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1.
文章基于密度泛函理论,研究了本征及Nb,Fe单原子掺杂单层MoSe 2的电子结构及光学性质。计算发现,本征单层MoSe 2和Nb-MoSe 2为直接带隙半导体,Fe-MoSe 2为间接带隙结构;Fe-MoSe 2较本征单层MoSe 2导电性大大提高,实现了由半导体向半金属的过渡。由态密度分析得出了本征及Nb,Fe单原子掺杂单层MoSe 2能量状态主要由Mo 4d,Se 4p轨道电子所贡献的结论,并对各原子掺杂体系轨道电子的能量贡献和掺杂类型做了探讨。此外,还详细分析了费米能级附近的自旋态密度、杂质带、磁性之间的联系。光学性质方面,比较了本征单层MoSe 2与各掺杂体系的复介电常数和光吸收系数,在红外光区Fe-MoSe 2的吸收系数高于本征单层MoSe 2。本征单层MoSe 2的光吸收系数为9.69×10 4 cm -1,是区域最大吸收峰。上述研究表明,通过对单层MoSe 2的Nb,Fe掺杂可使电子输运特性得到了增强,为高活性自旋电子和光电子器件设计和研究开辟了新的前景。 相似文献
2.
Solar-driven water splitting is a promising alternative to industrial hydrogen production. This study reports an elaborate design and synthesis of the integration of cadmium sulfide (CdS) quantum dots and cuprous sulfide (Cu2S) nanosheets as three-dimensional (3D) hollow octahedral Cu2S/CdS p–n heterostructured architectures by a versatile template and one-pot sulfidation strategy. 3D hierarchical hollow nanostructures can strengthen multiple reflections of solar light and provide a large specific surface area and abundant reaction sites for photocatalytic water splitting. Owing to the construction of the p–n heterostructure as an ideal catalytic model with highly matched band alignment at Cu2S/CdS interfaces, the emerging internal electric field can facilitate the space separation and transfer of photoexcited charges between CdS and Cu2S and also enhance charge dynamics and prolong charge lifetimes. Notably, the unique hollow Cu2S/CdS architectures deliver a largely enhanced visible-light-driven hydrogen generation rate of 4.76 mmol/(g·h), which is nearly 8.5 and 476 times larger than that of pristine CdS and Cu2S catalysts, respectively. This work not only paves the way for the rational design and fabrication of hollow photocatalysts but also clarifies the crucial role of unique heterostructure in photocatalysis for solar energy conversion. 相似文献
3.
利用Xα方法研究了氧化物La2-yBayCuO4的电子结构．研究结果显示,Ba掺杂对氧化物La2-yBayCuO4的电子态密度分布和能带结构有重要影响：（1）掺杂使由原来导电类型相反的两个基元组成的反铁磁绝缘体La2-yBayCuO4,变成了由导电类型相同的两个基元组成的超导体La2-yBayCuO4（2）掺杂使能带显著展宽,使电子态密度在Fermi面附近显著增大,并且d电子的贡献成为主要成分,而S电子的贡献却很小．说明高温超导主要是d波配对机制,S波配对是次要的,自旋涨落交换耦合可能是产生d波配对的主要原因．（3）Ba掺杂使Ba的电负性增强,O的电负性减弱,使La—O层、Cu—O层中的离子键、共价键特征演变成金属键特征,且使原团簇La8CuO6中Cu—O层由原来的接受电子特征变成提供电子的特征． 相似文献
4.
In the light of Ф-mapping method and the relationship between entropy and the Euler characteristic, the intrinsic topological structure of entropy of Kerr black holes is studied. From the Ganss-Bonnet-Chem theorem, it is shown that the entropy of Kerr black hole is determined by singularities of the Killing vector field of spacetime. These singularities naturally carry topological numbers, Hopf indices and Brouwer degrees, which can also be viewed as topological quantization of entropy of Kerr black holes. Specific results S = A/4 for non-extreme Kerr black holes and S = 0 for extreme ones are calculated independently by using the above-mentioned methods. 相似文献
5.
覆冰会改变绝缘子表面的电场分布,影响绝缘子闪络特性,如何得到覆冰条件下绝缘子表面的电场分布对防止绝缘子覆冰闪络具有重要意义。在总结国内外覆冰绝缘子电场分布研究的基础上,对覆冰绝缘子沿面电场测量、覆冰绝缘子沿面电场计算方法的优缺点进行了分析,并指出有限元法、边界元法等数值解法将是今后研究覆冰绝缘子表面电场分布的主要手段。 相似文献
6.
We report that the ultraviolet （UV） light induced photochromic behavior of layered organic-inorganic perovskite material of （C4H9NH3）2CuCl4, changed from yellow to brown after irradiation with UV light （10 mW/cm^2） and partially recovered through storage in the dark. （C4H9NH3）2CuCl4 exhibited two distinct absorption bands centered at 286 nm （band Ⅰ） and 384 nm （band Ⅱ）, which were attributed to the photo-induced exciton formed in 2D inorganic layers sandwiched by organic layers. The blue shift of band Ⅰ from 287 to 269 nm as well as the decrease of the intensity of band Ⅰ and band Ⅱ could be found when samples were irradiated under UV light for different length of time. The simultaneous weakening of the intensity of the N-H...Cl hydrogen bond as well as the vibration of the long Cu-Cl bond in the distorted CuCl6^4- octahedron could be detected from the Fourier transform infrared （FTIR） spectra, which resulted the change of charge distribution of the dissymmetric Cl-Cu...Cl bond and the resulting photochromic behavior. 相似文献
7.
本文中,首先概述了超导体的概念。然后,按照超导体的微观模型,用量子场理论得到超导体激发态。最后,指出该方法满足的条件。 相似文献
8.
The new intermetallic compound La3Cu3Bi4 was synthesized by arc melting method followed by annealing. The crystal structure refined using the Rietveld method and X-ray powder diffraction data showed to be Y3Au3Sb4 structure type with space group I-^43D （No.220）. The unit cell parameters were a = 0.997 797（7） nm and V = 0.993 41（2） nm^3. The structure was characterized by covalent Cu-Bi4 tetrahedron, which formed three-dimensional network by sharing corners and La atoms separated in the space of Cu-Bi4 tetragon. The expansion of La3Cu3Bi4 studied by using low temperature X-ray diffraction showed to be positive expansion and diminished with the temperature rising. 相似文献
9.
The photocatalytic reduction of CO2 is a promising strategy to generate chemical fuels. However, this reaction usually suffers from low photoactivity because of insufficient light absorption and rapid charge recombination. Defect engineering has become an effective approach to improve the photocatalytic activity. Herein, ultra-thin (~ 4.1 nm) carbon-doped Bi2WO6 nanosheets were prepared via hydrothermal treatment followed by calcination. The ultra-thin nanosheet structure of the catalyst not only provides more active sites but also shortens the diffusion distance of charge carriers, thereby suppressing charge recombination. Moreover, carbon doping could successfully extend the light absorption range of the catalyst and remarkably promote charge separation, thus inhibiting recombination. As a result, the as-prepared Bi2WO6 photocatalyst with ultra-thin nanosheet structure and carbon doping exhibits enhanced photocatalytic CO2 reduction performance, which is twice that of pristine ultra-thin Bi2WO6 nanosheet. This study highlights the importance of defect engineering in photocatalytic energy conversion and provides new insights for fabricating efficient photocatalysts. 相似文献
10.
Oxidative dehydrogenation (ODH) of mono and mixed-butenes to 1,3-butadiene (BD) was conducted using individual and dual bed catalyst systems, consisting of ZnFe 2O 4, Co 9Fe 3Bi 1Mo 12O 51 or both. The dual bed catalyst system gave improved catalytic performance. A mechanism based on synergy between the catalysts is proposed to explain the improved overall butene conversion. The proportion of the reactants differed between the catalyst beds in the dual bed system, making better use of the catalytic activity of the second bed. The existence of all butene isomers inhibited isomerization, leading to a higher proportion of ODH reactions and thus improved the conversion of butene and the yield of BD. The packing sequences and the volume ratio of the catalysts in the bed were optimized. The results indicated that the sequence with ZnFe 2O 4 on top and a catalyst packing ratio of between 4:6 and 6:4 led to better activity. 相似文献
11.
研究了一种基于图像分析绝缘子憎水性分级系统,介绍了系统各模块的功能。系统首先实现了对静态(序列)图像的实时采集,然后利用计算机图像处理技术对水珠进行识别,提取了水珠的特征,并在此基础上提取水珠图像的特征,最后根据这些特征利用SVM分类器对绝缘子憎水性进行分级。 相似文献
12.
We have developed an experimental setup that has been proven suitable for the study of photoresponse of high T
c superconductors. The distinguish feature of this experimental setup lies mainly in the data acquisition system which is equipped
with computer as well as the IEEE-488 interface bus, which ensures the accuracy to experimental results. Using the experimental
setup, the optical response to laser radiation in high- T
c superconductors has been examined, both of bolometric effect and nonequilibrium optical response are revealed.
The project was supported by the National Natural Science Foundation of China 相似文献
13.
This article reports first-principles band structure calculations for RMn 6Sn 6 ( R=Tb, Dy). The calculation uses the linear muffin-tin orbitals (LMTO) method in the atomic-sphere-approximation (ASA), and
yields results showing that both TbMn 6Sn 6 and DyMn 6Sn 6 are ferrimagnetic compounds with antiparallel aligned moments of R and Mn atoms. In this research the 4 f states of R atoms are treated as localized states, i.e., the hybridization of 4 f states with other valence electrons is neglected. The moments of Mn in both compounds were determined to be 2.43 μ B and 2.38 μ B, respectively. The considerably small additional moments for Mn from the spin-orbit coupling indicates that the spin-orbital
coupling is not dominated for Mn atoms. The total moments of Tb and Dy atoms are 10.28 μ B and 11.20 μ B. All the calculation findings accorded well with experimental results.
Project supported by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry
of China. 相似文献
14.
对架空线路中绝缘子的状态维修通常包括零（低）值绝缘子的检测、清扫、机电性能衰减的预测,调爬和更换等工作。为了节省大量的劳力和费用,减少工作的盲目性提高绝缘子健康水平,必须解决两个问题,一是如何确定每次的检测数量,二是根据抽样检测情况如何确定绝缘子的在线状态。 相似文献
15.
This paper contributes to the literatures on examinations, on self‐determination and dependence, and on small states. It draws particularly on materials for a Commonwealth Secretariat project on examination systems in small states. For the purposes of this paper, small states are defined as ones with populations below 3 million. The Commonwealth has 32 such states, scattered in different parts of the world. Review of systems for external secondary school examinations shows three basic models. Some small states operate their own examination systems, some participate in regional bodies, and some make use of examinations set in other countries. The paper notes the advantages and disadvantages of each model, and the reasons for variations. 相似文献
16.
Using carbon tetrachloride （CCl4） as extraction agent, the activated sludge from Tianjin Jizhuangzi Sewage Treatment Plant as inoculum, the test study on biodegradability of lubricants was carried out. The test flasks containing the mineral medium, the test oil and the inoculum were placed in incubation together with flasks containing poisoned blanks for periods of 0 and 21 days, respectively. Flasks containing the reference materials in place of the test oil were run in parallel. At the end of the incubation period, the contents of the flasks were subjected to sonic vibration, and were acidified and extracted by using CCI4. The extracts were then analysed by infra-red （IR） spectrometer to measure the maximum absorption of the C-H stretch of CH2-CH3 band at wavelength of 2 930 cm^-1. The absorption values were used to calculate the residual oil contents of the poisoned and test flasks. Consequently the biodegradability of the test oil was calculated. The test results indicate that the differences in the biodegradability of test materials in different tests are within 5.5%, and consistent with the data described in Coordinating European Council （CEC） L-33- A-93. The biodegradability of lubricants can be evaluated by this method effectively. 相似文献
17.
利用传输矩阵法理论,通过数值计算、模拟的方式,研究优化光子晶体量子阱透射能带结构的方法,结果表明：适当调整光子晶体的周期排列结构时,可拓宽光量子阱阱层光子晶体的能带,即可扩大光量子阱透射谱分布的频率范围;当组成光子晶体介质由双正材料置换成双负材料时,光量子阱阱层光子晶体的多能带结构合并成很宽且完整的单能带结构,即可使光量子阱透射谱实现连续频率分布的多通道滤波功能.光子晶体排列结构和不同介质对光量子阱透射能带结构的优化效果不同,对光子晶体量子阱的理论研究、实际设计和应用等,均有积极的指导作用. 相似文献
18.
In this article the impact of the tools being developed as part of the Second Generation Instructional Design (ID 2) Research Program on the process of instructional design is described. ID 2 supports rapid prototyping as a design and development process. Rapid prototyping is described and contrasted with the instructional
systems development (ISD) process.
This article is based on research supported by Utah State University, Human Technology Inc., and the U.S. Office of Personnel
Management. 相似文献
19.
Infrared （IR） absorption spectra and X-ray powder diffraction （XRD） patterrns of sexpenfine cat＇s eye from Sichuan Province have been investigated, and infrared absorption bands of the serpentine have been assigned in this paper. The results indicate that the bands near 3 600 - 3 700 cm^-1 belong to the stretching absorption band VOH, the bands in 948 - 1 100 cm^-1 axe assigned to the stretching vibraling band Usvo, and the bands at 600 570 and 440 cm^-1 respectively belong to the bending vibration band VOH, δMg-O and δSi-O. The serpentine cat＇ s eye includes two types： chrysotile and antigorite. Chrysotile has a sharp and intensive band at 3 688 cm^-1 and a weak band at 3 643 cm^-1 , while antigorite has only one intensive band in the region. At vibration band VSi-O, chrysotile and antigorite have a similar feature at 1 071 cm^-1, but the band at 980 cm^-1 in anfigorite has been split into two bands in chrysotile - a strong one at 1 027 cm^-1 and a weak one at 949 cm^-1. In addition, antigorite has a characteristic bending vibrating band δMg-O at 570 cm^-1. Based on the analysis of the feature of crystal structure, their IR differences axe well explained. 相似文献
20.
Because of the different ways in which contact materials work, the basic requirements for silver metal oxide contact materials are different. They are anti-welded and anti-erosion when closed, anti-erosion when broken, and arc easily moved and have smaller contact resistance. In this paper, La2O3 is used as a stable oxide in contact material to replace CdO. A new type of Ag/SnO2-La2O3-Bi2O3 contact material is first obtained through using powder metallurgical method. Then electrical contact material parameter tester is used to test the electrical contact performance of the contact material. Through experiments, the arcing voltage and current curves, arcing energy curves, fusion power curves while broken and contact resistance while closed were obtained. Analysis of the results showed that the addition of La2O3 makes the contact material have the following advantages： smaller electrical wear, smaller arc energy, smaller contact resistance and arc is more easily extinguished. 相似文献
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