Electric field driven phase transition and possible twining quasi-tetragonal phase in compressively strained BiFeO3 thin films

Highly compressively strained BiFeO₃ thin films with different thickness are epitaxially grown on (001) LaAlO₃ substrates and characterized using various techniques. The quasi-tetragonal phase with a giant axial ratio of ?? 1.25 and its thickness-dependent evolution are investigated. An interesting twining structure of the quasi-tetragonal phase is evidenced in thicker films through detailed reciprocal space mapping, which becomes more pronounced with increasing film thickness. Moreover, an interesting electric-field driven phase transition was evidenced in the film with a thickness of 38 nm, in which the quasi-tetragonal and rhombohedral phases are close to each other in energy landscape.     

C轴压力下ZnO晶体结构及电子性质的第一性原理研究

本文采用基于密度泛函理论(DFT)的第一性原理方法对ZnO晶体在c轴取向压力作用下的晶体结构、电子结构的变化进行了研究.结果表明,当压力在0～6 GPa区间时,晶格参数呈线性变化,带隙随压力增大而增大,显示弹性应变特征;当压力从6 GPa增大到10 GPa的过程中,晶体结构有了较大变化,出现了介于常压下纤锌矿结构和等静压高压下NaCl结构之间的类石墨结构(Graphitelike structure).伴随着这一结构相变,ZnO的晶格参数,能隙和态密度等电子结构出现了较大跃变.     

A note on a generalized circular summation formula of theta functions

In this note, we make a correction of the imaginary transformation formula of Chan and Liu?s circular formula of theta functions. We also get the imaginary transformation formulaes for a type of generalized cubic theta functions.     

Manipulating surface plasmon waves by transformation optics: Design examples of beam squeezer, bend, and omnidirectional absorber

We present several design examples of how to apply the transformation optics and curved space under coordinate transformation to manipulating the surface plasmon waves in a controlled manner. We demonstrate in detail the design procedure of the plasmonic wave squeezer, in-plane bend and omnidirectional absorber. We show that the approximation method of modifying only the dielectric material of a dielectric-metal surface of the plasmonic device could lead to acceptable performance, which facilitates the fabrication of the device. The functionality of the proposed plasmonic device is verified using three-dimensional full-wave electromagnetic simulations. Aiming at practical realization, we also show the design of plasmonic in-plane bend and omnidirectional absorber by an alternative transformation scheme, which results in simple device structure with a tapered isotropic dielectric cladding layer on the top of the metal surface that can be fabricated with the existing nanotechnology.     

六元瓜环与二氯化-1,8-二(2-苯并咪唑基)辛烷的自组装模式

采用¹H NMR、 荧光光谱和紫外吸收光谱法考察了主体六元瓜环与合成客体二氯化-1,8-二(2-苯并咪唑基)辛烷的自组装模式. 结果表明, 六元瓜环能与二氯化-1,8-二(2-苯并咪唑基)辛烷发生相互作用, 瓜环包结客体分子的苯并咪唑基团, 烷基链置于瓜环端口外侧. 自组装模式与主客体的摩尔比密切相关. 当主客体的摩尔比为1:1时, 1个瓜环包结客体分子的一端苯并咪唑基团形成棒槌形的包结配合物; 当主客体的摩尔比为2:1时, 2个瓜环分别包结客体分子的两端苯并咪唑基团形成哑铃型的主客体包结配合物.     

黑小麦麦麸戊聚糖的部分酸水解特征与甲基化分析

研究了黑小麦麦麸戊聚糖(AEPH)的部分酸水解特征及其糖链的取代度和取代方式等结构信息. 分别采用0.02, 0.1和0.2 mol/L的三氟乙酸(Trifluoroacetic acid, TFA)对AEPH进行部分酸水解, 结合甲基化分析、 GC-MS和HPLC等方法对AEPH的糖链结构和相对分子质量分布进行了分析. 结果表明, 戊聚糖AEPH的糖残基主要由阿拉伯糖(Araf)和木糖(Xylp)组成. 其取代度(A/X), 即Araf与Xylp的比值为0.60, 并具有较高的相对分子质量(M_w=3.81×10⁵). AEPH的主链由Xylp残基通过1→4连接形成木聚糖. 主链Xylp在O2, O3或O2/O3位被Araf单取代或双取代. 非取代(u)、 单取代(m)和双取代(d)Xylp残基的组成比例为57.7∶22.0∶6.2. 非取代与取代Xylp的比值为2.1, 双取代与单取代Xylp比值(d/m)为0.3. Araf主要以非还原性末端T-Araf以及通过1→2和1→5连接形成低聚阿拉伯糖的形式与主链Xylp相连, 或与T-Xylp相连形成戊聚糖分子的支链.     

过渡区p型氢化硅氧薄膜结构和光电特性的研究

采用射频等离子体增强化学气相沉积技术,利用二氧化碳(CO_2)、氢气(H_2)、硅烷(SiH_4)和乙硼烷(B_2H_6)作为气源,制备出一系列p型氢化硅氧薄膜.利用拉曼光谱、傅里叶变换红外光谱和暗电导测试,研究了不同二氧化碳流量对薄膜材料结构和光电特性的影响,获得了从纳米晶相向非晶相转变的过渡区P层.研究表明:随着二氧化碳流量从0增加到1.2 cm~3·min~(-1),拉曼光谱的峰值位置从520 cm~(-1)逐渐移至480 cm~(-1).材料红外光谱表明,随着二氧化碳流量的增加,薄膜中的氧含量逐渐增加,氢键配置逐渐由硅单氢键转换为硅双氢键.P层SiO:H薄膜电导率从3S/cm降为8.3×10~(-6)S/cm.所有p型SiO:H薄膜的光学带隙(Eopt)都在1.82—2.13 eV之间变化.在不加背反射电极的条件下,利用从纳米晶相向非晶相转变的过渡区P层作为电池的窗口层,且在P层和I层之间插入一定厚度的缓冲层,制备出效率为8.27%的非晶硅薄膜电池.     

Ferroelectricity in a diatomic Ising chain as investigated by the elastic Ising model

An elastic Ising model for a one-dimensional diatomic spin chain is proposed to explain the ferroelectricity induced by the collinear magnetic order with a low-excited energy state. A statistical theory based on this model is developed to calculate the electrical and magnetic properties of Ca₃CoMnO₆, a typical quasi-one-dimensional diatomic spin chain system. The calculated ferroelectric polarization and dielectric susceptibility show a good agreement with recently reported data on Ca₃Co_2-xMn_xO₆ (x ≈0.96) (Phys. Rev. Lett. 100 047601 (2008)), although the predicted magnetic susceptibility does not coincide well with experiment. We also address the rationality and deficiency of this model by including a first-order correction which improves the consistency between the model and experiment.     

固相燃烧法制备去顶角八面体LiZn0.08Al0.01Mn1.91O4正极材料及其电化学性能

通过固相燃烧法快速合成了包含{111}、{100}和{110}晶面的单晶去顶角八面体形貌LiZn_0.08Al_0.01Mn_1.91O₄正极材料。结果表明,Zn-Al共掺促进了尖晶石型LiMn₂O₄材料的晶体发育和晶面择优生长,形成了单晶去顶角八面体形貌晶粒,有效抑制了Jahn-Teller效应,减缓了Mn溶解,增强了其晶体结构稳定性,显著提升了合成材料的电化学性能。Li Zn_0.08Al_0.01Mn_1.91O₄在5C和10C下的首次放电比容量分别为92.6和76.5 mAh·g^-1,经过2 000次循环后的容量保持率分别为70.4%和74.8%。即使在15C高倍率下,仍有64.2 m Ah·g^-1的首次放电比容量,循环800次后容量保持率达到82.2%。与LiZn_0.08Mn_1.92O...