Monitoring the reaction between AICl3 and o-xylene by using terahertz spectroscopy

Terahertz time-domain spectroscopy （THz-TDS） is used to study the interaction between AlCl3 and o-xylene in a temperature range from 300 K to 368 K. For comparison, the three isomers of o-, m-, and p-xylene are measured by using THz-TDS. The o-xylene carries out isomerization reaction in the presence of catalyst AlCl3. The absorption coefficient of the mixed reaction solution is extracted and analyzed in the frequency range from 0.2 THz to 1.4 THz. The temperature dependence of the absorption coefficient, which is influenced by both the dissolution of AlCl3 and the production of the two other isomer resultants, is obtained, and it can indicate the process of the isomerization reaction. The results suggest that THz spectroscopy can be used to monitor the isomerization reaction and other reactions in chemical synthesis, petrochemical and biomedical fields.     

不同种类岩石的太赫兹光谱特征研究

准确认识不同种类的岩石特征对地质构造、结构与年代的判断至关重要。常规光学显微手段虽然可以对岩石的颜色与表面形貌进行直接观测,但是对岩石种类的判断往往凭靠经验,一些颜色相近的矿物容易混淆,所得结果并不准确。光谱方法能够在不同频段给出样品的多个光学参数信息,通过建立光学参数与样品自身物性的联系,可以从多个维度确定样品的性质,从而有望实现对不同矿物成分与含量定性、定量评价。太赫兹光谱具备一定的穿透能力,能够透过一定厚度的岩石,是研究岩石物理性质的合理手段。基于太赫兹光谱技术,对取自不同地区的花岗岩、灰岩、砂岩和油页岩样品进行测试,分别计算得到每个样品的等效折射率n、衰减系数a,并以a为横坐标、n为纵坐标作图,结果表明,相同岩性岩石的n与a基本呈线性相关关系,而对于不同类型的岩石,其n随a的线性变化趋势存在明显区别。进而研究了岩石中的组成、结构等信息与其太赫兹光谱响应的联系,分析了不同岩性岩石的光谱响应机制,结果表明：花岗岩与灰岩的结构较为致密,其矿物组成是影响太赫兹光谱响应的主要因素,利用太赫兹参数能够估算岩石中铁、镁元素的相对含量;砂岩的成分较为单一,太赫兹光谱响应受孔隙度的影响;而对于油页岩来说,由于有机质具有强吸收、低折射率的特点,其有机质含量越高,折射率越低,对太赫兹吸收越强。结果表明,太赫兹光谱技术有望成为岩石物理性质现有研究手段的合理补充,为其评价、分析提供新技术、新指标,有着极其光明的应用前景。     

基于二维相关中红外光谱技术的邻苯二甲酸二丁酯检测研究

利用二维相关红外光谱技术对正己烷中常用塑化剂邻苯二甲酸二丁酯(DBP)的浓度变化进行了检测研究。利用傅里叶变换红外光谱仪对溶于正己烷中的DBP进行检测,得到742,1 078,1 123,1 281,1 467,1 728,2 873,2 933和2 961cm~(-1)特征吸收峰。将红外光谱分为三个波段400~1 200,1 200~1 900和2 900~4 000cm~(-1),通过二维相关光谱分析技术得知在1 123cm~(-1)波段(苯环面外摇摆及O-—C—O单键伸缩运动)、1 728cm~(-1)(C—O双键的伸缩运动)、2 873和2 961cm~(-1)(CH3伸缩运动)以及3 436cm~(-1)(苯环C—H的面内伸缩运动)对DBP浓度变化比较敏感。结合红外光谱宏观指纹技术以及二维相关光谱分析方法,能够较准确的分析出正己烷中的DBP的浓度变化,为食品中塑化剂含量的检测以及研究塑化剂的迁移规律提供了新的思路和方法。     

火山岩的反射式太赫兹光谱成像实验研究

通过反射式太赫兹光谱成像系统获得火山岩表面的太赫兹时域光谱.提取火山岩不同位置扫描点的太赫兹时域光谱峰值,并与扫描点的位置坐标进行一一对应,得到反射式光谱投影图像.实验结果表明:在火山岩的孔隙处太赫兹波发生散射及衍射效应,孔隙处比其他处有更多损耗,太赫兹反射波的强度相差较为明显,因此可以利用反射式太赫兹光谱成像技术表征火山岩的孔隙形状和分布.     

Annealing Effect on Photovoltages of Quartz Single Crystals

We investigate the photovoltaic effects of quartz single crystals annealed at high temperatures in ambient atmosphere. The open-circuit photovoltages and surface morphologies strongly depend on the heating treatments. When the annealing temperature increases from room temperature to 900℃, the rms roughness of quartz single crystal wafers increases from 0.207 to 1.011 nm. In addition, the photovoltages decrease from 1.994μV at room temperature to 1.551 μV after treated at 500℃, and then increase up to 9.8μV after annealed at 900℃. The inner mechanism of the present photovoltaic response and surface morphologies is discussed.     

Heusler合金Mn2NiGa的第一性原理研究

运用基于密度泛函理论的投影缀加波方法研究了Heusler合金Mn₂NiGa的四方变形,对立方和四方结构的磁矩、电子结构、弹性常数及声子谱进行了计算和分析.Mn原子是Mn₂NiGa总磁矩的主要贡献者,但Mn（A）、Mn（B）原子磁矩的值不等且呈反平行耦合,因而Mn₂NiGa合金在两种状态下均表现为亚铁磁结构.四方变形中,Mn₂NiGa在c/a=0.94和c/a=1.27处出现总能的局域极小值和局域最小值,分别对应一个稳定的马氏体.弹性常数的计算结果显示,Mn₂NiGa的立方结构不满足立方相稳定性判据,四方结构（c/a=0.94和c/a=1.27）的弹性常数满足相应的稳定性判据.立方结构声子谱中存在虚频,而四方结构（c/a=0.94和c/a=1.27）则不存在虚频,验证了Mn₂NiGa四方结构比立方结构稳定.c/a=1.27的四方结构Mn₂NiGa转变为c/a=1.0的立方结构的相变温度在315 K左右.     

Simulation of Anisotropic Resistivity for Mixed-Phase Manganite La2／3Ca1／3MnO3 Thin Films

We utilize the random network model based on phase separation scenario to simulate the conductive behaviour and anisotropic characteristics of resistivity for La2/3Ca1/3MnO3 (LCMO) thin films. The simulated results agree well with our experimental data, showing a metal-to-insulator transition from a high-T paramagnetic (PM) insulating phase to a low-T ferromagnetic (FM) metallic phase in both the untilted film deposited on a (001) SrTiO3 (STO) substrate and the tilted film grown on a vicinal cut STO substrate. It is found that the resistivity of the tilted sample is higher than that of the untilted one, displaying prominent anisotropic characteristics. The studies reveal that the tilting not only decreases the conduction of the FM domains, but also increases the activation energy of the PM regions, inducing the enhancement of resistivity. All those results suggest that the intrinsic inhomogeneity in the phase separation system plays a significant role in the electrical conductivity and the resistive anisotropy is related to the structure of the crystal lattice.     

Ultraviolet photovoltaic characteristic of MgB2 thin film

Fast photoelectric effects have been observed in MgB₂ thin film fabricated by chemical vapour deposition. The rise time was $\sim $10 ns and the full width at half-maximum was \sim185\,ns for the photovoltaic pulse when the film was irradiated by a 308\,nm laser pulse of 25\,ns in duration. X-ray diffraction and the scanning electron microscope revealed that the film was polycrystalline with preferred c-axis orientation. We propose that nonequilibrium electron--hole pairs are excited in the grains and grain boundary regions for MgB₂ film under ultraviolet laser and then the built-in electric field near the grain boundaries separates carriers, which lead to the appearance of an instant photovoltage.     

Charge recombination mechanism to explain the negative capacitance in dye-sensitized solar cells

Negative capacitance(NC) in dye-sensitized solar cells(DSCs) has been confirmed experimentally. In this work, the recombination behavior of carriers in DSC with semiconductor interface as a carrier's transport layer is explored theoretically in detail. Analytical results indicate that the recombination behavior of carriers could contribute to the NC of DSCs under small signal perturbation. Using this recombination capacitance we propose a novel equivalent circuit to completely explain the negative terminal capacitance. Further analysis based on the recombination complex impedance show that the NC is inversely proportional to frequency. In addition, analytical recombination resistance is composed by the alternating current(AC) recombination resistance(Rrac) and the direct current(DC) recombination resistance(Rrdc), which are caused by small-signal perturbation and the DC bias voltage, respectively. Both of two parts will decrease with increasing bias voltage.     

Angle-sensitive and fast photovoltage of silver nanocluster embeded ZnO thin films induced by 1.064-μm pulsed laser

Silver nanocluster embedded ZnO composite thin film was observed to have an angle-sensitive and fast photovoltaic effect in the angle range from –90o to 90o, its peak value and the polarity varied regularly with the angle of incidence of the 1.064-μ m pulsed Nd:YAG laser radiation onto the ZnO surface. Meanwhile, for each photovoltaic signal, its rising time reached ～2 ns with an open-circuit photovoltage of ～2 ns full width at half-maximum. This angle-sensitive fast photovoltaic effect is expected to put this composite film a candidate for angle-sensitive and fast photodetector.