Effect of H impurity on misfit dislocation in Ni-based single-crystal superalloy: molecular dynamic simulations

The effect of H impurity on the misfit dislocation in Ni-based single-crystal superalloy is investigated using the molecular dynamic simulation. It includes the site preferences of H impurity in single crystals Ni and Ni₃Al, the interaction between H impurity and the misfit dislocation and the effect of H impurity on the moving misfit dislocation. The calculated energies and simulation results show that the misfit dislocation attracts H impurity which is located at the γ/γ' interface and Ni₃Al and H impurity on the glide plane can obstruct the glide of misfit dislocation, which is beneficial to improving the mechanical properties of Ni based superalloys.     

Investigations of impurity striations in potassium bichromate crystals

Impurity striations in potassium bichromate crystals (KBC, lopezite) formed during crystal growth from aqueous solution were revealed by chemical etching and analyzed. Striations were revealed as etch grooves, as rows of dislocation etch pits and as rows of flat‐bottomed etch pits. Various types and groups of striations have been visualized. Some striations were due to lateral segregation of impurities caused by convection flow of the mother solution, other were formed during growth stoppages whereas induced striations were generated by changes in hydrodynamical conditions. Growth rates changes resulted in zonal distribution of impurities, formation of planar lattice strain, rows of clusters of point defects and rows of dislocations. Generation of striations with different intensities in various sectors is a proof of the selective capture of impurities. Ratios of growth rates of various faces of KBC crystals growing in forced and free convection regimes were determined by induced striations. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electron Raman scattering in single and multilayered spherical quantum dots: Effects of hydrogenic impurity and geometrical size

Based on the effective mass and parabolic one-band approximations, the differential cross-section for the intersubband electron Raman scattering process in a single and multilayered spherical quantum dots is investigated. The influence of an on-center hydrogenic impurity and geometrical parameters such as the well and barrier widths on the differential cross-section is studied. Results show that the number, the position and the magnitude of the peaks of emission spectra, considerably depend on the presence of the hydrogenic impurity as well as geometrical parameters. Results also reveal that the magnitude of the peaks significantly depend on the polarization vectors of incident and scattered lights.     

对半导体杂质沉淀无损检测的若干结果

用XCD-H红外电视测微显微镜,通过无损检测来评价半导体材料与器件工艺的质量。本文仅对材料的完整性与芯片制造工艺导致杂质沉淀的问题进行讨论。     

Influence of local spin polarization to the Kondo effect

We use the spin non-degenerate single impurity Anderson model to investigate the influence of the local spin polarization to the Kondo effect. By using the Schrieffer-Wolff transformation, we obtain a generalized s-d exchange Hamiltonian, which describes the interaction between a polarized local spin and conduction electrons. In this case, the singlet is no longer an eigenstate as shown by variational calculations where the splitting of the local energy Δ = ɛ _d↑ − ɛ _d↓ can be arbitrarily small. The local spin polarization generates the instability of the singlet ground state of the S = 1/2 s-d exchange model.      

Back-Scattered Electron Imaging of Microscopic Segregation in (Si,Ge) Single Crystals

Compositional inhomogeneities of (Si,Ge) single crystals grown by the radio frequency (RF) heated float zone technique have been studied using the back-scattered electron (BSE) mode of a scanning electron microscope. Numerical analysis of the images by Fast Fourier Transformation (FFT) showed that the number of spatial frequencies with substantial amplitudes is increased when investigating longitudinal sections of crystals containing dislocations instead of dislocation-free crystals. This can be attributed to different growth conditions in terms of super-cooling.     

压力对金属铌中氦原子凝聚的影响

 采用零温条件下的赝势-平面波方法和有限温度下的Car-Parrinello分子动力学方法,模拟了不同压力环境下氦原子在金属铌中的行为特征,研究了宿主缺陷和氦泡的形成机制。结果表明,闭电子壳层的氦原子在金属铌中具有刚球模型特征,其占据区域为金属自由电子的禁区,从而破坏铌原子之间的金属性键合。在常温条件下,局域高浓度的氦原子优先凝聚于近邻宿主空位缺陷处,从而形成氦泡;完整晶格中高浓度的氦将促使铌原子易位,形成间隙-空位模式的宿主缺陷,氦原子聚集于空位区域。完整宿主在压力（40 GPa）的作用下,晶格参数减小,铌原子之间的相互作用增强,尽管氦原子的存在削弱了铌原子之间的相互作用,位于格点上的铌原子仍难以借助热振动偏离格点形成空位,因而未能形成间隙-空位对和氦泡。     

Kondo impurities in nanoscopic and mesoscopic systems

We present results for Kondo impurities in nanoscopic systems. Using Wilson's numerical renormalization group we analyze two different situations: an isolated system with a discrete spectrum of well-defined energy levels and a fixed number of electrons and a nanoscopic system weakly coupled to a macroscopic reservoir. In the latter case, new regimes not observed in macroscopic homogeneous systems are induced by the confinement of conduction electrons. These new confinement-induced regimes are very different depending on whether the Fermi energy is at resonance or between two quasi-bound states.     

W-S共掺杂锐钛矿TiO2第一性原理研究

采用基于密度泛函理论的第一性原理平面波超软赝势法,计算了未掺杂,WS单掺杂及W-S共掺杂TiO2的电子结构和光学性质．结果表明：掺杂后晶格畸变,晶格常数变大并在TiO2禁带中引入杂质能级．对于S单掺杂TiO2,禁带宽度减小和杂质能级的引入导致吸收光谱红移,而对于W单掺杂和W-S共掺杂,禁带宽度的明显增大致使掺杂后TiO2的吸收光谱蓝移．