[en] The influence of interfactants (Au, Ag) on the growth of Pb on Si(111) is studied by low-energy electron microscopy in the temperature range from 260 K to 460 K. On the Si(111)-(7x7) surface Pb grows in the Stranski-Krastanov mode, on the Si(111)-(√(3)x√(3))R30 deg. -Au and on the Si(111)-(6x6)-Au surface in the quasi-Frank-van der Merwe (layer-by-layer) mode. On the Si(111)-(√(3)x√(3))R30 deg. -Ag surface the growth mode changes from layer-by-layer below 300 K to the Stranski-Krastanov mode above 300 K. The temperature dependence of the growth cannot be explained by thermodynamics but is governed by kinetics. The analysis of the maximum island density in terms of the atomistic nucleation theory gives acceptable values for nucleus size and energies only in the layer-by-layer growth regime. In the Stranski-Krastanov growth regime abnormal values are obtained that are attributed to high cluster mobility on the initial two-dimensional layer. The conditions leading to quasi-Frank-van der Merwe growth are discussed

[en] The strong field approximation (SFA) formulated in terms of so-called ‘quantum orbits’ led to much insight into intense-laser driven ionization dynamics. In plain SFA, the emitted electron is treated as a free electron in the laser field alone. However, with improving experimental techniques and more advanced numerical simulations, it becomes more and more obvious that the plain SFA misses interesting effects even on a qualitative level. Examples are holographic side lobes, the low-energy structure, radial patterns in photoelectron spectra at low kinetic energies and strongly rotated angular distributions. For this reason, increasing efforts have been recently devoted to Coulomb corrections of the SFA. In the current paper, we follow a similar line but consider ionization of metal clusters. It is known that photoelectrons from clusters can be much more energetic than those emitted from atoms or small molecules, especially if the Mie resonance of the expanding cluster is evoked. We develop a SFA that takes the collective field inside the cluster via the simple rigid-sphere model into account. Our approach is based on field-corrected quantum orbits so that the acceleration process (or any other spectral feature of interest) can be investigated in detail. (paper)

[en] Non-dipole effects in strong-field photoelectron momentum spectra have been revealed experimentally (Smeenk et al 2011 Phys. Rev. Lett. 106 193002; Ludwig et al 2014 Phys. Rev. Lett. 113 243001). For certain laser parameters and photoelectron momenta the spectra were found to be shifted against the laser propagation direction whereas one would naively assume that the radiation pressure due to the $\mathit{v}\times <!--\; ??\; -->\mathit{B}$-force pushes electrons always in the propagation direction. Only the interplay between Lorentz and Coulomb forces may give rise to such counterintuitive dynamics. In this work, we calculate the momentum-dependent shift in and against the propagation direction by extending the quantum trajectory-based Coulomb-corrected strong-field approximation beyond the dipole approximation. A semi-analytical treatment where both magnetic and Coulomb forces are treated perturbatively but simultaneously reproduces the results from the full numerical solution of the equations of motion. (paper)

[en] The surface sorption process of Eu(III) onto smectite was investigated by TRLFS in the trace concentration range. With increasing pH the formation of an inner-sphere Eu(III) surface complex was observed. The differences in the spectra and the fluorescence emission lifetimes of the surface sorbed Eu(III) in presence and absence of carbonate indicate the formation of ternary clay/Eu(III)/carbonate complexes /1/. (orig.)

[en] A Fourier optics calculation of image formation in low energy electron microscopy (LEEM) is presented. The adaptation of the existing theory for transmission electron microscopy to the treatment of LEEM and other forms of cathode lens electron microscopy is explained. The calculation incorporates imaging errors that are caused by the objective lens (aberrations), contrast aperture (diffraction), imperfect source characteristics, and voltage and current instabilities. It is used to evaluate the appearance of image features that arise from phase objects such as surface steps and amplitude objects that produce what is alternatively called amplitude, reflectivity or diffraction contrast in LEEM. This formalism can be used after appropriate modification to treat image formation in other emission microscopies. Implications for image formation in the latest aberration-corrected instruments are also discussed.

[en] Quasi-elastic electron scattering may provide precise information on the S and the D-wave parts of the ³He ground-state wave function, the neutron form factors, and the role of spin-dependent reaction mechanism effects. An experiment is being performed at the AmPS storage ring at NIKHEF (Amsterdam, the Netherlands), where polarized electrons (up to 900 MeV) are used in combination with large acceptance electron and hadron detectors. Preliminary results from data at four-momentum transfer squared Q² = 0.15 GeV² are presented