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Cademartiri L Montanari E Calestani G Migliori A Guagliardi A Ozin GA 《Journal of the American Chemical Society》2006,128(31):10337-10346
We report here on a detailed study on PbS colloidal quantum dots. A characterization via X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) allowed us to reliably determine the diameter and the shape of the nanocrystals. These data, together with second-derivative analysis of the absorption spectra, allowed us to determine the size dependence of seven transitions in the absorption spectrum; some of these transitions were identified on the basis of their normalized confinement energy. The size dependence of the first excitonic transition was best modeled by a four-band envelope approach which considers the anisotropy of the band edges (Andreev, A. D.; Lipovskii, A. A. Phys. Rev. B: Condens. Matter Mater. Phys. 1999, 59, 15402-15404). The extinction coefficients were calculated using concentrations obtained from inductively coupled plasma atomic emission spectrometry (ICP-AES), and their size dependence was found to follow a power law with exponent equal to approximately 2.5. In contrast with what was expected from the effective mass approximation, the per particle absorption cross section of the lowest transition was found to be strongly dependent on the particle size. 相似文献
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Arturo Arduini Eleonora Ghidini Andrea Pochini Rocco Ungaro Giovanni Dario Andreetti Gianluca Calestani Franco Ugozzoli 《Journal of inclusion phenomena and macrocyclic chemistry》1988,6(2):119-134
From the reaction ofp-t-butylcalix[4]arene with -chloro-N,N-diethyl acetamide a new lipophilic ether-amide ligand (2) has been obtained in high yield. Solution studies show (2) to be a very strong cation receptor for alkali cations, especially sodium and potassium. The X-ray crystal structure determination of the free ligand (2) and two potassium complexes (KI and KSCN) shows the calix[4]arene in a fixed cone structure and the cation completely encapsulated in a polar cavity of eight oxygen atoms.
Supplementary Data relating to this article are deposited with the British Library as supplementary publication No. SUP 82059 (57 pages).Presented at the Fourth International Symposium on Inclusion Phenomena and the Third International Symposium on Cyclodextrins, Lancaster, U.K., 20–25 July 1986. 相似文献
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G. Amoretti E. Buluggiu A. Vera G. Calestani F. C. Matacotta 《Zeitschrift für Physik B Condensed Matter》1988,72(1):17-23
Various samples of single-phase YBa2Cu3O7–y
have been examined by X-band ESR in theg2 region forTT
c
.The observed spectra are attributed to oxygen coordinated Cu2+ ions with a large delocalization of the unpaired spins. These are probably due, in part, to the inclusion of some impurity phase. However, an analysis of the intensity as a function of the temperature in different samples indicates that a possible intrinsic contribution to the ESR signal of Cu2+ ions from the superconducting phase is due, at most, to 1% of the total copper in the formula. This small quantity of isolated Cu2+ ions may be due to the presence of low symmetry Cu3+ ions or, equivalently, non-magnetic centers such as Cu2+–O– pairs in the chains.CISM (M.P.I.) and GNSM (C.N.R.) 相似文献
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Bassanetti I Mezzadri F Comotti A Sozzani P Gennari M Calestani G Marchiò L 《Journal of the American Chemical Society》2012,134(22):9142-9145
The complexation of a preorganized thioether-functionalized bis(pyrazolyl)methane ligand (L) with silver precursors produces supramolecular structures organized at two hierarchical levels: [AgL](6)(X)(6) metal-organic cyclic hexamers and their organization in 3D architectures. The cyclic toroidal hexamers of 22-26 ? external diameter are found to be stable already in solution before self-assembly into the crystalline state. In the 3D lattice, the hexameric building block are arranged in different highly symmetric space groups as a function of a variety of anions (cubic Fd3 with PF(6)(-) or BF(4)(-) and rhombohedral R3 with CF(3)SO(3)(-) or NO(3)(-)) and form cavities with the geometrical shapes of Platonic solids (tetrahedron and octahedron) that can be occupied by a variety of solvent molecules. Upon evacuation, cubic crystals can produce stable frameworks with permanent porosity, which can absorb reversibly several vapors, CO(2) and CH(4). 相似文献
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L. Zanotti D. Calestani M. Villani M. Zha A. Zappettini C. Paorici 《Crystal Research and Technology》2010,45(6):667-671
Large‐yield zinc oxide (ZnO) nanosized tetrapods have been obtained by a standard vapour‐phase growth technique to which a few modifications have been added, such as the separation of the Zn source evaporation region from the Zn oxidation region inside the reactor setup. This modification allows to keep the growth conditions constant and continuous for a long time, thus favouring the obtainment of large amounts of ZnO tetrapod nanostructures. As some contaminations usually occur due to metallic Zn particles and/or different ZnO nanostructures, including not completely reacted ZnO1‐x solid phases, they can be removed by a three‐step “purification” procedure as described in the article. Further to that, a deposition method from suitable liquid suspensions is also reported, which allows to produce homogeneous distributions of ZnO tetrapods on large substrate areas. The proposed procedures are expected to be particularly appropriate for a large production of samples for device use. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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