物理学院“博约学术沙龙”系列报告
(总第 104 期)

时  间：   2015年11月11日（星期三）下午3:10--5:10
地  点：   中心教学楼610

报告一：博士生报告    时间：15:10-15:40
题  目：Realizing Ferromagnetic Coupling in Diluted Magnetic Semiconductor Quantum Dots
报告人： 韩琼琼                  指导老师： 石丽洁
摘要：Manipulating the ferromagnetic interactions in diluted magnetic semiconductor quantum dots (DMSQDs) is a central theme to the development of next-generation spin-based information technologies, but this remains a great challenge because of the intrinsic antiferromagnetic coupling between impurity ions therein. Here, we propose an effective approach capable of activating ferromagnetic exchange in ZnO-based DMSQDs, by virtue of a core/shell structure that engineers the energy level of the magnetic impurity 3d levels relative to the band edge. This idea has been successfully applied to Zn0.96Co0.04O DMSQDs covered by a shell of ZnS or Ag2S. First-principles calculations further indicate that covering a ZnS shell around the Co-doped ZnO core drives a transition of antiferromagnetic-to-ferromagnetic interaction, which occurs within an effective depth of 1.2 nm underneath the surface in the core. This design opens up new possibility for effective manipulation of exchange interactions in doped oxide nanostructures for future spintronics applications.

报告二：博士生报告    时间：15:40-16:10
题  目：射频空心阴极放电维持机制的研究
报告人：   王春晓                指导老师： 欧阳吉庭
摘要：
射频空心阴极放电既有空心放电的优点，具有时变电场的特殊性，虽然在工业上得到了广泛的应用。但是由于采用空心电极，即使在同样的射频电源驱动下，对于不同的气压、频率、电极材料等工作条件，放电将表现出不同的特性，其放电机理、放电特性和高密度等离子体的获得条件都有所不同。由于空心阴极为空腔状结构，实验测量其内部参数存在很大困难，有必要借助数值模拟的方法对其进行研究。流体模型可以有效地描述放电空间中粒子密度、电场、电势、电离率等物理量的变化过程，从而对放电特性进行分析并揭示其物理机制。因此，我们采用实验和理论相结合的方法对圆柱型空心阴极射频放电的形成及维持机制进行研究。研究射频空心阴极放电的放电图像以及电学特性；研究射频空心阴极放电产生空心阴极效应的稳定条件，了解放电条件对其放电特性的影响，讨论电子的加热方式，分析其物理形成机制。

报告三：博士生报告    时间：16:10-16:40
题  目：Nitrogen vacancy induced phase determination of Indium Nitride
时  间：   2015年11月11日（星期三）下午16:10
地  点：   中心教学楼610
报告人： 阙茂飞                 指导老师： 郭伟，石丽杰
摘要：
Nitrogen vacancy formation energy is taken into account to explain the coexistence, and sometimes even preference, of forming metastable zinc-blende phase of indium nitride, along with the globally most stable wurtzite phase. The most stable nitrogen vacancy configurations as well as their vacancy formation energies of two phases under different vacancy densities in a supercell with 32 atoms are calculated. We found that under the constraint of forming nitrogen vacancy due to nitrogen deficiency, the metastable zinc-blende phase is more energetically preferable when exceeds a certain nitrogen vacancy density, because the nitrogen vacancy formation energy of zinc-blende phase is lower than that of wurtzite phase and the difference is getting bigger along with the vacancy density. This provides an explanation for the formation of metastable zinc-blende phase.


报告四：博士生报告    时间：16:40-17:10
题  目：Spontaneous Air-Driven Separation in Vertically Vibrated Fine Granular Mixtures
报告人： 刘小娜                 指导老师： 郑宁
摘要：We report the observation of the spontaneous separation of vertically vibrated mixtures of fine bronze and glass spheres of similar diameters. At low frequencies and at sufficient vibrational amplitudes, a sharp boundary forms between a lower region of glass and an upper region of the heavier bronze. The boundary undergoes various oscillations, including periodic tilting motion, but remains extremely sharp. At higher frequencies, the bronze separates as a mid-height layer between upper and lower glass regions, and the oscillations are largely absent. The mechanism responsible for the separation can be traced to the effect of air on the granular motion.

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