Symmetry breaking in the growth of two-dimensional islands on Si(111)

We find that the shape of two-dimensional (2D) Si or Ge islands has a lower symmetry than the threefold symmetry of the underlying Si(111) substrate if Bi is used as a surfactant during growth. Arrow-shaped or rhomb-shaped 2D islands are observed by scanning tunneling microscopy. This symmetry breaking is explained by a mutual shift between the surface reconstructions present on the substrate and on the islands. Using the kinematic Wulff construction the growth velocities of the steps could be determined from the island shape if the nucleation center has been located by a marker technique.     

Size-dependent detachment-limited decay kinetics of two-dimensional TiN islands on TiN(111)

In situ high-temperature (T(a)=1050-1250 K) scanning tunneling microscopy was used to determine the coarsening and decay kinetics of two-dimensional TiN adatom and vacancy islands on atomically smooth TiN(111) terraces. We report the first observation of an abrupt decrease in decay rates, irrespective of T(a), of adatom islands with areas less than a critical value of 1600 A(2). However, no decay rate transition was observed for vacancy islands. We attribute the size-dependent island decay behavior, which is consistent with detachment-limited kinetics, to anisotropic attachment and detachment barriers.     

Dislocations on Ag(111)

Various dislocations on Ag(111) were imaged with a scanning tunneling microscope, e.g. screw dislocations, Lomer-Cottrell locks and stacking fault tetrahedron. The distortion field near a screw dislocation was measured.     

Ag(111)和Au(111)上铋的初始生长行为

半金属铋(Bi)的表面合金具有的Rashba效应,和其具体结构性质有重要关联.本文结合扫描隧道显微镜(STM)和密度泛函理论(DFT),系统地研究了Bi原子在Ag(111)和Au(111)上的不同初始生长行为.在室温Ag(111)上,连续的Ag2Bi合金薄膜会优先在Ag台阶边缘形成;在570 K Ag(111)上,随着...     

Surface-state depopulation on small Ag(111) terraces

The dependence of the local density of states near the Fermi energy E(F) on the width of terraces T is investigated by tunneling scanning spectroscopy on Ag(111) at 7 K. With decreasing T, the electronic density in the occupied surface state shifts monotonically towards E(F), leading to a depopulation at T=3.2 nm in quantitative agreement with a Fabry-Pérot model. Depopulation coincides with a switch from confinement by terrace modulation to step modulation.     

Ar and Kr adsorption on Ag(111)

Precise structural and thermodynamic studies of Kr and of Ar adsorbed on Ag(111) are made using low energy electron diffraction. The phase diagram, lattice constants of the unconstrained monolayer and of the monolayer in equilibrium with the bilayer, latent heats of adsorption and isosteric heats are measured. The results are similar to those of an earlier study of Xe adsorbed on Ag(111). The results are compared to model calculations using effective lateral interactions which are similar to those for Xe/Ag(111). Comparison of the results for Xe, Kr, and Ar on Ag(111) is made using corresponding states scalings. A comparison is also made with properties of the non-registry phases of Xe, Kr, and Ar on basal plane graphite.     

Xe adsorption on Ag(111): Experiment

Precise structural and thermodynamic studies of Xe adsorbed on Ag(111) are made using low-energy diffraction. Spacings are measured relative to those of bulk adsorbed film. Effective equilibrium experiments are done using a directed gas beam and cryopumping. The density of only that gas in the coherently diffracting area is measured by the attenuation of the Ag(01) beam. With decreasing temperature at fixed gas flux one observes the sequential of 2D gas, monolayer, bilayer and bulk films. The effective pressure of the impinging gas is determined from the known bulk vapor pressure so bypassing absolute pressure measurements. The phase diagram, lattice spacings in the film at equilibrium and at zero pressure, latent heats of adsorption and isosteric heats are determined.     

Reversible shape transition of pb islands on Cu(111)

Using low-energy electron microscopy, we have observed a reversible transition in the shape of Pb adatom and vacancy islands on Cu(111). With increasing temperature, circular islands become elongated in one direction. In previous work we have shown that surface stress domain patterns are observed in this system with a characteristic feature size which decreases with increasing temperature. We show that the island shape transition occurs when the ratio of the island size to this characteristic feature size reaches a particular value. The observed critical ratio matches the value expected from stress domains.     

Electroreflectance spectra of Ag(111) electrodes

Electroreflectance (ER) spectra of Ag(111) evaporated electrodes on mica in aqueous electrolytes were measured within the wavelength range of 500 to 200 nm for p- and s-polarized light as a function of the angle of incidence, bias potential and surface roughness. These spectra show structures which were not seen in previously obtained ER spectra on slightly rough, polycrystalline Ag electrodes. The effect of volume and surface plasma excitation on the spectra is clearly indicated. The experimental results cannot be reproduced satisfactorily by any currently employed theoretical model which takes only free electron effects into account. The influence of the electric field on the bound electrons in the surface layer obviously cannot be neglected. It is demonstrated that the surface plasma resonance is shifted in energy by the applied electric field.     

Intermolecular bond length of ice on Ag(111)

Water adsorbed in submonolayer coverage on Ag(111) at 70 K forms hydrogen-bonded networks. High resolution images in combination with calculation reveal that single protrusions represent a cyclic water hexamer with the intermolecular bond stretched to the silver lattice constant of 0.29 nm. Scanning tunneling spectroscopy indicates that the bond length within the two-dimensional hydrogen-bonded water layer is shortened. The spectra contain further information about the vibrational modes of water molecules.     

EELS studies of surface phonons on Ag(111)

High-resolution electron energy loss spectroscopy is used to study surface phonons in the direction of qG on Ag(111). The gap mode (S₂) at in the surface Brillouin zone is measured for the first time. We have also measured the Rayleigh mode and the resonance mode up to the zone boundary. The results are complementary to the earlier He atom scattering measurements and are in good agreement with the first-principles calculations performed recently.     

SPA-LEED studies of growth of Ag on Ag(111) at low temperatures

The surface morphology after deposition of Ag on Ag(111) at low temperatures (130–200 K) has been studied in detail with SPA-LEED (Spot-Profile Analysis of Low-Energy Electron Diffraction). The surface roughness and the mean terrace size have been quantitatively determined under various conditions. At 130 K the surface roughness increases with coverage exactly according to the relation = ^1/2, which indicates that the inter-layer diffusion can be neglected at 130 K. Although the mean terrace length decreases with increasing coverage (following an approximate power law of ^–2/3) for all studied coverages, it is much larger than expected for a pure random or Poisson-growth mode without any diffusion of the adatoms. Therefore, Ag grows on Ag(111) at this temperature without interlayer diffusion but with intra-layer diffusion. The intralayer diffusion barrierE _d has been determined by measuring the temperature dependence of the two-dimensional island density according to the nucleation theory (supposing a critical nucleus size of one). The obtained valueE _c=0.18 eV agrees with the theoretical calculations and previous measurements. Furthermore, from comparing measured and Monte-Carlo-simulated (MC) surface roughness at different deposition temperatures we obtain E=0.05 eV as a lower limit for the additional barrier at steps.     

High-resolution photoemission from Ag(100), Ag(110), and Ag(111)

Energy distribution curves of photoelectrons emitted normal to (100), (110), and (111) faces of silver have been obtained at photon energies of 21.22, 16.85, and 11.83 eV. The results are compared with Christensen's relativistic band structure calculation of bulk silver yielding a close correspondence between experiment and theory. A surface state in the L gap immediately below the Fermi level is identified.