分类: 材料科学 >> 电子、光学、磁材料 提交时间: 2023-10-26
摘要: Triboelectric nanogenerators (TENGs) are promising self-powering suppliesfor a diverse range of intelligent sensing and monitoring devices, especially due to their capability of harvesting electric energy from low frequency and small-scale mechanical motions. Inspired by the fact that contact-separation mode TENGs with small contact areas harvest high electrical outputs due to fringing effect, this study employed discontinuity on the dielectric side of contact-separation mode TENGs to promote fringing electric fields for the enhancement of electrical outputs. The results reveal that the TENGs with more discontinuities show higher overall electric performance. Compared to pristine TENGs, the TENGs with cross discontinuities increased the surface charge by 50% and the power density by 114%. However, one should avoid generating discontinuities on tribonegative side of TENGs using metal blade within a positive-ion atmosphere due to the neutralization through electrically conductive metal blade. The computational simulation validated that the TENGs with discontinuities obtained higher electrical outputs, and further investigated the effect of discontinuity gap size and array distance on TENGs performance. This study has provided a promising method for the future design of TENGs using discontinuous structures.
分类: 材料科学 >> 电子、光学、磁材料 提交时间: 2023-08-23 合作期刊: 《中国科学院院刊》
摘要: 镓体系半导体材料具有高效光电转换效率和光谱覆盖广的突出优点,是助力实现光电子信息产业 突破的关键基础材料。为抢占镓体系半导体科技制高点,文章在分析镓体系半导体科技的战略意 义、重大需求和国内外发展态势基础上,从建制化科研组织、基础研究、自主可控的平台建设等方面对我国 发展镓体系半导体科技提出了政策建议。
分类: 材料科学 >> 电子、光学、磁材料 提交时间: 2023-03-01
摘要: The intrinsic high frequency permeability spectra of ferromagnetic composites containing different volume fractions of iron and cobalt have been simulated. A law (called Mghans law) is proposed to explain the simulated results by assuming that there are plenty of LLG (Landau-Lifshitz-Gilbert) type natural resonances contributing to the intrinsic permeability spectra. The results clearly show that the spectra strongly depend on the distribution of local effective magnetic field, the interaction between the magnetic particles, the inhomogeneous damping constant of LLG precession, and the initial equilibrium states. Especially, the effect of particles shape distribution in each sampling on the local effective magnetic field. In view of this fact: it is absolutely impossible to have the same effect from these factors when someone prepares several measurement samples, an uncertainty principle is believed to hold for measuring the intrinsic permeability of an electromagnetic (EM) composite. Therefore, this law tells us that it should be cautious when comparing or evaluating the EM properties of composites (for instance, EM wave absorbing composites). Memory effect can be used to restore the intrinsic high frequency permeability for a specific defunct composite sample.
分类: 材料科学 >> 电子、光学、磁材料 提交时间: 2022-10-26 合作期刊: 《桂林电子科技大学学报》
摘要: 为了提高永磁薄膜的磁性能以及提高Ce元素的利用率,基于微磁学理论,采用OOMMF软件对双主相Nd2Fe14B/ Ce2Fe14B周期多层膜的磁化反转过程进行了模拟,系统地研究了磁化反转过程中磁层厚度和多层膜层数对周期多层膜磁 性能的影响,分析了体系的剩磁、矫顽力、磁滞回线和磁化反转过程中的能量变化以及磁体的矫顽力机制,为日后制备高含 量Ce的高性能磁体提供参考。研究结果表明:当固定多层膜厚度和层数不变时,随着磁层厚度的增加,体系的矫顽力和最 大磁能积均逐渐减小;周期多层膜的矫顽力机制主要由成核主导;在其他条件相同时,平行取向的周期多层膜的矫顽力和 磁能积均优于垂直取向的周期多层膜;周期多层膜总厚度的增加会降低取向对矫顽力的影响。研究结果将有助于加深对 双主相Nd-Fe-B/Ce-Fe-B磁体磁化反转机理的认识,为将来在实验中优化永磁薄膜的磁性能提供参考。
分类: 材料科学 >> 电子、光学、磁材料 分类: 物理学 >> 电磁学、光学、声学、传热、经典力学和流体动力学 提交时间: 2022-05-08
摘要: 本文研究近紫外飞秒激光脉冲在聚甲基戊烯内部刻写的应用技术。我们发现该热塑材料具有偏振敏感性的特征。首先刻写实验使用数字孔径为0.05的透镜聚焦, 通过对超连续光谱的分析,测得稳定成丝刻写的激光脉冲功率在2.2MW - 9.2MW区间内,并由此推断该种材料的非线性折射率为n2387=210-16cm2W-1,推算三阶susceptibility (3)为 1.110-14esu。稳定成丝加工长度在300m-1500m。然后,实验使用数字孔径为0.4的组合物镜聚焦刻写厚度为~700m,栅距为5m的布拉格光栅。通过对光栅产品的衍射效率测试,推断最大折射率的变化为~0.01,这比文献中的记录数据,提高一个数量级。实验结果证明了激光脉冲峰值强度对于诱导非线性吸收的重要性,而双光子吸收为温和可控改性的物理机制。本工作为科研人员和光学器件设计和制作提供了最新的参考。
分类: 材料科学 >> 电子、光学、磁材料 提交时间: 2022-03-07
摘要: In this paper, we reported a method to modify the crystallization of CZTSSe films by changing the microstructures of the precursor films. Precursor films with different microstructures were prepared and their crystallization processes were analyzed. We find even tiny differences in microstructures of the precursor films can result in significant alteration of the crystallization processes and the properties of CZTSSe films. Moreover, we found the S-to-Se substitution can be delayed to higher temperature depending on the microstructure of the precursor. This process plays critical roles in enhanceing the crystallization of CZTSSe films and can be used to eliminate the multi-layer crystallization in CZTSSe films. The detailed analysis on the crystallization processes revealed that different mechanism may dominate the crystallization of the films, which can determine the properties of CZTSSe films and solar cells. Moreover, a hybrid structure for precursor film was proposed which has different microstructures in different part of the film. In such a precursor film, different crystallization mechanism can work synergically during the preparation of the film. As the results, the comprehensive properties of the films were improved and solar cells with efficiencies up to 12.6% was prepared.
分类: 材料科学 >> 电子、光学、磁材料 提交时间: 2019-04-30
摘要: 我们成功合成了CsKNaLi(Li3SiO4)4:Eu2+ (CKNLLSO:Eu2+)作为UCr4C4型结构氧基家族的新成员。该荧光粉的基质化合物的晶体结构和能带结构分别通过Rieveld精修方法和密度泛函理论分析和计算。由于高度压缩和刚性的阴离子骨架,取代Cs格位的Eu2+在InGaN基紫外LED的激发下,发出了明亮的绿色荧光,半峰宽为55 nm.当温度升高到190℃时,CKNLLSO:Eu2+的稳定性仍然较好。采用浓度优化的CKNLLSO:4%Eu2+制成的LED器件发出的绿光的色坐标为(0.2320, 0.6016),相关色温为7314K。分析结果表明,这种荧光粉是一种很有前景的白光LED绿色荧光粉。
分类: 材料科学 >> 电子、光学、磁材料 提交时间: 2017-03-29
摘要: The phase transformation in two modes, including both displacive and massive growth of τ-phase from ε-MnAl(C), was in situ observed. Temperature dependence of magnetization curves of MnAl(C) under magnetic field were employed for the first time to determine the triggering temperatures of different phase transformation modes. The displacive growth of ε→τ in MnAl(MnAlC) occurs at temperatures below 650 K(766 K), above which both modes coexist. One third or less of the ε-phase can be transformed into τ via displacive mode while the remaining two thirds or more via massive mode. Most large τ-grains formed via massive mode are actually containing a large number of well-distributed τ-nanocrystallline formed via displacive mode. The typical massive growth rate of the τ-phase is 8-60 nm/s, while the displacive growth rate is quite low. The doping of C to MnAl prevents the growth of ε-phase along the basal plane and thus increases the activation temperatures of the phase transformations and the decomposition of τ-phase. Pure τ-phase with highest magnetizations up to 118.3 Am2/kg was obtained. No decomposition was observed in τ-MnAl and τ-MnAl(C) after long-time annealing at selected temperatures, which are crucial in preventing the metastable τ phase from decomposition. These results provide a more complete understanding of the ε→τ phase transformations and thus facilitate the development of high-performance MnAl-based magnets.