介质阻挡放电斑图中放电通道的相互作用研究

在近大气压介质阻挡放电中，研究了六边形斑图的空间波长随放电参数的变化，仔细观察了稳定的六边形中放电通道的产生及运动行为.结果表明空间波长随电压增加而减小，变化曲线与放电间隙和气压有关.电压升高，边界处生成新的放电丝，位于六边形最外层顶点处新生成的放电丝沿径向运动，而位于六边形边长上新生成的放电丝的运动方向平行于距其最近的C₂轴(过六边形顶点). 继续升高电压，放电丝变为条状进而形成螺旋波或靶波.在观察实验结果和分析放电丝受力的基础上，认为放电区域可能存在一种类似二维库仑晶体中存在的约束势. 关键词： 介质阻挡放电 斑图 放电通道 约束势     

大气压氩气介质阻挡放电中的四边形斑图和六边形斑图

在大气压氩气介质阻挡放电中，研究了斑图形成随放电条件的变化.观察到随电压的增加，斑图经历六边形—四边形—具有辉光背景的四边形—具有辉光背景的六边形的转变过程.其空间波长与放电丝密度也随之改变.在一定的放电条件下，斑图涌现出辉光背景，此时空间波长与放电丝密度保持不变，但放电丝每半周期放电脉冲数由一次变为两次. 关键词： 介质阻挡放电 四边形斑图 六边形斑图 空间波长     

大气压介质阻挡放电中的自组织斑图结构

采用水作为电极,对大气压介质阻挡放电中的自组织斑图结构进行了研究,观测到了规则的斑图结构(包括准六边形斑图和条带状斑图)和不规则的斑图结构.实验发现斑图中放电丝的密度随着电介质层厚度的增加及放电气隙宽度变大而减小,而随外加电压及频率增大而增大.采用空间相关函数的方法分析了准六边形斑图结构中的放电丝分布与驱动电源电压的关系 关键词： 介质阻挡放电 自组织斑图 放电丝密度 空间相关函数     

氩气/空气介质阻挡放电自组织超六边形斑图实验研究

采用双水电极介质阻挡放电装置,在氩气/空气混合气体放电中,在三种边界条件下得到了一种新型的超六边形斑图.给出了超六边形斑图的傅里叶变换及其不同模强度随旋转角的变化.实验测量了超六边形斑图随空气含量和外加电压变化的相图.研究了超六边形斑图的时空动力学,发现超六边形斑图是由两套子结构嵌套而成.在四边形边界条件下,研究了放电面积的大小对斑图模式选择的影响.发现超四边形斑图的形成受边界条件影响很大,而超六边形斑图则是自组织的结果. 关键词： 介质阻挡放电 超六边形斑图 时空动力学 边界条件     

介质阻挡放电系统中超四边形斑图形成的实验研究

采用水电极介质阻挡放电装置,在氩气和空气的混合气体放电中,对超四边形斑图的形成进行了实验研究.发现随着外加电压的升高,斑图类型经历了四边形斑图、准超点阵斑图、超四边形斑图、条纹斑图或六边形斑图的演化顺序.对这些斑图进行了傅里叶谱分析,得到了空间模式随电压的变化关系.此外,在外加电压升高的过程中,出现了具有不同空间尺度的两种超四边形斑图,它们满足不同的驻波条件.分析了壁电荷在超四边形斑图形成中的作用.实验测量了斑图类型随气隙间距和外加电压变化的相图以及超四边形斑图随气隙间距和气隙气压变化的相图.测量了击穿电 关键词： 介质阻挡放电 斑图 壁电荷 放电参量     

介质阻挡放电六边形斑图稳定过程的光谱研究

采用发射光谱法,首次研究了等离子体参数及激发状态对介质阻挡放电六边形斑图稳定性的影响。在氩气/空气混合气体的介质阻挡放电中,随着电压的升高,放电丝直径增大,六边形斑图逐渐稳定,同时放电颜色由紫色逐渐变为灰白色,说明其等离子体状态及参数可能发生了变化。测量了六边形斑图放电过程中氮分子谱线和氩原子谱线相对于氩原子763.51 nm的相对强度、分子振动温度和电子激发温度随外加电压的变化。结果发现：氮分子谱线相对强度随电压增加而降低,氩原子谱线相对强度却升高;分子振动温度与电子激发温度均随电压增加而增大。这些现象表明：随着电压增大,电子能量增加。由此,氩原子激发增多,放电丝直径增大,介质表面上沉积的壁电荷面积增大,放电丝之间的相互作用增强,六边形斑图趋于稳定。     

大气压氩气放电六边形斑图的电子激发温度研究

采用特殊设计的气体介质阻挡放电实验装置,对大气压氩气放电六边形斑图的放电信号及激发光谱进行了测量。采用发射光谱强度比法,计算了放电丝呈六边形斑图时的电子激发温度。实验发现,随着驱动电压频率的升高,六边形斑图的电子激发温度明显升高,各放电通道之间的放电时间相关程度提高。该工作对控制斑图的形成和研究斑图动力学具有重要参考价值。     

介质阻挡放电丝结构转变中的缺陷研究

在介质阻挡放电中,对放电丝结构从四边形向四边形格子态结构转变中的缺陷进行了研究.实验发现,在四边形向四边形格子态结构的转化中,存在两种缺陷:角缺陷及错位缺陷.为了研究缺陷的形成机理,实验测量了四边形格子态结构中不同放电丝的发光信号,结果发现八边形晶胞的中心放电丝发光强度强于边缘放电丝发光强度.通过引入准势场,研究了放电丝之间的相互作用及其对放电丝结构转变的影响,并由此分析了在转变过程中出现的缺陷,结果与实验符合得很好. 关键词： 介质阻挡放电 角缺陷 错位缺陷 超四边格子态     

介质阻挡放电丝模式和均匀模式转化的特性

利用水电极介质阻挡放电装置,采用电学方法和发射光谱,研究了空气中介质阻挡放电从微放电丝模式向均匀放电模式转化的过程. 结果表明,大气压下增大外加电压或者电压一定减小气压,放电都能够从微放电丝模式过渡到均匀模式. 高气压下放电为流光击穿而低气压下为辉光放电. 利用放电发射光谱,研究了高能电子比例随实验参数的变化. 结果表明气压减小时高能电子比例增大,电压增加时高能电子减少. 利用壁电荷理论对以上实验结果进行了定性分析. 结果对介质阻挡均匀放电的深入研究具有重要价值. 关键词： 介质阻挡放电 光学发射谱 微放电丝 均匀放电模式     

介质阻挡放电丝模式和均匀模式转化的特性

利用水电极介质阻挡放电装置，采用电学方法和发射光谱，研究了空气中介质阻挡放电从微放电丝模式向均匀放电模式转化的过程. 结果表明，大气压下增大外加电压或者电压一定减小气压，放电都能够从微放电丝模式过渡到均匀模式. 高气压下放电为流光击穿而低气压下为辉光放电. 利用放电发射光谱，研究了高能电子比例随实验参数的变化. 结果表明气压减小时高能电子比例增大，电压增加时高能电子减少. 利用壁电荷理论对以上实验结果进行了定性分析. 结果对介质阻挡均匀放电的深入研究具有重要价值.     

Parameter analysis of chaotic superlattice true random number source

Superlattices in chaotic state can be used as a key part of a true random number generator. The chaotic characteristics of the signal generated in the superlattice are mostly affected by the parameters of the superlattice and the applied voltage,while the latter is easier to adjust. In this paper, the model of the superlattice is first established. Then, based on this model,the chaotic characteristics of the generated signal are studied under different voltages. The results demonstrate that the onset of chaos in the superlattice is typically accompanied by the mergence of multistability, and there are voltage intervals in each of which the generated signal is chaotic.     

Structure and orientational ordering of nitrogen molecules physisorbed on graphite

The structure and orientational ordering of nitrogen molecules physisorbed on graphite have been studied by low-energy diffraction (LEED). A two-sublattice in-plane herringbone structure with glide lines along two perpendicular directions is inferred from LEED patterns at T < 30 K from the monolayer where the molecular centers have the commensurate $\text{(}\text{3}\text{×}\text{3}\text{)}$ 30° structure. The orientational order-disorder transition of this commensurate phase was examined by superlattice spot intensity and angular profile measurements for 20 < T < 38 K. A rapid drop in superlattice intensity is observed near 27 K. The persistence of some intensity to 38 K. is suggestive of residual short-range orientational ordering and perhaps finite size or heterogeneity effects. For increasing coverage at T = 15 K, there is first a transition to a previously unobserved uniaxial incommensurate phase and then a transition to an apparently triangular incommensurate phase. The orientational superlattice spots are clearly present in the uniaxial phase, but are much weaker in the triangular incommensurate phase. At 31 < T < 35 K, an apparently triangular incommensurate phase with no detectable orientational superlattice spots is observed. The lattice constant versus equilibrium vapor pressure curve has been determined in the latter case assuming a continuous transition. The lattice constants of the incommensurate phases are used to place limits on the extent of possible phase-coexistence regions between the commensurate, uniaxial incommensurate, and triangular incommensurate phases. The LEED patterns from the bilayer at T = 15 K indicate a double-period superlattice structure of the triangular incommensurate phase which does not have the glide line symmetries of the commensurate monolayer. Some effects of heterogeneity on these phase transitions are discussed. A phase diagram for 10 < T < 40 K is proposed.     

Spatial resonances and superposition patterns in a reaction-diffusion model with interacting Turing modes

Spatial resonances leading to superlattice hexagonal patterns, known as "black-eyes," and superposition patterns combining stripes and/or spots are studied in a reaction-diffusion model of two interacting Turing modes with different wavelengths. A three-phase oscillatory interlacing hexagonal lattice pattern is also found, and its appearance is attributed to resonance between a Turing mode and its subharmonic.     

超晶格相变的逾渗机制

把超晶格相变的哈密顿量写成Ising形式,由Ising模型与键逾渗间的对应关系,得到超晶格相变的短程序参量为P′=1-e^-2J/kT;由Monte-Carlo模拟定出L1₀结构的相变点为P′_bc=0.3436,L1₂结构的相变点为P′_bc=0.4924;建立了P′_bc与相应结构上普通键逾渗阈值P_bc间的关系P′_bcx=P_{b 关键词：}     

Hydrogen in Nb/Ta superlattices

The structural and thermodynamic properties of hydrogen dissolved in Nb/Ta superlattices are studied by in-situ x-ray scattering techniques. From the x-ray satellite intensities, it is found that H induces a strain modulation exhibiting a Curie-Weiss temperature dependence. The intensities are analyzed in terms of a mean field model of the modulated lattice gas, yielding quantitative information on the hydrogen-metal and hydrogen-hydrogen interaction energies. Critical behavior associated with a gas-liquid transition is also observed. Hydrogen density fluctuations with wavelengths shorter than a superlattice period are, however, suppressed by the superlattice, which represents a novel manifestation of a coherent phase transition. These experiments provide new and fundamental insight into the role of spacially varying two body interactions in critical phenomena.     

Microscopic neutron investigation of the Abrikosov state of high-temperature superconductors

Using small angle neutron scattering we have been able to observe for the first time a well-defined vortex lattice (VL) structure both in the hole-doped LSCO and electron-doped NCCO superconductors. Our measurements on optimally doped LSCO reveal the existence of a magnetic field-induced phase transition from a hexagonal to a square coordination of the VL. Various scenarios to explain such phase transition are presented. In NCCO also a clear square VL could be detected, which is unexpectedly kept down to the lowest measurable magnetic fields.      

Electron-lattice interaction and the CDW state of 1T-TiSe2

The electronic band structure in the CDW state (superlattice structure) of 1T-TiSe₂ is calculated on the basis of the band-type Jahn-Teller model by extending our theory of lattice instability in the normal phase. A strong coupling between the hole-band (Se p states) around the Λ point and the electron-bands (Ti d states) around the Λ points is caused by the electron-lattice interaction. Reflecting such a strong coupling remarkable changes appear in the dispersion curves near the Fermi energy and the largest CDW gap is obtained to be 0.2 eV. We have also calculated a change of the density of states near the Fermi energy due to the superlattice formation. The result is consistent with that observed by angle-integrated photoemmision by Margaritondo et al. It is also shown that the magnitude of the lattice distortion observed at low temperatures can be explained in a way consistent with the lattice dynamics in the normal phase.     

Ag掺杂氧化锌纳米材料的制备及高压相变拉曼光谱研究

宽禁带直接带隙半导体材料氧化锌（ZnO）,具有优异的光电性能、机械性能和化学特性。ZnO材料的结构对其性能影响较大,元素掺杂可改变ZnO晶体结构和带隙宽度,是提升ZnO材料性能的有效手段,当前常用Ag掺杂ZnO即为提高光催化反应效率。高压独立于温度、成分,是调控材料结构组织性能的重要手段,是产生新材料、发现新调控原理的重要因素。该研究通过对比纯ZnO晶体和Ag掺杂ZnO晶体的高压相变行为,揭示了元素掺杂对ZnO纳米晶体材料结构性能的影响。研究首先采用水热法辅助制备纯ZnO纳米微球和Ag掺杂ZnO纳米微球（1∶150Ag/ZnO）,表征结果显示水热法合成的纯ZnO和1∶150Ag/ZnO均为六角纤锌矿晶体结构,形貌均为几十纳米尺寸小颗粒堆积形成的微球,ZnO晶格常数随着Ag离子掺杂而变大,Ag掺杂导致ZnO晶格膨胀。随后应用金刚石压腔结合原位拉曼光谱技术测定了纯ZnO和Ag掺杂ZnO的高压结构相变行为。相比于纯ZnO拉曼峰,Ag掺杂ZnO的E₂（high）振动模式439 cm-1拉曼峰峰宽变窄,并呈现向低频方向移动的趋势,与无定形ZnO谱峰相近,表明Ag+取代Zn2+影响了Zn-O键,同时也影响了ZnO晶格结构的长程有序性。随体系压力增大,表征六角纤锌矿结构ZnO的拉曼特征峰439 cm-1出现瞬间弱化和宽化。压力增大至9.0 GPa时,纤锌矿结构ZnO拉曼特征峰439 cm-1消失,585 cm-1处出现新峰,ZnO晶体发生由六角纤锌矿向岩盐矿的结构转变。压力继续增大至11.5 GPa,新的拉曼峰显著增强,峰形变窄,同时向高波数方向移动,相变完成,岩盐矿结构ZnO性能稳定。1∶150 Ag/ZnO从六角纤锌矿结构到立方岩盐结构的相变压力为7.2 GPa,低于纯ZnO。相变压力降低表明晶体结构稳定性下降,可能的原因在于掺杂Ag导致ZnO晶格膨胀,晶体结构松弛,两相相对体积变化增加,从而导致相变势垒降低,使样品在较低压力下发生相变。纳米材料的高压研究揭示了元素掺杂对材料结构稳定性的影响,是纳米材料调控原理的潜在研究手段。