不同结构六边形斑图演化过程光谱特性

采用发射光谱法,研究了水电极介质阻挡放电中具有相同对称性的3种不同结构的六边形斑图演化过程的光谱特性。实验结果表明,随着外加电压的增加,放电首先形成六边形点阵斑图,然后是空心六边形斑图,最后是蜂窝六边形斑图。利用氩原子696.5 nm(2P_2→1S_5)谱线的展宽、氩原子763.2 nm(2P_6→1S_5)与772.1 nm(2P_2→1S_3)两条谱线强度比法和氮分子第二正带系(C~3Π_u→B~3Π_g)的发射谱线,研究上述3种斑图的电子密度、电子激发温度及分子振动温度。结果发现,随着外加电压的升高,六边形点阵斑图、空心六边形斑图和蜂窝六边形斑图的电子密度逐渐减小,而电子激发温度和分子振动温度逐渐增加。等离子体状态的改变直接影响着斑图的自组织。     

介质阻挡放电中超四边斑图沿面放电的光谱研究

利用水电极介质阻挡放电装置,在氩气和空气的混合气体中,首次观察到了超四边斑图沿面放电,它是由中心点和暗点组成的。通过观察普通相机的斑图照片,可以发现中心点位于周围四个暗点的中心处。利用高速录像机对斑图进行短曝光拍摄,观察发现中心点对应体放电,暗点对应沿面放电,暗点由这些沿面放电形成。中心点和暗点的亮度有所不同,这说明中心点和暗点的等离子体状态可能不同。采用发射光谱法,研究了超四边斑图沿面放电的的中心点和暗点的等离子体参量随氩气含量的变化趋势。利用氮分子第二正带系(C3Π_u→B3Π_g)发射谱线,计算得出了中心点和暗点的分子振动温度; 然后通过氩原子696.57 nm (2P₂→1S₅)谱线的展宽,研究了中心点和暗点的电子密度。实验结果表明： 在相同氩气含量下,暗点的分子振动温度和电子密度均高于中心点的相应等离子体参量; 在其他实验条件不变的情况下,随着氩气含量从90%增大到99.9%,中心点和暗点的分子振动温度和电子密度均逐渐增大。结果表明中心点和暗点的等离子状态不同,说明二者的放电机制可能不同。     

介质势垒放电(DBD)等离子体中NO荧光发射谱研究

利用介质阻挡放电 (DBD)等离子体技术对大气污染物NO分子进行了光谱研究 ,得到了低气压条件下放电等离子体在 2 1 0～ 2 80nm光谱范围内的荧光发射谱。该谱明显的表现为双峰结构 ,谱线均成对出现 ,强度分布符合Frank Condon原理 ,且最大峰值位置出现在 2 36nm处 ,将该组谱线归属为NO分子的A2 ΣA →X2 Π1 / 2 ,2 / 3 跃迁。荧光产生过程为 :基态NO分子与高能电子发生非弹性碰撞被激发至激发态A2 Σ 后自发跃迁回基态同时辐射出荧光。通过测量等离子体中NO分子和N2 分子 337nm谱线强度随时间的变化关系 ,初步证实了放电等离子体中存在的NO分子的分解机制为 :e NO→N O e,N NO→N2 O ,O NO→NO2 hν。     

LiF修饰阴极的双层有机电致发光器件的延时效应

基于载流子的注入、传输和复合过程,建立了双层有机发光器件的电致发光延时理论模型;讨论了电致发光延时随电压、注入势垒、内界面势垒、阳极区厚度及LiF缓冲层(BL)厚度的变化关系。结果表明:(1)低电压下,EL延时由复合过程主导,而高电压下,输运过程起着更重要的作用;(2)当δe/δh2时,M/O界面属于欧姆接触,电流是空间电荷限制的,注入势垒的变化对复合时间trec影响较大,当δe/δh2时,M/O界面成为接触限制,注入势垒的变化对trec几乎没有影响;(3)当内界面势垒超过0.3eV,H′h对trec的影响明显变弱,复合延迟时间基本上由电压和其它因素控制;(4)当电压较小时,随Lh/L的增大,trec增大;当电压超过某一值后,trec几乎不随Lh/L的变化而变化;(5)对于LiF/Ag阴极,在不同的偏压下,LiF的厚度在3.1nm左右时的复合时间最短,对应的EL延迟时间也最短,这与实验中从电致发光效率的角度得出的LiF最佳厚度一致。     

Double-ceramic-layer thermal barrier coatings based on La2(Zr0.7Ce0.3)2O7/La2Ce2O7 deposited by electron beam-physical vapor deposition

Double-ceramic-layer (DCL) thermal barrier coatings (TBCs) of La₂(Zr_0.7Ce_0.3)₂O₇ (LZ7C3) and La₂Ce₂O₇ (LC) were deposited by electron beam-physical vapor deposition (EB-PVD). The composition, interdiffusion, surface and cross-sectional morphologies, cyclic oxidation behavior of DCL coating were studied. Energy dispersive spectroscopy and X-ray diffraction analyses indicate that both LZ7C3 and LC coatings are effectively fabricated by a single LZ7C3 ingot with properly controlling the deposition energy. The chemical compatibility of LC coating and thermally grown oxide (TGO) layer is unstable. LaAlO₃ is formed due to the chemical reaction between LC and Al₂O₃ which is the main composition of TGO layer. Additionally, the thermal cycling behavior of DCL coating is influenced by the interdiffusion of Zr and Ce between LZ7C3 and LC coatings. The failure of DCL coating is a result of the sintering of LZ7C3 coating surface, the chemical incompatibility of LC coating and TGO layer and the abnormal oxidation of bond coat. Since no single material that has been studied so far satisfies all the requirements for high temperature applications, DCL coating is an important development direction of TBCs.     

Macrokinetic study on ozone boundary concentration. Effect of temperature

The process of ozone production in pure oxygen using the tubular, high voltage pulse supplied ozonizer was studied. The unusual methodology of conducting kinetics measurements of the ozone synthesis process was presented. It was shown how the process rate changes along the discharge gap. The effect of power density and gas residence time in the discharge gap on the process rate was analysed. The temperature influence on the course of the process, particularly on the ozone boundary concentration and ozone decomposition rate constant, was discussed.     

介质阻挡放电中的能量转换过程研究

研究了介质阻挡放电过程中的电流强度、电场强度以及电荷分布的演变规律，并对能量转换性质进行了分析.研究结果表明，在一个放电脉冲过程中，外加驱动电源所作的功、电场能量的增量均与起始时刻的壁电荷密度有关，而气体中放电电流所作的功即沉积于气体中的能量与起始时刻的壁电荷密度、放电电流的具体波形无关. 关键词： 介质阻挡放电 壁电荷 动力学过程 能量转换     

Internal transport barriers in plasmas with reversed plasma flow

Evidences of internal particle transport barriers have been observed in plasma discharges with reversed plasma flow. To investigate the influence of the radial electric field profile on these barriers, we apply a drift wave map that describe the plasma particle transport and allows the integration of particle drift in the presence of a given electrostatic turbulence spectrum. With this procedure we show that transport barriers due to the shearless flow invariant lines are created inside the plasma. Moreover, by varying the radial electric field profile, we observe the formation and destruction of internal transport barriers constituted by shearless invariant lines, as well as its effects on the transport in the map's phase space. Applicability of our results are discussed for the Texas Helimak, a toroidal plasma device in which the radial electric field can be changed by application of bias potential.     

双层钙钛矿La1.8Ca1.2Mn2O7磁性相关I-V非线性与电输运性质

采用传统固相反应法制备了双层钙钛矿结构锰氧化物La_1.8Ca_1.2Mn₂O₇陶瓷,并用X射线粉末衍射法,扫描电镜,HL5500PC Hall效应分析仪和综合物性测量系统(PPMS)对其磁、电性质进行了表征.结果表明:经过两次高温烧结可合成具有双层Sr₃Ti₂O₇型四方结构的La_1.8Ca_1.2Mn_2<     

砷化镓光电阴极光谱响应与吸收率关系分析

为了研究砷化镓(GaAs)光电阴极光谱响应与吸收率曲线间的关系,采用分子束外延法(MBE)和金属有机化合物化学气相沉积法(MOCVD)制备了两类GaAs光电阴极,并测试得到了样品吸收率和光谱响应实验曲线.对每个样品的这两条曲线在同一坐标系中做最大值归一化处理,将归一的光谱响应曲线与归一的吸收率曲线做除法,得到了类似光电阴极表面势垒的形状.结果表明,两种方法制备的光电阴极光谱响应曲线相比吸收率曲线都发生了红移,MBE样品偏移量稍大于MOCVD样品.短波吸收率不截止,光谱响应截止于500 nm左右;可见光波段上,光谱响应曲线的峰值位置相比吸收率曲线红移了几百meV;近红外区域,光谱响应曲线的截止位置相比吸收率曲线红移了几个meV.MOCVD样品中杂质对带隙的影响更小,光谱响应相比吸收率发生的能量偏移更小.这些结论对提高GaAs光电阴极光电发射性能有指导意义.