Evolution Of Surface Structure Research Articles

Mesoscale observations of surface fronts and low pressure centres in Canadian East Coast winter storms

The movements of surface cold and warm fronts and low pressure centres have been observed in several Atlantic Canada winter storms. Statistical aspects of the ‘well-defined’ surface fronts (7 warm and 6 cold) are presented. Surface wind direction change was considered as the best indicator of the boundaries of the front; frontal zone widths ranged from 23 to 144 km. Average values of wind shifts were 107° for the cold fronts and 85° for warm fronts. Several case studies are presented, based primarily on surface MesoNet data (near Halifax, Nova Scotia and on Sable Island). In two of the cold fronts, there was a two-stage surface structure and rapid evolution as the front passed over the MesoNet. In some cases, both warm and cold, the wind shift and temperature change were coincident while in others they were not. In particular we observed that wind shifts often started 20–30 min ahead of the start of a temperature decrease in these cold frontal passages. A possible mechanism for this is discussed. We found little or no evidence of along-front structure in our data although other investigators have found considerable along-front variation on scales of 0(10 km). Observations of the passage of one low pressure centre are presented. In a second case, surface temperature changes indicated an apparent low pressure centre passage through the Sable Island MesoNet but closer inspection provides an alternative interpretation.

The initial stage of epitaxial growth of Ge on Ge(111) as studied by X-ray diffraction

We present an in situ X-ray scattering study of the evolution of surface structure and morphology during deposition of Ge on Ge(111). The substrate temperature (300 K) was such that the growth proceeds through two-dimensional nucleation. We determined the sites on the c(2 × 8) reconstructed Ge(111) surface to which the first deposited Ge atoms bond. The arrangement of the deposited atoms was inferred from an analysis of the diffracted intensities along the integer-order rods of Bragg scattering perpendicular to the surface plane. We find the first deposited Ge atoms to occupy adsorption sites above the “rest atoms” in the reconstructed unit cell. For higher coverages islands of bilayer height are formed.

Global Martian surface structure and planetary evolution

A model is outlined shortly that explains the Martian surface asymmetry on the basis of interior processes.

Optical studies of silver clusters and larger surface structure evolution on a silver electrode during electrochemical cycling

Utilisation de la luminescence induite par laser et la generation du second harmonique optique pour suivre la formation et l'elimination de structures superficielles sur une electrode d'argent au cours des cycles d'oxydation-reduction dans un electrolyte a fluorure de sodium. Donnees sur les petits agregats d'argent

Molecular dynamics of ionic solid and liquid surfaces

Molecular-dynamics computer simulations of model alkali halide solids and melts were performed with the aim of elucidating the role of electrostatic interactions in the determination of bulk and interphasial behavior. Simplified pair potentials of the $n:1$ form are shown to compare favorably with the results of the more complicated Born-Mayer-Huggins potential, and have great corresponding states capability. New lattice-summation techniques for obtaining the long-range Coulomb correction are also discussed, which are markedly different from the usually adopted Ewald formulas. The properties of solid and liquid surface states were examined under the influence of vacuum and rigid-wall constraints. Both boundaries have noticeable effects on the material to a depth of 10-20 \AA{} into the bulk of the material. Charge separation in the vacuum interphase of model molten LiCl was not observed. The problems associated with definitions of pressure and diffusion coefficients in the interphase are discussed and results are presented. Attempts were made to produce surfaces which would be polar under steady-state conditions. An applied electric field in the direction perpendicular to the surface plane for a melt/vacuum interface did not induce any observable charge separation. It was necessary to apply an electric field equivalent to four times the rootmean-square force at equilibrium before ion desorption into the adjacent vacuum was observed. This took the form of infrequent departures of ion pairs. Slow surface structural evolution was demonstrated by applying an electric field parallel to the surface. The interphasial ionic mobilities were smaller there than in the bulk. The highly polar (111) model NaCl solid surface was unstable with respect to an, as yet, undetermined reconstructed form.

Solid phase epitaxial growth anisotropy of vacuum-deposited amorphous silicon

The crystallization of amorphous silicon deposited in ultra-high vacuum onto silicon crystalline substrates with different orientations is studied by low energy electron diffraction. Layer-by-layer epitaxial regrowth with an activation energy of (3.0 ± 0.2) eV is found to occur for all substrate orientations studied. The regrowth rate is strongly dependent on the orientation of the underlying silicon crystal: the regrowth rate in 〈100〉 direction is the fastest and is 2 and 20 times that in the 〈110〉 and 〈111〉 ones, respectively. A comparison is made of these results with those obtained by other investigators for ion-implanted Si and Ge. The proposed model explains the regrowth rate anisotropy by the difference in formation probabilities of atomic configurations typical for different crystal planes. The evolution of surface structure during crystallization is investigated. [Russian Text Ignored].

Time-resolved evolution of laser-induced periodic surface structure on germanium

We have time resolved the reflection and diffraction of a probe beam from germanium during creation of periodic surface structure by a 20-ns, 1.06-\ensuremath{\mu}m laser pulse. Large, transient diffracted signals typically precede the development of permanent structure while the maximum reflectivity is much less than the melt value. We conclude that inhomogeneous melting and resolidification of the surface occurs following the interference of the incident beam and a nonradiative electromagnetic field.

Phase Transitions in Two-Dimensional Absorbed Layers on Copper Investigated by LEED and Auger Spectroscopy

The equilibrium between one adsorbed phase of sulfur ions (loosely packed) and a reconstructed two-dimensional copper sulfide phase, is studied in ultrahigh vacuum on low index faces of copper. The nucleation from the loosely packed phase of nuclei of the two-dimensional sulfide is characterized under conditions for which sulfur dissolution or evaporation is negligible. The domain of the temperature-coverage diagram for which adsorbed sulfur is present at equilibrium in the two phases is determined. The data lead to an interpretation of adsorption isotherms at low temperature and point to the existence of a critical temperature above which the evolution of surface structure towards saturation proceeds without discontinuity.