硅酸盐学报2025，Vol.53Issue(9)：2421-2429,9.DOI:10.14062/j.issn.0454-5648.20250308
有序氧空位调控BiFeO3薄膜的极化与光学特性
Ordered Oxygen Vacancy Modulated Polarization and Optical Properties in BiFeO3 Thin Films
摘要
Abstract
Introduction Multiferroic BiFeO₃(BFO)exhibits coupled ferroelectric,antiferromagnetic,and ferroelastic orders at room temperature,enabling unique optoelectronic properties such as switchable photovoltaic effects and polarization-driven carrier separation.The multi-valance of Fe element in BFO also implies its potential to engineer the bandgap and conductivity to enhance the photoelectric properties.Besides,the large remnant ferroelectric polarization in BFO offers the opportunity of bulk photovoltaic effect,promising to develop the optoelectronic devices based on the unique optical and multiferroic properties.While defects like oxygen vacancies are known to critically influence functional properties in oxides,especially the BFO films.The oxygen vacancies are proved to influence the electronic and magnetic properties,electromechanical response and resistive switching.Furthermore,the concentration of oxygen vacancies is clarified to be influenced by the annealed conditions,which in turn tune the photoresponse of BFO thin films.However,previous studies mainly focus on the influence of the oxygen vacancies as the point defects on properties and the atomic-resolved analyses of oxygen vacancies behavior are lacking.Here,by combining advanced STEM,UV-Vis,XRD and first-principles calculations,we systematically investigate oxygen-vacancy-engineered BFO thin films to reveal how ordered vacancy planes modulate lattice structure,create charged domain walls,reduce bandgaps and improve UV-visible absorption property,thereby demonstrating a defect-property correlation crucial for designing multifunctional devices. Methods BFO polycrystalline ceramic target(1%Bi-enriched),SrTiO3(STO)ceramic target,and commercial single-crystal substrates of NdGaO3(NGO)(110)O and STO(001)were purchased from Hefei Kejing Materials Technology Co.,Ltd.BFO and BFO/STO films were grown on NGO(110)O substrates via pulsed laser deposition(PLD)using a Coherent ComPex PRO 201 F KrF excimer laser(λ=248 nm).The substrates were preheated to 850℃for 20 min and cooled to deposition temperature at 5℃/min.A 1%Bi-enriched BFO target was pre-sputtered for 20 min.The deposition parameters of 6 Hz repetition rate,800℃substrate temperature,370 mJ laser energy were used to fabricate the films.Post-deposition annealing at 800℃for 20 min was followed by cooling to 200℃at a rate of 5℃/min and natural cooling to RT under 200 Torr O₂ partial pressures.Four film systems were prepared by varying O₂ partial pressures:1)BFO film:growing at 90 mTorr,annealing at 200 Torr;2)BFO film:growing at 90 mTorr,annealing at 120 mTorr;3)BFO/STO film:BFO layer growing at 90 mTorr,STO capping layer growing at 70 mTorr,both layers were annealed at 120 mTorr;4)BFO/STO film:growing/annealing at 0.06 mTorr. Cross-sectional TEM specimens were prepared using a ThermoFisher Helios 5UX FIB system with sequential steps:C/W protective layer deposition,trenching,lift-out,thinning(30 kV/90 pA → 8 kV/47 pA),and amorphous layer removal(5 kV/47 pA → 2 kV/47 pA).The atomic-resolved HAADF-STEM images were acquired on ThermoFisher Spectra 300(300 kV,25 mrad convergence,71-200 mrad collection angles)with drift correction(DCFI in Velox).The strain analysis was performed using GPA via Gatan GMS3 software and the atomic positions were determined by 2D Gaussian fitting in MATLAB software.The UV-Vis measurements were performed in JASCO V-770.The RSMs were collected on Bruker D8 Advance(Cu Kα,λ=1.5406 Å).First-principles calculations were based on the density functional theory(DFT)calculation and performed with the Vienna ab initio simulation package(VASP). Results and discussion A series of BFO films were fabricated by modulating the oxygen environment to introduce the high-density oxygen vacancies.Using the Cs-STEM,the oxygen vacancy ordered plane was determined in BFO film annealed under the oxygen partial pressure of 120 mTorr,which displayed as the out-of-plane lattice expansion.Besides,the charged oxygen vacancy ordered plane would influence the surrounding polarization directions,stabilizing the tail-tail polarization distribution.By changing the annealed oxygen partial pressure and growing the capping layers,the concentration of oxygen vacancy ordered planes was evidently modulated,further extending the ultraviolet-visible absorption property of the BFO films.First-principles calculations revealed that the introduction of high-density oxygen vacancies could generate the vacancy-induced energy levels between the conduction and valance bands and thus reduce the bandgaps of BFO.The result was consistent with the UV-visible absorption measurement results. Conclusion The oxygen vacancy ordered planes were introduced in BiFeO3 film systems by controllable growth methods.Its concentration was tunable by decreasing the annealed oxygen partial pressure and/or growing capping layers.Obvious lattice expansion was observed in BFO films by the existence of oxygen vacancy ordered planes.Besides,the polarization configuration in BFO film was modulated by the electrostatic potential of positively charged oxygen vacancy layer,accompanying the formation of tail-to-tail polarization configuration.The introduced oxygen vacancy ordered planes also had further improved the optical absorption properties of BFO films.Our results provide a further insight into the interaction between oxygen vacancy ordered planes with the ferroelectric polarization and the optical properties in multiferroic oxides and facilitate the design of nanoscale photoelectronic devices and ferroelectric solar cells.关键词
铁酸铋薄膜/氧空位有序面/光吸收/第一性原理计算Key words
bismuth ferrite thin films/oxygen vacancy ordered planes/light absorption/first-principles calculations分类
化学化工引用本文复制引用
耿皖荣,江亦潇,朱银莲,马秀良..有序氧空位调控BiFeO3薄膜的极化与光学特性[J].硅酸盐学报,2025,53(9):2421-2429,9.基金项目
国家自然科学基金(52201018,51971223) （52201018,51971223）
广东省基础与应用基础研究基金(2021A1515110291,2023A1515012796) （2021A1515110291,2023A1515012796）
广东省量子科学战略计划(GDZX2202001,GDZX2302001,GDZX2402001) （GDZX2202001,GDZX2302001,GDZX2402001）
松山湖科学城显微科学与技术开放基金(202401202). （202401202）
