排序方式: 共有49条查询结果,搜索用时 31 毫秒
31.
采用价键分析和周期密度泛函理论相结合的方法, 研究了具有 M1 晶相结构的 MoVTeNbO 复合氧化物催化剂中各活性中心的 d 电子性质. 通过分析各活性中心配对出现的 d 电子和氧缺位的可能分布, 得到了最可能高效完成丙烷选择氧化反应的 M-M-Te(M = Mo 或 V) 活性中心组合. 此外, 根据各活性中心对骨架稳定的贡献, 说明了稳定的 M1 相骨架主要来自 MoO6 八面体中赤道面上的强共价 Mo–O 键, 而 VO6 八面体的贡献较小. 通常被认为稳定 M1 相的 Nb 物种主要以离子键的形式存在于五边形孔道中, 因而 Nb5+作为一种模板离子, 诱导五边形孔道乃至 M1 晶相结构的生成. 相似文献
32.
Evidence of GeO volatilization and its effect on the characteristics of HfO2 grown on a Ge substrate
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HfO2 films are deposited by atomic layer deposition(ALD) using tetrakis ethylmethylamino hafnium(TEMAH) as the hafnium precursor,while O3 or H2O is used as the oxygen precursor.After annealing at 500℃ in nitrogen,the thickness of Ge oxide's interfacial layer decreases,and the presence of GeO is observed at the H2 O-based HfO2 interface due to GeO volatilization,while it is not observed for the O3-based HfO2.The difference is attributed to the residue hydroxyl groups or H2 O molecules in H2 O-based HfO2 hydrolyzing GeO2 and forming GeO,whereas GeO is only formed by the typical reaction mechanism between GeO2 and the Ge substrate for O3-based HfO2 after annealing.The volatilization of GeO deteriorates the characteristics of the high-κ films after annealing,which has effects on the variation of valence band offset and the C-V characteristics of HfO2 /Ge after annealing.The results are confirmed by X-ray photoelectron spectroscopy(XPS) and electrical measurements. 相似文献
33.
A two-dimensional threshold voltage analytical model for metal-gate/high-k/SiO<sub>2</sub> /Si stacked MOSFETs
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In this paper the influences of the metal-gate and high-k/SiO 2 /Si stacked structure on the metal-oxide-semiconductor field-effect transistor(MOSFET) are investigated.The flat-band voltage is revised by considering the influences of stacked structure and metal-semiconductor work function fluctuation.The two-dimensional Poisson’s equation of potential distribution is presented.A threshold voltage analytical model for metal-gate/high-k/SiO 2 /Si stacked MOSFETs is developed by solving these Poisson’s equations using the boundary conditions.The model is verified by a two-dimensional device simulator,which provides the basic design guidance for metal-gate/high-k/SiO 2 /Si stacked MOSFETs. 相似文献
34.
Study of neutron activation yields in spallation reaction of 400 MeV/u carbon on a thick lead target
The spallation-neutron yield was studied experimentally by bombarding a thick lead target with 400 MeV/u carbon beam. The data were obtained with the activation analysis method using foils of Au, Mn, Al, Fe and In. The yields of produced isotopes were deduced by analyzing the measured γ spectra of the irradiated foils. According to the isotopes yields, the spatial and energy distributions of the neutron field were discussed. The experimental results were compared with Monte Carlo simulations performed by the GEANT4+FLUKA code. 相似文献
35.
利用液相沉淀法制备得到了不同形貌的纳米及微米SrB6O10·5H2O∶Eu3+,对产品进行了EDS、XRD、IR、SEM等表征。结果表明反应时间对产品的结晶度、形貌、粒径有较大的影响。此外,研究了产品的光致发光性能,结果发现所有产品的最强发射峰都位于λ=615 nm处,为红色发光;产品的发光随反应时间的增加而增强,而红橙比随反应时间的增加先增大后减小。当反应时间为48 h时,产品在激发波长为391 nm和250nm时的发光强度相当,但在391 nm时红橙比更高,是一种良好的近紫外激发红色发光材料。 相似文献
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37.
运用胶体化学法合成了尺寸可控的二氧化硅(SiO2)亚微米溶胶小球.透射电子显微镜(TEM)结果显示样品平均尺寸可从200nm变化至600nm,单分散性较高、平均标准偏差小于5%.通过自然沉积法,由溶胶SiO2小球自组织晶化制备了人工蛋白石晶体(opal晶体)结构.样品的剖面扫描电子显微镜(SEM)检测表明,样品为面心立方(fcc)结构.分析表明,较高的单分散性和缓慢的沉积过程是SiO2溶胶小球自组织晶化成三维有序结构的关键因素.反射谱中峰位在1320nm处的反射峰的出现,意味着样品在宏观尺度上的有序排列,
关键词:
亚微米二氧化硅溶胶小球
人工蛋白石晶体
方向带隙 相似文献
38.
针对FPGA输入输出信号微小延时的需求,根据FPGA的I/O特性和I/O逻辑资源,研究了一种基于FPGA的信号微小延时方法;采用FPGA的输入输出延时单元IODELAY,实现对输入输出信号的绝对延时,能够确保对FPGA的输入输出信号进行最小78ps的延时;根据实际需要可以通过参数选择实现对输入信号的固定延时和可变延时工作模式,以及对输出信号的固定延时工作模式;实际应用表明,文中实现的信号延时方法能够精确实现信号微小延时,延时效果稳定,受温度等外界环境变化影响较小,能够满足工程项目中对信号微小延时的实际需要。 相似文献
39.
Spallation neutrons were produced by the irradiation of Pb with 250 MeV protons. The Pb target was surrounded by water which was used to slow down the emitted neutrons. The moderated neutrons in the water bath were measured by using the resonance detectors of Au, Mn and In with a cadmium (Cd) cover. According to the measured activities of the foils, the neutron flux at different resonance energies were deduced and the epithermal neutron spectra were proposed. Corresponding results calculated with the Monte Carlo code MCNPX were compared with the experimental data to check the validity of the code. The comparison showed that the simulation could give a good prediction for the neutron spectra above 50 eV, while the finite thickness of the foils greatly effected the experimental data in low energy. It was also found that the resonance detectors themselves had great impact on the simulated energy spectra. 相似文献
40.
非负矩阵Perron根的上下界 总被引:9,自引:0,他引:9
1.引言 本文主要讨论非负矩阵,我们将用B≥0和B>0分别表示矩阵B是非负的和正的,也就是B的每一个元素是非负的和B的每一个元素是正的.用p(B)表示方阵B的谱半径,当B≥0时,p(B)也就是B的perron根. 设(n)={1,2,…,n},A=(ai,j)是n×n非负矩阵,我们称 相似文献