We use first-principles methods to investigate the adsorption of Cu, Pb, Ag, and Mg onto a H-terminated Si surface. We show that Cu and Pb can adsorb strongly while Ag and Mg are fairly inert. In addition, adsorption states of two types are seen to exist for Pb. We also study the clustering energetics of Cu and Pb on the surface and find that while Cu clusters eagerly, Pb may prefer to form onl...

Atomic force microscopy ~AFM! and high-resolution transmission electron microscope ~HRTEM! cross section imaging of individual gas cluster ion impact craters on Si~100! and Si~111! substrate surfaces is examined. The comparison between 3 and 24 kV cluster impacts from Ar and O2 gas sources is shown. Results for low fluence (10 ions/cm) 24 kV Ar individual cluster impacts onto a Si~100! and Si~1...

The transition from 2D to 3D growth of Ge on Si(001) has been investigated with scanning tunneling microscopy. A metastable 3D cluster phase with well-defined structure and shape is found. The clusters have Ge lattice constants and a (105) facet structure. Results suggest that these clusters provide an easy kinetic path for formation of "macroscopic" Ge islands.

We present a chemical abundance study of three inner old halo clusters NGC 6287, NGC 6293, and NGC 6541, finding [Fe/H] = −2.01 ± 0.05, −1.99 ± 0.02, and −1.76 ± 0.02 (internal), respectively, and our metallicity measurements are in good agreement with previous estimates. We also present the radial velocity measurements of the clusters. Our radial velocity measurements for NGC 6293 and NGC 6541...

To find low energy Si(n)C(n) structures out of hundreds to thousands of isomers we have developed a general method to search for stable isomeric structures that combines Stochastic Potential Surface Search and Pseudopotential Plane-Wave Density Functional Theory Car-Parinello Molecular Dynamics simulated annealing (PSPW-CPMD-SA). We enhanced the Sunders stochastic search method to generate rand...

We use XMM-Newton data to carry out a detailed study of the Si, Fe and Ni abundances in the cool cores of a representative sample of 26 local clusters. We have performed a careful evaluation of the systematic uncertainties related to the instruments, the plasma codes and the spectral modeling finding that the major source of uncertainty is in the plasma codes. Our Si, Fe, Ni, Si/Fe and Ni/Fe di...

BACKGROUND Diatoms are largely responsible for production of biogenic silica in the global ocean. However, in surface seawater, Si(OH)(4) can be a major limiting factor for diatom productivity. Analyzing at the global scale the genes networks involved in Si transport and metabolism is critical in order to elucidate Si biomineralization, and to understand diatoms contribution to biogeochemical c...

In order to develop an improved fundamental understanding of the microscopic effects of hole trapping by oxygen vacancy sites (VO) in amorphous a-SiO2, we have performed ab initio Hartree-Fock calculations of the structure and energy of model silicon dioxide clusters. Three different precursor clusters were employed in these calculations: (A) a 15 atom cluster without rings; (B) a 39 atom clust...