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Metal encapsulated silicon clusters M@Sin (M = Ti and Cr and n = 8-16) have been studied using ab-init ultrasoft pseudopotential method. Several structures for each cluster have been optimized to obtain the lowest energy isomers. Our results show that cage strucntures begin to form at the size of n = 12 for Cr@Sin and 13 for Ti@Sin. For Ti@Sin our results are in excellent agreement with the available experimental results. In smaller size, metal doped silicon clusters have basket structures to be of the lowest energy. The bonding nature in these clusters is discussed from the electronic charge distribution.

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Materials Transactions

Growth and magic behavior of metal encapsulated silicon clusters

Silicon clusters doped with a Cr atom have been studied using ab initio plane-wave ultrasoft pseudopotential and Gaussian methods. The most stable structures and magic clusters have been determined for SinCr (n=8-17) starting from many initial configurations. Our results show that for n=8-11 the number of Si atoms is not enough to surround a Cr atom fully and therefore the structures of these clusters are basket type in which the Cr atom has a bare part. A cage structure is formed for n=12. Cr@Si12 and Cr@Si 15 show magic behavior. Among the charged clusters, anion of Cr@Si12 and cation of Cr@Si13 have high stability. The ionization potentials and electron affinities have been calculated. The dynamical stability of clusters is studied from vibrational calculations. The results of Raman activities and infrared intensities are presented for selected clusters. These can be used to identify the structures from experiments. The bonding nature in Cr@Sin clusters is found to change depending on the structure even when the cluster size is the same. {\textcopyright} 2004 The American Physical Society.

Physical Review B - Condensed Matter and Materials Physics

Growth, magic behavior and electronic and vibrational properties of Cr-doped Si clusters

Fulltext

Physical Review Letters

Origin of spontaneous electric dipoles in homonuclear niobium clusters

The paper reports on the robust pattern classification of experimental data using a combined approach of symbolization followed by support vector machine (SVM) classification. Symbolization of data removes unwanted features such as noise whereas SVM provides the classification. The SVM parameters are tuned on-line using a genetic-quasi-Newton algorithm. Benchmark examples illustrate the proposed approach. © 2004 Elsevier B.V. All rights reserved.

Pattern Recognition Letters

Symbolization assisted SVM classifier for noisy data

We report a temperature-dependent scanning tunneling microscopy study of Na adsorption on the Si(111)-(7 X 7) surface by cooling the surface from room temperature to 80 K. While at room temperature Na atoms can diffuse freely on the surface to form a two-dimensional gas, their motion is confined within the 7 X 7 half-unit cells at 160 K. With further cooling to 80 K, Na atoms become localized within individual "basins." The estimated diffusion barriers of Na atoms on the Si(111)-(7 X 7) surface and nature of interaction among them agree well with our theoretical predictions.

Step-by-step cooling of a two-dimensional Na gas on the Si(111)-(7 X 7) surface

Proceedings of Ⅻ International Symposium on Small Particles and Inorganic {\ldots}

Magnetism in supported palladium clusters: Designing novel catalysts from ab initio simulations

The interaction of 3d transition metal atoms and dimers with a single-walled armchair carbon nanotube has been investigated by first-principles density functional calculations. For Fe-, Co- and Ni-doped (4,4) nanotubes, outside adsorption sites are the most favorable. The interactions are largely ferromagnetic for Fe and Co, with the local magnetic moments of the dimers being similar to the free dimers. However, for Ni most structures are nonmagnetic. We have also examined the effects of curvature with calculations for graphene and the (8,8) nanotube. For the (8,8) nanotube, the interaction of Co becomes more favorable inside the nanotube. Doping of a single Co atom transforms the (4,4) and (8,8) nanotubes into half-metals. These results are useful for spintronics applications and could help in the development of magnetic nanostructures and metallic nanotube coatings. {\textcopyright} 2004 The American Physical Society.

Stable geometries and magnetic properties of single-walled carbon nanotubes doped with 3d transition metals: A first-principles study

Recent studies using ab initio total energy calculations have shown exciting possibilities of developing novel metal encapsulated caged clusters of silicon with fullerene-like, Frank-Kasper and other polyhedral structures. In contrast to carbon for which empty cage fullerene structures are stable with 20 or more atoms, 10-16 atom silicon cage structures are stabilized by a guest metal atom. These nanoclusters are predicted to exhibit luminescence in the visible range and could find applications in biological systems, optoelectronics and as tagging material. The Raman and infrared spectra have been calculated and they could help in the experimental identification of the structures. Interaction of these clusters with metal as well as oxygen or hydrogen atoms show that the fullerene structure is stable. Also the interaction between clusters themselves is weak and the ionization potentials, large. These properties make them attractive for cluster assembled materials such as nanowires, nanotubes and other 2 and 3D structures. Studies on hydrogen interaction have led to the predictions of empty center hydrogenated silicon fullerenes SinHn with large HOMO-LUMO gaps. These could further be doped endohedrally or exohedrally to produce novel silicon fullerenes with a variety of properties opening new ways of using silicon for diverse applications. {\textcopyright} 2004 Elsevier B.V. All rights reserved.

Computational Materials Science

Predictions of novel nanostructures of silicon by metal encapsulation

We present a review of the determination of density of states (DOS) of quasicrystals using valence band photoemission spectroscopy. The absence of fine or spiky structure in the angle-integrated DOS of quasicrystals suggests the possibility of delocalized electronic states. These were confirmed with angle-resolved photoemission studies, which clearly establish the presence of dispersing features attributed to momentum-dependent bandstructure. Such dispersing states are observed not only for deeper-lying sp states, but also for d-derived bands near the Fermi level. Data from three different high symmetry surfaces of decagonal Al-Ni-Co, an ideal model system, are presented. We find that only a few dominant reciprocal lattice vectors are sufficient to describe the quasiperiodic potential and the implications for electronic properties are discussed. {\textcopyright} 2004 Elsevier Ltd. All rights reserved.