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Chemisorption of atoms and molecules controls many interfacial phenomena such as charge transport and catalysis. The question of how the intrinsic properties of the interacting materials define the electronic structure of their interface remains one of the most important, yet intractable problems in surface physics. Through two-photon photoemission spectroscopy we determine a common binding energy of ϳ1.8-2.0 eV with respect to the vacuum for the unoccupied resonance of the ns valence electron of alkali atoms ͑Li-Cs͒ chemisorbed at low coverage ͑less than 0.1 monolayer͒ on noble metal ͓Cu͑111͒ and Ag͑111͔͒ surfaces. We present a theoretical model based on the semiempirical potentials of the adsorbates and the substrates, their principal mode of interaction through the Coulomb interaction, and the ab initio adsorption structures. Our analysis reveals that atomic size and ionization potential independent interfacial electronic structure is a consequence of the Coulomb interaction among the ns electron, the alkali-atom ionic core, and the induced image charge in the substrate. We expect the same interactions to define the effective electronic potentials for a broad range of molecule/metal interfaces.

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We grew tetragonally distorted FexCo1-x alloy films on Pd(001). Theoretical first-principles calculations for such films predicted a high saturation magnetization and a high uniaxial magnetic anisotropy energy for specific values of the lattice distortion c/a and the alloy composition x. The magnetic anisotropy was investigated using the magneto-optical Kerr effect. An out-of-plane easy axis of magnetization was observed for Fe0.5Co0.5 films in the thickness range of 4 to 14 monolayers. The magnetic anisotropy energy induced by the tetragonal distortion is estimated to be almost 2 orders of magnitude larger than the value for bulk FeCo alloys. Using LEED Kikuchi patterns, a change of the easy axis of magnetization can be related to a decrease of the tetragonal distortion with thickness.

We report on an imaging spin-filter for electrons. The specular reflection of low-energy electrons at the surface of a tungsten single crystal is used to project a spin-filtered two-dimensional image onto a position sensitive detector. Spin-filtering is based on the spin-dependent reflectivity of electrons due to spin-orbit coupling in the scattering target, while a two-dimensional field of view, encoded in the angle of incidence, is conserved in the outgoing beam. We characterize the efficiency of the spin-filter by recording photoelectron emission microscopy images of the magnetic domain structure of 8 monolayers cobalt grown on copper (100).

The spins of a pair of spin-orbit split surface states at a metal surface are usually antiparallelly aligned, in accord with the Rashba model for a two-dimensional electron gas. By first-principles calculations and twophoton photoemission experiments we provide evidence that in the surface alloy Bi/Cu͑111͒ the spins of an unoccupied pair of surface states are parallelly aligned. This unconventional spin polarization, which is not consistent with that imposed by the Rashba model, is explained by hybridization of surface states with different orbital character and is attributed to the spin-orbit interaction. Since hybridization is a fundamental effect our findings are relevant for spin electronics in general.

Summary This paper presents a tutorial discussion of the principles underlying the depth‐dependent Kikuchi pattern formation of backscattered electrons in the scanning electron microscope. To illustrate the connections between various electron diffraction methods, the formation of Kikuchi bands in electron backscatter diffraction in the scanning electron microscope and in transmission electron microscopy are compared with the help of simulations employing the dynamical theory of electron diffraction. The close relationship between backscattered electron diffraction and convergent beam electron diffraction is illuminated by showing how both effects can be calculated within the same theoretical framework. The influence of the depth‐dependence of diffuse electron scattering on the formation of the experimentally observed electron backscatter diffraction contrast and intensity is visualized by calculations of depth‐resolved Kikuchi patterns. Comparison of an experimental electron backscatter diffraction pattern with simulations assuming several different depth distributions shows that the depth‐distribution of backscattered electrons needs to be taken into account in quantitative descriptions. This should make it possible to obtain more quantitative depth‐dependent information from experimental electron backscatter diffraction patterns via correlation with dynamical diffraction simulations and Monte Carlo models of electron scattering.

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