Fabrication and Induction Mechanism of Piezoelectric PVDF Micro/Nano-Fibrous Membranes by Electrospinning

聚偏氟乙烯(Polyvinylidenefluoride,PVDF)是目前唯一获得广泛应用的柔性压电材料，也是迄今为止发现的压电性最高的聚合物材料。PVDF至少存在五种晶相，即α、β、γ、δ和ε相，其中以β相的压电性能最好而引起人们的广泛关注。拉伸极化是获得PVDF压电薄膜的最基本工艺，但传统的冷拉伸高温强电场极化难以实现高含量β相，且存在工艺复杂、耗时、浪费资源等缺点，限制了其应用范围。静电纺丝是一个兼有机械拉伸和电极化一体化的技术，近年来已成为制备PVDF压电薄膜的研究热点。然而，要实现高性能PVDF压电薄膜的制备，必须解决静电纺丝的各项制备参数对PVDF膜的影响、其晶相变化规律及压电β相...The influences of key electrospinning parameters on electrospun PVDF membranes and their crystalline phases are systematically investigated. The method of Fourier Transformation Infrared (FTIR) in conjunction with X-Ray Diffraction (XRD) is adopted to analyse the membrane phases and the piezoelectric β and γ phases are successfully identified. The polymer solution concentration, solvent component ...学位：工学博士院系专业：物理与机电工程学院机电工程系_精密仪器及机械学号：1992009015365

Research Progress on SiCBased Composite Ceramic Prepared Through a SingleSourcePrecursor Route

在碳化硅(SiC)陶瓷中引入异质元素可赋予其更优异的性能,如良好的热稳定性和独特的电磁性能。采用单源聚合物先驱体法制备陶瓷,通过合成不同结构的单; 源聚合物先驱体,可在原子尺度设计、调控陶瓷的组成和微结构等方面,达到优化陶瓷性能的目的。根据近年来的研究成果,介绍了单源聚合物先驱体制备Si-B; -C、Si-M-C (M=Ti, Zr, Hf)和Si-M-C (M=Fe, Ni)复相陶瓷的研究动态,并展望了其今后的发展趋势。The introduction of heterogeneous elements into SiC ceramics can endow; the ceramics with more excellent performances, such as high temperature; stability and unique electromagnetic properties. When preparing ceramics; through a single-source-precursor route, the composition and; microstructure of ceramics can be designed and tailored by tuning the; architecture of single-source-precursors at the atomic scale for; optimizing the ceramic performance. The research trends on Si-B-C,; Si-M-C (M = Ti, Zr, Hf) and Si-M-C (M=Fe, Ni) ceramic composites derived; from a single-source-precursor route were elaborated according to the; research achievements in recent years, meanwhile, its development trend; in the future was discussed.福建省自然科学基金; 华侨大学2016年实验教学改革与建设课

Fabrication and Characteristics of InGaN Solar Cell

Ⅲ族氮化物宽禁带材料的研究与应用是目前半导体行业的前沿和热点，主要包括GaN、InN、AlN及其三元和四元合金(InGaN，AlGaN，InAlN和AlInGaN)。其中InGaN材料以其优越的光伏特性，迅速成为近年来国际上的研究热点。它具有连续可调的宽带隙（0.65eV~3.42eV），其吸收光与太阳光谱几乎完美匹配，在整个组分范围内均为直接带隙材料，还具有高电子迁移率、高吸收系数、高硬度、强抗辐射能力等优点，在发展高效多节电池和空间太阳能电池上具有广阔的应用前景。本文围绕电池性能，在外延材料生长、结构设计、器件制作、性能表征等多方面进行了系统深入的研究，主要工作内容包括以下几个方面： （1）制作的低In组分InxGa1-xNp-i-n同质结（HOJ）太阳能电池具有良好的光电响应特性，x=0.02电池的开路电压（Voc）和填充因子（FF）分别高达2.24V和69%。进一步研究表明，随着In组分的提高，短路电流密度（Jsc）变大，而Voc却急剧减小，且下降幅度远大于材料带隙引起的减小量。通过多种表征手段深入分析了此现象的内在机理，提出高In组分样品中高密度缺陷是导致Voc降低的重要因素，提高材料质量是关键。 （2）结合外量子效率（EQE）响应谱，分析了p-GaN厚度对电池高能光子响应的重要影响，并阐明窗口层设计方面应侧重考虑的问题。 （3）研究光强和温度对电池性能的影响。随着光强增大，Jsc呈线性增大，Voc呈对数式增大，而FF及η因受串联电阻影响先增大后减小。温度升高电池性能总体变差，表现为Voc和η随温度升高而降低。 （4）基于HOJ电池的研究基础，改进结构制作异质结（HEJ）电池，并对比了具有相同耗尽区宽度的HOJ和HEJ电池，发现HEJ电池在制备高质量高In组分的InGaN吸收层，降低串联电阻，提高入射光的吸收，调制光谱响应等方面具有明显的优势，为InGaN太阳能电池的发展提供新思路。 （5）设计、制备三种不同电流扩展层（CSL）的In0.135Ga0.865N/GaN太阳能电池，并对比研究它们的性能。结果表明，CSL对电池性能影响很大，以ITO-L电池性能最佳。入射光的吸收和光生载流子的收集存在此消彼长的关系，合理设计找寻二者的平衡点以及提高p型掺杂均至关重要。 （6）制作InGaN/GaN多量子阱结构太阳能电池，其响应谱拓展到500nm以上，添加Al反射镜的电池转换效率达到0.335%。进一步研究不同垒厚对载流子输运的影响，结果表明减小垒厚可增大遂穿几率，提高光生载流子的收集，但也可能引起Voc变小。此外，还研发设计了垂直结构InGaN太阳能电池，并提出了多量子阱结构太阳能电池效率的改善途径。 （7）针对高效多节电池所需子电池的带隙，以及MOCVD生长中InN的高挥发性和NH3的低分解率问题，采用MBE外延高In组分InGaN薄膜。研究表明增大In的流量比r（r=In/(In+Ga)），可提高薄膜In的结合率，调整Ⅲ、Ⅴ族源流量，可避免In液滴形成并快速提高In的组分，甚至获得更高质量的外延膜，此外，较低的生长温度也有利于In结合，这些工作对将来高In组分电池的研究具有重要意义。The group III nitride alloys and their application have become a hot research field in the semiconductor industry. Normally, they include GaN, InN, AlN and their ternary alloys (InGaN, AlGaN, InAlN) or quaternary alloys (AlInGaN). Recently, the InGaN alloy has attracted much attention due to its excellent photovoltaic properties. This alloy is of tunable direct bandgap (0.65 eV ~ 3.42 eV), with high carrier mobility, high absorption coefficient, high hardness, and superior radioresistance, and also showing the best match to the solar spectrum. The above properties promise to gain bright future of development of high-efficiency tandem cells and space solar cells (SCs). The present study concentrates on the solar cell performance and systematically investigates epitaxial growth, structural design, device fabrication, and performance characterization, etc. Main works are as follows: (1) The fabricated InxGa1-xN p-i-n homojunction (HOJ) SCs with low In content show excellent photoelectric response characteristics, e.g. when x = 0.02, an open circuit voltage (Voc) of 2.24 V and a fill factor (FF) of 69% are obtained. Further experiments on the cell performance depend on the In content reveal that with increasing In content, the short-circuit current density (Jsc) increases, but Voc decreases dramatically with a much larger value than the bandgap resulting reduction. Based on various characterization techniques, we investigated the possible mechanism and proposed that high density defect caused by high In content is the main reason for the dramatic Voc decrease, and the key is to improve the material quality. (2) Based on external quantum efficiency (EQE) spectra, we analyzed the effect of p-GaN layer thickness on the high-energy photon response and elucidated special references for the window layer design. (3) Law for the effect of light intensity and temperature on the cell performance. When light intensity is increased, Jsc increases linearly and Voc increases logarithmically; however, both FF and η first increase and then decrease due to the existing series resistance. On the other hand, with increasing temperature, the overall performance of the cells become worse, as suggested in Voc and η decrease. (4) Enlightened by HOJ SCs, we fabricate heterojunction (HEJ) SCs. Through comparison of HOJ and HEJ SCs, both having the same depletion width, we proposed that HEJ structure is a good alternative candidate for InGaN SCs. Because HEJ SCs show distinct advantages, such as growing high-quality InGaN absorption layer with high In content, reducing series resistance, improving the absorption of incident light, and modulating spectral response. (5) We have designed and fabricated In0.135Ga0.865N/GaN SCs with three different current spreading layers (CSLs). Results show that the cell with ITO layer type (ITO-L) presents the best performance. Also, there is a reciprocal relationship between the absorption of incident light and the collection of photo-induced carrier, suggesting that the importance of balance of the both and the p-type doping. (6) We also fabricate InGaN/GaN multiple quantum well SCs, whose response spectra expand above 500 nm. By adding Al-reflector, a conversion efficiency of 0.335% is obtained. Further study on barrier thickness and carrier transport suggests that thinning the barrier thickness increases the tunneling probability and improving the photo-induced carrier collection, but also result in the Voc reduction. Besides, we also develop the vertical structure InGaN SCs and put forward approaches for the efficiency improvement. (7) Aiming at the bandgap requirement for high efficiency tandem SCs, and high volatility in InN growth by MOCVD and the resulting low decomposition of NH3, we introduce MBE epitaxy to grow high In content InGaN films. Results show that increasing In flux ratio (r=In/(In+Ga)) and/or selecting low growth temperature can improve the combining rate of In, and by adjusting the ratio of group III and V sources, can avoid the In droplets formation such that improve the In content.学位：工学博士院系专业：物理与机电工程学院机电工程系_精密仪器及机械学号：1992009015365

Determining Sediment Concentration in Runoff Flow with γ Ray Attenuation and the Related Theoretical Algorithm

首次尝试采用 γ射线透射法测量土壤侵蚀径流中的含沙量。用两种不同土壤 (黄绵土、粘土 )、三种含沙量增量 (3%、5 %、10 % )和三种测量时间 (6 s、10 s、2 0 s)进行了含沙量测量实验 ,以验证用 γ射线测量泥沙含量的可行性、确定泥沙含量对 γ射线的响应特性。并推导了根据 γ射线透射强度计算含沙量的理论计算公式。将实验结果与理论计算值进行对比 ,以检验理论计算的准确性和测量实验与理论计算的一致性。结果表明 ,γ射线透射通过泥沙溶液的强度与水流含沙量间有极度显著的线性相关关系 ,并与理论计算结果高度一致 ,表明可由 γ射线透射强度稳定、可靠、准确地确定含沙量

我国农村废弃物分类资源化利用战略研究

本文围绕我国农村废弃物分类资源化利用问题，论述了农村废弃物的产生、危害以及资源化利用的重要意义，评估了我国农村废弃物的产生量、地区分布特征及资源化利用情况，深入分析了农村废弃物资源化利用存在的突出问题，结合美丽乡村建设及农村废弃物资源化利用的发展趋势，制定了农村废弃物资源化利用的发展战略及分阶段目标，提出了我国未来农村废弃物资源化开发利用的保障措施和政策建议

A Study on the Classification and Resource Utilization of Rural Waste in China

本文围绕我国农村废弃物分类资源化利用问题,论述了农村废弃物的产生、危害以及资源化利用的重要意义,评估了我国农村废弃物的产生量、地区分布特征及资源化利用情况,深入分析了农村废弃物资源化利用存在的突出问题,结合美丽乡村建设及农村废弃物资源化利用的发展趋势,制定了农村废弃物资源化利用的发展战略及分阶段目标,提出了我国未来农村废弃物资源化开发利用的保障措施和政策建议