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51.
52.
The synthesis, molecular and supramolecular structure, spectroscopy and electrochemistry of a dialkoxo-bridged diuranyl(VI) compound [(UO2)2(L)2(dimethylformamide)2] (1) derived from the Schiff base ligand H2L, obtained on condensation of 3-methoxysalicylaldehyde with 2-aminoethanol, have been described. The compound has been characterized by IR, UV–Vis, NMR and mass spectra, as well as by single crystal X-ray structure determination. The title compound crystallizes in the monoclinic P21/n space group with the following unit cell parameters a = 10.5713(2) Å, b = 11.9895(2) Å, c = 12.9372(2) Å, β = 102.773(3)° and Z = 2. The structure of 1 reveals that it is a dialkoxo-bridged dinuclear compound of uranium(VI) containing two deprotonated ligands, [L]2−, two dimethylformamide (dmf) molecules and two UO22+ centers. The coordination geometry around the uranium(VI) center is distorted pentagonal bipyramidal; two uranyl oxygens occupy the axial positions, while the basal pentagonal plane is defined by a phenoxo oxygen, two bridging alkoxo oxygens, one imine nitrogen, and one dmf oxygen. Three C–H?O type hydrogen bonds involving one uranyl oxygen, two dmf hydrogens and the imine hydrogen link the dinuclear units into a two-dimensional network. The ESI-MS spectrum of 1 in dimethylsulfoxide exhibits two peaks at m/z = 464.17 and 927.26, which are assignable to [(UO2)2L2H]+ (60%) and [(UO2)2LH]+ (100%) cations, respectively. Cyclic voltammetric measurements of 1 reveal that the uranium(VI) center is reduced quasireversibly at E1/2 = −1112 mV with ΔEP = 97 mV. 相似文献
53.
Porous Silica‐Coated Gold Nanorods: A Highly Active Catalyst for the Reduction of 4‐Nitrophenol
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The successful coating of thin porous silica layers of various thicknesses [(10±1), (12±1), and (14±1) nm] on cetyl trimethylammonium bromide (CTAB) capped gold nanorods was achieved through a modified Stöber procedure. The resulting material was applied as a novel catalyst for the reduction of 4‐nitrophenol. The catalytic activities of the gold nanorods increased up to eight times after coating with a layer of porous silica and the reaction followed a zero‐order kinetics, having a rate constant as high as 2.92×10?1 mol L?1 min?1. The spectral changes during the reduction reaction of 4‐nitrophenol were observed within a very short span of time and a complete conversion to 4‐aminophenol occured within 5–6 mins, including the induction period of ≈2 mins. The reusability of the catalyst was studied by running the catalytic reaction during five consecutive cycles with good efficiency without destroying the nanostructure. The methodology can be effectively applied to the development of composite catalysts with highly enhanced catalytic activity. 相似文献
54.
We demonstrate significant Fowler–Nordheim (FN) tunneling across Al/Al2O3/ZnO metal–insulator–semiconductor (MIS) and Ag/ZnO metal–semiconductor (MS) nanojunctions. The transport properties of ZnO nanostructures in the form of urchins and randomly distributed nanorods were investigated in terms of various conduction mechanism. The minimum voltage necessary for triggering Fowler–Nordheim (FN) tunneling, under forward biasing, was ~1.2 V and ~3.4 V; respectively, below which only direct tunneling and thermionic emission events were evident. Mediated through Al2O3 layer, the FN tunneling was more prominent across MIS junction than MS one. The weak FN tunneling across MS junction was owing to interfacial charge transfer process through the atomic scale gapping between adjacent nanostructures. The extent of such type of tunneling is found to be nanostructure morphology dependent and largely rely on the free electrons donated by the native donor defects in the crystal structure of ZnO. The significant FN tunneling across the MIS and MS junctions has a direct relevance in designing nanoscale field emission devices/components working at low voltage with high throughputs. 相似文献
55.
D. Mohanta S. Biswas A. Choudhury 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,55(3):679-683
In the present work, we show that Mach-Zehnder interferometry (MZI) can be an asset to explore the birefringence properties
of semiconductor nanocrystallites (NCs). A 0.352 μm thick polymer containing ZnSe–NCs (size dispersion: 2.5×1010/cm2) was kept on either of the arms of the MZI (λ=632.8 nm) and the phase angles were measured at the output, corresponding to
three selected spots of the specimen. Owing to the non-resonant excitation led transient polarization in the NCs, strong optical
Kerr-signals were detected with Kerr coefficient values ~1.87 × 10-9 m/V2. The approach may be extended to other optically
isotropic nanoscaled materials having a center of inversion including liquid crystals. 相似文献
56.
Manjit Borah Dambarudhar Mohanta 《Applied Physics A: Materials Science & Processing》2014,115(3):1057-1067
We report on the structural, optical and dielectric characterization of solid state derived, pseudo-cubic nanoscale barium titanates (BTs) with gadolinium (Gd3+) as substitutional dopant. Referring to X-ray diffractograms, apart from the BT peaks related to perovskite structure, the non-existence of any additional peaks due to byproducts has revealed that Gd3+ has undergone substitutional doping into the BT host lattice. The well-separated BT nanoparticles of typical size ~10–15 nm were observed through electron microscopy studies. Following a direct, allowed type carrier transition (n=1/2), a reduction in the optical band gap value (from 3.28 to 3.255 eV) was observed when the Gd-doping level was varied within 0–7 %. Conversely, the Urbach energy followed an increasing trend, from a value of 0.741 to 1.879 eV. Furthermore, the dielectric constant showed a decreasing tendency with doping content and with increasing frequency. However, in the low-frequency region, the loss tangent (tanδ), which is the combined result of orientational polarization and electrical conduction, was found to be quite high in the doped samples as compared to their un-doped counterpart. The frequency-dependent electrical data were also analyzed in the framework of conductivity and impedance formalisms. In particular, the ac conductivity which varies as ~ω s approaches ideal Debye behavior (s→1) for a low Gd level and a higher doping concentration did not show improved dielectric feature of the host. The incorporation of rare-earth (Gd3+) ions into the BT host system could greatly manifest dielectric relaxation and carrier conduction mechanisms, in a given frequency range, and thus can find immense scope in miniaturized nanoelectronic elements including ceramic capacitors and transducers. 相似文献
57.
The radiative decays of heavy mesons are considered in heavy quark symmetry formalism. Introducing the interpolating fields
for the heavy mesons we obtain the transition matrix element and the corresponding decay widths in the heavy quark symmetry
limits. The Isgur-Wise function present in the expression is determined by ISGW quark model. The results obtained agree reasonably
well with other estimations. 相似文献
58.
Rukmani Mohanta 《Physics letters. [Part B]》2002,540(3-4):241-246
The rare decay B+→Ds+φ can occur only via annihilation type diagram in the standard model. The small branching ratio predicted in the standard model makes this channel sensitive to new physics contributions. We analyze this decay mode, both in the standard model and in several extensions of it. The models considered are minimal supersymmetric model with R-parity violation and two Higgs doublet model. The experimental verification of our findings of large branching ratio and/or nonzero CP asymmetry may signal the presence of new physics. 相似文献
59.
The two body non-leptonic Λ
b
decays are analysed in the HQET with factorization approximation and largeN
c
limit. In this limit, Λ
b
and Λ
c
baryons can be treated as the bound states of chiral soliton and heavy meson, and consequently the Isgur-Wise function comes
out in a straight forward manner. The results obtained remain well below their previously predicted upper limit. 相似文献
60.