室温铁磁性蒲公英状氧化锌的制备及生长机理研究

以锌粉、醋酸锌和氢氧化钠为原料,采用水热法制备出了具有结构性缺陷的蒲公英状ZnO。通过X射线衍射仪、扫描电子显微镜、荧光光谱仪和超导量子干涉仪对产物的结构形貌和光学性能及磁学性能进行了表征,并对其生长机理进行了探讨。研究表明,蒲公英状氧化锌为六方纤锌矿结构,由许多顶端为锥尖形的棒自组装而成;其荧光本征发射峰在388nm处,属于激子跃迁发射。在波长450～492nm处所观察到的3个弱蓝光峰是由锌填隙原子中的电子到价带顶的跃迁所致;在波长492～580nm范围内出现的较为宽泛的绿光发射峰根源于电子从导带底到氧错位缺陷能级间的跃迁。蒲公英状ZnO中存在的结构性缺陷使得原本呈现抗磁性的ZnO具有了室温铁磁性,从而可作为一种稀磁半导体应用到自旋电子学领域中。     

基于机会约束规划的主动配电网能量优化调度研究

主动配电网(Active Distribution Network)的产生对于加大可再生能源的消纳能力、提高用电互动化水平、实现配电网的灵活智能管理发挥着重要的作用,逐渐成为未来智能电网发展的重要方向。其中主动配电网能量管理系统(DMSs)作为主动配电网的最高决策中心,通过对各分布式电源的有效控制和调度,保障配电网的全局优化运行。为提高主动配电网运行的经济性和可靠性,通过对主动配电网能量优化调度技术进行分析,考虑到风力发电和光伏发电的不确定性,结合随机模拟技术和惩罚函数方法,基于机会约束规划建立了含有风力发电机、光伏发电单元以及储能装置的主动配电网能量调度随机数学模型。在满足各种约束条件的基础上,使用改进的粒子群算法求解该模型。并以某地区实际系统为算例,通过与标准粒子群算法进行比较,验证所提模型的正确性与有效性。     

Magnetic Behaviors of Ferromagnetic Semiconductor Zn1?xCrxTe Grown by MBE

The magnetic and structural properties of MBE-grown films of Zn_1–xCr_xTe were investigated. The magnetization versus magnetic field (M–H) measurement of Zn_1–xCr_xTe (x = 0.01–0.17) showed clear hysteresis loop at low temperatures. The ferromagnetic transition temperature (T_C) estimated from the Arrott-plot analysis increased almost linearly with the Cr composition (x) up to 275 K at x = 0.17. However, in the magnetization versus temperature (M–T) measurement, the irreversibility between the zero-field-cooled (ZFC) and field-cooled (FC) processes was observed. This is typically observed in the magnetic random system such as spin-glass or superparamagnetic phase. In the high resolution transmission microscopy (HRTEM) observations, structural defects such as stacking faults and polycrystalline-like structure were observed at high Cr compositions, whereas any apparent precipitates of different phases were not seen in all the range of Cr compositions examined. The correlation of the observed magnetic randomness with the local structural defects was discussed.     

Sol-gel synthesis, structure and magnetic properties of Mn-doped ZnO diluted magnetic semiconductors

2.5, 5, 10 and 15% Mn-doped ZnO diluted magnetic semiconductors (DMSs) were prepared via an ethyl acetoacetate-aided sol-gel process. The 5% Mn-doped ZnO consists of 20-50 nm spheroid-like particles and has a wurtzite phase. Existence of nanoscale ZnMnO₃ clusters in this sample is confirmed by HRTEM analysis. Vegard's law calculation reveals that about 2.6% Mn atoms have been incorporated into ZnO lattice. Besides major wurtzite phase, ZnMnO₃ secondary phase is observed in the 10% and 15% Mn-doped samples. The Mn-doped ZnO shows red shift of photoluminescence (PL), which arises from defects caused by Mn incorporation. The magnetic measurements confirm that the 2.5% and 5% Mn-doped ZnO samples display room-temperature ferromagnetism as well as paramagnetism, while the 10% and 15% samples exhibit paramagnetic effects. The as-observed ferromagnetic behaviors likely originate from cooperative effect of intrinsic and extrinsic magnetisms.     

流变相反应法合成Zn_(1-x)Co_xO室温稀磁半导体

利用流变相反应法制备得到Zn1-xCoxO(x=0.02、0.04、0.06、0.08)稀磁半导体材料。X射线衍射分析,发现Co的掺杂并未改变ZnO的纤锌矿结构,并没有杂质相的生成,衍射峰的峰位随着Co掺杂向高角度移动,Co已进入ZnO晶格。电镜及吸收光谱进一步表明样品中没有第二相的出现,Co2+成功掺入ZnO晶格。采用超导量子干涉磁强仪测量Zn0.96Co0.04O的磁性,样品在300K存在明显的磁饱和现象和磁滞回线,表明具有室温下铁磁性,其磁性来源可以用束缚磁极化子(BMPs)模型解释。     

Co掺杂ZnO块材的晶体结构和磁性能研究

采用固相法制备了Zn1-xCoxO（x=0．05-0．25）块材,烧结温度和Co含量对Zn1-xCoxO（x=0．05-0．25）块材的晶体结构和室温磁性能影响强烈,当x≤0．1,烧结温度从800增加到1100℃时,Zn1-xCoxO（x=0．05-0．25）呈现出单相结构,但当x〉0．1,烧结温度为800℃时,样品中出现CoO相;随着烧结温度提高到900℃,样品再次获得纯的单相结构。为了获得高的饱和磁化强度Ms,最佳烧结温度应该根据Co含量进行调整。在最佳烧结温度条件下,当x从0．05提高到0．1时,Ms从0．79增加到了1．06μB/Co,但当x继续提高到0．2和0．25时,Ms分别降低到了0．59和0．41μB/Co。     

Room-temperature ferromagnetic ordering in Mn-doped ZnO thin films grown by pulsed laser deposition

The ferromagnetic ordering in Mn-doped ZnO thin films grown by pulsed laser deposition (PLD) as a function of oxygen pressure and substrate temperature has been investigated. Room-temperature ferromagnetic behaviors in the Mn-doped ZnO films grown at 700°C and 800°C under 10⁻¹ torr in oxygen pressure were found, whereas ferromagnetic ordering in the films grown under 10⁻³ torr disappeared at 300 K. The large positive magnetoresistance (MR), ∼10%, was observed at 5 K at low fields and small negative MR was observed at high fields, irrespective of oxygen pressure. In particular, anomalous Hall effect (AHE) in the Mn-doped ZnO film grown at 700°C under 10⁻¹ Torr has been observed up to 210 K. In this work, the observed AHE is believed to be further direct evidence demonstrating that the Mn-doped ZnO thin films are ferromagnetic.     

锰掺杂氧化锌纳米棒阵列的结构及其磁学性质

采用水热法制备出垂直于ITO基底生长的高密度的Mn掺杂ZnO纳米棒阵列。测试阵列的微观结构和磁性。XPS证实Mn已经成功的掺入到纳米棒中。同时,所有的Mn掺杂的ZnO纳米棒在室温都有铁磁性。而且饱和磁化强度随掺杂浓度的增加先增大后减小。5%Mn掺杂的ZnO纳米棒阵列的饱和磁化强度最大。铁磁性可能来源于Mn离子部分取代Zn离子,Mn离子之间的铁磁相互作用。     

Statistical model for atomic distances and site occupation in zinc-blende diluted magnetic semiconductors (DMSs)

The statistical strained-tetrahedra model is applied to describe the behaviour of zinc-blende ternary diluted magnetic semiconductors (DMSs) with manganese. Validation is confirmed by comparing calculated and published extended X-ray absorption fine structure (EXAFS) measurements relative to average nearest-neighbour and next nearest-neighbour inter-ion distances in zinc blende DMSs at different Mn contents. The sizes, shapes and site occupation preferences (SOPs) with respect to random, of elemental-configuration tetrahedra, are fully defined for ZnMnSe, ZnMnS and ZnMnTe. For CdMnTe and HgMnTe, all the tetrahedra are defined, with the exception of the configuration with a central Te ion and two cations of each kind at the vertices, which remains inaccessible due to lack of relative experimental data. It is shown that SOPs can normally be derived from EXAFS observation of the variation either of distance or of coordination-number measurements as a function of dilution, with both sets giving results in good agreement.