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The strategy of anchoring molecular catalysts on electrode surfaces combines the high selectivity and activity of molecular systems with the practicality of heterogeneous systems. The stability of molecular catalysts is, however, far less than that of traditional heterogeneous electrocatalysts, and therefore a method to easily replace anchored molecular catalysts that have degraded could make such electrosynthetic systems more attractive. Here, we apply a non-covalent “click” chemistry approach to reversibly bind molecular electrocatalysts to electrode surfaces via host-guest complexation with surface-anchored cyclodextrins. The host-guest interaction is remarkably strong and allows the flow of electrons between the electrode and the guest catalyst. Electrosynthesis in both organic and aqueous media was demonstrated on metal oxide electrodes, with stability on the order of hours. The catalytic surfaces can be recycled by controlled release of the guest from the host cavities and readsorption of fresh guest. This strategy represents a new approach to practical molecular-based catalytic systems.

We have investigated emission patterns and energy spectra of electrons from a tungsten nanotip induced by circularly polarized femtosecond laser pulses. Variations of emission patterns were observed for different helicities of circular polarization while the energy spectra remained almost identical. The physics behind this difference in emission patterns is the change in propagation directions of surface electromagnetic waves on the tip apex. The energy spectra showed the same spectroscopic signatures as the linearly polarized laser in a strong-field regime, which are a low-energy peak and a plateau feature. The low-energy peak is due to a delayed electron emission with respect to a prompt emission. The experimental data and plasmonic simulations support our previous conclusion, where the observed delayed emission processes originate from an inelastic rescattering process. This work demonstrates that the use of circular polarization is an easy means to add extra knobs to control the spatial and temporal emission from a nanotip at the nanometer and femtosecond scale. It could find applications as a helicity-driven subcycle optical switch.

We study the fate of the surface states of Bi$_2$Se$_3$ under disorder with strength larger than the bulk gap, caused by neon sputtering and nonmagnetic adsorbates. We find that neon sputtering introduces strong but dilute defects, which can be modeled by a unitary impurity distribution, whereas adsorbates, such as water vapor or carbon monoxide, are best described by Gaussian disorder. Remarkably, these two disorder types have a dramatically different effect on the surface states. Our soft x-ray ARPES measurements combined with numerical simulations show that unitary surface disorder pushes the Dirac state to inward quintuplet layers, burying it below an insulating surface layer. As a consequence, the surface spectral function becomes weaker, but retains its quasiparticle peak. This is in contrast to Gaussian disorder, which smears out the quasiparticle peak completely. At the surface of Bi$_2$Se$_3$, the effects of Gaussian disorder can be reduced by removing surface adsorbates using neon sputtering, which, however, introduces unitary scatterers. Since unitary disorder has a weaker effect than Gaussian disorder, the ARPES signal of the Dirac surface state becomes sharper upon sputtering., Comment: 5+2 pages. 4 figures

The hexagonal boron-nitride ‘nanomesh’ surface reconstruction on Rh(1 1 1) [Corso et al., Science 303 (2004) 217–220] has been investigated using surface X-ray diffraction utilizing synchrotron radiation. This unique structure has been found to be stable under ambient atmosphere which provides an important basis for technological applications like templating and coating. The previously suggested (12 × 12) periodicity of this reconstruction has been unambiguously confirmed and structural features are discussed in the light of the X-ray diffraction results.

The structure of hexagonal boron nitride (h-BN) on Pd(1 1 1) was studied with low energy electron diffraction (LEED), photoelectron spectroscopy and scanning tunnelling microscopy (STM). h-BN forms flat monolayers on the Pd(1 1 1) surface in contrast to Rh(1 1 1) where a complex self-assembled double layer structure, the nanomesh (M. Corso, W. Auwarter, M. Muntwiler, A. Tamai, T. Greber, J. Osterwalder, Science 303 (2004) 217), appears. The LEED patterns reveal a dominating 10 · 10 h-BN superstructure, with a second, distinct structure rotated by 30� and further azimuthally randomly oriented h-BN overlayers. This is consistent with STM images which show several different Moirepatterns associated with different rotation angles of the overlayer. Additionally the use of thin Pd(1 1 1) films instead of single crystal substrates was studied. No significant differences in the h-BN film quality were found. � 2006 Elsevier B.V. All rights reserved.

A new procedure is demonstrated for cross-correlating light and electron pulses in a time-resolved surface diffraction experiment using low-energy electrons: Ultrashort laser pulses produce a space charge that modulates the transmission of the electron pulses across a pinhole. The proposed method is easily implemented into present pump-probe setups and represents a simple means for establishing spatial and temporal overlap of light and electron pulses on the sample. Moreover, the ultrafast space-charge dynamics allow the temporal resolution of the electron pulses to be characterized down to a time scale of less than 20 ps.

The spin–orbit-split L-gap surface states on Au(111) are investigated by means of spin- and angle-resolved photoelectron spectroscopy and relativistic first-principles calculations, the latter including both electronic structure and photoemission. The dispersion, momentum distribution and spin polarization of the surface states are consistent with those of a two-dimensional electron gas with Rashba–Bychkov spin–orbit coupling (SOC). The surface symmetry manifests itself in the spin-integrated photoemission intensities, thereby providing details of the orbital composition of the surface states. For the spin polarization, modulations which show up in theory are below the experimental detection limit of 5%. The dependence of both dispersion and spin polarization on the SOC strength are addressed theoretically. The combination of experiment and theory establishes a consistent picture of the L-gap surface states. (Some figures in this article are in colour only in the electronic version)

On Cu(2 2 1) it is possible to grow long ordered one-dimensional chains of C 60 molecules aligned along the steps of this vicinal template. By scanning tunneling microscopy (STM) a unit cell with two distinctly imaged molecules is found. From distribution of the rare defects a bond energy difference of the two types of molecules is inferred. At least in one of the two species, the molecules have a well-defined orientation as determined by X-ray photoelectron diffraction (XPD).

The growth of hexagonal boron nitride (h-BN) on Ni(1 1 1) at submonolayer coverages results in triangular islands with two different orientations. In combining X-ray photoelectron diffraction and scanning tunneling microscopy it is demonstrated that these two island types correspond to fcc and hcp domains of h-BN/Ni(1 1 1). The domain boundaries appear as defect lines that are also present in complete h-BN monolayers. Based on the experimental data, structural models for the two domains and the defect lines are discussed. � 2003 Elsevier B.V. All rights reserved.

The electronic structure of an incommensurate Pb layer on Cu(1 1 1) is investigated by means of angle scanned ultraviolet photoemission. Despite of the rather complex atomic structure with three competing periodicities, we observe a well defined band structure, reflecting essentially the fundamental (1 1)-periodicity of the adlayer. Comparison with band structure calculations for a free standing Pb-layer shows that all observed bands can be fully attributed to the overlayer. 2003 Elsevier Science B.V. All rights reserved.

The growth of cobalt on a monolayer of hexagonal boron nitride on Ni(1 1 1) has been studied in a combination of scanning tunneling microscopy and X-ray photoelectron spectroscopy (XPS). A detailed picture of the growth kinetics is obtained. The Co sticking coefficient strongly decreases at high substrate temperatures. Co deposition results in two different morphologies: (i) three-dimensional clusters that grow on top of the hexagonal boron nitride ( h -BN) film and often align themselves to form chains and (ii) islands with a more two-dimensional character, which are intercalated below the h -BN film dominate at higher substrate temperatures. From XPS measurements at different deposition temperatures an activation energy for intercalation of ∼0.24 eV is inferred. The influence of observed defect lines in the h -BN overlayer on the growth kinetics is discussed.

Nickel (111) and the interface of hexagonal boron nitride on Ni(111) serve as model systems for an itinerant ferromagnet that is truncated with vacuum or a single layer insulator. These systems are investigated with angle-scanned He I and He II photoemission. Upon formation of the h-BN/Ni(111) interface the work function drops by 1.8 eV and the minority Ni Λ3d-band shifts by 0.13 eV to higher binding energy. This indicates that the Ni magnetic moment decreases in the interface. Spin-polarized band structure calculations from bulk nickel identify the observed minority and majority bands. The experimental Fermi surface maps show that h-BN distorts a minority d-band in a way which is consistent with the decreasing magnetic moment. It can be seen that h-BN affects the scattering of the electrons. Effects in the photoemission final and initial state are recognized.

By means of spin- and angle-resolved photoelectron spectroscopy we studied the spin structure of thin films of the topological insulator Bi2Se3 grown on InP(111). For thicknesses below six quintuple layers the spin- polarized metallic topological surface states interact with each other via quantum tunneling and a gap opens. Our measurements show that the resulting surface states can be described by massive Dirac cones which are split in a Rashba-like manner due to the substrate induced inversion asymmetry. The inner and the outer Rashba branches have distinct localization in the top and the bottom part of the film, whereas the band apices are delocalized throughout the entire film. Supported by ab initio calculations, our observations help in the understanding of the evolution of the surface states at the topological phase transition and provide the groundwork for the realization of two-dimensional spintronic devices based on topological semiconductors.

For the first time we extended the RABBITT technique to condensed matter. Simultaneous measurement with a reference argon target allowed us to resolve photoemission delays in noble metals. The results show attosecond dynamics beyond transport.

We have investigated the atomic and electronic structure of the incommensurate ‘quasi-5×5’ surface obtained by annealing about 1 ML of Cu on Si(1 1 1). Si 2p core level photoemission reveals the presence of only one chemically non-equivalent site in the overlayer. Valence band ultraviolet photoelectron diffraction (UPD) in the Cu 3d region shows a threefold symmetry of the surface electronic states not observed before. X-ray photoelectron diffraction (XPD) measured on the Cu 2p level gives an almost sixfold pattern and indicates a Cu terminated surface, in agreement with Auger electron diffraction measurements of Chambers and coworkers [1] . Simulations of the Cu 2p XPD pattern were performed in the single-scattering-cluster spherical-wave approximation, and a good agreement with the data was reached for a Cu2Si model proposed by Zegenhagen and coworkers [2] , which is also consistent with the threefold features observed in UPD. A structural refinement was performed for the vertical positions of the Si and the two Cu atoms within this two-dimensional silicide layer.

In angle-resolved photoemission from single-crystal samples, the shape of the Fermi edge can be severely distorted by electronic bands crossing the Fermi energy. Analysing temperature-dependent angle-resolved photoemission data from the (111) surface of nickel metal, we explored how far the spectral background below such bands can be described by a Fermi–Dirac distribution function and, intimately connected with this discussion, how far we can deduce the temperature of the sample from this background. For this purpose, we present a fitting procedure that is applicable to angle- and energy-resolved photoemission data sets which permits one to selectively remove band transitions from such data and to extract this background in a reliable fashion. The sample temperature can be reasonably, but not quantitatively, determined by this procedure.

Full kk-maps of the electronic structure near the Fermi level of dierently doped cuprates measured with angle-scanned photoelectron spectroscopy are presented. The valence band maximum of the antiferromagnetic insulator Sr2CuO2Cl2, which is taken as a representative of an undoped cuprate, and the Fermi surfaces of overdoped, optimally doped and underdoped Bi2Sr2CaCu2O8+ high-temperature superconductors are mapped in the normal state. The results conrm the existence of large Luttinger Fermi surfaces at high doping with a Fermi surface volume proportional to (1 +x), where x is the hole concentration. At very low doping, however, we nd that this assumption based on Luttinger's theorem is not fullled. This implies a change in the topology of the Fermi surface. Furthermore the intensity of the shadow bands observed on the Fermi surface of Bi2Sr2CaCu2O8+ as a function of the doping is discussed. PACS. 79.60.-i Photoemission and photoelectron spectra { 74.25.Jb Electronic structure { 71.18.+y Fermi surface: calculations and measurements; eective mass, g factor

The routine measurement of full hemispherical photoemission intensity maps gives us the possibility for the combined investigation of structural and electronic phenomena at surfaces. As an example the growth of ultrathin films of Co on Cu(111) is studied as a function of film thickness. While X-ray photoelectron diffraction (XPD) shows the early appearance of stacking faults as a precursor of the hcp structure, Fermi surface maps reveal the very fast evolution of the Co Fermi surface that can be compared to measurements on a clean Co(0001) crystal. For the system O/Rh(111), XPD brings up important structural clues, relating changes in surface reactivity to small amounts of subsurface oxygen, which forces adjacent oxygen atoms to occupy new and more reactive adsorption sites. In the course of this last study we observed for the first time the weak backscattering signals in the angular pattern of adsorbate emission. These cone-like features are extremely sensitive to the adsorbate–substrate bond length.

The doping of a C60/Ag(100) interface with K is studied by high resolution valence band photoemission spectroscopy. With increasing potassium exposure the progressive filling of the C60 lowest unoccupied molecular orbital (LUMO) derived band is observed. The charge transfer onto the C60 molecules is quantified from the observed binding energies of the LUMO derived band. Up to a half filled LUMO no rigid band shift is found. Furthermore the intensity of the highest occupied molecular orbital is not constant but shows in normal emission a pronounced dip between half and complete LUMO filling.

An anatase thin film, TiO 2 (001), has been grown by metal–organic chemical vapor deposition on a SrTiO 3 (001) substrate. The electronic and structural properties of the anatase thin film were investigated by X-ray photoelectron spectroscopy, low energy electron diffraction (LEED), and X-ray photoelectron diffraction (XPD). Comparisons of the core-level binding energies for O 1s and Ti 2p 3/2 photoelectrons was made between anatase and rutile, and were found to be identical for both polymorphs. Structurally, the surface gave a (1×1) LEED pattern with a high background, indicating regions of good long-range order. Comparison between experimental XPD data and single-scattering cluster calculations indicate that there is good agreement with an anatase crystal termination, and poor agreement with a rutile crystal termination. Furthermore, good agreement was found at low takeoff angles for experiment and calculations suggesting that the thin film has good short-range order at the surface. This study indicates that anatase is stable and does not undergo a transformation to the rutile polymorph when exposed to atmosphere after film growth or after heating to low temperatures in ultrahigh vacuum.

Monolayers of hexagonal boron nitride have been grown by the reaction of benzene-like borazine (BN)3H6 with Ni(111) at 1050 K. The resulting layers are analyzed by means of Si Kα excited N 1s and B 1s X-ray photoelectron diffraction (XPD) and scanning tunneling microscopy (STM). STM shows large terraces without defects and resolves two different atomic species that are commensurate with Ni(111). From XPD it is found that the system discriminates fcc from hcp adsorption sites, that the h-BN layer is corrugated and that nitrogen terminates the surface. The B–N corrugation is determined quantitatively by R-factor analysis between single scattering cluster calculations and experiment. The results are discussed in connection with an existing LEED analysis on the same system [Y. Gamou, M. Terai, A. Nagashima, C. Oshima, Sci. Rep. RITU A 44 (1997) 211].

A Rh(111) surface has been exposed to oxygen under conditions that favour the formation of a subsurface oxygen species. After exposure to 10 5 L O 2 at a surface temperature of 470 K X-ray photoelectron diffraction data of O 1s emission reveal that (5±2)% of a monolayer of oxygen atoms occupy octahedral interstitial sites just underneath fcc adsorption sites. The occupation of such a site forces the oxygen atoms adsorbed in its close vicinity to switch from the stable fcc site to the hcp adsorption site. Implications of this finding for the interpretation of temperature-programmed desorption spectra, as well as for the catalytic behaviour of the oxidized Rh(111) surface, are discussed.

The dependence of the height of the elastic peak and the Auger signal on the incidence angle of the primary electron beam was used to investigate the crystalline structure of the Ag/Cu(001) adsorption system. For the clean Cu(001) face experimental elastic peak profiles were compared with results of single scattering cluster (SSC) calculations, where main intensity maxima are reproduced. Auger scans for Cu M2,3VV and LMM transitions and elastic peak scans exhibit similar maxima for the same Ep=2.0 keV. For 8 ML of Ag the populations of four possible domains of Ag(111) were determined by an R-factor analysis. The growth of one domain was found to be preferred which can be rationalised by the miscut of the sample and the resulting step orientation.

Using a monochromatized high-flux He discharge lamp, we have investigated the electronic bands of hexagonal-closed packed (hcp) Co(0001) near the Fermi energy at room temperature. Particularly, sections through the Fermi surface have been measured by high-resolution photoemission using photon energies of 21.2 eV and 40.8 eV. Compared to analogous measurements from copper and nickel surfaces, the features here are less sharp, even though LEED patterns indicate a similar degree of surface order. Still, an interpretation of these data in terms of calculated Fermi surface contours is possible. The Fermi wave vectors of the minority d-hole pocket centered at the Γ-point, are well reproduced. This is furthermore corroborated by polar-angle dependent dispersion measurements along two high-symmetry azimuths.

This work was partially funded by the Spanish agency DGCYT under Grant No. PB94-0022-c02-01 and PB92- 0030 .

A particularly interesting phenomenon of rare-earth metals and their compounds is the mixed valence, which is intimately connected with the structural properties of a material. We report structural and spectroscopic results from the [Formula: see text] interface, with particular emphasis on the interplay between surface structure and valence. A strong reconstruction of the substrate surface is observed, with the Yb atoms occupying substitutional sites. A small fraction of Yb atoms is identified to occupy second-layer sites in otherwise unreconstructed surface patches. It is shown that these subsurface Yb atoms are in a mixed-valent 4f14-δ state, whereas the surface atoms in the [Formula: see text] geometry persist in the divalent 4f14 state.

Angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) data are usually measured spectrum by spectrum at various emission angles or photon energies in order to observe the dispersion of energy bands in solids and on their surfaces. In these lecture notes an alternative experimental procedure is described which yields a direct mapping of constant energy surfaces within the band structure, and specifically of the Fermi surface. This approach appears very promising, in particular when applied to magnetic systems and systems with narrow bands. Fermi surfaces of surface states are seen in direct relation to the underlying bulk Fermi surface.

By extending the RABBITT technique to noble metal surfaces the authors observed, for the first time, sub-cycle resolved dynamics with attosecond pulse trains in condensed matter systems. In contrast to streaking, this method is applicable to low-energetic harmonics and the required IR field strength is significantly lower. A simultaneously recorded RABBITT trace in argon allowed the proponents to evaluate the absolute, surface specific contribution to the transition phase.

Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence., By angle-resolved photoemission spectroscopy (ARPES) we observe a giant Rashba-type spin splitting in the electronic bulk conduction and valence bands of the semiconductor BiTeCl. This material belongs to the group of bismuth tellurohalides BiTeX (X = Cl,Br,I) which are layered non-centrosymmetric materials with strong spin-orbit interaction. By photon energy-dependent ARPES, we separate the bulk and surface contribution of the electronic structure and show that the tellurium-terminated (0001) crystal surface hosts spin-split two-dimensional surface states. On the chlorine-terminated surface at the opposite side of the crystal no surface states are observed due to photon-induced surface chemistry. © IOP Publishing and Deutsche Physikalische Gesellschaft., This work was supported by the Swiss National Science Foundation and the Ministry of Education and Science of the Russian Federation (grant no. 2.8575.2013).

Room temperature ultraviolet photoemission data taken with high angular and energy resolution from Ni(110) are presented. Recording the total photoelectron intensity in a small energy window near the Fermi energy (EF) on a polar scan along the [1 1 0] azimuth allows to clearly distinguish several bands, and in particular an exchange-split sp-band, by their different positions in k-space. Moreover, we present six two-dimensional cuts through k-space obtained by extended angular scanning at different electron binding energies at and near EF. Well defined lines in these maps can be clearly assigned to minority and majority sp- and d-bands and their location in k-space can be determined accurately thus providing sections through their constant-energy surfaces.

We measured the normal state Fermi surface of a Pb 0.42 Bi 1.73 Sr 1.94 Ca 1.3 Cu 1.92 O 8+x (001) single crystal using angle resolved photoemission. Our experimental approach allows us to see the full topology and symmetry of this essentially two-dimensional system. The geometrical structure is probed using x-ray photoelectron diffraction and transmission electron microscopy. Structural effects on Fermi surface features are discussed. Moreover, a series of energy distribution curves is measured for an azimuthal scan of emission angles and a quantitative analysis of the bands crossing the Fermi level is given.

BiTeI has a layered and noncentrosymmetric structure where strong spin-orbit interaction leads to a giant Rashba spin splitting in the bulk bands. We present direct measurements of the bulk band structure obtained with soft x-ray angle-resolved photoemission (ARPES), revealing the three-dimensional Fermi surface. The observed spindle torus shape bears the potential for a topological transition in the bulk by hole doping. Moreover, the bulk electronic structure is clearly disentangled from the two-dimensional surface electronic structure by means of high-resolution and spin-resolved ARPES measurements in the ultraviolet regime. All findings are supported by ab initio calculations. © 2012 American Physical Society., This work was supported by the Swiss National Science Foundation.

Au films 0.24 to 5.9 monolayers thick were evaporated on Pt(011), and the growth mode was investigated with X-ray photoelectron diffraction. At 0.5 monolayer coverage most Au atoms are found in the second layer below the surface while a few atoms diffuse as far as four layers deep even though Au is not miscible with Pt in the bulk at low concentrations. With increasing coverage the missing rows of the Pt(011) (2×1) reconstruction are gradually filled by replaced Pt atoms and further Au atoms, but the top layer relaxation is not changed significantly. At high coverages Au grows epitaxially as Au(011) on the Pt(011) surface and exhibits a poorly developed missing-row reconstruction.

We observe time-resolved and polarization dependent two-, three-, and four-photon transitions from a Ni(111) surface covered with a monolayer of hexagonal boron nitride. The spectra show features due to transitions involving two unoccupied intermediate states: the n=1 image potential state of Ni(111) and a boron nitride-related interface state. We use these transitions in order to track the effects of space-charge on the spectra in view of pump-probe experiments, at high excitations densities. A simple model is presented, which reproduces the measured energy shifts and broadenings in great detail, allowing the ultrafast dynamics and the space-charge effects to be disentangled. Moreover, owing to the high excitation densities an additional particular three-photon transition via both the interface state and a virtual intermediate state could be measured and identified. The polarization-dependent transient of this transition has successfully been simulated, allowing the lifetime of the involved intermediate state to be extracted from the data.

6 páginas, 4 figuras.-- PACS number(s): 71.20.Tx, 71.38.-k, 79.60.-i, 31.70.-f.-- et al., The low-energy single-particle excitations of highly ordered C60 chains adsorbed on a vicinal copper substrate are investigated by angle-resolved photoemission spectroscopy. The interface state previously identified on C60/Cu(111) shows a one-dimensional dispersion on Cu(553). In contrast, no significant momentum dependence is detected for emission from the lowest unoccupied molecular orbital (LUMO). The LUMO displays similar phonon features as in C60/Cu(111) but it does not peak toward the Fermi level for all considered potassium dopings and its photoemission lineshape is broader than in any other monolayer system investigated so far. This behavior is not easily reconciled with existing theory and indicates that the one-dimensional character of the chains affects the electronic structure of the monolayer in an intricate way., The project was supported by the Swiss National Science Foundation.

The valence-band electronic structure of a clean Ni(111) surface is investigated by spin-resolved photoemission. At room temperature the orientation of the photoelectron spins on the Bloch sphere and the exchange splitting of surface and bulk states along the surface normal $(\overline{\ensuremath{\Gamma}})$ are determined. All investigated states are found to have a sizable exchange splitting $g50\text{ }\text{meV}$. Since the splitting is smaller than the intrinsic line width in the spin-integrated spectrum this is only seen with a spin-resolved technique. At room-temperature photoemission reaching above the Fermi level directly shows that the Shockley type surface state ${S}_{1}$ has an occupied majority and an unoccupied minority band with a splitting $\ensuremath{\Delta}{E}_{ex}=62\ifmmode\pm\else\textpm\fi{}15\text{ }\text{meV}$. The surface states below the Fermi energy show a larger exchange splitting for in-plane hybridization $[\ensuremath{\Delta}{E}_{ex}({S}_{3})=160\text{ }\text{meV}]$ than for out-of-plane hybridization $[\ensuremath{\Delta}{E}_{ex}({S}_{2})=55\text{ }\text{meV}]$.

The concept of vectorial spin analysis in spin and angle resolved photoemission is illustrated in this report. Two prototypical systems, Bi/Ag(111)(sqrt3 x sqrt3)R30 and Pb/Ag(111)(sqrt3 x sqrt3)R30, which show a large Rashba type spin-orbit splitting, were investigated by means of spin and angle resolved photoemission. The spin polarization vectors of individual bands are determined by a two-step fitting routine. First, the measured intensities are fitted with an appropriate number of suitable peaks to quantify the contributions of the individual bands, then the measured spin polarization curves are fitted by varying for each band the polarization direction and its magnitude. We confirm that the surface states experience a large spin splitting. Moreover, we find that all surface state bands are 100 percent spin polarized, and that for some states spin polarization vectors rotate out of the surface plane.

The (114) surface of the semimetal Bi is found to support a quasi-one-dimensional, metallic surface state. As required by symmetry, the state is degenerate along the Gamma-Y line of the surface Brillouin zone with a highest binding energy of approximately 150 meV. In the Gamma-X direction the degeneracy is lifted by the strong spin-orbit splitting in Bi, as directly shown by spin-resolved photoemission. This results in a Fermi contour consisting of two closely separated, parallel lines of opposite spin direction. It is argued that similar states on related insulators would give rise to a one-dimensional quantum spin Hall effect.

An extended set of temperature-dependent ARUPS data from Ni(111) is presented. The ferromagnetic and the paramagnetic state as well as the phase transition are examined in great detail. Rather new and unconventional modes of data acquisition in ARUPS are applied with high angular and energy resolution, exhibiting great power near the Fermi energy EF. Even up to 5kBT above EF energy bands are readily observed. The understanding of these ARUPS data is strongly enhanced by spin-polarized band structure calculations. Exchange-split bands of both, sp- and d-character, are resolved in angular scans and in photoemission Fermi-surface maps. From two-dimensional data sets in energy and angle the dispersion and the exchange splitting are obtained with high precision. All the observed sp- and d-bands clearly exhibit a Stoner-like collapsing-band behavior. The exchange splitting ΔEex vanishes above TC in all cases, and ΔEex closely follows the temperature dependence of the macroscopic magnetization. The apparent deviations from the Stoner-like band behavior stated in P. Aebi et al. , Phys. Rev. Lett. 76, 1150 (1996) are explained. Furthermore we detect anomalously high intensity from a minority d-band close to an sp-band. This strongly suggests that sp-d-fluctuations at the Fermi level are a driving force for the magnetic phase transition of nickel.

A section through the three-dimensional Fermi surface of Ni has been mapped perpendicular to the [110] direction using angle-scanned photoemission. Regions of minority and majority spin bands, well separated in k space, can clearly be identified through comparison with a band structure calculation. The behavior of the different bands is observed for temperatures below and above the Curie temperature TC. We find bands which move and bands which stay in place for going from TTC.

High-resolution angle-resolved photoemission reveals a complex electronic structure at the interface between a highly ordered ${\mathrm{C}}_{60}$ monolayer and the Cu(111) surface. The Shockley-type surface state of the clean substrate is pushed to higher energies by the overlayer and strongly couples to intramolecular ${\mathrm{C}}_{60}$ phonons. A second interface state with a bandwidth spanning the entire HOMO-LUMO gap disperses with the periodicity of the ${\mathrm{C}}_{60}$ superstructure. Density functional theory calculations indicate that this state is due to strong hybridization of molecular orbitals and substrate electronic states at the ${\mathrm{C}}_{60}$/metal interface. This finding sheds light on the issue of self-doping in molecular layers on metal surfaces.

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY)., A strong spin-orbit interaction leads to a Rashba-type splitting of the bulk bands of BiTeCl, which results in toroidal Fermi surfaces with distinct spin structures depending on the chemical potential. Here, we present spin- and angle-resolved photoelectron spectroscopy measurements of the three-dimensional spin-orbit split state at the top of the valence band. Its polarization is systematically studied in dependence of the photon energy and compared to ab initio calculations of the initial state. The measured spin orientation is in plane to the (0001) surface and perpendicular to the momentum, independently of the photon energy., We acknowledge partial support from the Basque Country Government, Departamento de Educacion, Universidades e Investigacion (Grant No. IT-756-13), the Spanish Ministerio de Ciencia e Innovacion (Grant No. FIS2010-19609-C02-01), the Ministry of Education and Science of the Russian Federation (Grant No. 2.8575.2013), the Russian Foundation for Basic Research (Grants No. 15-02-02717, No. 15-02-01797), and the Saint Petersburg State University (Project No. 11.50.202.2015). This work was supported by the Swiss National Science Foundation Project No. PP00P2_144742/1.

We present full Fermi surface maps of differently doped Bi 2 Sr 2 CaCu 2 O 8+ x crystals measured with angle-resolved photoemission. We find, for overdoped and optimally doped samples, a large Fermi surface centered at ( π , π ). For an underdoped sample with a T c of 30K the contours of a large Fermi surface are still visible, but the photoelectron intensity is strongly reduced around ( π ,0). The valence band maximum of the undoped antiferromagnetic insulator Sr 2 CuO 2 Cl 2 forms maxima at ( π /2, π /2) and equivalent points.

Photoemission intensities from angle-resolved photoelectron spectroscopy with polarized synchrotron radiation were measured and calculated for a magnetization averaged Ni(111) single-crystal surface. Concentrating on the large variations of intensity in dependence on the experimental geometry and parameters, we discuss the exchange-split $sp$ bands crossing ${E}_{F}$ and identify strong matrix-element effects that are not dependent on selection rules involving parity. Comparison of experimental intensities with ab initio photoemission calculations provides a firm basis for disentangling symmetry from intrinsic effects due to the initial state. The calculated spectra provide a direct connection between ground-state properties (given by the spectral function) and the experimental intensities.

X-ray photoelectron diffraction reveals that ${\mathrm{C}}_{60}$ molecules adsorbed in a monolayer on Ag(111) take different orientations depending on the level of potassium doping. For half filling $({\mathrm{K}}_{3}{\mathrm{C}}_{60})$ and complete filling $({\mathrm{K}}_{6}{\mathrm{C}}_{60})$ of the lowest unoccupied molecular orbital, two distinct orientations are identified, exposing a hexagon or a 6-6 bond to the surface, respectively. For all the intermediate doping levels, the two orientations coexist, which is consistent with phase separation. Characteristic changes in the density of states, calculated for the two orientations within density functional theory, suggest intermolecular electron hopping as a driving force for the molecular reorientation.

The character of the surface state wave function on regularly stepped Cu(111) is reinvestigated. It is shown that the qualitative change at terrace lengths around 17 A observed previously by Ortega et al. [Phys. Rev. Lett. 84, 6110 (2000)]] must necessarily be described as a change from a propagating superlattice state to a terrace-confined quasi-one-dimensional state. This reconciles previous, apparently contradictory experimental results and sheds new light on the behavior of nearly free electrons in nanostructures. Possible mechanisms driving the localization are discussed on the basis of the surface state bulk penetration depth, which has been measured in both regimes.

Visible and UV light spectra display striking differences in optical reflectivity for the two types of monatomic steps on copper (111) surfaces. Electronic structure calculations trace these differences to the specific contributions of p(axially) and p(radially) local densities of states, parallel and perpendicular to the steps, of the distinctly coordinated corner atoms. The local origin of the spectral reflectance anisotropy is further corroborated by experiments on Cu(111) surfaces with varying step densities. Site specificity of the electronic structure of atoms in low coordinated sites on Cu(111) vicinals is thus revealed by reflectance anisotropy spectroscopy which can thereby detect step atom densities down to 10(13) atoms/cm(2).

The influence of CO adsorption on the Shockley type surface state on vicinal Cu(111) surfaces is investigated using angle resolved photoemission. As the steps are decorated with CO the surface state shifts to higher binding energies, which is opposite to the known behavior on flat Cu(111). This is described within a one-dimensional potential model in which clean steps represent repulsive barriers and decorated steps become attractive wells. From the coverage dependence the integrated CO well potential can be quantified. It is ${U}_{\mathrm{CO}}a\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}2.9\phantom{\rule{0ex}{0ex}}\mathrm{eV}\AA{}$ on both Cu(332) and Cu(221) surfaces. Density functional calculations reveal that this attractive potential is due to the very local charge transfer from the Cu step atom to the adsorbed molecule.

The low-energy electronic excitations in cobalt are studied by a theoretical method that includes many-body effects and a realistic description of the band structure. Angle-resolved photoemission spectra measured on a thick film of hexagonal close-packed Co on Cu(111) agree well with calculated spectral functions. Because of many-body effects no sharp quasiparticle peaks exist for binding energies larger than $2\mathrm{eV}$ and in this energy region the spectrum is essentially incoherent. The many-body corrections are much stronger in the majority-spin channel and drastically affect the spin polarization of the spectra.