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International audience; We present the commissioning of the FAB10 beamline (Femtosecond to Attosecond Beamline at 10 kHz repetition rate) that has been developped and operated in the last few years at the ATTOLab facility of Paris-Saclay University. Based on the high harmonic generation process, the beamline is dedicated to investigations of ultrafast dynamics in a broad variety of systems ranging from gas phase to condensed matter in pump-probe arrangements. Its design and operation has been strongly influenced by both the laser and the large scale instruments communities, which makes it unique in several aspects. In particular, it is possible to tune the extreme ultraviolet (XUV, 10–100 eV) bandwidth from 0.2 to 20 eV – with corresponding pulse duration from 30 to 0.3 femtoseconds (fs) – thanks to an original and fully automated XUV spectral filter with three operation modes. After a general overview of the beamline features, each of those operation modes is described, characterized and illustrated with commissioning experiments.

International audience; The goal of the present review is to cross-compare theoretical predictions with selected experimental results on bismuth thin films exhibiting topological properties and a strong Rashba effect. The theoretical prediction that a single free-standing Bi(1 1 1) bilayer is a topological insulator has triggered a large series of studies of ultrathin Bi(1 1 1) films grown on various substrates. Using selected examples we review theoretical predictions of atomic and electronic structure of Bi thin films exhibiting topological properties due to interaction with a substrate. We also survey experimental signatures of topological surface states and Rashba effect, as obtained mostly by angle- and spin-resolved photoelectron spectroscopy.

The two-dimensional electron gas (2DEG) at oxides interfaces and surfaces has attracted large attention in physics and research due to its unique electronic properties and possible application in optoelectronics and nanoelectronics. The origin of 2DEGes at oxide interfaces has been attributed to the well known "polar catastrophe" mechanism. On the other hand, recently a 2DEG was also found on a clean SrTiO3(001) surface where it is formed due to oxygen vacancies. However, these 2DEG systems have been until now found mostly on atomically perfect crystalline samples usually grown by pulsed laser deposition or molecular beam epitaxy i.e. samples which are difficult to be prepared and require specific experimental conditions. Here, we report on the fabrication of SrTiO3 thin films deposited by magnetron sputtering which is suitable for mass-production of samples adapted for nanoelectronic applications. The characterization of their structural and electronic properties was done and compared to those of SrTiO3 single crystals. XRD patterns and SEM micrography show that the deposited films are amorphous and their structure changes to polycrystalline by heating them at 900 {\deg}C. Photoemission spectroscopy (XPS and UPS) was used to study the electronic properties of the films and the crystal. In both, we observe the 2DEG system at Fermi level and the formation of Ti3+ states after heating the surface at 900 {\deg}C., Comment: 6 pages, 3 figures

Femtosecond laser excitations in half-metal (HM) compounds are theoretically predicted to induce an exotic picosecond spin dynamics. In particular, conversely to what is observed in conventional metals and semiconductors, the thermalization process in HMs leads to a long living partially thermalized configuration characterized by three Fermi-Dirac distributions for the minority, majority conduction, and majority valence electrons, respectively. Remarkably, these distributions have the same temperature but different chemical potentials. This unusual thermodynamic state is causing a persistent nonequilibrium spin polarization only well above the Fermi energy. Femtosecond spin dynamics experiments performed on Fe3O4 by time- and spin-resolved photoelectron spectroscopy support our model. Furthermore, the spin polarization response proves to be very robust and it can be adopted to selectively test the bulk HM character in a wide range of compounds. Funding Agencies|UK EPSRC Grant [GR/M50447]; STFC; FERMI FEL project; Austrian Science Fund (FWF) through Lise Meitner Grant [M1925-N28]; Nanyang Technological University, NAP-SUG; CEDAMNF [CZ 02.1.01/0.0/0.0/15_003/0000358]; ERDF

In this work, chemical vapor deposition (CVD) is performed for the synthesis of MoS2 films on SiO2 and epi-grade sapphire with 0001 orientation substrates. Structural properties of obtained samples are examined by means of Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), Raman spectroscopy, Energy-Dispersive X-ray Spectroscopy (EDX) and optical microscopy. SEM and optical microscopy show MoS2 monocrystalline domains with lateral dimensions up to 80 m when deposited on SiO2 and up to 240 m on sapphire. The thickness of MoS2 domains is determined by AFM. By EDX the elemental composition is obtained for MoS2. In future, it is planned to create vertical heterostructures based on dichalcogenides of transition metals and graphene.

Bi films deposited on InAs(111) A and B sides have been studied by photoemission electron microscopy. A series of snapshots acquired during sequential annealing of the interfaces at temperatures below and above the melting temperature of Bi allowed obtaining a comprehensive image of the topographic and chemical evolutions of the Bi films that are found to be InAs side dependent. On the A side, a morphology of circular patterns controlled by Bi atoms mobility is observed. The patterns are formed on the pristine In-terminated InAs(111) surface covered by a weakly bonded Bi bilayer. On the B side, no particular morphology is observed due to a stronger chemical interaction between Bi and As atoms as evidenced by the spatially-resolved core-level photoelectron spectra. (C) 2016 Elsevier B.V. All rights reserved.

Experiments directly probing the electronic states using angle-resolved photoemission (ARPES) were carried out on La2/3Sr1/3MnO3 in order to elucidate its electronic properties. ARPES is a surface sensitive technique where bulk and surface states are usually both present. We present high-resolution ARPES studies in the (1 0 0) and (1 1 0) mirror planes and compare them with simulated ARPES based on GGA + U band structure calculations. In the (1 1 0) mirror plane we identify surface umklapps accounted by (root 2 x root 2)R45 degrees surface reconstruction which couple to bulk electronic states. As predicted by the simulated spectra there is additional spectral intensity at the Fermi level detected in ARPES data due to k(perpendicular to)-broadening effects in the photoemission final states. We demonstrate that this additional spectral intensity is a convenient spectral marker for determination of the k(F) Fermi momenta. (C) 2010 Elsevier B.V. All rights reserved.

X-ray magnetic circular dichroism and resonant photoemission at the Fe and Ni L2,3 edges have been used to investigate the electronic structure of NiFe2O4 (NFO) thin films. The results, when compared to those obtained on Fe3O4, indicate that in a 12 nm NFO film the Ni atoms occupy mainly B sites, as in bulk NFO, and that a decrease in the thickness of the film results in a modification of the nickel hybridization.

Mn0.06Ge0.94 samples have been grown by molecular-beam epitaxy on Ge(001)2 x 1. High-resolution transmission electron microscopy shows the coexistence of an ordered diluted Mn0.06Ge0.94 film and of nanoscopic crystallites, which were identified as Mn5Ge3 by electron diffraction. The magnetic properties of the Mn0.06Ge0.94 samples show a superposition of a paramagnetic behavior, due to the interaction of Mn atoms diluted in the Ge host, and a ferromagnetic behavior attributed to the Mn5Ge3 crystallites dispersed into the films. The Mn L-2.3 X-ray absorption spectra of the Mn0.06Ge0.94 films exhibit a lineshape typical of metallic Mn, with considerably reduced multiplet structure. (C) 2006 Elsevier B.V. All rights reserved.

The prospect of optically inducing and controlling a spin-polarized current in spintronic devices has generated wide interest in the out-of-equilibrium electronic and spin structure of topological insulators. In this Letter we show that only measuring the spin intensity signal over several orders of magnitude by spin-, time-, and angle-resolved photoemission spectroscopy can provide a comprehensive description of the optically excited electronic states in Bi2Se3. Our experiments reveal the existence of a surface resonance state in the second bulk band gap that is benchmarked by fully relativistic ab initio spin- resolved photoemission calculations. We propose that the newly reported state plays a major role in the ultrafast dynamics of the system, acting as a bottleneck for the interaction between the topologically protected surface state and the bulk conduction band. In fact, the spin- polarization dynamics in momentum space show that these states display macroscopically different temperatures and, more importantly, different cooling rates over several picoseconds.

We have investigated the temperature effect on Mn dilution into InSb substrates by means of high-resolution core level spectroscopy, surface EXAFS, and by X-ray Magnetic Circular Dichroism (XMCD) using synchrotron radiation. Samples were prepared by manganese deposition of 1, 2, 4 and 8 ML at room temperature (RT) and at 500K on InSb(001) (4 x 2)c(8 x 2) surfaces. By fitting In 4d and Sb 4d core level spectra with Voigt-functions, we identify metallic In and Sb atoms segregated on the surface. EXAFS results show MnSb-like compound formation with hexagonal structure in which Mn atoms replace some antimony atoms in the first nearest neighbours shell.

The electronic structure of the single crystal La0.7Sr0.3MnO3 in ferromagnetic metallic phase has been investigated by photoelectron spectroscopy. Valence band spectra were measured at 40 K for various photon energies, in the range of 45–70 eV. The Mn 3d partial density of states was derived from resonant photoemission near the Mn 3p–3d threshold. Besides the occupied 3d states, resonant photoemission data has provided information about the unoccupied 3d states. The value of the on-site Coulomb interaction strength (correlation energy) was estimated to be 6.7 eV.

We report results obtained by resonant photoemission (RPE) and X-ray magnetic circular dichroism (XMCD) in absorption with photon energies around the L 2/3 edges of manganese. The samples contain manganese in different environments and details about the dynamics of electronic structure on one side, magnetic structure on the other side are being discussed. We will present studies on the following samples: submonolayers of Mn on Cu(100), Mn in InAs and thin films of the manganese perovskite LSMO.

We report the studies of electronic structure of the InAs(0 0 1)4 × 2-c(8 × 2) surface by performing angle-resolved photoemission spectroscopy, LEED and STM measurements. The reconstruction of the clean surface was obtained by ion bombardment and annealing procedure. STM pictures show an ordered array of In-chains, and the photoemission experiments reveal new electronic surface structures. The intensity of these structures, which are located at binding energy of −2.94 and −1.05 eV, strongly depend on the surface preparation, and on the light polarization. They are non-dispersive with the photon energy.

We have performed angle-resolved photoemission spectroscopy on InAs(0 0 1)4×2-c(8×2) clean surfaces in order to investigate two new electronic surface states related to the In-terminated InAs(0 0 1)4×2-c(8×2) clean surface. The experiments were carried out at normal emission as a function of photon energy using s- and p-polarized light. The surface states are strongly resonant at photon energies of 31 and 61 eV, respectively. These energies correspond also to transitions from bulk electronic states localized at high symmetry points X6, X7 and Γ7, Γ6 of the calculated InAs band structure. The intensities of the two surface states decrease when passing from s- to p-polarization of the radiation: such behaviour directly establishes the orientation of the surface state bonds.

We have studied Mn/InAs(0 0 1)(4×2) c (8×2) interfaces by high-resolution core-level spectroscopy, surface EXAFS and by X-ray magnetic circular dichroism (XMCD). The growth of manganese is found to depend strongly on the temperature of InAs. At low temperatures (room and liquid nitrogen temperature (LNT)), Mn atoms form the compound MnAs in the surface region leaving metallic In islands on the surface. Manganese deposition at 530 K results in strong diffusion of Mn into the substrate followed by formation of the compound In 1− x Mn x As in which Mn atoms are substituted in indium-sites. We show by XMCD that In 1− x Mn x As is ferromagnetic with a relatively high value of an average magnetic moment per Mn atom, exceeding 0.7 μB at low temperatures and with an individual magnetic moment of about 2.4 μB. The temperature dependence of the Mn magnetic moment follows the Brillouin function and it drops to zero at temperature of about 150 K for measurements in an external magnetic field of 5 T.

Interface reaction and magnetism of epitaxially-grown Fe on InAs(100) are studied by core-level photoemission (As 3d and In 4d) and Fe 2p X-ray magnetic circular dichroism using synchrotron radiation. The reactivity of Fe/InAs(100) is relatively low compared to that of other interfaces involving deposition of 3d metals on III-V semiconductors. As a consequence, we observe a magnetic signal at Fe L2, 3 edges for the lowest thicknesses studied (1 ML). The atomic magnetic moment reaches a value close to that of the bulk ?-Fe (2.2 ? B) for Fe coverages exceeding 5 ML. A ferromagnetic compound with approximate stoichiometry of FeAs is formed at the interface. The orbital magnetism represents between 12 and 20% of the total momentum, due to 3d density of states depletion and to crystal-field modification of the electronic levels. These properties make the Fe/InAs(100) interface very promising for spin-tunneling devices.

We have investigated clean In-terminated InAs(0 0 1)(4×2)-c(8×2) surface by LEED, STM and high-resolution core-level and valence band (VB) spectroscopies. The In4d and As3d core levels showed the presence of chemically shifted components. The decomposition of In4d core level exhibited a new surface component located close to that of free indium metal. This indicates that the origin of the electron emission at the Fermi level measured in the VB spectra is probably due to the free In charge. STM measurements showed a uniform distribution of charge on the In-rows, which are highly ordered over large areas of the surface.

In contrast with the other interfaces involving deposition of 3d transition metals on III–V semiconductors (mostly GaAs), the Fe/InAs(1 0 0) interface exhibits magnetic properties even at the lowest coverage (1 monolayer, ML) investigated. The reactivity of the interface is also lower compared with Fe/GaAs. It involves formation of an interface compound of approximate stoichiometry of FeAs mixed with metallic In islands for Fe coverages lower than 3 ML, followed by the growth of relaxed bulk α-Fe in a Vollmer–Weber mode.

We have studied the growth of Fe thin layers on In-terminated InAs(100) surfaces by X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and reflection high energy electron diffraction (RHEED). Islanding is observed at the early stages of Fe deposition, then the growing mechanism is layer-by-layer. In thicker films, iron atoms are arranged in an unstrained bcc structure with a lattice constant close to that of bulk α-Fe. Arsenic diffuses through the Fe layer within a typical diffusion length of around 7 A. In turn, indium atoms remain at the interface.

In CeRh3 and Ce7Rh3 compounds, strong resonant effects are observed in the Ce 3d and 4d photoemission spectra at the Ce L3 and M4,5 absorption edges respectively. These resonances show unambiguously that interference effects exist in core level spectroscopies. In the CeRh3 mixed valent compound, the resonances of photoemission peaks corresponding to 4f0, 4f1 and 4f2 final state character occur at different photon energies, making it possible to unravel the X-ray absorption profiles. Moreover, resonant L3M4,5N4,5 Raman Auger lines are observed up to 10 eV above the L3 absorption edge, showing the strong localized character of the core excited state.

We studied the magnetic properties of ultra-thin Mn films deposited on Ag (001) held at 80 K with soft X-ray absorption and magnetic circular dichroism. The observed shape and branching ratio of the Mn 2p absorption edge as a function of Mn coverage demonstrate that, up to \(\), the Mn adopts a stable high spin state similar to the Mn atom Hund's rule 6S5/2 ground state. Above this coverage a rapid transition from localized high spin to itinerant low spin behavior of the Mn 3d electrons is evidenced. Magnetic circular dichroism shows no sign of long range ferromagnetic order in these films at 80 K. The data, first confirm the large atomic-like local magnetic moment, and second are in line with the in-plane \(\) antiferromagnetic order, reported recently (Phys. Rev. B 57, 1141 (1998)), for Mn in the nearly ideal on-top Mn monolayer formed by 0.9 ML deposited at 80 K.

Iron silicide thin films (200 A Fe(Si 1− x Fe x ) with 0⩽ x ⩽1 and local cubic CsCl structure) have been grown by coevaporation at room temperature (RT) on Si(1 1 1). X-ray magnetic circular dichroism (XMCD) and magneto-optic Kerr effect (MOKE) measurements indicate that the films are ferromagnetic at RT for x ranging from 1 (pure Fe) to 0.15 (Fe 1.35 Si). The magnetization is parallel to the film surface, and the magnetic anisotropy is uniaxial, with the easy axis lying along a [1 0 1] Si crystallographic direction and the hard axis along a [1 2 1] Si direction of the substrate. MOKE measurements show that the magnitude of the saturation field increases with increasing Si concentration, while XMCD data indicate that the average local magnetic moment carried by the Fe atoms decreases with decreasing Fe concentration. Models which involve the diminution of the number of Fe nearest neighbors are proposed for the description of the behavior of the Fe moments.

International audience

In the last few years, magnetism at the surfaces and interfaces of transition metals has attracted considerable experimental and theoretical attention. The reduced symmetry and the lower coordination number offer the possibility of inducing new and exotic phenomena. In this context, vanadium has played a fundamental role since the prediction of a sizable magnetic moment in one or two vanadium monolayers on top of Ag(100) or Fe(100). We have investigated the magnetic properties of V deposited onto Fe(100) and Ag(100) by X-ray magnetic circular dichroism at the VL 2,3 absorption edges. No evidence of ferromagnetic ordering of the V layer (1–2 atomic layers) on silver was found for temperatures as low as 100 K. On the other hand, we observed room temperature antiferromagnetic alignment between V (1–25 atomic layers) and the iron substrate. The intensity of the dichroic signal decreases as the thickness of the V film increases. This dependence is discussed.

Mn5Ge3(001) thin films grown on Ge(111)-c(2 x 8) reconstructed surfaces were studied by angle-resolved photoemission using synchrotron radiation in the 14-94 eV photon energy range. The results obtained in the Gamma ALM plane and in the Gamma AHK plane are in agreement with simulations starting with band structure calculations based on the density functional theory. This provides a unique validation of band structure calculations for a proper description of the electronic properties of Mn5Ge3. Only the spectral feature very close to the Fermi level cannot be well explained by the simulation. This departure is discussed in terms of the three-dimensional nature of the sample and of correlation effects.

We have performed angle- and spin-resolved photoemission measurements on Fe${}_{3}$O${}_{4}$(0 0 1)/MgO(0 0 1). Despite intrinsic electron-lattice (polaron) interaction a Fe ${t}_{2g}$ band dispersion is observed, as well as a Fermi surface. The states close to the Fermi level show a spin polarization up to $\ensuremath{-}72$$%$ as measured with a 4.65 eV laser light. All the data can be simulated starting from GGA+U bulk band-structure calculations and taking into account the polaron and initial-state lifetime broadening involved in the photoemission process. This conciliates the electronic structure of Fe${}_{3}$O${}_{4}$ with a band model and confirms the half-metallic nature of Fe${}_{3}$O${}_{4}$.

We discuss the magnetic circular dichroism observed in the Lα and Lβ x-ray fluorescence spectra of the 3d ferromagnets when excited by circularly polarized photons. Excitation by polychromatic photons or under resonance conditions (i.e., by photons tuned to the L2 or L3 threshold energy) are considered. We take the example of nickel to show how the x-ray fluorescence dichroism may be damped by L2-L3M4,5 Coster-Kronig transitions when the incoming photon energy is above the L2 threshold.

Magnetic circular x-ray-dichroism measurements at the Co ${L}_{2,3}$ edges of the Co/Pt(111) interface are presented. Ultrathin Co films, deposited and measured at room temperature, order magnetically above a thickness of 1.8 monolayers and show magnetic anisotropy perpendicular to the surface up to coverage of at least 5 monolayers. An enhancement of the orbital magnetic momentum relative to the bulk value of Co metal is observed. A further increase after addition of a thick Pt overlayer reveals the influence of hybridization at the Co/Pt interface. Observations of magnetic surface alloys with perpendicular anisotropy are also reported.

Densely packed epitaxial Mn-doped Si(0.3)Ge(0.7) nanodots self-assembled on Si(100) have been obtained. Their structural properties were studied using reflection high-energy electron diffraction, energy dispersive x-ray diffraction, atomic force microscopy, extended x-ray absorption fine structure measurements and high-resolution transmission electron microscopy. Mn(5)Ge(1)Si(2) crystallites embedded in Si(0.3)Ge(0.7) were found. They exhibit a ferromagnetic behaviour with a Curie temperature of about 225 K.

The room temperature deposition of small amounts of Cs on the InAs(110) surface induces the highest Fermi-level pinning position (~ 0.6 eV) above the conduction band minimum ever met for any semiconductor. The Fermi-level movement is monitored by core level photoemission spectroscopy using synchrotron radiation. This striking behaviour is explained in terms of donor-type surface states induced by few Cs atoms present on InAs(110) and suggests the existence of a two-dimensional electron gas at the surface.

A comparative study of the adsorption of benzene, C 6 H 6 , on Si(111)2X1 and on Si(111)7X7 by angle-resolved synchrotron radiation photoemission is reported. The chemisorption-induced valence spectral features are very similar in the two cases in what concerns number, energy position and angular dependence. The main difference is the relative intensity, which is much higher for benzene on the cleaved surface. The higher sticking coefficient detected on the 2X1-reconstructed surface can be related to the higher number of defects (such as the cleavage steps) present on the cleaved surface with respect to the annealed one. Further complementary experiments are needed to reveal other possible differences between the chemical reactivity of the two surface reconstructions with respect to aromatic molecules.

Upon studying with very high resolution synchrotron radiation photoemission spectroscopy the ideally H-terminated Si(111)1×1 surfaces prepared by wet chemical procedure we prove for the first time that both n-type and p-type surfaces do not posses any surface states in the gap and thus give flat band conditions at the surface. Starting from such unpinned n-type surfaces, totally unusually, a downward band bending is obtained for a prototypical system formed by condensing in situ a lead overlayer under UHV. Moreover, by using differently prepared initial Si(111) surfaces, with just this one metal, it is possible to move the Fermi level position from 130 meV above the valence band maximum to 100 meV below the conduction band minimum, which is totally at variance with all results known for metal-silicon interfaces.

The growth and structure of ultra thin films of terbium deposited on Co(1010) have been studied by X-ray photoemission, Auger spectroscopy and low energy electron diffraction at 600 K. Two stages are observed in the growth mode: the growth of about two Tb layers is followed by an interdiffusion process, leading to the formation of an alloy. We also show that two-dimensional ordering of the film occurs at 600 K in the monolayer range.

Resonant photoemission spectroscopy was applied to investigate the electronic structure of semimagnetic semiconductor (SMSC) Pb0.2Sn0.72Mn0.08Te and the contribution of Mn 3d electrons to the valence band. The set of energy distribution curves (EDC) was taken for energies in the region close to the Mn 3p-Mn 3d transition (50eV). The spectra contain extended valence bands (with core-like electrons of Pb 6s, Sn 5s and Te 5s), and core electrons of Pb 5d, Sn 4d, Te 4d and Mn 3p. The electrons Mn 3d hybridize and contribute to the valence band electrons of the crystal; their main contribution to the density of states appears in the energy 3.7 ± 0.3eV below the valence band edge.

International audience; An investigation of the structural, magnetic and electronic properties of ≈ 3 nm thick Mn5Ge3 films epitaxially grown on a Ge(1 1 1)-c(2 × 8) reconstructed surface is reported. High resolution transmission electron microscopy and selected area electron diffraction give evidence of 2.2% in-plane compressive strain between the Mn5Ge3 film and the Ge substrate. Magnetooptical Kerr effect measurements show that the films are ferromagnetic with a Curie temperature of ≈ 325 K. The analysis of Ge 3d core level photoelectron spectra of the Mn5Ge3 films allows determining an upper limit of 76 meV for the Ge 3d5/2 core-hole lifetime broadening. The Ge 3d3/2 core-hole lifetime broadening is found to be 15 meV larger than that of the Ge 3d5/2 core hole, because of the existence of a Coster–Kronig decay channel due to the metallic character of Mn5Ge3.

Circular dichroic x-ray photoemission spectroscopy (CDXPS) experiments have been performed on the 2p core-level spectra of polycrystalline Fe films deposited directly on a Ni 3 Fe (μ-metal) substrate that was magnetized by a low excitation field. Because of the polycrystalline state of the iron films, CDXPS studies in the remanent mode were not possible, thus the experiments were performed with the magnetic field switched on during the experiment. Our work on this polycrystalline iron gives some insight into the understanding of the magnetic circular dichroism mechanism. The results show a similar angular variation for the measured asymmetry, as observed on an Fe bcc (100) single crystal remanently magnetized in the (100) direction

Room temperature NH3 adsorption on Si(100)2 × 1 and Si(111)2 × 1 has been studied by angle-resolved photoemission using synchrotron radiation. The experiments confirmed previous results showing that the adsorption on Si(100)2 × 1 is a dissociative process leading to NH2 and H. A single N 2s component of the NH2 species has been identified in the photoemission spectra at 20 eV below the Fermi level (EF). The adsorption on the cleaved Si(111)2 × 1 surface is more complex as ascertained by the presence of the same NH2 features as for Si(100), along with a second N2s component at 17 eV and a new valence band feature at 8 eV below EF. The second N 2s component at 17 eV is identified by annealing experiments as due to atomic nitrogen. Thus, a given part of the adsorbed NH3 molecules may be completely dissociated at RT owing to surface states which are specific to the cleaved 2 × 1 reconstructed Si(111) surface.

The effect of alkali-metal overlayers (K, Cs) on the room-temperature oxidation of the Ge (100)2 × 1 surface in the presence of molecular oxygen was investigated by core-level and valence-band photoemission spectroscopy using synchrotron radiation. In strong contrast to the behavior observed for many other elemental or compound semiconductor surfaces, the presence of a K or Cs layer does not enhance the oxidation rate as expected but rather poisoned it since the K (Cs) covered Ge (100)2 × 1 surface exhibits significantly smaller amount of oxides for the same oxygen exposures. This behavior indicates that K does not act as a catalyst as observed in the cases of many other semiconductor surfaces, but as an oxygen acceptor, in agreement with a classical model of electron affinity.

The initial electronic structure of the pseudomorphic InAs/GaAs(100) heterostructure as well as that of the Ag/InAs(110) interface at 20 K have been studied by synchrotron radiation photoelectron spectroscopy. In the first case we find that the valence band spectra show no evidence for the formation of bulk-like energy bands. In the second case we prove for the first time that upon deposition of minute amounts of Ag at low temperature onto cleaved InAs(110) substrates one induces a giant movement of the Fermi level well into the conduction band thus creating a strong two-dimensional electron channel at the surface.

The valence and core level spectra of chemically prepared, ideally H-terminated Si(111) surfaces are characterized by remarkably sharp features. The valence band levels and their dispersion are well described by first-principles calculations using a quasiparticle self-energy approach within the GW approximation. From the ${\mathrm{Si}}_{2\mathit{p}}$ spectra, an upper limit of 35\ifmmode\pm\else\textpm\fi{}10 meV is derived from the core hole lifetime broadening, a value substantially lower than previously measured.

Deposition of antimony on Ge(100)2 X 1 results in a well-ordered, highly passivated surface. From a comparison between core-level data and angle-resolved photoemission data, we conclude that the ob ...

Photoelectron diffraction of the bulk and surface components of the Ge 3d core-level has been measured from the Ge(111)- c (2 × 8) reconstructed surface at room temperature and on the Ge(111)-(1 × 1) surface at 400°C. Calculations show good agreement with the results of recent X-ray diffraction work on the c(2 × 8) surface. Results for the (1 × 1) surface show no change in the short-range structure at the surface across the phase transition suggesting that the adatom-restatom building block structure accepted for the c(2 × 8) surface remains intact after the phase transition. This method of measuring the photoelectron diffraction from resolved surface core-levels provides a direct method for assigning these levels to specific species at the surface. In addition, significant variations in the branching ratios as a function of azimuthal angle have been found which are due to differences in the final state for the two spin-orbit components of the Ge 3d photoemission peak.

Angle-resolved photoemission spectroscopy has been used to study the valence band structure of the Zn0.15Hg0.85Te alloy. Data were collected for emission along the normal to the cleaved (110) face of these crystals as a function of UV photon energy in the range 54–94 eV. By assuming a free electron final state in the bulk (G vector equal to 0 and crystal potential E0 = 12.15 eV), the observed data allow the generation of the experimental bulk valence band in the гKX direction. Comparison with the calculated valence band of ZnTe shows that more realistic final states are required (G vectors with G-components in the (110) plane): these “umklapp” processes may be related to the poor crystalline quality of the Hg-rich alloy. The alloy dispersion E(k) is weaker than for ZnTe, a probable effect of the non-periodic alloy potential.

We compare the valence band photoemission signatures of the CoSi 2 (111) surfaces observed on a bulk-grown single crystal and on thin films epitaxially grown on Si(111). Taking advantage of the characteristic surface states in the 2.60–3.00 eV binding energy range at λ allows us to identify unambiguously the various surface structtures observed on epitaxial films obtained with different preparation methods: a Co-rich low-temperature form labeled CoSi 2 (111)-Co, an intermediate surface termination labeled CoSi 2 (111) and stable up to 420°C and a high-temperature Si bilayer terminated form observed upon annealing above 550°C and labeled CoSi 2 (111)-Si. We find that bulk-grown single-crystal surfaces prepared by ion etching and annealing up to temperatures as high as 900°C invariably show the surface electronic structure corresponding to the intermediate surface termination labeled CoSi 2 (111). This surface corresponds to the ideal crystal termination with a Si Co Si silicide top layer. This surface atomic structure, is confirmed by high-resolution Si(2p) core level photoemission measurements. We show that the spectrum displays only one surface component shifted by 0.60 eV towards lower binding energies in contrast with CoSi 2 (111)-Si which shows three surface components. Finally, we find that the CoSi 2 (111)-Si surface can also be prepared on a bulk-grown CoSi 2 crystal by appropriate annealing of ultrathin Si deposits.

We have studied the development of Schottky barrier heights during the initial formation of Bi/Si(100) and Bi(111) interfaces. In the submonolayer regime we have followed the band bending changes using synchrotron radiation core-level spectroscopy. It has been observed that the annealing of the interface can influence the Schottky barrier height. We compare these results with recent measurements on Pb/Si(100) and Pb/Si(111) interfaces.