Search results for "Clusters"
showing 10 items of 1274 documents
Study of short-lived tin isotopes with a laser ion source
1995
A chemically selective laser ion source based on resonance ionization of atoms in a hot cavity has been applied for the study of short-lived silver isotopes at CERN/ ISOLDE. Silver atoms were ionized by two resonant excitations and final laser ionization into the continuum. Decay properties of the neutron-rich isotopes121–127Ag were studied with a neutron long-counter and aβ-detector.
Graphene and Fullenene Clusters
2017
Interacting induced-dipoles polarization in code POLAR permits calculating molecular polarizability, which is tested with endohedral metallofullerenes Scn@Cm and clusters Cn (fullerene, graphene, GR). Polarizability identifies aggregates with dissimilar numbers of atoms and separates isomers. Results are of the same order of magnitude as reference computations performed with code PAPID. Polarizability bulk limit is estimated from Clausius–Mossotti relationship. Polarizability trend for clusters vs. size is unexpected: they are more polarizable than bulk. Theory yielded the same for small Sin, Gen and GanAsm; however, experiment oppositely deferred for larger Sin, GanAsm and GenTem. Smaller …
Ab initio LCAO study of the atomic, electronic and magnetic structures and the lattice dynamics of triclinic CuWO4
2013
Abstract The electronic, structural and phonon properties of antiferromagnetic triclinic CuWO 4 have been studied using the first-principles spin-polarized linear combination of atomic orbital (LCAO) calculations based on the hybrid exchange–correlation density functional (DFT)/Hartree–Fock (HF) scheme. In addition, the local atomic structure around both Cu and W atoms has been probed using extended X-ray absorption fine structure (EXAFS) spectroscopy. We show that, by using the hybrid DFT–HF functional, one can accurately and simultaneously describe the atomic structure (the unit cell parameters and the atomic fractional coordinates), the band gap and the phonon frequencies. In agreement w…
Self assembled hydrophobic nanoclusters of poly(methyl methacrylate) embedded into polyvinyl alcohol based hydrophilic matrix: Preparation and water …
2009
Hydrophilic matrices containing nanosized clusters of hydrophilic moieties have demonstrated potential applications in biomedical field. A novel hydrogel containing nanosized domains (20–35 nm) of hydrophobic moieties of poly(methyl methacrylate) (PMMA) was prepared by grafting crosslinked poly(acrylic acid-co-methyl methacrylate) chains onto polyvinyl alcohol (PVA) backbone using an efficient redox system. The graft copolymerization process was investigated to observe the influence of gel components on the kinetic parameters of grafting such as rate of grafting (Rg), grafting yield (Gy) and grafting efficiency (Ge). The prepared graft nanohydrogel was evaluated for its water sorption poten…
Investigation of E0 Transition in 74Kr
2000
The N = Z+2 nucleus 74Kr has been investigated by in-beam conversion electron (CE) and γ ray spectroscopy. The electric-monopole (E0) decay was examined in order to confirm the evidence for a low-lying isomeric 0+2 state and to give insight into the mixing between the predicted coexisting prolate and oblate shapes.
Cluster calculations for H2dissociation on Cu and Ni
1988
Self-consistent cluster calculations have been carried out for hydrogen dissociation on Cu and Ni clusters using local-density theory and the LCAO-DVM expansion. We find physisorption, chemisorption and dissociation minima in the resulting two-dimensional potential energy surfaces, and for the Ni cluster, also an indication of the associative molecular chemisorption state. For Cu we find a considerable barrier at the seam separating the molecular chemisorption and dissociative minima. The analysis of one-electron levels supports the picture of Harris and Andersson that the s to d conversion present on Ni surfaces does not similarly lower the barrier on Cu surface.
Chemically Selective Imaging of Individual Bonds through Scanning Electron Energy-Loss Spectroscopy: Disulfide Bridges Linking Gold Nanoclusters
2020
As proof-of-principle of chemically selective, spatially resolved imaging of individual bonds, we carry out electron energy-loss spectroscopy in a scanning transmission electron microscopy instrument on atomically precise, thiolate-coated gold nanoclusters linked with 5,5'-bis(mercaptomethyl)-2,2'-bipyridine dithiol ligands. The images allow the identification of bridging disulfide bonds (R-S-S-R) between clusters, and X-ray photoelectron spectra support the finding.
Momentum and energy dissipation of hot electrons in a Pb/Ag(111) quantum well system
2021
The band structure of multilayer systems plays a crucial role for the ultrafast hot carrier dynamics at interfaces. Here, we study the energy- and momentum-dependent quasiparticle lifetimes of excited electrons in a highly ordered Pb monolayer film on Ag(111) prior and after the adsorption of a monolayer of 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA). Using time-resolved two-photon momentum microscopy with femtosecond visible light pulses, we show that the electron dynamics of the Pb/Ag(111) quantum well system is largely dominated by two types of scattering processes: (i) isotropic intraband scattering processes within the quantum well state (QWS) and (ii) isotropic interband sca…
Carrier-induced quenching processes on the erbium luminescence in silicon nanocluster devices
2006
The luminescence-quenching processes limiting quantum efficiency in Er-doped silicon nanocluster light-emitting devices are investigated and identified. It is found that carrier injection, while needed to excite Er ions through electron-hole recombination, at the same time produces an efficient nonradiative Auger deexcitation with trapped carriers. This phenomenon is studied in detail and, on the basis of its understanding, we propose device structures in which sequential injection of electrons and holes can improve quantum efficiency by avoiding Auger processes. © 2006 The American Physical Society.
Silicon-based light-emitting devices: Properties and applications of crystalline, amorphous and er-doped nanoclusters
2006
In this paper, we summarize the results of an extensive investigation on the properties of MOS-type light-emitting devices based on silicon nanostructures. The performances of crystalline, amorphous, and Er-doped Si nanostructures are presented and compared. We show that all devices are extremely stable and robust, resulting in an intense room temperature electroluminescence (EL) at around 900 nm or at 1.54 μm. Amorphous nanoclusters are more conductive than the crystalline counterpart. In contrast, nonradiative processes seem to be more efficient for amorphous clusters resulting in a lower quantum efficiency. Erbium doping results in the presence of an intense EL at 1.54 μm with a concomit…