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排序方式: 共有459条查询结果,搜索用时 15 毫秒
421.
Hojin Ryu 《Physica B: Condensed Matter》2008,403(18):3195-3198
CaAl2O4:Eu2+ co-doped with varying concentrations of Er3+ was prepared by solid-state reaction method. Prepared materials with 1 mol% Eu2+ and 2-10 mol% of Er3+ were investigated for their photoluminescence properties. Phase, morphology and crystalline structure were investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Broad band UV-excited luminescence was observed for CaAl2O4:Eu2+, Er3+ in the blue region (λmax=440 nm) due to transitions from 4f65d1 to the 4f7 configuration of the Eu2+ ion. The Er3+ ion co-doping generates deep traps, which results in longer decay time for phosphorescence. 相似文献
422.
Gong-Yi Li Xiao-Dong Li Hao Wang Zhong-Quan Li 《Applied Physics A: Materials Science & Processing》2008,93(2):471-475
Long silicon nitride (Si3N4) nanowires with high purity were synthesized by heating mixtures of SiO2 powders and short carbon fibers at 1430°C for 2 h in a flowing N2 atmosphere. The nanowires had the length of 1–2 millimeters and the diameters of 70–300 nm, and were mainly composed of ⍺-Si3N4, growing along the [001] direction. The vapor–solid (VS) mechanism was employed to interpret the nanowires growth. 相似文献
423.
M.S.F. da Rocha T.E.A. Santos V.R. Hering J.H. Vuolo V.P. Mammana 《Applied Surface Science》2008,254(6):1859-1869
A statistical data analysis methodology was developed to evaluate the field emission properties of many samples of copper oxide nanostructured field emitters. This analysis was largely done in terms of Seppen-Katamuki (SK) charts, field strength and emission current. Some physical and mathematical models were derived to describe the effect of small electric field perturbations in the Fowler-Nordheim (F-N) equation, and then to explain the trend of the data represented in the SK charts. The field enhancement factor and the emission area parameters showed to be very sensitive to variations in the electric field for most of the samples. We have found that the anode-cathode distance is critical in the field emission characterization of samples having a non-rigid nanostructure. 相似文献
424.
From the results of first principles tight-binding linear muffin-tin orbital (TB-LMTO) calculations, half-metallic ferromagnetism is proposed in Zn(TM)O2 with a chalcopyrite structure. The calculated electronic and magnetic property shows that consistent with the integer value for the total magnetic moment, half metallicity is obtained for ZnCrO2, ZnMnO2, ZnFeO2, ZnCoO2 and ZnNiO2. A careful analysis of the spin density reveals the ferromagnetic coupling between the p–d states and the cation dangling-bond p states, which is believed to be responsible for the stabilization of the ferromagnetic phase. The calculated heat of formation, bulk modulus and cohesive energy are reported. 相似文献
425.
Hongzhi Luo Zhiyong Zhu Li Ma Shifeng Xu Guangheng Wu Heyan Liu Jingping Qu Yangxian Li Xiaoxi Zhu Chengbao Jiang Huibin Xu 《Journal of magnetism and magnetic materials》2008
The effect of doping with Cr on the electronic structure and magnetism of Co3Al has been studied by density functional calculations. It has been found that the Cr atom has a strong site preference for the B-site in Co3Al. With the substitution of Cr for Co, the total densities of states (DOS) change obviously: A DOS peak appears at EF in the majority spin states and an energy gap is opened in the minority spin states. The effect of Cr in Co3Al is mainly to push the antibonding peak of the Co (A,C) atoms high on the energy scale and to form the energy gap around EF, and also to contribute to the large DOS peak at EF in the majority spin direction. The calculations indicate a ferromagnetic alignment between the Co and Cr spin moments. The calculated total magnetic moment decreases and becomes closer to the Slater–Pauling curve with increasing Cr content. This is mainly due to the decrease of the Co (A,C) spin moments. At the same time, the moments of Co (B) and Cr (B) only change slightly. 相似文献
426.
Wei Chen Steen Mørup Mikkel F. Hansen Tobias Banert Urs A. Peuker 《Journal of magnetism and magnetic materials》2008
We have prepared magnetic beads consisting of iron oxide nanoparticles in a polymethyl methacrylate (PMMA) and a polyvinyl butyral (PVB) matrix. High-field Mössbauer studies show that the particles have an almost perfect collinear spin structure and magnetization measurements show that they are superparamagnetic at room temperature at a time scale of seconds. We have followed the oxidation of the particles, which initially have a stoichiometry close to magnetite. The oxidation is fast during the first 2–3 weeks and then continues slowly such that even after 30 weeks the particles have not completely transformed to maghemite. The PVB beads are hydrophilic and biocompatible and are therefore well suited for applications in medicine and biology. 相似文献
427.
Ranajit Saha Sudip Pan Gabriel Merino Pratim K. Chattaraj 《Angewandte Chemie (International ed. in English)》2019,58(25):8372-8377
Is it possible to facilitate the formation of a genuine Be?Be or Mg?Mg single bond for the E2 species while it is in its neutral state? So far, (NHCR)Be?Be(NHCR) (R=H, Me, Ph) have been reported where Be2 is in 1Δg excited state imposing a formal Be?Be bond order of two. Herein, we present the formation of a single E?E (E=Be, Mg) covalent bond in E2(NHBMe)2 (E=Be, Mg; NHBMe=(HCNMe)2B) complexes where E2 is in 3∑u+ excited state having (nσg+)2(nσu+)1((n+1)σg+)1 (n=2 for Be and n=4 for Mg) valence electron configuration and it forms electron‐shared bonding with two NHBMe radicals. The effects of bonding with nσu+ and (n+1)σg+ orbitals will cancel each other, providing the former E?E bond order as one. Be2(NHBMe)2 complex is thermochemically stable with respect to possible dissociation channels at room temperature, whereas the two exergonic channels, Mg2(NHBMe)2 → Mg + Mg(NHBMe)2 and Mg2(NHBMe)2 → Mg2 + (NHBMe)2, are kinetically inhibited by a free energy barrier of 15.7 and 18.7 kcal mol?1, respectively, which would likely to be further enhanced in cases of bulkier substituents attached to the NHB ligands. Therefore, the title complexes are first viable systems which feature a neutral E2 moiety with a single E?E covalent bond. 相似文献
428.
Ultra-sensitive mid-infrared cavity leak-out spectroscopy using a cw optical parametric oscillator 总被引:1,自引:0,他引:1
A. Popp F. Müller F. Kühnemann S. Schiller G. von Basum H. Dahnke P. Hering M. Mürtz 《Applied physics. B, Lasers and optics》2002,75(6-7):751-754
We report a portable, all-solid-state, mid-infrared spectrometer for trace-gas analysis. The light source is a continuous-wave
optical parametric oscillator based on PPLN and pumped by a Nd:YAG laser at 1064 nm. The generated single-frequency idler
output covers the wavelength region between 2.35 and 3.75 μm. With its narrow line width, this light source is suitable for
precise trace-gas analysis with very high sensitivity. Using cavity leak-out spectroscopy we achieved a minimum detectable
absorption coefficient of 1.2×10-9 /cm (integration time: 16 s), corresponding, for example, to a detection limit of 300 parts per trillion ethane. This sensitivity
and the compact design make this trace-gas analyzer a promising tool for various in situ environmental and medical applications.
Received: 19 September 2002 / Published online: 15 November 2002
RID="*"
ID="*"Corresponding author. Fax: +49-228/733-474, E-mail: frank.kuehnemann@iap.uni-bonn.de 相似文献
429.
In this study, the internal friction (IF) of a CuAlBe alloy during reverse martensitic transformation (MT) was investigated under isothermal and non-isothermal conditions. It was found that the IF decreases regularly with the aging time in the temperature range of phase transformation. It is thought that this phenomenon is caused by the defect movement. The defects diffuse to the interfaces between martensite and austenite and pin there gradually, thus leading to the IF decrease. 相似文献
430.
模拟生物进化的机理,建立了优化团簇结构的理论程序,并对Si和Be团簇结构进行了优化计算。并成功地得到了用其它方法已发现的团簇基态结构,还发现了用其它方法尚未得到的团簇基态结构;所得到的团簇基态能量等于或小于已发表的用其它方法所得到的相应团簇的基态能量,说明此方法对于优化团簇基态结构是可行和有效的。 相似文献