碳纤维微电极研究 ⅩⅩ.甲苯胺盐在碳纤维微盘电极上的电化学性质

研究了甲苯胺盐在碳纤维微盘电极上的电化学行为,探讨了pH 对甲苯胺盐电极反应过程的影响,确定在pH<3.7,3.75.5时,参与电极过程的H^+数分别为3,2和1,测定了甲苯胺盐的扩散系数及在碳纤维微盘电极上的电荷转移系数α,标准电子转移速率常数k^α和式量电位E^α,提出了不同pH下电极反应的机制.对甲苯胺盐在碳纤维微盘电极上的吸附性能进行了探索, 并测定了吸附控制条件下的动力学参数     

Jahn－Teller变形后C60－的结构和电子光谱

用INDO系列方法对C₆₀^－进行几何构型优化,得到D_3d对称性的构型,表明C₆₀^－确实发生了Jahn-Teller畸变,导致单键变短,双键变长,形成10种键,6种不等同碳原子,并以此构型为基础,计算了C₆₀^－的电子光谱,与实验结果吻合;同时对光谱进行了理论指认;最后对C₆₀^－的3种构型：D_5d,D_3d,D_2h的几何构型、能量、光谱和反应特性进行了分析、比较和总结。     

部分水解聚丙烯酰胺在海泡石上的吸附

研究了水解的聚丙烯酰胺(HPAM)在海泡石上的吸附及水解度, pH值和离子强度对吸附的影响, HPAM在海泡石上的吸附等温曲线发现属Langmuir型. 吸附能为-17到-20kJ/mol. 吸附量随HPAM水解度和pH的增长而减少, 随盐的浓度增大而增大.     

周期异方差时间序列的季节单位根检验

为检验带异方差的季节时间序列中的单位根,提出基于最小二乘估计的统计量.在原假设下得到检验统计量的极限分布.用M on te C arlo方法计算同方差下的经验分位数并考虑异方差对检验水平的影响.实例分析表明了用该方法检验季节单位根的有效性.     

[Au(PH_3)]~+芳香基发光材料的光谱性质研究

用二阶微扰(MP2)法和单激发组态相互作用(CIS)法分别优化了发光材料H3PAuPh和(H3PAu)2(1,4-C6H4)2的基态和激发态的几何结构,并用含时密度泛函(TD-DFT)法计算了各发光材料的吸收光谱与磷光发射光谱。计算结果表明,H3PAuPh和(H3PAu)2(1,4-C6H4)2的磷光发射光谱均具有在Au(6p)→C(2p)的金属向配体的电荷转移(MLCT)参与下的pπ*(Ph)→pπ(Ph)跃迁的本质,并伴有Au(6p)→Au(5d)的金属中心电荷转移(MCCT)的性质。(H3PAu)2(1,4-C6H4)2是由两个H3PAuPh连接而成的。因此(H3PAu)2(1,4-C6H4)2的分子轨道也是由H3PAuPh的分子轨道组合而成的。在磷光发射中,由于轨道组合中存在pπ*或pπ的相互作用,所以(H3PAu)2(1,4-C6H4)2的最低能量磷光发射光谱谱线的波长大于H3PAuPh的相应值。     

The virial theorem in refined Thomas－Fermi－Dirac theory for the interior of atoms in a solid

The virial theorem in refined Thomas－Fermi－Dirac theory for the interior of atoms in a solid is given and proven.     

The charge storage of the nc—Si layer

Sandwiched structures (a-SiN_x/a-Si/a-SiN_x) have been fabricated by the plasma enhanced chemical vapour deposition technique. A Si nanocrystal (nc-Si) layer was formed by crystallization of an a-Si layer according to the constrained crystallization principle after quasi-static thermal annealing at 1100℃ for 30 min. Transmission electron microscopy (TEM) and Raman scattering spectroscopy clearly demonstrated that nc-Si grains were formed in the as-deposited a-Si layer after annealing. The density of nc-Si grains is about 10¹¹cm^-2 as shown by TEM photographs. Using capacitance－voltage (C－V) measurements we investigated the electrical characteristics of the sandwiched structures. The charge storage phenomenon of the nc-Si layer was observed from the shift of flat-band voltage (V_FB) in C－V curves at a high frequency (1 MHz). We estimated the density of nc-Si grains to be about 10¹¹cm^-2 from the shift value of V_FB, which is in agreement with the result of TEM photographs. At the same time, we found that the shift of V_FB increased with the increase of the applied constant dc voltage or the thickness of the nc-Si layer.     

Investigation of the growth process of Si nanowires using the vapour－liquid－solid mechanism

Silicon nanowires have been grown by the thermal decomposition of silane via the vapour－liquid－solid (VLS) mechanism. Three different stages of VLS growth (eutectic alloy formation, crystal nucleation and unidirectional growth) were studied separately using a scanning electron microscope and a high-resolution transmission electron microscope. Very short silicon nanowires prepared under particular conditions provide direct evidence of the VLS mechanism on a nanometre scale. Our results will be very helpful for the controllable synthesis of Si nanowires.     

Second harmonic generation of propagating collective excitations in Bose－Einstein condensates

We consider a possible second harmonic generation (SHG) of propagating collective excitations in a two-component Bose－Einstein condensate (BEC) with repulsive atom－atom interactions. We show that the phase-matching condition for the SHG can be fulfilled if the wave vectors and frequencies of the excitations are chosen adequately from different dispersion branches. We solve the nonlinear amplitude equations for the SHG derived using a method of multiple-scales and provide SHG solutions similar to those obtained for a SHG in nonlinear optical media. A possible experimental realization of the SHG for the propagating collective modes in a cigar-shaped two-component BEC is also discussed.     

Nonlinear current－voltage characteristics of sintered tungsten－vanadium oxide

We have studied the densification behaviour, microstructure and electrical properties of WO_3 ceramics with V_2O_5 as the additive ranging from 0.5 to 15mol%. Scanning electron microscopic photos indicated that the grain size of WO_3－V_2O_5 specimens is smaller than that of pure WO_3. The addition of V_2O_5 to WO_3 showed a tendency to enhance the densification rate and to restrict the grain growth. Electrical properties of all specimens were measured for different electrodes at different temperatures. The formation of the grain boundary barrier layer was confirmed by the non-ohmic I－V behaviour. The nonlinear coefficient was obtained at the current density J=0.01, 0.1 and 1mA/cm^2 for a series of WO_3－V_2O_5 samples. The V0.5mol% specimen showed an abnormal phenomenon that the nonlinear characteristics appeared at 350℃ and disappeared at lower and higher temperatures. This implies that it could be applied as a high-temperature varistor. The double Schottky barrier model was adopted to explain the phenomena for the WO_3-V_2O_5 varistors.