Growth of monodisperse nanospheres of MnFe_2O_4 with enhanced magnetic and optical properties

Highly dispersive nanospheres of MnFe204 are prepared by template free hydrothermal method. The nanospheres have 47.3-nm average diameter, narrow size distribution, and good crystallinity with average crystallite size about 22 nm. The reaction temperature strongly affects the morphology, and high temperature is found to be responsible for growth of uniform nanospheres. Raman spectroscopy reveals high purity of prepared nanospheres. High saturation magnetization （78.3 emu/g）, low coercivity （45 Oe, 10e = 79.5775 A.cm-1）, low remanence （5.32 emu/g）, and high anisotropy constant 2.84 × 10^4 J/m3 （10 times larger than bulk） are observed at room temperatures. The nearly snperparamagnetic behavior is ~ spin due to comparable size of nanospheres with superparamagnetic critical thameter Dcr spm The high value of Keff may be due to coupling between the pinned moment in the amorphous shell and the magnetic moment in the core of the nanospheres. The nanospheres show prominent optical absorption in the visible region, and the indirect band gap is estimated to be 0.98 eV from the transmission spectrum. The prepared Mn ferrite has potential applications in biomedicine and photocatalysis.     

The effects of strain and surface roughness scattering on the quasi-ballistic characteristics of a Ge nanowire p-channel field-effect transistor

The effects of strain and surface roughness scattering on the quasi-ballistic hole transport in a strained gate-all-around germanium nanowire p-channel field-effect transistor （pFET） are investigated in this work. The valence subbands are shifted up and warped more parabolically by the influence of HfO2 due to the lattice mismatch. However, the boundary force only shifts the subbands downwards and has little effect on the reshaping of bands. Strain induced by HfO2 increases both the hole mobility and ON-current （/ON）, but has little effect on the hole mobility. The/ON is degraded by the surface roughness scattering in both strained and unstrained devices.     

High-mobility two-dimensional electron gases at oxide interfaces： Origin and opportunities

Our recent experimental work on metallic and insulating interfaces controlled by interfacial redox reactions in SrTiO3-based heterostructures is reviewed along with a more general background of two-dimensional electron gas(2DEG)at oxide interfaces.Due to the presence of oxygen vacancies at the SrTiO3surface,metallic conduction can be created at room temperature in perovskite-type interfaces when the overlayer oxide ABO3has Al,Ti,Zr,or Hf elements at the B sites.Furthermore,relying on interface-stabilized oxygen vacancies,we have created a new type of 2DEG at the heterointerface between SrTiO3and a spinelγ-Al2O3epitaxial film with compatible oxygen ion sublattices.This 2DEG exhibits an electron mobility exceeding 100000 cm2·V 1·s 1,more than one order of magnitude higher than those of hitherto investigated perovskite-type interfaces.Our findings pave the way for the design of high-mobility all-oxide electronic devices and open a route toward the studies of mesoscopic physics with complex oxides.     

用于农田土壤监测的高光谱成像仪

土壤光谱分析技术具有分析速度快、成本低、无危险、无破坏、可同时反演多种成分等特点,基于高光谱成像技术可以快速获取土壤性质及其空间分布特征。本文针对农田土壤监测的需求,设计了一种无人机载高光谱成像仪,选择Offner凸光栅光谱成像系统实现了无谱线弯曲和无色畸变的设计结果。400～1 000nm波长范围内的衍射效率为15%～30%,对地成像效果清晰,在3 km飞行高度可以获得覆盖宽度为0.6km、地面分辨率为0.6 m的地物目标高光谱图像,可提供0.4～1.0μm波长范围内120个谱段的高光谱图像,光谱数据准确、稳定。结果表明,该高光谱成像仪满足设计要求且可以快速获得高精度成像光谱信息,适合用于对农田土壤的监测。     

Al组分对MOCVD制备的AlxGa1-xN/AlN/GaN HEMT电学和结构性质的影响

采用金属有机化合物化学气相沉积（MOCVD）方法制备了不同Al组分（x=0.19,0.22,0.25,0.32）的Al_xGa_1-xN/AlN/GaN 结构的高电子迁移率晶体管（HEMT）材料。研究了Al_xGa_1-xN势垒层中Al组分对HEMT材料电学性质和结构性质的影响。研究结果表明,在一定的Al组分范围内,二维电子气（2DEG）浓度和迁移率随着Al组分的升高而增大。然而,过高的Al组分导致HEMT材料表面粗糙度增大,2DEG迁移率降低,该实验现象在另一方面得到了原子力显微镜测试结果的验证。在最佳Al组分（25%）范围内,获得的 HEMT材料的2DEG浓度和室温迁移率分别达到1.2×10¹³ cm^-2和1 680 cm²/（V·s）,方块电阻低至310 Ω/□。     

基于低空成像高光谱系统探测植被日光诱导叶绿素荧光

植被叶绿素荧光与光合作用关系密切,被认为是光合作用的有效探针。该研究利用成像高光谱传感器和无人飞艇构建了一套适用于低空叶绿素荧光探测的系统。针对低空叶绿素荧光探测中,太阳下行辐射光谱难以获取的情况,基于已有的aFLD方法,提出一种新的叶绿素荧光提取方法a3FLD,该方法利用了非荧光发射体,且考虑植被反射率在夫琅和费线附近的变化。通过模拟数据以及实测数据对两种提取结果进行了比较。模拟数据分析结果显示：当地物的反射率在夫琅和费线附近存在一定的变化时,a3FLD计算得到的荧光值误差小于aFLD,地物反射率变化越大,a3FLD的改进越明显。对低空高光谱影像数据的分析显示：aFLD和a3FLD提取不同植被的日光诱导叶绿素荧光相对大小关系相一致,与作物所处的生长阶段吻合。但aFLD荧光提取值比a3FLD高15%左右。aFLD的结果中有部分非荧光发射体得到较强荧光,a3FLD能改进此问题。结果显示,利用该系统和方法能够成功地提取到植被叶绿素荧光,且所提出a3FLD方法提取的结果优于aFLD方法。     

高氧空位浓度对金红石TiO2导电性能影响的第一性原理研究

采用基于密度泛函理论的平面波超软赝势方法研究了 纯的和不同高氧空位浓度金红石型TiO_2-x (x=0, 0.083, 0.125, 0.167, 0.25)超胞的能带结构分布、态密度分布.同时, 采用局域密度近似+U方法调准了带隙.结果表明, 高氧空位浓度越高, 金红石型TiO₂的最小带隙越变窄、电子有效质量越减小, 自由电子浓度越高, 电子迁移率越低、电导率越低.计算结果与实验结果的变化趋势相符合. 关键词： 高氧空位 2')" href="#">金红石型TiO₂ 电导率 第一性原理     

X-ray spectra of high temperature tungsten plasma calculated with collisional radiative model

Tungsten is regarded as an important candidate of plasma facing material in international thermonuclear experimental reactor （ITER）, so the determination and modeling of spectra of tungsten plasma, especially the spectra at high temperature were intensely focused on recently. In this work, using the atomic structure code of Cowan, a collisional radiative model （CRM） based on the spin-orbit-split-arrays is developed. Based on this model, the charge state distribution of tungsten ions is determined and the soft X-ray spectra from high charged ions of tungsten at different temperatures are calculated. The results show that both the average ionization charge and line positions are well agreed with others calculations and measurements with discrepancies of less than 0.63% and 1.26%, respectively. The spectra at higher temperatures are also reported and the relationship between ion abundance and temperature is predicted in this work.     

Multilayers with high-reflectivity at 19.5 nm and low-reflectivity at 30.4 nm

The multilayer （ML） mirror with high-reflectivity （HR） at a specific emission line of 19.5 nm （Fe line） and low-reflectivity （LR） at 30.4 nm （He line） is needed to be designed and fabricated for observing the image of sun. Based on a variety of optimizations utilized different structures, the design is performed and the final results demonstrate that the reflectivity at 30.4 nm does not achieve minimum value when the reflectivity at 19.5 nm reaches the maximum value. The tradeoff should be done between the HR at 19.5 nm and LR at 30.4 nm. One optimized mirror is fabricated by direct current magnetron sputtering and characterized by grazing-incident X-ray diffraction （XRD） and synchrotron radiation （SR）. The experimental results demonstrate that the ML achieves the reflectivity of 33.3% at 19.5 nm and of 9.6× 10-4 at 30.4 nm at the incident angle of 13°.