The study of optical,dielectric and optoelectronic properties of dodecylbenzene sulfonic acid doped polyaniline

Soluble polyaniline (PANI) doped with dodecylbenzene sulfonic acid (DBSA) was synthesized by chemical oxidation method and was cast on glass using homemade spray, a simple technology used for coating thin film in order to replace other costly complicated techniques. The PANI–DBSA was characterized by FTIR, XRD and UV–vis techniques. The TGA results illustrated that they are three major stages of weight loss of the PANI–DBSA sample. D.C. and A.C. study was performed by pelletizing the sample. D.C. conductivity obtained at room temperature was 3.753 × 10⁻³ S/cm. The A.C. conductivity and dielectric properties was analyzed in the frequency range 100–1000 kHz which indicates that the value of dielectric constant and loss tangent increases with increase in temperature and decreases with increase in frequency and in addition it supports the hopping mechanism. Current density–voltage (J–V) measurements was used to characterize ITO/PANI–DBSA/Al device. The value of various junction parameters such as ideality factor, barrier height and saturation current density was calculated.     

First-principles calculations of the dielectric and vibrational properties of ferroelectric and paraelectric BaAl2O4

First-principles calculations have been conducted to study the structural, dielectric, and vibrational properties of ferroelectric and paraelectric BaAl₂O₄. High-frequency and static dielectric constants, and phonon frequencies at the Brillouin zone center are reported. Both BaAl₂O₄ polymorphs are promising infrared-transparent materials due to their low electronic dielectric constants. The ferroelectric and paraelectric BaAl₂O₄ have much smaller permittivity compared to the classical ferroelectric materials. From an atomic nanostructure standpoint, the abnormally low permittivity of BaAl₂O₄ polymorphs is mainly related to low coordination numbers of Ba (9) and Al (4).     

Comparative Plasma Chemical Reaction Studies of CH4/Ar and C2Hm/Ar (m = 2,4,6) Gas Mixtures in a Dielectric Barrier Discharge

Plasma chemical reactions in CH4/Ar and C₂H_m/Ar (m = 2, 4, 6) gas mixtures in a dielectric barrier discharge at medium pressure (300 mbar) have been investigated. From mass spectrometry the production of H₂ and formation of larger hydrocarbons such as C_nH_m with up to n = 12 is inferred. Hydrogen release is most pronounced for CH₄ and C₂H₆ gas mixtures. Fourier Transform InfraRed (FTIR) spectroscopy reveals the formation of substituted alkane (sp³), alkene (sp²), and alkyne (sp) groups from the individual gases which are used in this work. Abundant formation of acetylene occurs from C₂H₄ and to a lesser extent from C₂H₆ and CH₄ precursor gases. The main reaction pathway of acetylene leads to the formation of large molecules via C₄H₂ and, eventually, to nano‐size particles. The experimental results are in reasonable agreement with simulations which predict a pronounced electron temperature and gas pressure dependency. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

叶片多角度偏振光谱特性影响因素的实验研究

通过测量绿萝、银杏、苹果三种叶片的多角度偏振光谱,采用斯托克斯矢量法计算了叶片的多角度光谱偏振度,并通过PROSPECT模型反演得到叶片的叶绿素、水分含量,进而分析了叶绿素、水分含量对叶片多角度光谱偏振度的影响,探索了观测几何条件与不同波段叶片偏振度间的关系。结果表明,相对于近红外波段,红光波段的偏振度受叶绿素含量变化的影响较小,而水分含量对这两个波段的偏振度基本均无明显影响。在反映叶片偏振度随观测几何变化方面,近红外波段较另外两个波段有着更好的敏感性和稳定性,但其偏振度值较另外两个波段偏小。     

基于半导体光放大器中非线性偏振旋转效应单一光缓存环全光时隙交换处理能力研究

对基于半导体光放大器(SOA)中非线性偏振旋转效应(NPR)效应的单一光缓存环多数据包的全光时隙交换(TSI)处理能力进行了理论和实验研究,在使用归纳法导出单一缓存环实现多数据包全光时隙(TSI)必要条件的基础上,针对各种全光TSI操作要求得出了相应光数据包的调度方案,在实验上,以基于SOA中NPR效应的单一光缓存环实验系统,开展了多数据包全光TSI操作的实验研究,根据上述光数据包理论调度方案进行相应系统参数设定,进行了速率为10 Gb/s的3个和4个数据包的全光TSI实验,实验结果与理论预期相符合,研究成果为减少昂贵SOA元件的用量、简化基于光缓存环全光TSI系统的结构提供了可靠依据,对推进全光TSI技术的发展具有重要意义。     

空位对纤锌矿型AlN自发极化影响的最大局域化Wannier函数方法研究

采用基于密度泛函理论的第一性原理平面波超软赝势方法,计算了纤锌矿型AlN中引入不同电荷态的N空位和Al空位时结构中最大局域化Wannier函数,并根据Wannier函数的空间分布及空间分布的几何中心位置,对空位引起的晶体电子结构变化及[0001],[ˉ1010],[ˉ12ˉ10]晶向上的自发极化进行了研究.结果表明,利用最大局域化Wannier函数分析电子结构具有直观的特点,清晰地表明N—Al键具有较强的离子性.研究发现,N空位结构中悬挂键上电荷向空位处转移,而Al空位结构中悬挂键上电荷则远离空位,沿悬挂键方向移动到N原子一侧.同时发现,空位的引入破坏了[ˉ1010],[ˉ12ˉ10]晶向上的中心对称结构,产生了极化,且极化强度随着空位电荷态的增加而增大.在[0001]晶向上,随着N空位电荷态的增加,空位周围电子结构发生了剧烈变化,使得自发极化发生了逆转,极化强度随着电荷态的增加而增大;而在Al空位中,随着电荷态的增加,自发极化沿原方向显著增加,但没有发生极化反转.     

基于焦斑空间频率全域优化的偏振匀滑设计

偏振匀滑是利用光束偏振特性降低焦斑对比度的一种技术,它最大可降低焦斑对比度为原来的1/√2. 焦斑的频谱分析显示,传统楔形晶体的偏振匀滑对焦斑对比度的改善只集中在某些特定的空间频率,本文因此提出了一种可全域降低焦斑空间频率的偏振匀滑方法,它采用单轴晶体对入射光的角度不同而产生的相移不同的方法,实现激光两种正交偏振态在靶点的分离. 理论分析和数值模拟表明,新方法可以实现焦斑空间频率中高频段的全频域降低,焦斑对比度也可同时达到1/√2的最大程度的改善. 分析了连续相位板作为新方法引入激光入射角分布不同的条件,确定了刻蚀连续相位板面形的晶体同时实现焦斑整形和偏振匀滑的边界条件. 关键词： 偏振匀滑 焦斑功率谱 响应函数 焦斑整形     

AlGaN合金中局域态和极化电场的竞争机制

通过MOVPE方法生长了不同Al组分的3块Al_xGa_1-xN样品,利用稳态光谱和时间分辨光谱对其样品的光学特性进行了分析。鉴于影响氮化物发光性质的极化电场或局域态的单一机制不能充分解释我们的实验现象,提出了局域态-内部极化电场竞争的机制。通过对实验数据的分析,得出如下重要结论：样品PL峰位蓝移的温度起点基本对应于局域态和极化电场起作用的交替点,PL峰位发生蓝移的温度起点与光强-温度曲线的斜率出现明显变化的温度点一致;随着温度的升高,若AlGaN合金样品中PL峰位存在二次蓝移,则说明样品中电场分布不均匀。     

多偏振飞秒激光制备彩色铁

采用四个不同偏振方向的线偏振和圆偏振态飞秒激光扫描处理金属铁表面来制备不同的彩色铁。从不同角度观察被处理区域时,线偏振扫描处理的彩色区域呈现不同的色彩,而圆偏振扫描处理的区域没有明显的颜色变化。扫描电子显微镜图片显示,线偏振激光扫描处理金属铁表面形成了nm量级的激光诱导周期表面结构,其方向始终与激光偏振方向垂直;圆偏振激光扫描处理金属铁表面形成的条纹结构不明显且有大量的纳米颗粒结构。