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Origin of Ferroelectricity in Epitaxial Si-doped HfO2 Films
摘要： HfO2-based unconventional ferroelectric (FE) materials were recently discovered and have attracted a great deal of attention in both academia and industry. The growth of epitaxial Si-doped HfO2 films has opened up a route to understand the mechanism of ferroelectricity. Here, we used pulsed laser deposition (PLD) to grow epitaxial Si-doped HfO2 films in different orientations of N-type SrTiO3 substrates. Using piezoforce microscopy, polar nanodomains can be written and read, and these domains are reversibly switched with a phase change of 180o. Films with different thicknesses displayed a coercive field Ec and a remnant polarization Pr of approximately 4～5 MV/cm and 8～32 μC/cm2, respectively. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) results identified that the as-grown Si-doped HfO2 films have strained fluorite structures. The ABAB stacking mode of the Hf atomic grid observed by HRTEM clearly demonstrates that the ferroelectricity originates from the noncentrosymmetric Pca21 polar structure. Combined with soft X-ray absorption spectra (XAS), it was found that the Pca21 ferroelectric crystal structure manifested as O sublattice distortion by the effect of interface strain and Si dopant interactions, resulting in further crystal-field splitting as a nanoscaled ferroelectric ordered state.
关键词： HRTEM,PLD,XRD,Ferroelectricity,PFM,XAS,Epitaxial Si-doped HfO2 thin films,N-type SrTiO3 substrates
更新于2025-11-14 17:04:02
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[IEEE 2018 IEEE International Power Electronics and Application Conference and Exposition (PEAC) - Shenzhen, China (2018.11.4-2018.11.7)] 2018 IEEE International Power Electronics and Application Conference and Exposition (PEAC) - Performance Comparison of Primary Side PFM and Secondary Side PWM for SS Wireless Power Transfer CC/CV Control Strategy
摘要： Wireless Power Transfer (WPT) system for Electric Vehicle (EV) battery charging application popularity is increasing due to the safety, convenience, and eco-friendly issue. Nowadays, Lithium-Ion battery is well known as one of the potential for EV. However, Constant Current/Constant Voltage (CC/CV) control strategy needs to be adopted for achieving high efficiency charging and maintaining battery lifetime. By analyzing the gain curve, Pulse Frequency Modulation (PFM) can be used to perform CC/CV charging due to the load variation. The operating switching frequency needs to be considered and limited to prevent instability of the system. A typical drawback in the PFM control is the use of serial communication module for feedback data transmission from the secondary to the primary side. Therefore, the rectifier side controlled WPT can be a solution to remove the feedback communication part. In this paper, Pulse Width Modulation (PWM) applied in the secondary side (rectifier) for achieving CC/CV charging is investigated and compared with the traditional PFM control. The comparison study is verified by implementing a 3kW Series-Series (SS) WPT topology in the Power Simulation (PSIM) software. It shows that the secondary side PWM control strategy can achieve 94% efficiency during the 35 Ω load in CC mode, while the primary side PFM control only can achieve 88% efficiency.
关键词： PFM Controlled WPT,Wireless Power Transfer (WPT),CC/CV Mode,PWM Controlled WPT
更新于2025-09-23 15:22:29
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Study of BiFeO3 thin film obtained by a simple chemical method for the heterojunction-type solar cell design
摘要： Polycrystalline BiFeO3 (BFO) films of different thickness were synthesized by a 2-methoxyethanol (acid)-free simple chemical method. A rhombohedral-type pure phase with a crystallite size less than 18.8 nm was obtained. SEM micrographs showed that BFO has a flat and homogeneous morphology when it was deposited on different semiconductor substrates (ZnO, Ni doped ZnO, and CdS). The highest roughness value (8.6 nm) was observed when BFO was deposited on CdS. The optical response showed that the optical band gap slightly changes as thickness increases. The photovoltaic response of the BFO film was assessed employing different solar cell architectures (p-BFO-n and BFO-n). The results showed that the solar cell based on the Ag/PbS/BFO/CdS/FTO/glass structure presented a short-circuit current density of JSC ? 239:6 mA=cm2 and a power conversion efficiency of h ? 7:65 (cid:2) 10(cid:3)3 %. Photoelectrochemical and ferroelectric measurements were employed to explain the photovoltaic response.
关键词： Mott-Schottky,XPS,PFM,BiFeO3 thin films
更新于2025-09-23 15:21:01