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排序方式: 共有387条查询结果,搜索用时 62 毫秒
31.
We present a formulation of ab initio electronic structure calculations in a finite magnetic field, which retains the simplicity and efficiency of techniques widely used in first principles molecular dynamics simulations, based on plane-wave basis sets and Fourier transforms. In addition we discuss results obtained with this method for the energy spectrum of interacting electrons in quantum wells, and for the electronic properties of dense fluid deuterium in a uniform magnetic field. 相似文献
32.
G.?PadelettiEmail author P.?Fermo S.?Gilardoni A.?Galli 《Applied Physics A: Materials Science & Processing》2004,79(2):335-339
In order to recover the ancient tradition concerning the materials used for the decoration, majolica shards produced during the Renaissance period in Casteldurante, a famous centre for ceramic production in Italy (Marche), have been examined. In the present study, pigments used for the decorations have been investigated by means of inductively coupled plasma optical emission spectrometry (ICP-OES), scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM-EDX) and diffuse-reflectance UV-Vis spectroscopy. Ochre, lead antimonate yellow, copper-based pigment and smalt have been used as colourants to obtain respectively yellow-orange, yellow, green and blue decorations in accordance with what is reported by the ancient recipes. PACS 81.05.Mh; 82.80.-d; 61.66.Fn; 61.66.Hq 相似文献
33.
Draeger EW Grossman JC Williamson AJ Galli G 《The Journal of chemical physics》2004,120(22):10807-10814
The effect of preparation conditions on the structural and optical properties of silicon nanoparticles is investigated. Nanoscale reconstructions, unique to curved nanosurfaces, are presented for silicon nanocrystals and shown to have lower energy and larger optical gaps than bulk-derived structures. We find that high-temperature synthesis processes can produce metastable noncrystalline nanostructures with different core structures than bulk-derived crystalline clusters. The type of core structure that forms from a given synthesis process may depend on the passivation mechanism and time scale. The effect of oxygen on the optical of different types of silicon structures is calculated. In contrast to the behavior of bulklike nanostructures, for noncrystalline and reconstructed crystalline structures surface oxygen atoms do not decrease the gap. In some cases, the presence of oxygen atoms at the nanocluster surface can significantly increase the optical absorption gap, due to decreased angular distortion of the silicon bonds. The relationship between strain and the optical gap in silicon nanoclusters is discussed. 相似文献
34.
We present density functional and quantum Monte Carlo calculations of the stability and optical properties of semiconductor nanomaterials with reconstructed surfaces. We predict the relative stability of silicon nanostructures with reconstructed and unreconstructed surfaces, and we show that surface step geometries unique to highly curved surfaces dramatically reduce the optical gaps and decrease excitonic lifetimes. These predictions provide an explanation of both the variations in the photoluminescence spectra of colloidally synthesized nanoparticles and observed deep gap levels in porous silicon. 相似文献
35.
Masciocchi N Ardizzoia GA Brenna S Castelli F Galli S Maspero A Sironi A 《Chemical communications (Cambridge, England)》2003,(16):2018-2019
Two new 3D homoleptic binary imidazolates, Cd(im)2 and Hg(im)2 (Him = imidazole), as well as [Hg(im)]NO3, containing 1D polycations of [Hg(im)]n(n+) formulation, have been prepared and characterized by ab-initio XRPD methods. 相似文献
36.
Galli F Ramakrishnan S Taniguchi T Nieuwenhuys GJ Mydosh JA Geupel S Ludecke J van Smaalen S 《Physical review letters》2000,85(1):158-161
We report the observation of a new type of charge-density wave (CDW) in the large magnetic-moment rare-earth intermetallic compound, Er5Ir4Si10, which then orders magnetically at low temperatures. Single crystal x-ray diffraction shows the development of a 1D incommensurate CDW at 155 K, which then locks into a purely commensurate state below 55 K. The well-localized Er3+ moments are antiferromagnetically ordered below 2.8 K. We observe very sharp anomalies in the specific heat at 145 and 2.8 K, signifying the bulk nature of these transitions. Our data suggest the coexistence of strongly coupled CDW with local-moment antiferromagnetism in Er5Ir4Si10. 相似文献
37.
Bunyamin Karagoz Giancarlo Galli Hakan Durmaz Gurkan Hizal Umit Tunca Niyazi Bicak 《Colloid and polymer science》2010,288(5):535-542
A novel strategy was developed for tailoring of SiO2 and TiO2 nanoparticle surfaces with poly(ε-caprolactone) (PCL). Thus, a self-curable polyester, poly(2-hydroxypropylene maleate) was
adsorbed on the nanoparticle surfaces and heated to 180 °C to give a cross-linked polyester layer with residual hydroxyalkyl
groups on their surfaces. Surface-initiated polymerization of ε-caprolactone from hydroxyalkyl groups on the surfaces yielded
core-shell nanoparticles with cross-linked core and PCL shells (22.2–71.4%). The organic shell layers around the nanoparticle
cores were evidenced by transmission electron microscopy, dynamic light scattering, and thermogravimetric analyses techniques.
The core-shell nanoparticles were then employed in preparing the stable and the homogenous dispersions with poly(methyl methacrylate-stat-butyl acrylate) solutions. An application of the solutions onto glass substrates yielded uniform and nearly transparent free
standing films (40–60 μm) with good homogeneity as inferred from scanning electron microscopy pictures. 相似文献
38.
Elisa Barea Dr. Giulia Tagliabue Wen‐Guo Wang Dr. Manuel Pérez‐Mendoza Dr. Laura Mendez‐Liñan Francisco J. López‐Garzon Prof. Simona Galli Dr. Norberto Masciocchi Prof. Jorge A. R. Navarro Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(3):931-937
The novel coordination polymers [Cu(Hoxonic)(H2O)]n ( 1 ) and [Cu(Hoxonic)(bpy)0.5]n ? 1.5 n H2O ( 2?H2O ) (H3oxonic: 4,6‐dihydroxy‐1,3,5‐triazine‐2‐carboxylic acid; bpy: 4,4′‐bipyridine) have been isolated and structurally characterised by ab initio X‐ray powder diffraction. The dense phase 1 contains 1D zig‐zag chains in which Hoxonic dianions bridge square‐pyramidal copper(II) ions, apically coordinated by water molecules. On the contrary, 2?H2O , prepared by solution and solventless methods, is based on 2D layers of octahedral copper(II) ions bridged by Hoxonic ligands, further pillared by bpy spacers. The resulting pro‐porous 3D network possesses small hydrated cavities. The reactivity, thermal, magnetic and adsorptive properties of these materials have been investigated. Notably, the adsorption studies on 2 show that this material possesses unusual adsorption behaviour. Indeed, guest uptake is facilitated by increasing the thermal energy of both the guest and the framework. Thus, neither N2 at 77 K nor CO2 at 195 K are incorporated, and CH4 is only minimally adsorbed at 273 K and high pressures (0.5 mmol g?1 at 2500 kPa). By contrast, CO2 is readily incorporated at 273 K (up to 2.5 mmol g?1 at 2500 kPa). The selectivity of 2 towards CO2 over CH4 has been investigated by means of variable‐temperature zero coverage adsorption experiments and measurement of breakthrough curves of CO2/CH4 mixtures. The results show the highly selective incorporation of CO2 in 2 , which can be rationalised on the basis of the framework flexibility and polar nature of its voids. 相似文献
39.
Egle M. Beccalli Prof. Elena Borsini Stefano Brenna Dr. Simona Galli Dr. Micol Rigamonti Gianluigi Broggini Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(5):1670-1678
The isolation of σ‐alkylpalladium Heck intermediates, possible when β‐hydride elimination is inhibited, is a rather rare event. Performing intramolecular Heck reactions on N‐allyl‐2‐halobenzylamines in the presence of [Pd(PPh3)4], we isolated and characterized a series of stable bridged palladacycles containing an iodine or bromine atom on the palladium atom. Indolyl substrates were also tested for isolation of the corresponding complexes. X‐ray crystallographic analysis of one of the indolyl derivatives revealed the presence of a five‐membered palladacycle with the metal center bearing a PPh3 ligand and an iodine atom in a cis position with respect to the nitrogen atom. The stability of the σ‐alkylpalladium complexes is probably a consequence of the strong constraint resulting from the bridged junction that hampers the cisoid conformation essential for β‐hydride elimination. Subsequently, the thus obtained bridged five‐membered palladacycles were proven to be effective precatalysts in Heck reactions as well as in cross‐coupling processes such as Suzuki and Stille reactions. 相似文献
40.
Mahelet Aweke Tadesse Carlo Galli Patrizia Gentili 《Journal of Physical Organic Chemistry》2011,24(7):529-538
The aminoxyl radical 6‐trifluoromethyl‐benzotriazol‐N‐oxyl (TFNO) has been generated from the parent hydroxylamine 6‐CF3‐1‐hydroxy‐benzotriazole (TFBT) by one‐electron oxidation with a CeIV salt and characterized by spectrophotometry and cyclic voltammetry (CV). Rate constants of H‐abstraction (kH) by TFNO from a number of H‐donor benzylic substrates have been determined spectrophotometrically in MeCN solution at 25 °C. A radical H‐atom transfer (HAT) route of oxidation is substantiated for TFNO by several pieces of evidence. The kinetic data also testify the relevance of stereoelectronic effects upon the HAT reactivity of TFNO. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献