Large coercivity and unconventional exchange coupling in manganese-oxide-coated manganese gallium nanoparticles

The microstructures and magnetic properties of nanoparticles, each composed of an antiferromagnetic （AFM） manganese-oxide shell and a ferromagnetic-like core of manganese-gallium （MnGa） compounds, are studied. The coreshell structure is confirmed by transmission electron microscope （TEM）. The ferromagnetic-like core contains three kinds of MnGa binary compounds, i.e., ferrimagnetic （FI） DO22-type MnaGa, ferromagnetic （FM） Mn8Gas, and AFM DO19-type Mn3Ga, of which the first two correspond respectively to a hard magnetic phase and to a soft one. Decoupling effect between these two phases is found at low temperature, which weakens gradually with increasing temperature and disappears above 200 K. The exchange bias （EB） effect is observed simultaneously, which is caused by the exchange coupling between the AFM shell and FM-like core. A large coercivity of 6.96 kOe （1Oe = 79.5775 A·m^-1） and a maximum EB value of 0.45 kOe are achieved at 300 K and 200 K respectively.     

Interfacial and electrical properties of HfAlO/GaSb metal-oxide-semiconductor capacitors with sulfur passivation

Interfacial and electrical properties of HfAlO/GaSb metal-oxide-semiconductor capacitors(MOSCAPs) with sulfur passivation were investigated and the chemical mechanisms of the sulfur passivation process were carefully studied. It was shown that the sulfur passivation treatment could reduce the interface trap density Ditof the HfAlO/GaSb interface by 35% and reduce the equivalent oxide thickness(EOT) from 8 nm to 4 nm. The improved properties are due to the removal of the native oxide layer, as was proven by x-ray photoelectron spectroscopy measurements and high-resolution cross-sectional transmission electron microscopy(HRXTEM) results. It was also found that GaSb-based MOSCAPs with HfAlO gate dielectrics have interfacial properties superior to those using HfO2 or Al2O3 dielectric layers.     

二维正方光子晶体波导中的慢光传输

采用平面波展开法分析了正方晶格光子晶体线缺陷波导中的慢光传输.数值模拟结果表明,介质柱光子晶体线缺陷波导中,缺陷模的群速度与填充比、缺陷处介质柱半径及与波导相邻介质柱半径有关,其中缺陷处介质柱半径对缺陷模的群速度影响最大|随着填充比和缺陷处介质柱半径的增大及与波导相邻介质柱半径的减小,缺陷模的群速度逐渐减小且最小减至0.015c.进而对比研究空气柱光子晶体线缺陷波导,发现缺陷模的群速度随着缺陷处空气柱半径的减小而减小,最小减至0.008c.     

Deposition of Au/TiO2 film by pulsed laser

Au nanoparticles, which were photoreduced by a Nd:YAG laser in HAuCl₄ solution containing TiO₂ colloid and accompanied by the TiO₂ particles, were deposited on the substrate surface. The film consisting of Au/TiO₂ particles was characterized by the absorption spectra, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The adhesion between the film and substrate was evaluated by using adhesive tape test. It was found that the presence of TiO₂ dramatically enhanced the adhesion strength between the film and the substrate, as well as the deposition rate of film. The mechanism for the deposition of Au/TiO₂ film was also discussed.     

New terahertz dispersive device for single-shot spectral measurements of terahertz pulse

A new terahertz dispersive device designed for single-shot spectral measurements of broadband terahertz pulses is proposed. With two-dimensional quasi-randomly distributed element design, the device exhibits approximately the dispersive property of single-order diffraction in far field. Its far-field diffraction pattern is experimentally verified employing a continuous terahertz source centered at 2.52 THz and a pyroelectric focal-plane-array camera, which is in good agreement with the numerical result. The device provides a new approach for direct single-shot spectral measurements of broadband terahertz waves.     

Temperature dependence of surface and structure properties of ZnCdO film

Zn1-xCdx O films are grown on c-sapphire substrates by laser molecular beam epitaxy(LMBE) at different temperatures. Their crystallographic structures, compositions, surface electronic structures are investigated. The a-axis lattice constant of Zn0.95Cd0.05 O is 3.20. Moreover, the epitaxial relationship shows a 30°-in-plane rotation of the film with respect to the c-sapphire substrate. When the substrate temperatures arrives at 500℃, the in situ reflection high-energy electron diffraction(RHEED) pattern of Zn Cd O film shows sharp streaky pattern. The maximum Cd content of Zn Cd O film grown at low substrate temperatures increases up to about 29.6 at.%, which is close to that of the ceramic target. In situ ultraviolet photoelectron spectroscopy(UPS) measurements demonstrate that Zn Cd O film exhibits intense peaks at 4.7 e V and 10.7 e V below the Fermi level, which are assigned to the O 2p and Zn 3p states. Energetic distance between Zn 3d and Cd 4d is 0.60 e V. Above 470 nm, the thin film shows excellent optical transmission.     

Image reconstruction tomography with only a method for laminar optical single Monte-Carlo simulation

Laminar optical tomography （LOT） is a new mesoscopic functional optical imaging technique. Currently, the forward problem of LOT image reconstruction is generally solved on the basis of Monte-Carlo （MC） methods. However, considering the nonlinear nature of the image reconstruction in LOT with the increasing number of source positions, methods based on MC take too much computation time. This letter develops a fast image reconstruction algorithm based on perturbation MC （pMC） for reconstructing the absorption or scattering image of a slab medium, which is suitable for LOT or other functional optical tomography system with narrow source-detector separation and dense sampling. To calculate the pMC parameters, i.e., the path length passed by a photon and the collision numbers experienced in each voxel with only one baseline MC simulation, we propose a scheme named as the trajectory translation and target voxel regression （TT＆TVR） based on the reciprocity principle. To further speed up the image reconstruction procedure, the weighted average of the pMC parameters for all survival photons is adopted and the region of interest （ROI） is extracted from the raw data to save as the prior information of the image reconstruction. The method is applied to the absorption reconstruction of the layered inhomogeneous media. Results demonstrate that the reconstructing time is less than 20 s with the X - Y section of the sample subdivided into 50 × 50 voxels, and the target size quantitativeness ratio can be obtained in a satisfying accuracy in the source-detector separations of 0.4 and 1.25 mm, respectively.     

弯曲氧化锌微米线微腔中的回音壁模

本文用微区共聚焦荧光光学显微镜在垂直于氧化锌微米线c轴的方向测量微米线上不同位置的光谱,通过对比直的和弯曲的微米线上TE和TM偏振的光谱,观察到了弯曲氧化锌微米线中不同位置的回音壁模式的移动,其机理是在弯曲应力作用下激子能级发生了移动,带边附近的介电常数也随之变化,导致微腔中的回音壁模式发生移动.     

Temperature anomaly of the Cd hyperfine field in a trivacancy complex in Ni

The temperature dependence of the Cd hyperfine field in a trivacancy complex in Ni between 25 and300 K is reported. It was found that, unlike the Cd substitutional field in Ni which follows the temperature dependence of the magnetization, the Cd hyperfine field in a trivacancy complex is essentially temperature independent. This temperature anomaly is compared with other temperature anomaly of impurity hyperfine fields in ferromagnetic hosts.     

软x射线近贴显微技术

软x射线近贴显微技术不但可使活的生物样品成象,分辨率高于光学显微镜,而且人为的样品准备程序在该技术中都可避免。本文描述了用高功率激光打靶产生的等离子体作为软x射线源而进行的近贴显微研究,并得到了分辨率好于1μm的结果。