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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.

Monolayer MoS2 is a promising two-dimensional material for electronic and optoelectronic devices. In this work, chemical vapor deposition (CVD) is performed for the synthesis of MoS2 films on SiO2. Electron properties of obtained samples are examined by means of x-ray photoelectron spectroscopy (XPS) and angle-resolved photoemission spectroscopy (ARPES). The effect of defects on the electron transport properties of MoS2 compared using density functional theory (DFT) as implemented in the Quantum ESPRESSO software package.

The dosing of layered materials with alkali metals has become a commonly used strategy in ARPES experiments. However, precisely what occurs under such conditions, both structurally and electronically, has remained a matter of debate. Here we perform a systematic study of 1T-${\mathrm{HfTe}}_{2}$, a prototypical semimetal of the transition metal dichalcogenide family. By utilizing photon energy-dependent angle-resolved photoemission spectroscopy (ARPES), we have investigated the electronic structure of this material as a function of potassium (K) deposition. From the ${k}_{z}$ maps, we observe the appearance of 2D dispersive bands after electron dosing, with an increasing sharpness of the bands, consistent with the wave-function confinement at the topmost layer. In our highest-dosing cases, a monolayerlike electronic structure emerges, presumably as a result of intercalation of the alkali metal. Here, by bringing the topmost valence band below ${E}_{F}$, we can directly measure a band overlap of $\ensuremath{\sim}0.2$ eV. However, 3D bulklike states still contribute to the spectra even after considerable dosing. Our work provides a reference point for the increasingly popular studies of the alkali metal dosing of semimetals using ARPES.

We combined a spin-resolved photoemission spectrometer with a high-harmonic generation (HHG) laser source in order to perform spin-, time- and angle-resolved photoemission spectroscopy (STARPES) experiments on the transition metal dichalcogenide bulk WTe$_2$, a possible Weyl type-II semimetal. Measurements at different femtosecond pump-probe delays and comparison with spin-resolved one-step photoemission calculations provide insight into the spin polarization of electrons above the Fermi level in the region where Weyl points of WTe$_2$ are expected. We observe a spin accumulation above the Weyl points region, that is consistent with a spin-selective bottleneck effect due to the presence of spin polarized cone-like electronic structure. Our results support the feasibility of STARPES with HHG, which despite being experimentally challenging provides a unique way to study spin dynamics in photoemission., 6 pages, 4 figures

The growth of Bi on both the In-terminated (A) face and the As-terminated (B) face of InAs(1 1 1) has been investigated by low-energy electron diffraction, scanning tunnelling microscopy, and photoelectron spectroscopy using synchrotron radiation. The changes upon Bi deposition of the In 4d and Bi 5d 5/2 photoelectron signals allow to get a comprehensive picture of the Bi/InAs(1 1 1) interface. From the early stage the Bi growth on the A face is epitaxial, contrary to that on the B face that proceeds via the formation of islands. Angle-resolved photoelectron spectra show that the electronic structure of a Bi deposit of ≈10 bi-layers on the A face is identical to that of bulk Bi, while more than ≈30 bi-layers are needed for the B face. Both bulk and surface electronic states observed are well accounted for by fully relativistic ab initio calculations performed using the one-step model of photoemission. These calculations are used to analyse the dichroic photoemission data recorded in the vicinity of the Fermi level around the Γ ¯ point of the Brillouin zone.

Cobalt ferrite ultrathin films with the inverse spinel structure are among the best candidates for spin filtering at room temperature. High-quality epitaxial CoFe2O4 films about 4nm thick have been fabricated on Ag(001) following a three-step method: an ultrathin metallic CoFe2 alloy was first grown in coherent epitaxy on the substrate and then treated twice with O-2, first at room temperature and then during annealing. The epitaxial orientation and the surface, interface and film structure were resolved using a combination of low-energy electron diffraction, scanning tunnelling microscopy, Auger electron spectroscopy and in situ grazing-incidence X-ray diffraction. A slight tetragonal distortion was observed, which should drive the easy magnetization axis in-plane due to the large magneto-elastic coupling of such a material. The so-called inversion parameter, i.e. the Co fraction occupying octahedral sites in the ferrite spinel structure, is a key element for its spin-dependent electronic gap. It was obtained through in situ resonant X-ray diffraction measurements collected at both the Co and Fe K edges. The data analysis was performed using FDMNES, an ab initio program already extensively used to simulate X-ray absorption spectroscopy, and shows that the Co ions are predominantly located on octahedral sites with an inversion parameter of 0.88(5). Ex situ X-ray photoelectron spectroscopy gives an estimation in accordance with the values obtained through diffraction analysis.

Molybdenum dichalcogenides are probably the most studied single layer TMDCs by virtue of being appealing for sundry possible applications suchlike transistors, diodes, solar cells or more fundamental studies of spin or valley pseudospin and their interactions. Tungsten-based counterparts are on the other hand evincing much stronger spin-orbit coupling due to which all the spin-related effects are more stable at room temperature and thus more feasible for application. WTe2, a type-II Weyl semimetal is in particular interesting due to having two pairs of spin-differentiated Weyl points above Fermi energy. We have conducted several experiments following the evolution of the band dispersion in the vicinity of X and Y points of the Brillouin zone of WTe2 which is substantial for understanding the fundamental properties of the structure-property relation of the system. Ab-initio set of photoemission calculations was performed using SPR-KKR package and compared to experimental results.

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

APCOM2018 - 24th International conference Applied Physics of Condensed Matter, Štrbské Pleso, Slovaquie, 20 to 22/06/2018"Solid State Physics and Radioactive Irradiation"; International audience; Thin Bi films are interesting candidates for spintronic applications due to a large spin-orbit splitting that, combined with the loss of inversion symmetry at the surface, results in a band structure that is not spin-degenerate. In recent years, applications for topological insulators based on Bi and Bi alloys have as well attracted much attention. Here we present angle-resolved photoemission spectroscopy studies of the Bi/InAs(100) interface. Bismuth deposition followed by annealing of the surface results in the formation of one full Bi monolayer decorated by Bi nanolines. We found that the building up of the interface does not affect the electronic structure of the substrate. As a consequence of weak interaction, Bi states are placed in the gaps of the electronic structure of InAs(100). We observe a strong resonance of the Bi electronic states close to the Fermi level; its intensity depends on the photon energy and the photon polarization. These states show nearly no dispersion when measured perpendicular to the nanolines, confirming their onedimensionality.

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

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.

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.

Mn5Ge3(001) thin films grown on Ge(111) were studied by angle-and spin-resolved photoemission using synchrotron radiation in the 17-40 eV photon energy range. The photoelectron spectra were simulated starting from a first-principles band-structure calculation for the ground state, using the free-electron approximation for the final states, taking into account photohole lifetime effects and k(perpendicular to) broadening plus correlation effects, but ignoring transition matrix elements. The measured spin polarizations for the various k points investigated in the Gamma MLA plane of the Brillouin zone are found to be in fair enough agreement with the simulated ones, providing a strong support to the ground-state band-structure calculations. Possible origins for the departures between either simulations and experiments or previous and present experiments are discussed. (Less)

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.

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.

The structural and magnetic properties of the evaporated Fe/V multilayers with a fixed V-layer thickness (tV = 1.5 nm) and variable Fe layer thicknesses (0.75 nm < or = tFe < or = 6 nm) have been studied by X-ray reflectivity and high-angle X-ray diffraction, conversion-electron Mossbauer spectrometry, and vibrating sample magnetometry. The results show that multilayers are formed with a broad Fe/V interface and pure crystalline bcc-Fe layers in the center of the individual subsystems. The Fe spin orientation is aligned in the film plane in the individual centers as well in the interfacial regions. The interfacial anisotropy constant Ks was estimated to be equal to 0.04 mJ/m2. This parallel magnetic anisotropy is discussed in terms of reduced symmetry effects on the hybridized 3d states.

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.

The growth and structure of cobalt on a platinum (111) single crystal is studied using X-ray absorption spectroscopy at the cobalt K-edge. A polarisation dependent analysis of the EXAFS spectra shows first neighbours distances in Co Pt (111) films identical to those in bulk cobalt for thicknesses between 2 and 10 monolayers. The full shell spectra polarisation dependence indicates the hexagonal stacking of the thicker film. Influences of annealing and recovering by platinum on the structure of the cobalt films are also described.

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${}_{4}$.

Mn5Ge3(001) thin films grown on Ge(111)-c(2 × 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 ALM plane and in the 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

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.

A polarization dependent first shell analysis of the EXAFS spectra shows that cobalt grows on Cu(100) and Cu(111) in perfect epitaxy : the mean nearest neighbour distance between cobalt atoms parallel to the surface is 2.55 Å (same value as in bulk copper) and the interlayer bond length is 2.50 Å. The contraction of the lattice parameter perpendicular to the surface is in agreement with the continuum elasticity theory. The analysis of further neighbour shells is done with the FEFF code (multiple scattering) modified to take into account the structural anisotropy. Simulations are compared to experiments and show anumbiguously that cobalt has an fcc tetragonal structure on Cu 100, but a distorted hcp structure on Cu(111). The (111) surface of copper is hexagonal. An fcc structure means an ..ABCABC.. stacking, and an hcp structure an ..ABAB.. stacking . The main difference between these two structures is the absence of alignment of the first and fourth neighbours in the hcp structure in grazing incidence . This effect is clear in the calculated and in the experimental Fourier Transforms of the EXAFS spectra.

Extended X-ray absorption fine structure (EXAFS) was used to determine the local structure of luminescent centres in Tb3+-, Ce3+- and Eu2+-doped calcium sulphide thin films. In the concentration range studied (3.8−10.4%) the rare earths are located at substitutional sites both in thin films and in powder samples which were prepared for comparison and reference. The parameters for EXAFS analysis were optimized in the case of substitutional structure and can also be used for other II–VI thin films.

The stable structure of cobalt is hexagonal closed-packed (hcp), but cobalt can be stabilized in a distorted face-centered cubic structure (fcc) by epitaxy on Cu(001). The deviation from the isotropic fcc structure is determined by surface-extended X-ray absorption fine structure (EXAFS). A polarization dependent first shell analysis of the EXAFS spectra shows that the Co/Cu(001) films have a face-centered tetragonal structure (fct): the mean nearest-neighbour distance parallel to the surface is 2.55A(same value as in bulk copper) and the interlayer bond length is 2.50A: the films are in perfect epitaxy on copper (001) with a contraction of the lattice parameter perpendicular to the surface of 4%, in agreement with the continuum elasticity theory. A constant tetragonalization is observed for films of 2 to 15 monolayers. A simulation of the EXAFS spectra is also done using the FEFF code. In order to simulate the polarization dependence of the experimental spectra, we have introduced in this theoretical calculation a polarization dependence of the paths (single scattering and multiple scattering ones) based on a plane wave approximation. This simple model gives a good agreement between calculated and experimental polarization dependent EXAFS spectra both on bulk hcp cobalt and on the face-centered tetragonal films Co/Cu(001); this agreement confirms the structure determined from the first shell analysis.

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.

Surface EXAFS is used to determine the crystallographic structure of iron films prepared by deposition on Cu(100). These metastable films have structural and vibrational properties strongly dependent on their thickness and on their growth temperature. A well defined fee structure is obtained in films grown at a temperature higher than 350 K and in thick films (8 monolayers) grown at room temperature. The thinner films (2 to 5 monolayers) grown at room temperature do not have an fee structure: the first shell radial distribution function is very broad and anisotropic. The origin of this first shell broadening can be random static disorder in the layer or a well defined reconstruction inducing different nearest neighbour distances. These different crystallographic structures are apparently connected to the different magnetic properties measured in these films.

The valence bands and core levels of ultrathin Fe layers deposited on a Cr(100) surface at room temperature are studied by ARPES, UPS and XPS. Transitions from Fe minority and majority spin bands are still observed for coverages of about 1 monolayer, showing that Fe retains its magnetic ground state; the persistence of the magnetic satellite in the Fe 3s core levels also supports this conclusion. These studies agree with theoretical calculations which predict an enhanced magnetic moment for ultrathin Fe layers on Cr(100).

The valence bands of ultrathin Fe and Co layers deposited on a Cr(100) surface at room temperature are studied by ARPES and UPS. Transitions from Fe minority and majority spin bands are still observed for coverages of about 1 monolayer, showing that Fe remains ferromagnetic. These studies agree with theoretical calculations which predict an enhanced magnetic moment for ultrathin Fe layers on Cr(100). Measurements on Co layers let us suppose that a Stranski-Krastanov growth mode occurs, with a bcc Co phase for the very first layers.

We present an angle- and spin-resolved photoemission study of half-metallic three-dimensional perovskite ${\mathrm{La}}_{2∕3}{\mathrm{Sr}}_{1∕3}\mathrm{Mn}{\mathrm{O}}_{3}$ thin films grown with pulsed laser deposition. The experiments are performed in the (100) mirror plane. The experimental results are related to GGA+U calculations through simulations of photoemission spectra, which take into account the final state broadening in surface-perpendicular momentum and the initial-state broadening in energy. We demonstrate that due to the three-dimensional nature of ${\mathrm{La}}_{2∕3}{\mathrm{Sr}}_{1∕3}\mathrm{Mn}{\mathrm{O}}_{3}$, these intrinsic mechanisms of the photoemission process give rise to deviations of the photoemission spectrum from the spectral function corresponding to the strict momentum conservation. In the spin-integrated data, we identify ghost spectral intensity coming from states with different momenta and, in particular, nonvanishing intensity filling the whole interior of the central Fermi surface spheroid. In the spin-resolved data, we find experimental polarization values near the Fermi surface of 55% at the normal emission and 80% at off-normal emission. Despite a seeming contradiction to the half-metallic picture, such a reduction in spin contrast is reproduced by our simulations as a result of the broadening mechanisms and is consistent with the half-metallic nature of ${\mathrm{La}}_{2∕3}{\mathrm{Sr}}_{1∕3}\mathrm{Mn}{\mathrm{O}}_{3}$.

International audience; We investigated the structural and magnetic properties of MnxGe1−x, with 0.02 ⩽ x ⩽ 0.1. The MnxGe1−x samples were grown on Ge(0 0 1)2 × 1 by molecular beam epitaxy, at a substrate temperature of 520 K. The samples were characterized in situ by reflection high-energy electron diffraction and ex situ by high-resolution transmission electron microscopy, energy dispersive X-ray reflectivity and magneto-optical Kerr effect. From microscopy images we evidenced on all samples the presence of Mn5Ge3 nanocrystallites in addition to the MnxGe1−x diluted magnetic semiconductor with an estimated Mn concentration x ≈ 1.5%. The size and the density of the Mn5Ge3 precipitates were found to increase with increasing the Mn concentration x. Magnetic analysis showed ferromagnetism with a Curie temperature of 280 K for all samples.

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Mn0.06Ge0.94 samples have been grown by molecular-beam epitaxy on Ge(001)2 · 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 L2,3 X-ray absorption spectra of the Mn0.06Ge0.94 films exhibit a lineshape typical of metallic Mn, with considerably reduced multiplet structure.