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991.
B. Díaz A. Malachias P.H.O. Rappl E. Abramof V.A. Chitta A.B. Henriques 《Journal of Crystal Growth》2010,312(19):2828-2833
Semiconductor magnetic quantum dots are very promising structures, with novel properties that find multiple applications in spintronic devices. EuTe is a wide gap semiconductor with NaCl structure, and strong magnetic moments S=7/2 at the half filled 4f7 electronic levels. On the other hand, SnTe is a narrow gap semiconductor with the same crystal structure and 4% lattice mismatch with EuTe. In this work, we investigate the molecular beam epitaxial growth of EuTe on SnTe after the critical thickness for island formation is surpassed, as a previous step to the growth of organized magnetic quantum dots. The topology and strain state of EuTe islands were studied as a function of growth temperature and EuTe nominal layer thickness. Reflection high energy electron diffraction (RHEED) was used in-situ to monitor surface morphology and strain state. RHEED results were complemented and enriched with atomic force microscopy and grazing incidence X-ray diffraction measurements made at the XRD2 beamline of the Brazilian Synchrotron. EuTe islands of increasing height and diameter are obtained when the EuTe nominal thickness increases, with higher aspect ratio for the islands grown at lower temperatures. As the islands grow, a relaxation toward the EuTe bulk lattice parameter was observed. The relaxation process was partially reverted by the growth of the SnTe cap layer, vital to protect the EuTe islands from oxidation. A simple model is outlined to describe the distortions caused by the EuTe islands on the SnTe buffer and cap layers. The SnTe cap layers formed interesting plateau structures with easily controlled wall height, that could find applications as a template for future nanostructures growth. 相似文献
992.
L.M. Chen W. Tao Z.Y. Zhao Q.J. Li W.P. Ke X.M. Wang X.G. Liu C. Fan X.F. Sun 《Journal of Crystal Growth》2010,312(21):3243-3246
The bulk single crystals of low-dimensional magnet (CH3)2NH2CuCl3 (DMACuCl3 or MCCL) are grown by a slow evaporation method with different kinds of solvents, different degrees of super-saturation of solution and different temperatures of solution, respectively. Among three kinds of solvent, methanol, alcohol and water, alcohol is found to be the best one for growing MCCL crystals because of its structural similarity to the raw materials and suitable evaporation rate. The best growth temperature is in the vicinity of 35 °C. The problem of the crystals deliquescing in air has been solved through recrystallization process. The crystals are characterized by means of X-ray diffraction, specific heat and magnetic susceptibility. 相似文献
993.
994.
Vakhid A. Mamedov Dina F. Saifina Venera R. Ganieva Dimitry V. Rakov Oleg G. Sinyashin 《Tetrahedron letters》2010,51(50):6503-6506
A highly efficient, one-step, versatile method for the synthesis of 2-benzimidazol-2-ylquinolines has been developed on the basis of an acid-catalyzed rearrangement proceeding via a novel ring contraction of 3-(β-2-aminostyryl)quinoxalin-2(1H)ones. 相似文献
995.
CAO Ling-di FANG Yan FANG Chun-hui . Key Laboratory of Salt Resources Chemistry 《高等学校化学研究》2011,(3):490-495
Detailed time-and-space-averaged structure of MgSO4 in the concentrated aqueous solutions was investigated via X-ray diffraction with an X’pert Pro θ-θ diffractometer at 298 K, yielding structural function and radial distribution function(RDF). The developed KURVLR program was employed for the theoretical investigation in consideration of the ionic hydration and ion association. Multi-peaks Gaussian fitting method was applied to deconvolving the overlapping bands of Differential radial distribution function... 相似文献
996.
An efficient curvilinear non‐hydrostatic free surface model is developed to simulate surface water waves in horizontally curved boundaries. The generalized curvilinear governing equations are solved by a fractional step method on a rectangular transformed domain. Of importance is to employ a higher order (either quadratic or cubic spline function) integral method for the top‐layer non‐hydrostatic pressure under a staggered grid framework. Model accuracy and efficiency, in terms of required vertical layers, are critically examined on a linear progressive wave case. The model is then applied to simulate waves propagating in a canal with variable widths, cnoidal wave runup around a circular cylinder, and three‐dimensional wave transformation in a circular channel. Overall the results show that the curvilinear non‐hydrostatic model using a few, e.g. 2–4, vertical layers is capable of simulating wave dispersion, diffraction, and reflection due to curved sidewalls. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
997.
Abstract [(CH3)4N]2cdI4 exhibits a phase transition at 233 K from Pnma to P2 1/c as shown by single-crystal X-ray measurements and differential scanning calorimetry. The observed entropy change amounts to approximately 8.4 J.mole?1 K?1 and the spontaneous strain is about – 18.10?3. The symmetry change can be interpreted in the framework of the Landau theory. 相似文献
998.
999.
H. Pizzala M. Carles W. E. E. Stone A. Thevand 《Journal of Molecular Structure》2000,526(1-3):261-268
The crystal structure of the N-(3-hydroxysalicylidene)-4-methoxyaniline has been studied by single-crystal X-ray diffraction and solid-state NMR spectroscopy. This is the first example of a Schiff base derived from 3-hydroxysalicylaldehyde which displays in the asymmetric unit, four distinct molecules linked together in the crystal lattice by two types of intermolecular O–HO hydrogen bonds and formed by two independent tetramers. The 13C CPMAS NMR study corroborates the above results; the presence of different tautomeric equilibria in the same crystal structure is demonstrated and a qualitative estimation of the equilibrium mixture composition is given. 相似文献
1000.
Yun Long ZHANG Liang Ren ZHANG* Zhen Jun YANG Ji Mei MIN Li He ZHANG* Yang LU Ning Bo GONG Qi Tai ZHENG National Research Laboratory of Natural Biomimetic Drugs Peking University Beijing Institue of Materia Medica Chinese 《中国化学快报》2001,(5)
Tubercidin (4-amino-7--D-riobofuranosyl-7-H-pyrrolo[2,3-d]pyrimidine) 1, an antibio-tic substance produced in the culture broth of Streptomyces tubericidus1, is an adenosine analog in which N-7 is replaced by a carbon atom. It has attracted much attention due to the biological activities for the growth inhibition of certain tumors, and many derivatives of tubercidin have been synthesized2-5.For the synthesis of tubercidin analogs, 4-chloro-7-H-pyrrolo[2,3-d]pyrimidine-2,3,5-tri-O-acetyl--D-r… 相似文献