Search results for " Clusters"
showing 10 items of 1091 documents
Production of dianionic and trianionic noble metal clusters in a Penning trap
2003
Abstract Metal clusters, Aun−, Agn−, and Cun−, from a laser vaporization source are transferred to a Penning trap and subjected to a bath of simultaneously stored electrons. After some reaction period multiply charged anionic gold, silver, and copper clusters are observed if the clusters under investigation are large enough. The cluster sizes for the onset of the formation of dianions and trianions are compared to a charged sphere model. The description of the experimental findings is largely improved if the repulsive Coulomb barrier is taken into account which prevents autodetachment of the surplus electrons on the experimental time scale of a second.
Ab-initio Calculation of the Properties of Permalloys Used in Electrical Machines
2006
In this paper an ab-initio calculation that allows to describe the main features of permalloys is presented. The calculation is bawd on Korringa-Kohn-Rostoker electronic structure method. The dependence of the magnetocryttalline anisotropy and of the magnetostriction on the concentration of non magnetic addiction is computed.
Semi-empirical indo and shell-model calculations for perovskites
1999
Abstract Structural, phonon and some elastic and dielectric properties have been calculated for various paraelectric or ferroelectric phases of the perovskites KNbO3 and SrTiO3, using either the semi-empirical INDO (Intermediate Neglect of Differential Overlap) method or a temperature-dependent shell model. The INDO method was used to calculate the energy changes resulting from [100], [110] or [111] displacements of Nb atoms in the cubic perovskite cell of KNbO3, at 0K. The conventional shell model gives a good account of the elastic, dielectric and phonon properties of the cubic phase of strontium titanate at room temperature, but difficulties remain in modelling the permittivity and elast…
Complex permittivity of FeCl3/AOT/CCl4 microemulsions probed by AC impedance spectroscopy
2009
Abstract The complex permittivity of FeCl 3 /AOT/CCl 4 microemulsions in the 1–10 5 Hz frequency range has been measured by the conventional AC complex impedance technique. Measurements as a function of the volume fraction of the dispersed phase (FeCl 3 + AOT) and temperature at fixed salt-to-AOT molar ratio ( R , R = 0.5) show that the entrapment of FeCl 3 clusters significantly enhances the local permittivity of the AOT reverse micelles and the number density of charge carriers resulting from the peculiar state of the confined inorganic salt. An estimate of the apparent static permittivity of the FeCl 3 ionic clusters entrapped in the core of AOT reverse micelles gives the very high an…
Long-distance spin-transport across the Morin phase transition up to room temperature in ultra-low damping single crystals of the antiferromagnet α-F…
2020
Antiferromagnetic materials can host spin-waves with polarizations ranging from circular to linear depending on their magnetic anisotropies. Until now, only easy-axis anisotropy antiferromagnets with circularly polarized spin-waves were reported to carry spin-information over long distances of micrometers. In this article, we report long-distance spin-transport in the easy-plane canted antiferromagnetic phase of hematite and at room temperature, where the linearly polarized magnons are not intuitively expected to carry spin. We demonstrate that the spin-transport signal decreases continuously through the easy-axis to easy-plane Morin transition, and persists in the easy-plane phase through …
Ferroelastic phase transitions of alkali halide-alkali cyanide mixed crystals
1990
Abstract The alkali cyanides and their CN-rich mixtures with alkali halides are proper ferroelastics with transitions from the cubic high temperature phase into the various non-cubic low temperature phases. As the CN concentration is reduced, the transformations temperature decreases and eventually the ferroelastic low temperature state is suppresse in favour of a glass-like state. The structural and elastic properties of these compounds are discussed with a special emphasis on the martensitic aspect of the transitions.
On the interpretation of the experimental Raman spectrum of β-eucryptite LiAlSiO4 from atomistic computer modeling
2000
Abstract The vibrational spectrum of β-eucryptite LiAlSiO4 with stuffed high quartz structure – commercially relevant for zero-expansion glass ceramics – was calculated by lattice energy minimization and diagonalization of the dynamical matrix using an ab initio based ion-pair shell model potential. A full symmetry analysis of the vibrational modes was carried out. Raman activity of vibrations was calculated under parameterization of individual polarizability factors for each type of interatomic bonds in β-eucryptite LiAlSiO4. Calculated vibrational energies agree with the experimental energies within ±2.3%. Agreement of calculated spectroscopic Raman intensities with experimental intensiti…
Semiempirical Correlation between Optical Band Gap Values of Oxides and the Difference of Electronegativity of the Elements. Its Importance for a Qua…
1997
A semiempirical correlation between the optical band gap of binary oxides and the difference of electronegativity between the oxygen and metallic elements (Pauling's extraionic energy) is proposed. In the frame of the proposed correlation an estimate of the repulsive term in the total lattice energy of ionic oxides is obtained in very good agreement with the existing data. An extension of the correlation to the ternary oxides and hydroxides is proposed by using the concept of average cationic or anionic group electronegativity. The usefulness of the proposed correlation for the in situ characterization of passive films on metals and alloys by photocurrent spectroscopy is illustrated by repo…
Photoionization of metal clusters.
1996
The photoionization cross section of metal clusters is studied using simple theoretical models. In the case of small clusters, the plasmon is well below the photoionization threshold and the photoionization is dominated by simple independent-particle processes: One electron absorbs all the energy of the photon and immediately leaves the cluster. For large sodium clusters the photoionization efficiency curve is a result of a two-step process: First, the photon excites a plasmon and then the plasmon decays, either by emitting a photoelectron or by heating the cluster. A simple expression for the photoionization cross section near the threshold is derived. \textcopyright{} 1996 The American Ph…
Structural and chemical characterization of CdSe-ZnS core-shell quantum dots
2018
Abstract The structural and compositional properties of CdSe-ZnS core-shell quantum dots (QDs) with a sub-nm shell thickness are analyzed at the atomic scale using electron microscopy. QDs with both wurtzite and zinc blende crystal structures, as well as intermixing of the two structures and stacking faults, are observed. High-angle annular dark-field scanning transmission electron microscopy suggests the presence of a lower atomic number epitaxial shell of irregular thickness around a CdSe core. The presence of a shell is confirmed using energy dispersive X-ray spectroscopy. Despite the thickness irregularities, the optical properties of the particles, such as photoluminescence and quantum…