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Electron spectroscopy with the unprecedented transmission of angle-resolved time-of-flight detection, in combination with pulsed X-ray sources, brings new impetus to functional materials science. We showcase recent developments towards chemical sensitivity from electron spectroscopy for chemical analysis and structural information from photoelectron diffraction using the phase transition properties of 1T-TaS2. Our development platform is the SurfaceDynamics instrument located at the Femtoslicing facility at BESSY II, where femtosecond and picosecond X-ray pulses can be generated and extracted. The scientific potential is put into perspective to the current rapidly developing pulsed X-ray source capabilities from Lasers and Free-Electron Lasers. [ABSTRACT FROM AUTHOR]

In this work, we study the interface obtained by depositing a monolayer of a Blatter radical derivative on polycrystalline cobalt. By examining the occupied and unoccupied states at the interface, using soft X‐ray techniques, combined with electronic structure calculations, we could simultaneously determine the electronic structure of both the molecular and ferromagnetic sides of the interface, thus obtaining a full understanding of the interfacial magnetic properties. We found that the molecule is strongly hybridized with the surface. Changes in the core level spectra reflect the modification of the molecule and the cobalt electronic structures inducing a decrease in the magnetic moment of the cobalt atoms bonded to the molecules which, in turn, lose their radical character. Our method allowed us to screen, beforehand, organic/ferromagnetic interfaces given their potential applications in spintronics. [ABSTRACT FROM AUTHOR]

In this work, we study the interface obtained by depositing a monolayer of a Blatter radical derivative on polycrystalline cobalt. By examining the occupied and unoccupied states at the interface, using soft X‐ray techniques, combined with electronic structure calculations, we could simultaneously determine the electronic structure of both the molecular and ferromagnetic sides of the interface, thus obtaining a full understanding of the interfacial magnetic properties. We found that the molecule is strongly hybridized with the surface. Changes in the core level spectra reflect the modification of the molecule and the cobalt electronic structures inducing a decrease in the magnetic moment of the cobalt atoms bonded to the molecules which, in turn, lose their radical character. Our method allowed us to screen, beforehand, organic/ferromagnetic interfaces given their potential applications in spintronics. [ABSTRACT FROM AUTHOR]

The implementation of a high-transmission, angular-resolved time-of-flight electron spectrometer with a 1.25 MHz pulse selector at the PM4 soft X-ray dipole beamline of the synchrotron BESSY II creates unique capabilities to inquire electronic structure via photoelectron spectroscopy with a minimum of radiation dose. Solid-state samples can be prepared and characterized with standard UHV techniques and rapidly transferred from various preparation chambers to a 4-axis temperature-controlled measurement stage. A synchronized MHz laser system enables excited-state characterization and dynamical studies starting from the picosecond timescale. This article introduces the principal characteristics of the PM4 beamline and LowDosePES end-station. Recent results from graphene, an organic hole transport material for solar cells and the transition metal dichalcogenide MoS 2 are presented to demonstrate the instrument performances. [ABSTRACT FROM AUTHOR]

The local structure of germanium dioxide, in its crystalline (quartzlike and rutilelike) and amorphous (α-GeO2) solid phases, has been investigated by means of x-ray absorption spectroscopy (XAS). The short-range distance and angular distributions have been determined by modeling the experimental spectra with multiple-scattering contributions associated with selected n-body atomic configurations. Even for α-GeO2, the experimental x-ray absorption signal ends up being significantly affected by the intra-tetrahedral (Due to image restrictions,multiple line equation(s) cannot be graphically displayed) and inter-tetrahedral (Due to image restrictions,multiple line equation(s) cannot be graphically displayed) angle distributions. Results from the present XAS structural refinements, including experimental determination of the local bond-angle distributions, are compared with previous experiments and molecular dynamics simulations. [ABSTRACT FROM AUTHOR]

The article discusses a research study conducted by M. Benedetta Casu et al. on the hybridization of molecules deposited on polycrystalline cobalt surfaces. The study found that the molecules experience charge transfer from the cobalt, leading to a modification of the interface electronic structure and a decrease in the magnetic moment of the cobalt atoms bonded to the molecules. This research provides a method, based on X-ray spectroscopies, to screen organic/ferromagnetic interfaces for potential applications in spintronics. The authors of the study include Ewa Malgorzata Nowik-Boltyk, Tobias Junghoefer, Erika Giangrisostomi, Ruslan Ovsyannikov, Chan Shu, Andrzej Rajca, Andrea Droghetti, and Maria Benedetta Casu. [Extracted from the article]

The article titled "Inside Back Cover: Radical-Induced Changes in Transition Metal Interfacial Magnetic Properties: A Blatter Derivative on Polycrystalline Cobalt" discusses the hybridization of molecules deposited on polycrystalline cobalt and the resulting charge transfer from the cobalt. This leads to a modification of the interface electronic structure, causing a decrease in the magnetic moment of the cobalt atoms bonded to the molecules. The authors present a method using X-ray spectroscopies to screen organic/ferromagnetic interfaces for potential applications in spintronics. The authors of the article are M. Benedetta Casu et al. and the research was conducted by a team of authors including Ewa Malgorzata Nowik-Boltyk, Tobias Junghoefer, Erika Giangrisostomi, Ruslan Ovsyannikov, Chan Shu, Andrzej Rajca, Andrea Droghetti, and Maria Benedetta Casu. [Extracted from the article]

The layered dichalcogenide MoS 2 is relevant for electrochemical Li adsorption/intercalation, in the course of which the material undergoes a concomitant structural phase transition from semiconducting 2H-MoS 2 to metallic 1T-Li x MoS 2 . With the core hole clock approach at the S L 1 X-ray absorption edge we quantify the ultrafast directional charge transfer of excited S3p electrons in-plane (‖ ) and out-of-plane (⊥ ) for 2H-MoS 2 as τ 2 H , ‖ = 0.38 ± 0.08 fs and τ 2 H , ⊥ = 0.33 ± 0.06 fs and for 1T-Li x MoS 2 as τ 1 T , ‖ = 0.32 ± 0.12 fs and τ 1 T , ⊥ = 0.09 ± 0.07 fs. The isotropic charge delocalization of S3p electrons in the semiconducting 2H phase within the S-Mo-S sheets is assigned to the specific symmetry of the Mo-S bonding arrangement. Formation of 1T-Li x MoS 2 by lithiation accelerates the in-plane charge transfer by a factor of ∼ 1.2 due to electron injection to the Mo-S covalent bonds and concomitant structural repositioning of S atoms within the S-Mo-S sheets. For excitation into out-of-plane orbitals, an accelerated charge transfer by a factor of ∼ 3.7 upon lithiation occurs due to S-Li coupling. [ABSTRACT FROM AUTHOR]

The simultaneous detection of energy, momentum and temporal information in electron spectroscopy is the key aspect to enhance the detection efficiency in order to broaden the range of scientific applications. Employing a novel 60° wide angle acceptance lens system, based on an additional accelerating electron optical element, leads to a significant enhancement in transmission over the previously employed 30° electron lenses. Due to the performance gain, optimized capabilities for time resolved electron spectroscopy and other high transmission applications with pulsed ionizing radiation have been obtained. The energy resolution and transmission have been determined experimentally utilizing BESSY II as a photon source. Four different and complementary lens modes have been characterized. [ABSTRACT FROM AUTHOR]

The temperature dependent dehydrogenation of naphthalene on Ni(111) has been investigated using vibrational sum-frequency generation spectroscopy, X-ray photoelectron spectroscopy, scanning tunneling microscopy, and density functional theory with the aim of discerning the reaction mechanism and the intermediates on the surface. At 110 K, multiple layers of naphthalene adsorb on Ni(111); the first layer is a flat lying chemisorbed monolayer, whereas the next layer(s) consist of physisorbed naphthalene. The aromaticity of the carbon rings in the first layer is reduced due to bonding to the surface Ni-atoms. Heating at 200 K causes desorption of the multilayers. At 360 K, the chemisorbed naphthalene monolayer starts dehydrogenating and the geometry of the molecules changes as the dehydrogenated carbon atoms coordinate to the nickel surface; thus, the molecule tilts with respect to the surface, recovering some of its original aromaticity. This effect peaks at 400 K and coincides with hydrogen desorption. Increasing the temperature leads to further dehydrogenation and production of H2 gas, as well as the formation of carbidic and graphitic surface carbon. [ABSTRACT FROM AUTHOR]

The Elastic and Inelastic Scattering (EIS) beamline at the free-electron laser FERMI is presented. It consists of two separate end-stations: EIS-TIMEX, dedicated to ultrafast time-resolved studies of matter under extreme and metastable conditions, and EIS-TIMER, dedicated to time-resolved spectroscopy of mesoscopic dynamics in condensed matter. The scientific objectives are discussed and the instrument layout illustrated, together with the results from first exemplifying experiments. [ABSTRACT FROM AUTHOR]

High intensity pulses obtained by modern extreme ultraviolet (EUV) and x-ray photon sources allows the observation of peculiar phenomena in condensed matter. Experiments performed at the Fermi@Elettra FEL-1 free-electron-laser source at 23.7, 33.5, and 37.5 eV on Al thin films, for an intermediate-fluence range up to about 20J/cm2, show evidence for a nonmonotonic EUV transmission trend. A decreasing transmission up to about 5-10J/cm2 is followed by an increase at higher fluence, associated with saturable absorption effects. The present findings are interpreted within a simplified three-channel model, showing that an account of the interplay between ultrafast electron heating and saturation effects is required to explain the observed transmission trend. [ABSTRACT FROM AUTHOR]

Tin is a suitable element for inclusion in extreme ultraviolet photoresists because of its relatively high-absorption cross section at 92 eV. The electrons emitted after photon absorption are expected to generate secondary electrons in the solid film. In this way, several pathways lead to reactive species that cause a solubility switch. Here, we report the photoelectron spectra of tin oxo cage photoresists over the photon energy range 60–150 eV, and the relative yields of photoelectrons from the valence band of the resist, from the Sn 4d orbitals, and of inelastically scattered electrons. The experimental excitation spectra differ considerably from those predicted by commonly used database cross section values, and from the combined computed subshell spectra: the maximum efficiency of ionization of Sn 4d both in the photoresists and in Sn metal occurs near the industrially relevant EUV wavelength of 13.5 nm. [ABSTRACT FROM AUTHOR]

Time-resolved photoelectron spectroscopy can give insights into carrier dynamics and offers the possibility of element and site-specific information through the measurements of core levels. In this paper, we demonstrate that this method can access electrons dynamics in PbS quantum dots over a wide time window spanning from pico- to microseconds in a single experiment carried out at the synchrotron facility BESSY II. The method is sensitive to small changes in core level positions. Fast measurements at low pump fluences are enabled by the use of a pump laser at a lower repetition frequency than the repetition frequency of the X-ray pulses used to probe the core level electrons: Through the use of a time-resolved spectrometer, time-dependent analysis of data from all synchrotron pulses is possible. Furthermore, by picosecond control of the pump laser arrival at the sample relative to the X-ray pulses, a time-resolution limited only by the length of the X-ray pulses is achieved. Using this method, we studied the charge dynamics in thin film samples of PbS quantum dots on n-type MgZnO substrates through time-resolved measurements of the Pb 5d core level. We found a time-resolved core level shift, which we could assign to electron injection and charge accumulation at the MgZnO/PbS quantum dots interface. This assignment was confirmed through the measurement of PbS films with different thicknesses. Our results therefore give insight into the magnitude of the photovoltage generated specifically at the MgZnO/PbS interface and into the timescale of charge transport and electron injection, as well as into the timescale of charge recombination at this interface. It is a unique feature of our method that the timescale of both these processes can be accessed in a single experiment and investigated for a specific interface. [ABSTRACT FROM AUTHOR]

Abstract: The effect of intermolecular H‐bonding interactions on the local electronic structure of N‐containing functional groups (amino group and pyridine‐like N) that are characteristic of polymeric carbon nitride materials p‐CN(H), a new class of metal‐free organophotocatalysts, was investigated. Specifically, the melamine molecule, a building block of p‐CN(H), was characterized by X‐ray photoelectron (XPS) and near edge X‐ray absorption fine structure (NEXAFS) spectroscopy. The molecule was studied as a noninteracting system in the gas phase and in the solid state within a H‐bonded network. With the support of DFT simulations of the spectra, it was found that the H‐bonds mainly affect the N 1s level of the amino group, leaving the N 1s level of the pyridine‐like N mostly unperturbed. This is responsible for a reduction of the chemical shift between the two XPS N 1s levels relative to free melamine. Consequently, N K‐edge NEXAFS resonances involving the amino N 1s level also shift to lower photon energies. Moreover, the solid‐state absorption spectra showed significant modification/quenching of resonances related to transitions from the amino N 1s level to σ* orbitals involving the NH2 termini. [ABSTRACT FROM AUTHOR]

Abstract: We present a newly developed resonant Raman scattering instrument working in the UV spectral range. This set-up, which exploits the UV synchrotron radiation source available at Elettra (Trieste, Italy), results in an innovative spectroscopic facility to be used for addressing a large array of open problems, ranging from the electronic properties of nanostructures and strongly correlated materials to biochemistry. [Copyright &y& Elsevier]

Interface properties of iron phthalocyanine (FePc) and perfluorinated iron phthalocyanine (FePcF16) on rutile TiO2(100) and TiO2(110) surfaces were studied using X-ray photoemission spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and low-energy electron diffraction (LEED). It is demonstrated that the interaction strength at the interfaces is considerably affected by the detailed preparation procedure. Weak interactions were observed for all studied interfaces between FePc or FePcF16 and rutile, as long as the substrate was exposed to oxygen during the annealing steps of the preparation procedure. The absence of oxygen in the last annealing step only had almost no influence on interface properties. In contrast, repeated substrate cleaning cycles performed in the absence of oxygen resulted in a more reactive, defect-rich substrate surface. On such reactive surfaces, stronger interactions were observed, including the cleavage of some C–F bonds of FePcF16. [ABSTRACT FROM AUTHOR]

For the layered transition metal dichalcogenide 1T-TaS2, we establish through a unique experimental approach and density functional theory, how ultrafast charge transfer in 1T-TaS2 takes on isotropic three-dimensional character or anisotropic two-dimensional character, depending on the commensurability of the charge density wave phases of 1T-TaS2. The X-ray spectroscopic core-hole-clock method prepares selectively in- and out-of-plane polarized sulfur 3p orbital occupation with respect to the 1T-TaS2 planes and monitors sub-femtosecond wave packet delocalization. Despite being a prototypical two-dimensional material, isotropic three-dimensional charge transfer is found in the commensurate charge density wave phase (CCDW), indicating strong coupling between layers. In contrast, anisotropic two-dimensional charge transfer occurs for the nearly commensurate phase (NCDW). In direct comparison, theory shows that interlayer interaction in the CCDW phase - not layer stacking variations - causes isotropic three-dimensional charge transfer. This is presumably a general mechanism for phase transitions and tailored properties of dichalcogenides with charge density waves. [ABSTRACT FROM AUTHOR]

We report a time-resolved study of the relaxation dynamics of Al films excited by ultrashort intense free-electron laser (FEL) extreme ultraviolet pulses. The system response was measured through a pump-probe detection scheme, in which an intense FEL pulse tuned around the Al L2,3 edge (72.5 eV) acted as the pump, while a time-delayed ultrafast pulse probed the near-infrared (NIR) reflectivity of the Al film. Remarkably, following the intense FEL excitation, the reflectivity of the film exhibited no detectable variation for hundreds of femtoseconds. Following this latency time, sizable reflectivity changes were observed. Exploiting recent theoretical calculations of the EUV-excited electron dynamics [N. Medvedev et al., Phys. Rev. Lett. 107, 165003 (2011)], the delayed NIR-reflectivity evolution is interpreted invoking the formation of very-long-living nonthermal hot electron distributions in Al after exposure to intense EUV pulses. Our data represent the first evidence in the time domain of such an intriguing behavior. [ABSTRACT FROM AUTHOR]