制备工艺对溶胶-凝胶法制备BeFeO3薄膜的影响

利用溶胶-凝胶法在Pt/Ti/SiO2/Si基体上制备了BiFeO3薄膜,构架了Pt/BiFeO3/Pt电容器。对不同退火温度和保温时间制备薄膜的微观形貌和铁电性能做了研究。X射线衍射仪（XRD）结果显示,不同的退火温度和保温时间并没有改变BiFeO3（BFO）的钙钛矿结构,但温度的改变会产生不同的晶相。通过扫描电子显微镜（FE-SEM）可以观察到,随着烧结保温时间的延长,薄膜晶粒有减小的趋势。P-E曲线结果表明,BFO薄膜在外加电场较高时易击穿,难以得到清晰饱和的电滞回线。     

Optical properties of epitaxial BiFeO3 thin film grown on SrRuO3-buffered SrTiO3 substrate

The BiFeO₃ (BFO) thin film was deposited by pulsed-laser deposition on SrRuO₃ (SRO)-buffered (111) SrTiO₃ (STO) substrate. X-ray diffraction pattern reveals a well-grown epitaxial BFO thin film. Atomic force microscopy study indicates that the BFO film is rather dense with a smooth surface. The ellipsometric spectra of the STO substrate, the SRO buffer layer, and the BFO thin film were measured, respectively, in the photon energy range 1.55 to 5.40 eV. Following the dielectric functions of STO and SRO, the ones of BFO described by the Lorentz model are received by fitting the spectra data to a five-medium optical model consisting of a semi-infinite STO substrate/SRO layer/BFO film/surface roughness/air ambient structure. The thickness and the optical constants of the BFO film are obtained. Then a direct bandgap is calculated at 2.68 eV, which is believed to be influenced by near-bandgap transitions. Compared to BFO films on other substrates, the dependence of the bandgap for the BFO thin film on in-plane compressive strain from epitaxial structure is received. Moreover, the bandgap and the transition revealed by the Lorentz model also provide a ground for the assessment of the bandgap for BFO single crystals.     

Observation of oxygen pyramid tilting induced polarization rotation in strained BiFeO3 thin film

Oxygen octahedral tilting has been recognized to strongly interact with spin, charge, orbital, and lattice degrees of freedom in perovskite oxides. Here, we observe a strain-driven stripe-like morphology of two supertetragonal (monoclinic Cc and Cm ) phases in the strained BiFeO₃/LaAlO₃ thin films. The two supertetragonal phases have a similar giant axial ratio but differences in oxygen pyramid tilting mode. Especially, the competition between polar instability and oxygen pyramid tilting is identified using atomically resolved scanning transmission electron microscopy, leading to the polarization rotation across the phase boundary. In addition, microtwins are observed in the Cc phase. Our findings provide new insights of the coupling between ferroelectric polarization and oxygen pyramid tilting in oxide thin films and will help to design novel phase morphology with desirable ferroelectric polarization and properties for new applications in perovskite oxides.     

An in situ resonant photoemission and x-ray absorption study of the BiFeO3 thin film

Multiferroic bismuth ferrite (BiFeO₃) thin films were prepared using the pulsed laser deposition (PLD) technique. The electronic structure of the film was studied in situ using photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS). Both the Fe 2p PES and XAS spectra show that the Fe ions were initially in a+3 valence state. The Fe 2p and O K edge XAS spectra indicate that the oxygen octahedral crystal ligand field divides the unoccupied Fe 3d state into t_2g↓and e_g↓states. Valence band Fe 2p–3d resonant photoemission results indicate that hybridization between Fe 3d and O 2p plays an important role in the multiferroic properties of BiFeO₃ thin films.     

Low temperature hydrothermal epitaxy of heteroepitaxial BiFeO3 film

Heteroepitaxial BiFeO₃ films were fabricated on a single crystal SrTiO₃ substrate by hydrothermal epitaxy. There were two different BiFeO₃ layers on the SrTiO₃ substrate; first interfacial layer and bulk-like second layer. Microstructure development of the BiFeO₃ film was dependent on the precursor concentration, mineralizer concentration, and fill factor of the reaction vessel. This two step growth mechanism was discussed by comparing with earlier reports.     

Solution-processed BiFeO3 thin films with low leakage current

Bismuth ferrite (BiFeO₃) is an attractive multiferroic material that shows strong ferroelectric and antiferromagnetic properties. Nevertheless, producing high-quality oriented BiFeO₃ on technology-important platinized silicon substrates by low-cost solution deposition methods is still challenging. In this work, polycrystalline Mn and Ti co-doped BiFeO₃ (BFO) thin films were fabricated on platinized silicon substrates by a solution deposition method. PbTiO₃ nanocrystals were used as a seed layer between the electrode and the BFO thin films to induce a preferential (100) pseudocubic orientation. We show that the introduction of a PbTiO₃ seed layer strongly reduces the leakage current. The films show excellent room-temperature ferroelectric properties at low frequencies (300 Hz), with epitaxial-like remanent polarization as high as 51 μC/cm² and coercive field of 500 kV/cm.     

Structural and ferroelectric properties of chemical solution deposited (Nd,Cu) co-doped BiFeO3 thin film

Effects of (Nd, Cu) co-doping on the structural, electrical and ferroelectric properties of BiFeO₃ polycrystalline thin film have been studied. Pure and co-doped thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. Significant improvements in the electrical and the ferroelectric properties were observed for the co-doped thin film. The remnant polarization (2P_r) and the coercive field (2E_c) of the co-doped thin film were 106 μC/cm² and 1032 kV/cm at an applied electric field of 1000 kV/cm, respectively. The improved properties of the co-doped thin film could be attributed to stabilized perovskite structures, reduced oxygen vacancies and modified microstructures.     

Enhanced ferroelectric properties of Ce-substituted BiFeO3 thin films on LaNiO3/Si substrates prepared by sol–gel process

The effects of Ce substitution on the structural and electrical properties of multiferroic BiFeO₃ thin films grown on LaNiO₃/Si(1 0 0) substrates by a sol–gel process have been reported. X-ray diffraction data confirmed the substitutions of Ce into the Bi site with the elimination of all secondary phases under a substitution ratio x = 15%. The dielectric constants of the films increased from 90 to ～260 below 100 kHz with 5% molar Ce substitution and the films showed enhanced dielectric behavior. We observed a substantial increase in the remnant polarization (P_r) with Ce substitution and obtained a maximum value of ～71 μC/cm² by 5% molar Ce incorporation. The leakage current behavior at room temperature of the films was studied and it was found that the leakage current density decreased from 10^?6 to 10^?8 A/cm² for 5% molar Ce-substituted films under a field 150 kV/cm. The reduction of dc leakage current of Ce-substituted films is explained on the basis of relative phase stability and improved microstructure of the material.     

Tunable multiferroic properties of Mn substituted BiFeO3 thin films

The current study explored the influence of Mn substitution on the electrical and magnetic properties of BiFeO₃ (BFO) thin films synthesized using low cost chemical solution deposition technique. X-ray diffraction analysis revealed that pure rhombohedral phase of BiFeO₃ was transformed to the tetragonal structure with P4mm symmetry on Mn substitution. A leakage current density of 5.7×10⁻⁴ A/cm² which is about two orders of magnitude lower than pure BFO was observed in 3% Mn doped BFO thin film at an external electric field >400 kV/cm. A well saturated (p-E) loops with saturation polarization (P_sat) and remanent polarization (2P_r) as high as 60.34 µC/cm² and 25.06 µC/cm² were observed in 10% Mn substituted BFO thin films. An escalation in dielectric tunability (n_r), figure of merit (K) and quality factor (Q) were observed in suitable Mn doped BFO thin films. The magnetic measurement revealed that Mn substituted BFO thin films showed a large saturation magnetization compared to pure BFO thin film. The highest saturation ~31 emu/cc was observed for 3% Mn substituted BFO thin films.     

Origin of antipolar clusters in BiFeO3 epitaxial thin films

The microstructure of BiFeO₃ (BFO) thin films is investigated using high-resolution transmission electron microscopy. Both (001)- and (101)-type domain boundaries are found in the BFO films. The antipolar clusters induced by antiparallel cation displacements are observed in the pure BFO film, and the cation displacements in the films are proved to originate from the lattice strain which can be adjusted by introduction of a buffer layer. Combining transmission electron microscopy (TEM) with fast Fourier transformation techniques, both γ-Fe₂O₃ and FeO phases were discovered. The γ-Fe₂O₃ phase stems from the decomposition of stoichiometric BFO due to the volatilization of Bi, while the FeO phase results from the decomposition of BFO with oxygen vacancies which could come from ion milling process during the TEM sample preparation. Our work sheds light on the origin of the cation displacements and provides a new idea to control the physical properties of BFO films.     

Suppressing the non-switching contribution in BiFeO3-Bi4Ti3O12 based thin film composites to produce room-temperature multiferroic behavior

Exploiting the exceptional multiferroic characteristics of BiFeO₃-based systems depends largely on controlling the high leakage currents that often constrain the ferroelectric response of this material. This limiting circumstance is even more restrictive in the film geometry, where the high area/volume ratio can add complications related to the uncontrolled loss of a particularly volatile element such as bismuth. In this work we address the suppression of such non-switching contribution by preparing BFO-BiT thin film composites and using a low-temperature processing protocol in a fully aqueous medium. With an adequate and systematic doping of both oxides, the produced composites show both magnetic and ferroelectric response at room temperature, in a process that is also related to the fine matching between the two crystal lattices involved. The results obtained further indicate the possibility of applying a simple, sustainable protocol with high scalability prospects to fabricate exploitable multiferroic systems, i.e. with no need for large energy inputs nor sophisticated equipment.     

Lead-free BiFeO3 film on glass fiber fabric: Wearable hybrid piezoelectric-triboelectric nanogenerator

Constructing hybrid nanogenerators (NGs) based on triboelectric effect and piezoelectric effect can combine the merits of the individual type of NG thus have drawn great attention in flexible wearable electronics. Herein, we prepared flexible BiFeO₃ (BFO) film in a simple and cost-effective way, which was used to fabricate a wearable hybrid piezoelectric-triboelectric nanogenerator (H–P/TENG) with silk fiber. By optimizing the experimental conditions, the highest open-circuit voltage of 110 V and short-circuit current density of 3.67 μA/cm² were achieved under 1 Hz contact-separation movement. The device also showed the best output power density of 151.42 μW/cm² with load resistance of 250 MΩ. Stimulating by moving body, the fabricated H–P/TENG successively realized the harvest and conversion of mechanical energy into electric energy, demonstrating great potential to monitor posture and establish a self-powered system. Moreover, the proposed H–P/TENG exhibited great stable output after 1800 contact-separation cycles, indicating the outstanding structure stability and fatigue resistance. This work will provide not only a facile and viable way to realize the application of ferroelectric materials in H–P/TENG but also new opportunities for developing monitor posture and self-powered systems.     

汉高第三代薄膜前处理工艺的应用

总结了汉高第三代薄膜前处理技术的工艺和设备应用情况,对目前研究中存在的问题和难点提出了解决思路,展望了今后的研究方向.     

Study on polystyrene thin film on glass substrate by scanning acoustic microscope

Acoustic micrograph and V(z) curves of polystyrene thin films on hydrophobic modified and unmodified alumino silicate glass substrates were studied in the frequency range from 170 to 450 MHz by a scanning acoustic microscope. The bright and dark parts in the acoustic micrograph of the unmodified glass samples appeared owing to permeation of water into the film. The blister was observed after about 20 s from dropping water. Sizes of the blister depended on the time and the thickness of thin films. On the other hand, the acoustic micrograph of the hydrophobic modified samples was a uniform image and the peeling of the thin film was not observed. V(z) curves of polystyrene thin film on the modified glass substrates had two oscillation periods in a certain frequency range that depended on the thickness of thin films. The short cycle and the long cycle components were assigned to a leaky surface acoustic wave (LSAW) and a leaky pseudo Sezawa wave, respectively. Velocities of the LSAW decreased linearly with an increase in film thickness.     

Analysis of process peculiarities of thin film disalination plants

In this article a large complex of researches on hydrodynamics and heat transfer is carried out on a current of thin film in up flow, down flow and horizontal-tube falling film desalination plants. Based on the results of observation of the mode of movement of a film on such heating surfaces and steam formation, explanations of physical features of hydrodynamics are given, and heat transfer for seawater and their essential difference in relation to distillate is shown. By results of data processing the currents, ensuring stability, minimal charge of seawater are offered for these processes, as well as an equation for calculation of average and maximal thickness of a film. The equations of heat transfer characteristics for all these thin film regimes are obtained.     

Interface-layer-assisted reliable ferroelectricity in BiFeO3 thin films by chemical solution deposition

BiFeO₃ thin films, specifically those fabricated by chemical solution deposition, suffer from severe leakage that hinder the acquirements of their intrinsic high polarizations and are thus normally not considered for use in practical electronics. The controlled fabrication of thin films with reduced leakage is of vital importance. In the present work, BiFeO₃ films (with thicknesses below ~300 nm), assisted by an interfacial amorphous layer, were fabricated by chemical solution deposition on Pt/Ti/SiO₂/Si substrates. This facile method facilitates the growth of the mentioned amorphous layer, and the ferroelectric properties of the obtained films were greatly enhanced. The conducting mechanisms of both types of thin films were systematically investigated to understand the impact of the designed interface. The results not only advance the potential use of BiFeO₃ thin films in electromechanical devices but also promote chemical solution deposition as a promising methodology for the fabrication of high-quality ferroelectric films with compressed leakage.     

Semi-transparent thin film solar cells by a solution process

Easily processed, low cost, and highly efficient solar cells are desirable for photovoltaic conversion of solar energy to electricity. We present the fabrication of precursor solution processed CuInGaS2 (CIGS) thin film solar cells on transparent indium tin oxide (ITO) substrates. The CIGS absorber film was prepared by a spin-coating method, followed by two successive heat treatment processes. The first annealing process was on a hot plate at 300 °C for 30 min in air to remove carbon impurities in the film; this was followed by a sulfurization process at 500 °C in an H₂S(1%)/Ar environment to form a polycrystalline CIGS film. The absorber film with an optical band-gap of 1.52 eV and a thickness of about 1.1 µm was successfully synthesized. Because of the usage of a transparent glass substrate, a bifacial CIGS thin film device could be achieved; its power conversion efficiency was measured to be 6.64% and 0.96% for front and rear illumination, respectively, under standard irradiation conditions.     

Heat and mass transfer on the wavy film absorption process

Recently the absorption heat pumps and chillers have received considerable attention due to their low electricity consumption rate. Therefore, it is important to understand the transport mechanism of an absorption process. In this paper, a numerical study of the heat and mass transfer taking place on a wavy falling liquid film of an absorption process is presented. With previously solved periodic wavy film flow solutions, the finite difference method is employed to solve the heat and mass transport equations. The numerical solution indicates that the waves significantly increase the transport rates. A comparison of the transfer rates of the wavy film to that of the smooth film is presented to show that the mass transfer rate can be doubled.     

Temperature self-monitoring photothermal nano-particles of Er3+/Yb3+ Co-doped zircon-tetragonal BiVO4

Self-monitored photo-thermal therapy (PTT) still faces huge challenge in cancer treatment, which aims to realize the real-time temperature reading during the course of optical heating. Exploiting new-type photo-thermal therapeutic agent (PTA) with thermometric function is considered to be one of effective methods to fulfill self-monitored PTT. In this work, spindle-like zircon-tetragonal (z-t) phase BiVO₄:Yb³⁺/Er³⁺ up-conversion (UC) nano-particles as self-monitored PTAs were prepared through the combination of co-precipitation and hydrothermal method. Under 980 nm laser diode excitation, real-time thermometry was accomplished by monitoring thermo-responsive emission intensity ratio of Er³⁺ (²H_11/2/⁴S_3/2 → ⁴I_15/2) transitions. Meanwhile, the photo-thermal conversion effect associated with UC process was trigged via the non-radiative transition channels. Considering the balance between UC emission intensity and heat generation, the optimal sample composition was determined as BiVO₄:20%Yb³⁺/3%Er³⁺. Their maximum absolute sensitivity (S_a) reached 0.0125 K^-1 at 460 K as the thermometer and the ability of photo-thermal conversion up to 3.32 K cm²/W as PTAs. Their potential applications in controlled subcutaneous photo-thermal treatment were estimated through ex vivo experiments. Results provided a new choice for nano-materials to realize real-time temperature feedback in the single host material (z-t BiVO₄) during the course of PTT.     

老化工艺对纳米多孔二氧化硅薄膜微观结构影响

本文主要探讨了老化时间与处理温度对纳米多孔二氧化硅薄膜结构的影响。结果表明随着老化时间的增加,薄膜的三维网状结构越明显、孔径分布更均匀、孔隙率越高、孔径越大。经450℃高温热处理后,颗粒长大,孔径增大,孔径分布不均匀,且薄膜厚度几乎不受老化时间的影响,说明湿凝胶薄膜在异丙醇气氛下老化后的强度是足够抵抗凝胶薄膜在异丙醇溶剂中老化放生的变化过程而引起的薄膜收缩。