co-dopants leads the diffraction angles to shift to smaller angles and to decrease the crystal size. Doped-BiFeO3 samples were characterized by UV-vis in the wavelength range of 200 nm-800 nm. The transmittance value of Bi1-xNdxFe1-yMnyO3 samples decreased in the wavelength range of 400-800 nm (UV light). The addition of Nd and Mn co-dopants to BiFeO3 caused light dispersion and refractive index to decrease.

Fabrication of Nb nanopin electrodes and their influence on multiferroic properties of BiFeO3 thin films

We report enhanced multiferroic properties of BiFeO3 (BFO) thin films by depositing them on Nb nanopin bottom electrodes via spin-coating. The well-aligned Nb nanopin array was prepared from wet etching of an anodic aluminum oxide (AAO) nanotemplate. X-ray diffraction (XRD) measurement revealed that the BFO thin films were polycrystalline. The BFO thin films fabricated on Nb nanopin electrodes exhibited improved ferroelectricity with a remnant polarization (Pr) of 37.5 μC/cm2 and a coercive electric field (Ec) of 98 kV/cm, which was better than those (Pr ~ 32.9 μC/cm2 and Ec ~ 217 kV/cm) on the Nb film electrodes. We investigated leakage current, polarization switching speed as well as ferromagnetism, which also exhibited the improvement of BFO thin films on Nb nanopin electrodes. Significantly, we suggest that an enhanced electric field and surface-volume ratio of the Nb nanopin electrodes contribute to enhancement of the multiferroic properties of the BFO thin films.

Effects of Mn doping on ferroelectric, ferromagnetic and optical properties of BiFeO3 thin films

Mn-doped BiFeO3 films were prepared by chemical solution deposition method on fluorine doped tin oxide conductive glass via spin-coating technique. XRD pattern reveals the presence of the impurity phase of Bi2Fe4O9 in BiFeO3 films, while no impurity phase is found in the Mn-doped thin films. XPS spectrum demonstrates the purity of prepared thin films by exhibiting the desired elements alone and it also shows that Mn-doping restrains the change of Fe3+ valency. The leakage current result shows that Mn-doping causes the change of conduction mechanism led by the change of microstructure and the restraint of Fe ions valence. BiFe0.95Mn0.05O3 thin film has a good ferroelectric performance with high remnant polarization (Pr) value of 27 μC/cm2. Mn doped BiFeO3 films have stronger saturation magnetization than the BiFeO3 thin films. UV vis NIR transmittance spectra depicts the optical property, which shows the optical band gap decreases with the concentration of Mn increases.

Impact of defects on the electrical properties of BiFeO3 thin films

The impact of defects on the electrical properties of bismuth ferrite thin films has been studied. Secondary phases and oxygen vacancies were the main defects considered. Thin films with secondary phases show higher conductivities than single-phase films. Monophasic films annealed in oxygen atmosphere shows lower conductivity than the non-annealed film. For selected thin film with secondary phase, the relaxation in the grain boundary was predominant with activation energy eV, suggesting the first ionization oxygen vacancies as the relaxation mechanism in the studied films. The electric field effect on relaxation processes was similarly to Arrhenius thermally activated process.

Effect of Thermal Annealing on Photocatalytic Properties of BiFeO3 Thin Films

Improving photocatalytic activity of traditional photocatalysts is one of the actual topics. We fabricated the single phase multiferroic BiFeO3 thin films on SiO2/Si substrates using sol_gel method and analyzed the effect of thermal annealing on photocatalytic properties of the film. Experimental results show that all the samples had a single perovskite rhombohedral structure and are randomly oriented. The estimated band gap values of the films are 2.63, 2.88, and 2.92 eV, respectively. BiFeO3 thin films show good photocatalytic properties in the degradation of methylene blue solution under visible-light irradiation. These results indicate that the microstructure, optical, and photocatalytic properties of BiFeO3 thin films have a strong dependence on annealing temperature. We hope that this work could provide a new route for preparation of highly efficient photocatalysts.