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Nowadays, a wide number of applications based on magnetic materials rely on the properties arising at the interface between different layers in complex heterostructures engineered at the nanoscale. In ferromagnetic/heavy metal multilayers, such as the [Co/Pt]N and [Co/Pd]N systems, the magnetic proximity effect was demonstrated to be asymmetric, thus inducing a magnetic moment on the Pt (Pd) layer that is typically higher at the top Co/Pt(Pd) interface. In this work, advanced spectroscopic and imaging techniques were combined with theoretical approaches to clarify the origin of this asymmetry both in Co/Pt trilayers and, for the first time, in multilayer systems that are more relevant for practical applications. The different magnetic moment induced at the Co/Pt interfaces was correlated to the microstructural features that are in turn affected by the growth processes that induce a different intermixing during the film deposition, thus influencing the interface magnetic profile.

Hybridization of electronic states and orbital symmetry in transition metal oxides are generally considered key ingredients in the description of both their electronic and magnetic properties. In the prototypical case of ${\mathrm{La}}_{0.65}{\mathrm{Sr}}_{0.35}{\mathrm{MnO}}_{3}$ (LSMO), a landmark system for spintronics applications, a description based solely on Mn $3d$ and O $2p$ electronic states is reductive. We thus analyzed elemental and orbital distributions in the LSMO valence band through a comparison between density functional theory calculations and experimental photoelectron spectra in a photon energy range from soft to hard x rays. We reveal a number of hidden contributions, arising specifically from La $5p$, Mn $4s$, and O $2s$ orbitals, considered negligible in previous analyses; our results demonstrate that all these contributions are significant for a correct description of the valence band of LSMO and of transition metal oxides in general.

Recent theoretical calculations predict the presence of Dirac nodal lines with ? Berry phase and related topological surface states in elemental alkaline-earth metals. Here we provide experimental and theoretical evidence for the existence of similar nodal lines also in hexagonal close-packed Yb, an element of the lanthanide series, in the limit of zero spin-orbit coupling. These topological properties emerge after taking into account self-energy corrections, which permit one to correctly describe the experimental low-energy electronic structure of Yb. By angle-resolved photoemission spectroscopy we demonstrate the occurrence of topological surface states in Yb which are robust in the presence of the large spin-orbit coupling.

Angle resolved-Auger-photoelectron coincidence spectroscopy (AR-APECS) has been exploited to investigate the role that electron correlation plays in the exchange-coupling at the ferromagnetic/antiferromagnetic interface of a Fe/CoO bilayer growth on Ag(001). The effective correlation energy U$_{\textrm{eff}}$, usually employed to assess the energy distribution of core-valence-valence Auger spectra, has been experimentally determined for each possible combination of the orbital (e$_g$ or t$_{2g}$) and the spin (majority or minority) of the two valence electrons involved in the Auger decay. Coulomb and exchange interactions have been identified and compared with the result obtained on the Fe/Ag system. The presented analysis reveals in the Fe/CoO interface an enhancement of the Coulomb interaction for the e$_g$ orbital and of the exchange interaction for the t$_{2g}$ orbital with respect to the Fe/Ag case that can be associated to the stronger electron confinement and to the exchange coupling between the two layers, respectively., Comment: 37 pages, 6 figures

An experimental and computational investigation of the space-charge effects occurring in ultrafast photoelectron spectroscopy from the gas phase is presented. The target sample CF$_3$I is excited by ultrashort (100 fs) far-ultraviolet radiation pulses produced by a free-electron laser. The modification of the energy distribution of the photoelectrons, i.e. the shift and broadening of the spectral structures, is monitored as a function of the pulse intensity. The experimental results are compared with computational simulations which employ a Barnes-Hut algorithm to calculate the effect of individual Coulomb forces acting among the particles. In the presented model, a survey spectrum acquired at low radiation fluence is used to determine the initial energy distribution of the electrons after the photoemission event. The spectrum modified by the space-charge effects is then reproduced by $N$-body calculations that simulate the dynamics of the photoelectrons subject to the individual mutual Coulomb repulsion and to the attractive force of the positive ions. The employed numerical method accounts for the space-charge effects on the energy distribution and allows to reproduce the complete photoelectron spectrum and not just a specific photoemission structure. The simulations also provide information on the time evolution of the space-charge effects on the picosecond scale. Differences with the case of photoemission from solid samples are highlighted and discussed. The presented simulation procedure, although it omits the analysis of angular distribution, constitutes an effective simplified model that allows to predict and account for space-charge effects on the photoelectron energy spectrum in time-resolved photoemission experiments with high-intensity pulsed sources., 21 pages, 5 figures, 1 table

A set of electron-correlation energies as large as 10 eV have been measured for a magnetic 2ML Fefilm deposited on Ag(001). By exploiting the spin selectivity in angle-resolved Auger-photoelectroncoincidence spectroscopy and the Cini-Sawatzky theory, the core-valence-valence Auger spectrumof a spin-polarized system have been resolved: correlation energies have been determined for eachindividual combination of the two holes created in the four sub-bands involved in the decay: majorityand minority spin, as well asegandt2g. The energy difference between final states with paralleland antiparallel spin of the two emitted electrons is ascribed to the spin-flip energy for the final ionstate, thus disentangling the contributions of Coulomb and exchange interactions., Comment: 5 pages, 2 figures, 1 table

Here we report on our study to quantitatively describe the intensities of the valence band hard x-ray photoemission spectra (HAXPES) of a rare earth element containing 3d transition metal oxides. Using LaCoO3 as a representative model compound, we compared the experimental data to the results of ab initio one-step photoemission band structure calculations as well as to the sum of the partial density of states of the atomic constituents weighted by their tabulated photoionization cross sections. We discovered that the semicore La 5p density of states surprisingly contributes in a significant manner to the valence band spectrum: Although the La 5p partial density of states in the valence band region is negligible compared to that of the O 2p or the Co 3d, the La 5p cross section in the hard x-ray range is found to be orders of magnitude larger than that of the other subshells. This explains the long-standing issue of why the hard x-ray valence band spectra of a rare-earth element containing materials have line shapes that are very different from those taken at lower photon energies and why they cannot be described in terms of partial density of states of the subshells usually considered for the lower photon energy spectra. We infer that the contribution of the rare-earth 5p must be taken into account and cannot be ignored.

The longstanding problem of interpretation of satellite structures in core-level photoemission spectra of metallic systems with a low density of conduction electrons is addressed using the specific example of Sb-doped SnO2. Comparison of ab initio many-body calculations with experimental hard x-ray photoemission spectra of the Sn 4d states shows that strong satellites are produced by coupling of the Sn core hole to the plasma oscillations of the free electrons introduced by doping. Within the same theoretical framework, spectral changes of the valence band spectra are also related to dynamical screening effects. These results demonstrate that, for the interpretation of electron correlation features in the core-level photoelectron spectra of such narrow-band materials, going beyond the homogeneous electron gas electron-plasmon coupling model is essential.

We report on our investigation of the electronic structure of Ti2O3 using (hard) x-ray photoelectron and soft x-ray absorption spectroscopy. From the distinct satellite structures in the spectra, we have been able to establish unambiguously that the Ti-Ti c-axis dimer in the corundum crystal structure is electronically present and forms an a(1g)a(1g) molecular singlet in the low-temperature insulating phase. Upon heating, we observe a considerable spectral weight transfer to lower energies with orbital reconstruction. The insulator-metal transition may be viewed as a transition from a solid of isolated Ti-Ti molecules into a solid of electronically partially broken dimers, where the Ti ions acquire additional hopping in the a-b plane via the e(g)(pi) channel, the opening of which requires consideration of the multiplet structure of the on-site Coulomb interaction.

APL materials 6(7), 076104 (2018). doi:10.1063/1.5038773, Published by AIP Publ., Melville, NY

Journal of electron spectroscopy and related phenomena 190(Part B), 228 - 234 (2013). doi:10.1016/j.elspec.2013.01.002, Designing, understanding and controlling the properties of engineered and functional materials, based on oxides and buried interfaces, is one of the most flourishing research fields and one of the major challenges faced by contemporary solid state science and technology. Often, a reliable spectroscopic analysis of such systems is hindered by surface effects, as structural distortion, stoichiometry changes, strong reactivity to external agent and major atomic and/or electronic reconstruction to name but a few. Hard X-Ray PhotoEmission Spectroscopy (HAXPES) is a powerful technique to overcome such limitations, allowing to monitor truly bulk sensitive properties. We report selected HAXPES results for manganese-based oxides, both in films and crystal forms, and for buried metal–organic interfaces, with the aim of highlighting some of the important features such technique brings in the analysis of electronic properties of the solids., Published by Elsevier, New York, NY [u.a.]

Cu 2 p core levels spectra measured by X-ray photoemission spectroscopy of selected as-grown Nd 2− x Ce x CuO 4+ δ samples are presented and discussed. The presence of a satellite peak in the 2 p core level of Nd 2− x Ce x CuO 4+ δ single crystal by hard X-ray photoemission is confirmed in all non-superconducting samples, films and single crystals investigated in this work. The comparison of the spectral features of the different samples suggests that the presence and the intensity of this satellite peak is not related to the electric transport properties, but to the texture characteristics.

We have correlated the surface conductivity of hydrogen-terminated diamond to the electronic structure in the Fermi region. Significant density of electronic states (DOS) in proximity of the Fermi edge has been measured by photoelectron spectroscopy (PES) on surfaces exposed to air, corresponding to a $p$-type electric conductive regime, while upon annealing a depletion of the DOS has been achieved, resembling the diamond insulating state. The surface and subsurface electronic structure has been determined, exploiting the different probing depths of PES applied in a photon energy range between 7 and 31 eV. Ab initio density functional calculations including surface charge depletion and band-bending effects favorably compare with electronic states measured by angular-resolved photoelectron spectroscopy. Such states are organized in the energy-momentum space in a twofold structure: one, bulk-derived, band disperses in the $\mathrm{\ensuremath{\Gamma}}\text{\ensuremath{-}}X$ direction with an average hole effective mass of $(0.43\ifmmode\pm\else\textpm\fi{}0.02){m}_{0}$, where ${m}_{0}$ is the bare electron mass; a second flatter band, with an effective mass of $(2.2\ifmmode\pm\else\textpm\fi{}0.9){m}_{0}$, proves that a hole gas confined in the topmost layers is responsible for the conductivity of the $(2\ifmmode\times\else\texttimes\fi{}1)$ hydrogen-terminated diamond $(100)$ surface.

The space-charge effect, due to the instantaneous emission of many electrons after the absorption of a single photons pulse, causes distortion in the, photoelectron energy spectrum. Two calculation methods have been applied to simulate the expansion during a free flight of clouds of mono- and bi-energetic electrons generated by a high energy pulse of light and their results have been compared. The accuracy of a widely used tool, such as SIMION (R), in predicting, the energy distortion caused by the space-charge has been tested and the reliability of its results is verified. Finally we used SIMION (R) to take into account the space-charge effects in the simulation of simple photoemission experiments with a time-of-flight analyzer. (C) 2016 Elsevier B.V. All rights reserved.

The basic properties of a simple afocal optical system, namely a two-lens Keplerian telescope, are reviewed and compared with measurements that can be easily performed with instrumentation available in a university optical laboratory. The object-image conjugation, along with the Lagrangian invariant of the systems, are made clear by the comparison between theory and experiments, highlighting also the limits of the Gaussian approximation in the chosen experimental realization.

Hard X-ray PhotoEmission Spectroscopy (HAXPES) is a new tool for the study of bulk electronic properties of solids using synchrotron radiation. We review recent achievements of HAXPES, with particular reference to the VOLPE project, showing that high energy resolution and bulk sensitivity can be obtained at kinetic energies of 6–8 keV. We present also the results of recent studies on strongly correlated materials, such as vanadium sesquioxide and bilayered manganites, revealing the presence of different screening properties in the bulk with respect to the surface. We discuss the relevant experimental features of the metal–insulator transition in these materials. To cite this article: G. Panaccione et al., C. R. Physique 9 (2008).

The advent of Free Electron Lasers (FELs), able to provide short (2-100 fs) and intense (10(33) photons/s/mm(2)/mrad(2)/0.1%bandwidth) pulses of light also in the hard X-ray regime (h omega> 2000 eV), opens new possibilities to study the ultrafast dynamics of processes, exploiting the capability of Hard X-ray Photoelectron Spectroscopy (HAXPES) to measure core-level spectra of elements with bulk sensitivity. In order to detect the intense bursts of high kinetic energy electrons generated by the X-ray pulses with an energy resolution comparable to the existing category of electron analyzers, a new class of spectrometers must be designed. We present a characterization of two different TOF spectrometers, namely one based on a retarding cylindrical lens and another one based on the spherical reflector geometry. SIMION (R) software has been used in order to evaluate electron trajectories of high kinetic energy electrons (5000-10,000 eV) and extract transmission properties, angular acceptance and energy resolution. It resulted that while the linear system is able to accept a larger solid angle (similar to 50 msr), the spherical mirror offers a better resolving power (around 71,000). Both analyzers are capable of a transmission above 90% within range of kinetic energies wide enough to measure the full line-shape of a core photoionization peak. Furthermore, we proved that both instruments are able to discriminate between two consecutive electron bunches having a temporal separation inferior than 220 ns, which is the distance between two consecutive photon pulses at the European X-ray Free Electron Laser (EXFEL), which is currently under construction in Hamburg.

We have investigated the efficiency and limits of polarization dependent hard X-ray photoelectron spectroscopy (HAXPES) in order to establish how well this method can be used to unravel quantitatively the contributions of the orbitals forming the valence band of solids. By rotating the energy analyzer rather than the polarization vector of the light using a phase retarder, we obtained the advantage that the full polarization of the light is available for the investigation. Using NiO, ZnO, and Cu2O as examples for solid state materials, we established that the polarization dependence is much larger than in photoemission experiments utilizing ultra-violet or soft X-ray light. Yet we also have discovered that the polarization dependence is less than complete on the basis of atomic calculations, strongly suggesting that the trajectories of the outgoing electrons are affected by appreciable side-scattering processes even at these high kinetic energies. We have found in our experiment that these can be effectively described as a directional spread of +/- 18 degrees of the photoelectrons. This knowledge allows us to identify, for example, reliably the Ni 3d spectral weight of the NiO valence band and at the same time to demonstrate the importance of the Ni 4s for the chemical stability of the compound. (C) 2014 Elsevier B.V. All rights reserved.

The magnetization reversal of the magnetically soft permalloy ( Fe 20 Ni 80 ) layer in a spin-valve-like FeNi/Cu/Co trilayer was studied using photoelectron emission microscopy combined with X-ray magnetic circular dichroism, which allows to image the magnetic domain structure in an element-selective way. Nanosecond-short magnetic field pulses with amplitudes between 3.3 and 16.3 mT were applied one by one to reverse the magnetization of the FeNi layer. Images of the magnetic domain structure were taken after application of each pulse, and the mobility of magnetic domain wall motion in the FeNi layer was deduced. The reversal mechanism of the FeNi layer was found to depend on the applied pulse length, amplitude, and on the energy and direction of the coupling between the two ferromagnetic layers.

The as-grown magnetic domain patterns of epitaxial single-crystalline Co/FeMn bilayers and Co/Cu/FeMn trilayers were investigated by magnetic circular dichroism domain imaging using a photoelectron emission microscope. Small domains were observed when Co was deposited directly on top of antiferromagnetic FeMn films. On inserting a Cu spacer layer between the ferromagnetic Co layer and the antiferromagnetic FeMn layer, the as-grown domain size increases continuously with increasing Cu layer thickness, which is attributed to the decrease of the interlayer exchange coupling between the Co and FeMn layers. Domain images of the Co layer acquired after applying different external magnetic fields confirm the relation between as-grown domain size and interface coupling to the antiferromagnetic FeMn layer across the non-magnetic Cu spacer layer. It is found that a field of 44 Oe is sufficient to annihilate most small domains in the area where Co and FeMn are coupled through the Cu wedge, while it has no effect on the domain configuration of a Co/FeMn bilayer. By analysing the dependence of the average domain size of the Co layer on the Cu thickness in terms of interface coupling between the Co and FeMn layers across the Cu layer, the apparent estimated coupling energy was found to be different for different Co thickness. This is ascribed to kinetic barriers hindering the formation of larger domains from smaller ones.

By using a photoemission electron microscope in combination with X-ray magnetic circular dichroism, the domain configuration in a single crystalline Co film exchange coupled to an Fe 50 Mn 50 film is obtained. The effect of the ferromagnetic/antiferromagnetic interaction is observed to be different in Co domains with different magnetization direction, establishing the fact that the exchange bias is locally set by the magnetization of the ferromagnetic layer, without external field.

The micromagnetic properties of a Ni film in a Cu/Ni crossed-wedge on Cu(0 0 1) are investigated by a combination of photoelectron emission microscopy and X-ray magnetic circular dichroism. Two spin-reorientation transitions (SRT) from in-plane to perpendicular to the film plane and back to in-plane were observed with increasing Ni thickness. Whereas no clear Cu thickness dependence of the former SRT has been observed, the latter strongly depends on Cu thickness, and is shifted to thinner Ni thicknesses by increasing Cu overlayer thickness. Furthermore, the size and the shape of the ferromagnetic domain structure in the perpendicular magnetization region also depend on Cu thickness. The average domain size decreases with increasing Ni thickness near the second SRT line. It is observed for the first time that these domain structure changes also depend on Cu overlayer thickness.

Advanced functional materials 27(45), 1702282 (2017). doi:10.1002/adfm.201702282, Published by Wiley-VCH, Weinheim

Exponential decay is a prototypical functional behaviour for many physical phenomena, and therefore it deserves great attention in physics courses at an academic level. The absorption of the electromagnetic radiation that propagates in a dissipative medium provides an example of the decay of light intensity, as stated by the law of Lambert–Beer–Bourguer. We devised a very simple experiment to check this law. The experimental setup, its realization, and the data analysis of the experiment are definitely simple. Our main goal was to create an experiment that is accessible to all students, including those in their first year of academic courses and those with poorly equipped laboratories. As illustrated in this paper, our proposal allowed us to develop a deep discussion about some general mathematical and numerical features of exponential decay. Furthermore, the special setup of the absorbing medium (sliced in finite thickness slabs) and the experimental outcomes allow students to understand the transition from the discrete to the continuum approach in experimental physics.

The dynamic Preisach model is applied to the study of Fe-based and Go-based amorphous alloys characterized by different microstructural conditions. It is shown that all static and dynamic hysteresis properties are correctly predicted by the dynamic Preisach model by associating with each material a structural parameter, lambda, which represents the linear dimension of the correlation regions providing coherent magnetization changes. The dependence of this correlation length on annealing treatments is compared with Kerr-effect domain observations and structural data obtained by differential scanning calorimetry. It is found that lambda has a role comparable to that of grain size in micro-crystalline alloys. In particular, it is shown that the linear relation holds, H-c = H-c0 + c/lambda, between the static coercive field H-c and 1/lambda, where the slope c depends on the magnetostriction constant of the material and the amount of quenched-in stresses, whits the offset H-c0 is connected to surface characteristics.

""Spin selectivity in angle-resolved Auger photoelectron coincidence spectroscopy (AR-APECS) is used to. probe electronic structure in antiferromagnetic thin films. In particular, exploiting the AR-APECS capability to. discriminate Auger electron emission events characterized by a different spin of the ion in its final state, a sharp. multiplet structure in the Ni MVV Auger line shape of NiO\\\/Ag(001) thin films is measured below the critical. Néel temperature. The assignment of multiplet terms follows from a close comparison of the experimental. AR-APECS line shapes with the predictions based on semiempirical calculations on a cluster model and an. open-band extension of the Cini-Sawatzky approach. In analogy to CoO, also in NiO, above the Néel temperature. a more featureless Auger spectrum appears and AR-APECS does not disentangle anymore high-spin and low-spin. contributions to the total Auger intensity. Such a behavior, which seems to be a general result for metal oxide. antiferromagnetic systems, is discussed.""

We have investigated the role of the electroforming process in the establishment of resistive switching behaviour for Pt/Ti/Pr0.5Ca0.5MnO3/SrRuO3 layered heterostructures (Pt/Ti/PCMO/SRO) acting as non-volatile Resistance Random Access Memories (RRAMs). Electron spectroscopy measurements demonstrate that the higher resistance state resulting from electroforming of as-prepared devices is strictly correlated with the oxidation of the top electrode Ti layer through field-induced electromigration of oxygen ions. Conversely, PCMO exhibits oxygen depletion and downward change of the chemical potential for both resistive states. Impedance spectroscopy analysis, supported by the detailed knowledge of these effects, provides an accurate model description of the device resistive behaviour. The main contributions to the change of resistance from the as-prepared (low resistance) to the electroformed (high resistance) states are respectively due to reduced PCMO at the boundary with the Ti electrode and to the formation of an anisotropic np junction between the Ti and the PCMO layers.

The magnetic domain patterns of epitaxial single-crystalline Co/FeMn bilayers and Co/Cu/FeMn trilayers were investigated by magnetic circular dichroism domain imaging using photoelectron emission microscopy. The as-grown domain size increases continuously with increasing Cu layer thickness, which is attributed to the decrease of the interlayer exchange coupling between ferromagnetic Co and antiferromagnetic FeMn layers. Domain images of the Co layer acquired after applying different external magnetic fields show a decrease in coercivity with increasing Cu layer thickness, confirming the reduction of magnetic coupling energy with increasing Cu thickness.

X-ray photoemission electron microscopy (X-PEEM) is a powerful imaging technique that can be used to perform element selective magnetic domain imaging on heterogeneous samples with different magnetic layers, like spin valves and tunnel junctions. We have performed nanosecond time-resolved X-PEEM measurements, on the permalloy layer of a Ni80Fe20 (5 nm)/Cu (10 nm)/Co (5 nm) trilayer deposited on Si(111). We used the pump-probe mode, synchronizing a magnetic pulse from a microcoil with the x-ray photon bunches delivered by the BESSY synchrotron in single bunch mode. Images could be acquired during and after the 20 ns long and 80 Oe high field pulses. The nucleation and subsequent growth of reversed domains in the permalloy could be observed, demonstrating the feasibility of element selective and time-resolved domain imaging using X-PEEM.

A direct and element-specific measurement of the local Fe spin moment has been provided by analyzing the Fe 3$s$ core level photoemission spectra in the parent and optimally doped CeFeAsO${}_{1\ensuremath{-}x}$F${}_{x}$ ($x$ $=$ 0, 0.11) and Sr(Fe${}_{1\ensuremath{-}x}$Co${}_{x}$)${}_{2}$As${}_{2}$ ($x$ $=$ 0, 0.10) pnictides. The rapid time scales of the photoemission process allowed the detection of large local spin moments fluctuating on a 10${}^{\ensuremath{-}15}$ s time scale in the paramagnetic, antiferromagnetic, and superconducting phases, indicative of the occurrence of ubiquitous strong Hund's magnetic correlations. The magnitude of the spin moment is found to vary significantly among different families, 1.3${\ensuremath{\mu}}_{B}$ in CeFeAsO and 2.1${\ensuremath{\mu}}_{B}$ in SrFe${}_{2}$As${}_{2}$. Surprisingly, the spin moment is found to decrease considerably in the optimally doped samples, 0.9${\ensuremath{\mu}}_{B}$ in CeFeAsO${}_{0.89}$F${}_{0.11}$ and 1.3${\ensuremath{\mu}}_{B}$ in Sr(Fe${}_{0.9}$Co${}_{0.1}$)${}_{2}$As${}_{2}$. The strong variation of the spin moment against doping and material type indicates that the spin moments and the motion of itinerant electrons are influenced reciprocally in a self-consistent fashion, reflecting the strong competition between the antiferromagnetic superexchange interaction among the spin moments and the kinetic energy gain of the itinerant electrons in the presence of a strong Hund's coupling. By describing the evolution of the magnetic correlations concomitant with the appearance of superconductivity, these results constitute a fundamental step toward attaining a correct description of the microscopic mechanisms shaping the electronic properties in the pnictides, including magnetism and high-temperature superconductivity.

""\\"Low-energy photoemission spectroscopy in the photon energy range between 5.5 and 21 eV is used to investigate the valence electronic structure of Yb polycrystalline films. With the lowering of the photon energy below 11 eV, additional spectral features, nearly absent at higher photon energy, become predominant, in particular a peak located right at the Fermi level. With the help of an ab initio theoretical calculation, we interpret the peak as due to the joint influence of filled and empty densities of states, identifying a p-band contribution close to the Fermi level, whose intensity is strongly enhanced at certain photon energies corresponding to modulation of the empty d band.\\"""

Spin selectivity in angle-resolved Auger photoelectron coincidence spectroscopy (AR-APECS) is used to probe electron correlation in ferromagnetic thin films. In particular, exploiting the AR-APECS capability to discriminate Auger electron emission events characterized by valence hole pairs created either in the high or in the low total spin state, a strong correlation effect in the Fe M2,3VV Auger line shape (measured in coincidence with the Fe 3p photoelectrons) of Fe/Cu(001) thin films is detected and ascribed to interactions within the majority spin subband. Such an assignment follows from a close comparison of the experimental AR-APECS line shapes with the predictions of a model based on spin polarized density functional theory and the Cini-Sawatzky approach.

A simple didactic experiment has been designed and realized, in order to illustrate to undergraduate students in scientific faculties some basic concepts lying behind the fundamentals of geometrical optics. The spectral response of a human-eye-calibrated lux meter was measured using a very trivial experimental arrangement. The white light of a halogen lamp was decomposed into its spectral components through a diffraction grating, so that collecting the radiation at different dispersion angles allowed one to measure the intensity as a function of wavelength. The experiment can be used to effectively illustrate the concepts of spectral distribution, the radiometry versus photometry conversion and photopic response, and the famous historical experience by Herschel on the ?temperature of colours?.

International audience; We investigated the electronic properties of MnAs nano-clusters embedded in GaAs by bulk sensitive photoemission spectroscopy and cross-sectional scanning tunneling microscopy/spectroscopy. We report experimental evidences that the clusters are metallic MnAs, in close resemblance to MnAs thin films, and display a sharp interface with the surrounding GaAs. These results are supported by the comparison with GaMnAs and MnAs film in the same experimental condition. Furthermore, we observe a clear Coulomb blockade effect, as due to confinement and their nanometric size. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4704778]

Secondary electron spectra emitted from polycrystalline Al have been measured in coincidence with 500 eV electrons reflected after undergoing a given energy loss. Contributions from bulk- and surface-plasmon decay have been observed, as well as contributions from LVV Auger electrons and electron-electron scattering.

The absence of sharp structures in the core-valence-valence Auger line shapes of partially filled bands has severely limited the use of electron spectroscopy in magnetic crystals and other correlated materials. Here by a novel interplay of experimental and theoretical techniques we achieve a combined understanding of the Photoelectron, Auger %$M_{23}M_{45}M_{45}$ and Auger-Photoelectron Coincidence Spectra (APECS) of CoO. This is a prototype antiferromagnetic material in which the recently discovered Dichroic Effect in Angle Resolved (DEAR) APECS reveals a complex pattern in the strongly correlated Auger line shape. A calculation of the \textit{unrelaxed} spectral features explains the pattern in detail, labeling the final states by the total spin. The present theoretical analysis shows that the dichroic effect arises from a spin-dependence of the angular distribution of the photoelectron-Auger electron pair detected in coincidence, and from the selective power of the dichroic technique in assigning different weights to the various spin components. Since the spin-dependence of the angular distribution exists in the antiferromagnetic state but vanishes at the N\'eel temperature, the DEAR-APECS technique detects the phase transition from its local effects, thus providing a unique tool to observe and understand magnetic correlations in such circumstances, where the usual methods (neutron diffraction, specific heat measurements) are not applicable., Comment: Accepted by: Physical Review Letters

We report an extensive study on the intrinsic bulk electronic structure of the high-temperature superconductor ${\text{CeFeAsO}}_{0.89}{\text{F}}_{0.11}$ and its parent compound CeFeAsO by soft and hard x-ray photoemissions, x-ray absorption, and soft x-ray emission spectroscopies. The complementary surface/bulk probing depth, and the elemental and chemical sensitivity of these techniques allow resolving the intrinsic electronic structure of each element and correlating it with the local structure, which has been probed by extended x-ray absorption fine-structure spectroscopy. The measurements indicate a predominant $4{f}^{1}$ (i.e., ${\text{Ce}}^{3+}$) initial-state configuration for cerium and an effective valence-band-to-$4f$ charge-transfer screening of the core hole. The spectra also reveal the presence of a small $\text{Ce}\text{ }{f}^{0}$ initial-state configuration, which we assign to the occurrence of an intermediate-valence state. The data reveal a reasonably good agreement with the partial density of states as obtained in standard density-functional calculations over a large energy range. Implications for the electronic structure of these materials are discussed.

We present a comprehensive study of the photon energy dependence of the valence band photoemission yield in the prototype Mott-Hubbard oxide ${\text{V}}_{2}{\text{O}}_{3}$. The analysis of our experimental results, covering an extended photon energy range (20--6000 eV) and combined with GW calculations, allows us to identify the nature of the orbitals contributing to the total spectral weight at different binding energies, and in particular to locate the $\text{V}\text{ }4s$ states at about 8 eV binding energy. From this comparative analysis, we conclude that the intensity of the quasiparticle photoemission peak, observed close to the Fermi level in the paramagnetic metallic phase upon increasing photon energy, does not have a significant correlation with the intensity variation in the $\text{O}\text{ }2p$ and $\text{V}\text{ }3d$ yield, thus, confirming that bulk sensitivity is an essential requirement for the detection of this coherent low-energy excitation.

The core and valence levels of β-PbO2 have been studied using hard X-ray photoemission spectroscopy (hν = 6000 eV and 7700 eV). The Pb 4f core levels display an asymmetric lineshape which may be fitted with components associated with screened and unscreened final states. It is found that intrinsic final state screening is suppressed in the near-surface region. A shift in the O 1s binding energy due to recoil effects is observed under excitation at 7700 eV. It is shown that conduction band states have substantial 6s character and are selectively enhanced in hard X-ray photoemission spectra. However, the maximum amplitude in the Pb 6s partial density of states is found at the bottom of the valence band and the associated photoemission peak shows the most pronounced enhancement in intensity at high photon energy. © 2008 Elsevier B.V. All rights reserved.

We present a magnetic domain imaging study of polycrystalline exchange biased ferromagnet/antiferromagnet Co/FeMn bilayers using x-ray photoelectron emission microscopy. At low FeMn thicknesses, where the system exhibits no exchange bias, a magnetic fine structure due to fluctuations of the local anisotropy axis is observed in the ferromagnetic Co layer. We find that upon increasing the FeMn layer thickness, this dispersion of the magnetization of the ferromagnetic layer is increasingly suppressed. This can be interpreted as influence of the exchange bias field on the spin structure of the ferromagnetic layer, mediated by the interface coupling, if the "exchange length" (analogous to a domain-wall width) of the antiferromagnetic layer is larger than that of the ferromagnetic layer. The same behavior is observed for both the induced Fe and Mn ferromagnetic moments in the antiferromagnetic layer. We illustrate that the final spin structure at the Co/FeMn interface is not only governed by the magnetic spin structure of the Co layer alone (which is the general perception) but is also an exchange average of both the Co and FeMn layers.

The mechanism of secondary electron emission by impact of 100-eV electrons on an Al(100) surface has been investigated by measuring the secondary electron spectrum in coincidence with loss features in the spectrum of reflected electrons. Distinct peaks are observed at energies corresponding accurately to the surface and bulk plasmon energies minus the work function of the analyzer, demonstrating that plasmons excited by electron energy losses predominantly decay via creation of single-electron-hole pairs that act as a source for the secondary electron spectrum. These findings suggest a mechanism for emission of secondary electrons very similar to photoelectron (PE) emission, the difference being the step leading to electron liberation, i.e., plasmon decay in the present case versus photoionization in the case of PE.

The M(3)M(4,5)M(4,5) Auger transition from a Cu(111) surface is studied using Angular Resolved Auger-PhotoElectron Coincidence Spectroscopy (AR-APECS). In the experiment two different geometrical configurations of the electron analyzers allow us to sample different emission angles of the ejected electrons leading to different weights of the singlet and triplet contributions in the studied transition. The experimental spectra are modeled within a two-step approach using the Cini theory for the closed band case so as to properly consider the spin-orbit interaction and the hole-hole correlation energy. Ingredients for the theory, like density of states, are obtained fully ab-initio in the framework of density functional theory by performing all-electron calculations. The obtained results confirm the recently discovered selectivity of AR-APECS in the final spin-state. RI Fratesi, Guido/A-4637-2010; Da Pieve, Fabiana /G-2497-2011

We present an x-ray spectromicroscopic investigation of single-crystalline magnetic $\mathrm{Fe}\mathrm{Mn}∕\mathrm{Co}$ bilayers on Cu(001), using x-ray magnetic circular dichroism and x-ray magnetic linear dichroism (XMLD) at the Co and Fe ${L}_{3}$ absorption edges in combination with photoelectron emission microscopy. Using the magnetic coupling between the ferromagnetic Co layer and the antiferromagnetic FeMn layer, we are able to produce magnetic domains with two different crystallographic orientations of the magnetic easy axis within the same sample at the same time. We find a huge difference in the XMLD contrast between the two types of magnetic domains, which we discuss in terms of intrinsic magnetocrystalline anisotropy of XMLD of the Co layer. We also demonstrate that due to the high sensitivity of the method, the small number of induced ferromagnetic Fe moments at the FeMn-Co interface is sufficient to obtain magnetic contrast from XMLD in a metallic system.

Threshold photoemission spectroscopy (TPES) is used to measure the Fe 2p spectrum of a stainless steel sample. The obtained spectrum is compared with analogous spectra measured by X-ray photoemission and absorption spectroscopies. The results of this comparison suggest that resonant two-electron autoionization processes, rather than direct photoemission from the core level, are the main mechanisms contributing to the signal. Limits and applicability of this experimental approach to investigate bulk electronic properties in solids are discussed.

The recently discovered capabilities of Auger-photoelectron coincidence spectroscopy (APECS), i.e., the emission depth selectivity and the final spin state selectivity, are reviewed and discussed as a tool for the study of complex systems like magnetic thin films and multilayers. After a brief overview of these recent findings and a description of a clear experimental evidence for a dichroic effect in angle resolved (DEAR) APECS, results of coincidence Auger line shape applied to Co film on Cu(001), are presented. The geometrical configurations used, achieved by means of the high degree of freedom available in the experimental apparatus, are discussed in detail, as well as all the possible combinations that can provide a spin final state selectivity are presented. Due to the very high statistics achieved in the measurement, some finer details can be resolved at energies corresponding to transitions involving electrons from the top and the bottom of the valence band, when comparing singlet versus triplet contributions. As a first attempt and in the simplest approach, the observed dichroism can be explained by appropriate convolutions of the majority and minority densities of states, possibly corrected by a Cini-Sawatzky model for taking into account spin dependent correlation effects. (c) 2006 Elsevier B.V. All rights reserved.

We have measured bulk sensitive photoemission spectra of pure vanadium sesquioxide (V2O3) in its metallic phase as a function of different surface preparations. We observe the presence of a clear coherent peak in the vicinity of the Fermi level and of satellites intensities at the V 2p core level. After scraping, the coherent intensities are almost completely suppressed in both core level and valence band. Our results suggest a remarkable change of the screening properties in strongly correlated systems when going from the surface to the volume. (C) 2006 Elsevier B.V. All rights reserved.

A detailed comparison of the surface sensitivity of x-ray photoemission spectroscopy for hard and soft x rays is presented and discussed. Electron scattering parameters and their energy dependence are given for Si and two Si spectra are analyzed: a Mg K alpha (h nu=1253.6 eV) excited spectrum of the Si 2p and 2s lines and a hard x-ray excited spectrum (h nu=5925 eV) of the Si 1s line. The differential inelastic scattering characteristics for Si are extracted from reflection electron energy loss spectra taken at energies of 1500 and 4000 eV. Using these scattering characteristics and electron mean free paths from the literature, simulated spectra are compared with experiment. The experimental spectra are deconvoluted to give the true intrinsic line shape corresponding to the theoretical collision statistics when interference effects between intrinsic and extrinsic scattering are neglected. The magnitude of interference effects cannot be assessed by our analysis. Within the (unknown) uncertainty introduced by neglecting interference effects, it is possible to determine the relative intensity of intrinsic and extrinsic excitations. In this way, it is found that in the case of the soft x-ray excited photoelectron spectrum of the shallower electronic shells (2p and 2s), intrinsic plasmon creation is rather weak, and the apparent asymmetric line shape of the spectrum might be interpreted as the fact that electron-hole pair creation dominates the intrinsic loss spectrum, while an alternative explanation in terms of surface core level shifted components is also proposed. For the deeper core electronic shell, probed with hard x rays, the opposite situation is observed: while intrinsic electron-hole pair creation was not observed, a strong contribution of intrinsic plasmon losses of about 30% was seen.