Doped Clusters Research Articles

Optical response of bimetallic Li x Na8?x (0?x?8) and of doped Na8Zn clusters

Using the time dependent local density approximation we calculate the photoabsorption spectra of bimetallic Li x Na8−x (0≦x≦8) and of doped Na8Zn clusters. Ground state cluster geometry and electronic structure are obtained by minimization of total energy from Kohn-Sham self-consistent calculations within the spherically averaged pseudopotential method. For Li x Na8−x clusters we obtain two nearly isomeric geometries. In both cases the corresponding photoabsorption spectra show a single collective excitation (surface plasmon) at increasing frequency as the number of lithium atoms increases. For a given number of lithium atoms, the plasmon frequency of the cluster in the ground state geometry is ∼0.1 eV blueshifted with respect to that in the isomeric state. The equilibrium geometry of doped Na8Zn cluster is formed by a nearly spherical shell of eight Na atoms enclosing the Zn impurity at the cluster center. The corresponding optical spectrum shows two peaks at higher frequencies than the surface plasmon of pure Na8 cluster, in agreement with recent photodepletion spectroscopy experiments.

Optical response of bimetallic and doped alkali clusters

We calculate the photoabsorption spectra of bimetallic Li x Na 20− x (0⩽ x⩽20) and of doped Li 9H and Na 9X (X = F, Cl, Br, I) alkali clusters by means of the time dependent local density approximation. The ground state geometry and electronic structure are obtained by minimization of total energy from Kohn-Sham self-consistent calculations within the spherically averaged pseudopotential method. The results are discussed in relation to the ionic and electronic structures and composition of the clusters. For each cluster in the series Li x Na 20− x with a given content of lithium we obtain several ionic configurations with nearly the same total energy. These isomeric clusters yield however distinguishable photoabsorption spectra. For doped clusters we assume that the impurity atom is located at the center of the cluster and the alkali atoms form a spherical shell around, resulting photoabsorption spectra in qualitative agreement with available photodepletion experiments.

Cobalt clusters in substituted YBa 2 (Cu 1−y Co y ) 3 O 6+x

Abstract This paper reports electron and X-ray diffraction studies along with XAS data of Co-substituted 123 phase. From the geometry and the evolution of diffuse scattering we propose a model based on a Co-cluster formation inducing local orthorhombic/tetragonal deformation in oxidized samples. In these doped samples, Co clusters and YBa2Cu3O6+x domains are juxtaposed. By varying the Co content, the YBa2Cu3O6+x domains size vary and consequently the symmetry of the sample change.Reduction process occur mainly in YBa2Cu3O6+x domains while cobalt coordination is nearly unchanged.