We measured the temperature and azimuthal dependence of the diffusion rates of hydrogen ( 1 H) and deuterium ( 2 H) on Ni(111) from 65 to 240 K where the diffusion rates vary by 8 orders of magnitude. The diffusion of hydrogen crosses over from an activated behavior above 110 K to another activated behavior below 110 K with a smaller activation energy. By ruling out the possibility of a step effect, we suggest that the crossover is from a classical overbarrier hopping to a quantum mechanical underbarrier tunneling. [S0031-9007(97)
Using an optical-reflectivity-difference technique, we monitored the growth of multilayer Xe films on a commensurate monolayer of Xe on Ni͑111͒ from 35 to 60 K. A transition occurs near 40 K from rough growth at low temperature to quasi-layer-by-layer growth characterized by persistent oscillations in the reflectivity difference. We discuss this transition in terms of changes in the island formation process and the onset of second-layer nucleation. The Xe sticking coefficient at 40 K is obtained from the period of the oscillations in the reflectivity difference. We find that the sticking coefficient decreases with increasing film thickness at fixed Xe pressure.
Pulsed laser deposition with simultaneous in situ real-time monitoring of optical spectroscopic ellipsometry and reflection high-energy electron diffraction Rev. Sci. Instrum. 84, 043902 (2013); 10.1063/1.4798621 Thermal diffusion of Co into atomically flat ZnO(000-1) surfaces investigated by scanning probe microscopies and low energy electron diffraction Physical damage and contamination by magnetized inductively coupled plasmas and effects of various cleaning and annealing methods J. Vac. Sci. Technol. A 15, 590 (1997); 10.1116/1.580689Characterization study of GaAs(001) surfaces using ion scattering spectroscopy and x-ray photoelectron spectroscopy
We have studied the electronic properties of Zintl phase KSi, by the ab initio density functional pseudopotential method. Our interest in this Zintl compound is in its current use as a reagent in the synthesis of Si nanoclusters. The structure consists of isolated Si 4 tetrahedra with K atoms situated above each face. The crystal system is cubic with the symmetry of the P4 h3m space group. Band structure calculations show a band gap of 1.3 eV. The presence of K atoms has widened the band gap over that found between occupied and unoccupied energy levels in the Si 4 cluster. The valence bandwidth lies between the valence bandwidth of crystalline Si with diamond structure and the width of the occupied energy levels of the Si 4 cluster. The density of states shows four major structures for the occupied bands. The lowest energy band of conduction states is also given in the density of states plot. The nature of the bonding in the crystal is revealed by an examination of the charge density associated with each of the structures in the density of states. It is found that the dominant bonding between Si atoms is not the covalent bonding of sp 3 hybridized orbitals, as found in diamond structure Si, but is rather a mutual overlap of s-and p-like mixed atomic states from each Si atom. These overlapped states form a bonding state located at the center of the tetrahedron. Furthermore, each K atom is ionized by the nearest Si 4 tetrahedra, allowing the Si atom to fill its 3s and 3p shells.
Theoretical Study of Electronic Properties of Zintl Phase KSi.-The electronic properties of the title compound are studied by the ab initio pseudopotential method. This Zintl compound acts as a reagent in the synthesis of Si nanoclusters. The structure consists of isolated Si 4 tetrahedra with the K atoms situated above each face. KSi crystallizes in the cubic space group P43m. The dominant bonding between Si atoms is not the covalent bonding of sp 3 hybridized orbitals, as found in diamond-type Si, but is rather a mutual overlap of s-and p-like mixed atomic states from each Si atom. -(YANG, L. H.; CONSORTE, CHARLES D.; FONG, C. Y.; PASK, J. E.; NABIGHIAN, E.; KAUZLARICH, SUSAN M.; NELSON, J. S.; Chem. Mater. 10 (1998) 12, 4025-4029; Dep. Phys., Univ. Calif., Davis, CA 95616, USA; EN)
Using an unusual arrangement of optical techniques, we studied the full azimuthal dependence of hydrogen diffusion on a 0.1°-miscut Ni͑111͒ surface vs temperature. From such a dependence, we arrived at the conclusion that the extra energy barrier for a hydrogen adatom to cross a ͓110͔ step edge must be less than 60 meV or 1.5 kcal/mol. ͓S0163-1829͑98͒51336-7͔
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