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“Dip-coatings” are a completely new technology for depositing a carbon-based overcoating on the reflecting surface of X-ray mirrors. This simple deposition process is controllable and repeatable, as well as scalable and inexpensive, and can be carried out without the requirement for specialistic equipment or trained personnel. We have considered the use of these coatings on different materials, in particular Ir monolayers and Ir/Cr bilayers, which can be convenient coatings for ATHENA mirrors. We measured the X-ray reflectivity of tens of samples in three different beamlines (one laboratory source and two synchrotron radiation facilities), covering a broad range of angular and energetic ranges. Results are in excellent agreement with the model and show that the technology has a good potential for application to X-ray optics and telescopes. More details can be found in the reference paper., {"references":["Cotroneo et al. (2022), \"Dopamine dip-liquid overcoatings for soft x-ray reflectivity enhancement,\" Proc. SPIE 12181, Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray, 1218117, https://doi.org/10.1117/12.2630212"]}

Multilayer beamsplitter polarizers have been developed for improved solar polarimetry at key spectral lines. The advantage of beamsplitter polarizers is that a single device separates s from p polarization; this helps minimize attenuation and enables a more compact and lighter polarimeter, which is important for space instruments. Polarizers based on Al/AlF3 multilayers were prepared for both C IV (155 nm) and Mg II (280 nm) lines, and based on Al/MgF2 multilayers for H Lyman α line (121.6 nm). Polarizers were designed to mainly reflect (transmit) s (p) polarization. Beamsplitter performance and throughput are shown to compare advantageously with polarizers in the literature. Beamsplitter polarizers kept a valuable performance after several years of ageing.

The absorption of extreme ultraviolet (EUV) radiation by a photoresist strongly depends on its atomic composition. Consequently, elements with a high EUV absorption cross section can assist in meeting the demand for higher photon absorbance by the photoresist to improve the sensitivity and reduce the photon shot noise induced roughness. In this work, we enhanced the EUV absorption of the methacrylic acid ligands of Zn oxoclusters by introducing fluorine atoms. We evaluated the lithography performance of this fluorine-rich material as a negative tone EUV photoresist along with extensive spectroscopic and microscopic studies, providing deep insights into the underlying mechanism. UV-vis spectroscopy studies demonstrate that the presence of fluorine in the oxocluster enhances its stability in the thin films to the ambient atmosphere. However, the EUV photoresist sensitivity (D50) of the fluorine-rich oxocluster is decreased compared to its previously studied methacrylic acid analogue. Scanning transmission X-ray microscopy and in situ X-ray photoelectron spectroscopy in combination with FTIR and UV-vis spectroscopy were used to gain insights into the chemical changes in the material responsible for the solubility switch. The results support decarboxylation of the ligands and subsequent radical-induced polymerization reactions in the thin film upon EUV irradiation. The rupture of carbon-fluorine bonds via dissociative electron attachment offers a parallel way of generating radicals. The mechanistic insights obtained here will be applicable to other hybrid materials and potentially pave the way for the development of EUV materials with better performance.

We present here a method for the quantitative prediction of the spectroscopic specular reflectivity line-shape in anisotropic layered media. The method is based on a 4 &times, 4 matrix formalism and on the simulation from the first principles (through density functional theory&mdash, DFT) of the anisotropic absorption cross-section. The approach was used to simulate the reflectivity at the oxygen K-edge of a 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) thin film on Au(111). The effect of film thickness, orientation of the molecules, and grazing incidence angle were considered. The simulation results were compared to the experiment, permitting us to derive information on the film geometry, thickness, and morphology, as well as the electronic structure.

Mn dissolution is the main drawback of LiMn2O4 cathodes, leading to capacity fading and anode poisoning. It is well known that improved capacity/cycling performances have been obtained by the Al2O3 coating. It is less clear what is the effect of the coating from the point of view of the fundamental processes occurring within the active material and on the interface with the active material, especially during the first cycle, when a dynamical interaction at a high voltage with an electrolyte and a binder leads to the formation of a passivation layer. We present here the close comparison of coated and uncoated electrodes' X-ray absorption analysis at the interface during the measurements of several charged/discharged states of the electrode. The Al(2)O(3 )coating is significantly effective for stopping the high voltage instability of the battery, especially, when the Mn-O couple reacts with organic species, limiting Mn capture and the electrolyte reaction with the oxide surface. In the low-voltage discharge, on the other hand, more complex structure/electronic modifications occur. The presence of the coating limits disproportionation, preventing a general corrosion with dissolution of the Mn2+ species, and hence improves the electrode performance. From the structural point of view, the signatures of the transformations and a reversible modification of the surface character of the nanoparticles from a spinel to a defective phase are observed, while no charge transfer between the coating and manganese oxide is found. The role of nonthermodynamic interphase formation by means of proton transfer is enhanced for the coated oxide particles.

Since their first appearance, organic-inorganic perovskite absorbers have been capturing the attention of the scientific community. While high efficiency devices highlight the importance of band level alignment, very little is known on the origin of the strong n-doping character observed in the perovskite. Here, by means of a highly accurate photoemission study, we shed light on the energy alignment in perovskite-based devices. Our results suggest that the interaction with the substrate may be the driver for the observed doping in the perovskite samples.

Cr/C multilayer optics are a suitable choice for the tender X-ray range (1–4 keV) that covers the K absorption edges of P, S, Cl and 3d transition metals as well as the L absorption edges of 4d transition metals. In particular, these optics are studied in order to optimize the optical properties of collimated plane-grating monochromators. In this paper, the structure, stress and optical properties of Cr/C multilayers (fabricated using direct-current magnetron sputtering) with bi-layer number of 20 and the same period (about 11.64 nm) but different Cr thickness ratio (0.20–0.80) are investigated. Firstly, the grazing-incidence X-ray reflectivity at 8.04 keV was measured. These measurements were fitted assuming a multilayer structure with a four-layer and non-periodic model. Results and fitting show that interface widths increase with the Cr thickness ratio. The results obtained from X-ray diffraction at 8.04 keV were consistent with high-resolution transmission electron microscopy which showed an increase in grain size of the Cr layers. In addition, the stresses of the Cr/C multilayers have been measured and the results show that the stress value approaches zero when the Cr thickness ratio is about 0.45. The reflectivity of a Cr/C multilayer with Cr thickness ratio of 0.37 was measured and reaches 26.6% at 1.04 keV. The measured reflectivity matches very well with the predicted value using the four-layer and non-periodic model, which confirmed the viability of the prediction. Thus, the reflectivity at 1.04 keV of a Cr/C multilayer with different Cr thickness ratio was predicted and was found to drastically decrease when the Cr thickness ratio is larger than 0.37. It has been determined that a Cr thickness ratio value of 0.37 is the best choice for a Cr/C multilayer in view of high reflectivity and low stress.

International audience; X-ray spectroscopy of lithium is very difficult, even impossible, with wavelength dispersive spectrometers commonly deployed on scanning electron microscopes or electron microprobe analyzers. This is due to the absence of crystals and lack of efficient periodic multilayer for this spectral range, around 50 eV. To address this issue, we propose using a Be/Si/Al multilayer having a period of about 29 nm. The multilayer was deposited by magnetron sputtering and its reflectivity measured as a function of the glancing angle in the spectral range of the Li K emission and as a function of the incident energy up to ~200 eV. This characterization demonstrates that the designed multilayer is suitable to efficiently perform spectroscopy in the range of the Li K emission in terms of reflectance (0.32 at 51.5 eV), bandwidth (around 3.5 eV) and rejection of high order diffracted radiation.

The optical properties of mono‐ and trilayer graphene on SiO2/Si substrate are studied at hydrogen Lyman‐alpha (121.6 nm) spectral line for the first time. The optical anisotropy of graphene at this wavelength is experimentally demonstrated by retrieving the anisotropic “effective” optical constants. The results confirm that the axis of symmetry is nearly perpendicular to the surface and coherently related to the π‐orbitals’ structural orientation. Furthermore, it is observed that graphene strongly affects the performances of the substrate by inducing a pseudo‐Brewster angle downshift, which depends on the number of graphene layers. This finding is in contrast with what occurs in the visible spectral range, where the upshift of the pseudo‐Brewster angle is experienced in similar samples.

A liquid carbon ($l$-C) sample is generated through constant volume heating exposing an amorphous carbon foil to an intense ultrashort laser pulse. Time-resolved x-ray absorption spectroscopy at the C $K$ edge is used to monitor the dynamics of the melting process revealing a subpicosecond rearrangement of the electronic structure associated with a sudden change of the C bonding hybridization. The obtained $l$-C sample, resulting from a nonthermal melting mechanism, reaches a transient equilibrium condition with a temperature of about 14 200 K and pressure in the order of 0.5 Mbar in about 0.3 ps, prior to hydrodynamic expansion. A detailed analysis of the atomic and electronic structure in solid-density $l$-C based on time-resolved x-ray absorption spectroscopy and theoretical simulations is presented. The method can be fruitfully used for extending the experimental investigation of the C phase diagram in a vast unexplored region covering the ${10}^{3}--{10}^{4}\text{ }\text{ }\mathrm{K}$ temperature range with pressures up to 1 Mbar.

Optical characterization of magnesium fluoride thin films is performed in a wide spectral range from far infrared to extreme ultraviolet (0.01-45 eV) utilizing the universal dispersion model. Two film defects, i.e. random roughness of the upper boundaries and defect transition layer at lower boundary are taken into account. An extension of universal dispersion model consisting in expressing the excitonic contributions as linear combinations of Gaussian and truncated Lorentzian terms is introduced. The spectral dependencies of the optical constants are presented in a graphical form and by the complete set of dispersion parameters that allows generating tabulated optical constants with required range and step using a simple utility in the newAD2 software package.

International audience; Advanced Telescope for High-Energy Astrophysics is a large-class astrophysics space mission selected by the European Space Agency to study the theme "Hot and Energetic Universe." The mission essentially consists of a large effective area x-ray telescope and two detectors: the X-ray Integral Field Unit (X-IFU) and the Wide Field Imager (WFI). Both instruments require filters to shield from out-of-band radiation while providing high transparency to x-rays. The mission is presently in phase B; thus, to consolidate the preliminary design, investigated filter materials need to be properly characterized by experimental test campaigns. We report results from high-resolution x-ray transmission measurements performed using different synchrotron radiation beamlines to assess the filter calibration accuracy and mitigate the risk related to selecting a unique calibration facility. The main goals of these test campaigns are (i) to verify the compliance of the investigated filter design to the scientific requirements, (ii) to develop an accurate x-ray transmission model, and (iii) to start identifying suitable measurement facilities and achievable accuracy for the flight filters calibration program. In particular, the x-ray transmission model of the X-IFU and WFI filters has been refined within the edges of Al, C, N, and O by deriving the optical constants from two reference samples measured by synchrotron light. The achievable filter calibration accuracy has been estimated by evaluating the agreement between the best-fit according to the developed transmission model and the experimental data.

We have probed the structural and magnetic properties of a ferromagnetic/organic interface constituted by a polycrystalline Co layer deposited on a fullerene thin film through resonant soft X-ray reflectivity measurements. The fitting analysis of the reflectivity indicates the formation of a sharp interface with limited intermixing and a null remanent magnetization in a & x007E;1 nm thick region of the Co film at the interface with C60. This information contributes to elucidate the role of organic & x2013;inorganic interfaces in the charge and spin transport inside organic spintronic devices.

International audience; We characterize nano-scale periodic Sc/Mg two-layer, Sc/Mg/Co tri-layers and Sc/Co/Mg/Co quadri-layer designed as dispersive elements for x-ray spectroscopy in the nitrogen K range (390 eV). The samples are prepared by magnetron sputtering with Mg and Sc layers being a few nanometers thick and Co layers being of sub-nanometric thickness. We apply non-destructive (x-ray reflectivity and x-ray fluorescence in standing wave mode) and destructive (transmission electron microscopy) techniques to obtain a relevant description of the deposited stacks. It turns out that a strong interdiffusion takes place in the two-layer leading to poor reflective properties. Interdiffusion also occurs in the tri-layers and quadri-layer but between the Sc and Co layers. These systems can be considered as periodic ScCo/Mg two-layers with well-defined layers. As a consequence, the Sc/Co/Mg/Co multilayer is found interesting to use for spectroscopy as a reflectance of 32% is expected in the N K range in the water window range.

A thin orthorhombic LaLuO3 film, grown on SrTiO3 substrate by pulsed laser deposition, is characterized using multi-angle spectral extreme ultraviolet reflectometry (EUVR). Layer structure parameters and optical constants of LaLuO3 are determined simultaneously by fitting angular reflectivity curves in a wide spectral range (70–200 eV). From near-edge optical constant analysis, La:Lu stoichiometry ratio and the film density are derived. Sample structure is additionally analyzed using XRR, AFM and TEM methods. EUVR as a method of structural characterization is discussed in comparison with XRR. Correlation error analysis of the layer structure parameters, obtained from independent EUVR and XRR fits, is presented.

Since their first appearance, organic-inorganic perovskite absorbers have been capturing the attention of the scientific community. While high efficiency devices highlight the importance of band level alignment, very little is known on the origin of the strong n-doping character observed in the perovskite. Here, by means of a highly accurate photoemission study, we shed light on the energy alignment in perovskite-based devices. Our results suggest that the interaction with the substrate may be the driver for the observed doping in the perovskite samples.

International audience; The Kossel effect is the diffraction by a periodically structured medium, of the characteristic X-ray radiation emitted by the atoms of the medium. We show that multilayers designed for X-ray optics applications are convenient periodic systems to use in order to produce the Kossel effect, modulating the intensity emitted by the sample in a narrow angular range defined by the Bragg angle. We also show that excitation can be done by using photons (X-rays), electrons or protons (or charged particles), under near normal or grazing incident geometries, which makes the method relatively easy to implement. The main constraint comes from the angular resolution necessary for the detection of the emitted radiation. This leads to small solid angles of detection and long acquisition times to collect data with sufficient statistical significance. Provided this difficulty is overcome, the comparison or fit of the experimental Kossel curves, i.e., the angular distributions of the intensity of an emitted radiation of one of the element of the periodic stack, with the simulated curves enables getting information on the depth distribution of the elements throughout the multilayer. Thus the same kind of information obtained from the more widespread method of X-ray standing wave induced fluorescence used to characterize stacks of nanometer period, can be obtained using the Kossel effect.

Electron photoemission influences spacecraft surface potentials and the surrounding plasma, and many modern spacecraft use new uncharacterized materials. The angle-dependent photoemission properties were measured for niobium C103 alloy, molybdenum TZM alloy, tantalum tungsten alloy, Elgiloy, graphite lubricant epoxy (DAG213) and titanium nitride at the Bending for Emission Absorption and Reflectivity beam line. The properties of tungsten were also studied to verify the method with past data. The materials were prepared similarly to flight materials. The properties were measured from 0 (normal) to 80 deg (grazing) incidence preannealed and postannealed conditioning of the samples. The yield was measured in all cases for both p and s polarization at each angle of incidence. Results are presented for the photoelectric threshold and photoelectron yield for photon energies up to 30 eV. The work function was also found for each material tested. An analytical equation was then used to fit the normal photoelectron yield for each material to help obtain photocurrents, which were calculated assuming solar illumination at 1 astronomical unit (AU) at normal incidence.

Optical and structural properties of Niobium and Zirconium bilayer structures (Nb/Zr and Zr/Nb) were investigated in order to develop free-standing transmittance filters in the Extreme Ultraviolet region (EUV) between 5 and 20 nm. Samples of Nb/Zr and Zr/Nb were deposited on Silicon Nitride (Si3N4) membranes by magnetron sputtering technique, using metallic targets of Nb and Zr. A single layer of Zr and Nb on Si3N4 membrane has also been deposited and studied for a better understanding of the performance of these structures and their optical and mechanical properties. Optical microscope images of Zr and Zr/Nb structures on the membranes reveal compressive stress while Nb and Nb/Zr structures present tensile stress behavior. Nb and Nb/Zr self-standing filters were obtained by etching the silicon nitride membrane, with free-standing areas up to 3 × 3 mm2 with 100 nm of thickness. The transmittance performance of the samples has been measured by using EUV synchrotron radiation. The results show the highest peak transmittance of 60% at 7.02 nm and very good performance in the targeted range.

Vertical cross-bar devices based on manganite and cobalt injecting electrodes and metal-quinoline molecular transport layer are known to manifest both magnetoresistance and electrical bistability. The two effects are strongly interwoven, inspiring new device applications such as electrical control of the magnetoresistance and magnetic modulation of bistability. To investigate the full device functionality, we first identify the mechanism responsible for electrical switching by associating the electrical conductivity and the impedance behavior with chemical states of buried layers obtained by in operando photoelectron spectroscopy. These measurements revealed that a significant fraction of oxygen ions migrates under voltage polarity, resulting in a modification of the electronic properties of the organic material and of the oxidation of interfacial layer with ferromagnetic contacts. Variable oxygen doping of the organic molecule represents the key element for correlating bistability and magnetoresistance and our measurements provide the first experimental evidence in favor of the impurity band model describing the spin transport in organic semiconductors in similar devices.

A combination of ultraviolet and X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and first principle calculations was used to study the electronic structure at the interface between the strong molecular acceptor 1,3,4,5,7,8-hexafluorotetracyano-naphthoquinodimethane (F6TCNNQ) and a graphene layer supported on either a quartz or a copper substrate. We find evidence for fundamentally different charge redistribution mechanisms in the two ternary systems, as a consequence of the insulating versus metallic character of the substrates. While electron transfer occurs exclusively from graphene to F6TCNNQ on the quartz support (p-doping of graphene), the Cu substrate electron reservoir induces an additional electron density flow to graphene decorated with the acceptor monolayer. Remarkably, graphene on Cu is n-doped and remains n-doped upon F6TCNNQ deposition. On both substrates, the work function of graphene increases substantially with a F6TCNNQ monolayer atop, the effect being more pronounced (~1.3 eV) on Cu compared to quartz (~1.0 eV) because of the larger electrostatic potential drop associated with the long-distance graphene-mediated Cu-F6TCNNQ electron transfer. We thus provide a means to realize high work function surfaces for both p- and n-type doped graphene. (Graph Presented).

Pd/Y multilayers are high reflectance mirrors designed to work in the 7.5-11 nm wavelength range. Samples, prepared by magnetron sputtering, are deposited with or without B4C barrier layers located at the interfaces of Pd and Y layers to reduce interdiffusion, which is expected by calculating mixing enthalpy of Pd and Y. Grazing incident x-ray reflectometry is used to characterize these multilayers. B4C barrier layers are found effective on reducing the Pd-Y interdiffusion. Details of the composition of the multilayers are revealed by hard x-ray photoemission spectroscopy under x-ray standing waves effect. It consists in measuring the photoemission intensity from samples that perform an angular scan in the region corresponding to the multilayer period and the incident photon energy according to the Bragg law. The experimental result indicates that Pd does not chemically react with B nor C at the Pd-B4C interfaces while Y does at the Y-B4C interfaces. The formation of Y-B or Y-C chemical compound can be the reason why the interfaces are stabilized. By comparing the experimentally obtained angular variation of the characteristic photoemission with the theoretical calculation, the depth distribution of each component element can be interpreted., 13 pages, 8 figures, 1 tables, 19 references

Herein, we describe the use of soft X-ray reflectivity at the carbon K-edge to study the molecular organization (orientation, structure, and morphology) of pentacene active films in a top-contact transistor geometry. This technique is not affected by sample charging, and it can be applied in the case of insulating substrates. In addition, the sampling depth is not limited to the near-surface region, giving access to buried device interfaces (metal/organic and dielectric/organic). Spectral lineshape simulations, based on ab-initio calculations using a realistic 3D layer-by-layer model, allow us to unravel the details of the molecular organization in all the specific and crucial areas of the active film, overcoming the limitations of conventional approaches. The tilt angle of the long molecular axis in the whole film is found to progressively decrease with respect to the substrate normal from 25° to 0° with the increasing film thickness. A full vertical alignment, optimal for in-plane charge hopping, is reached only after the complete formation of the first five monolayers. Remarkably, starting from the first one in contact with the dielectric substrate, all the monolayers in the stack show a change in orientation with the increasing thickness. On the other hand, at the buried interface with a gold top-contact, the molecules assume a flat orientation that only propagates for two or three monolayers into the organic film. Top-contact devices with the highest performances can thus be obtained using films of at least ten monolayers. This explains the observed thickness dependence of charge mobility in pentacene transistors.

We present a study of the functionalization of a monocrystalline ZnO surface using aromatic dithiols. The aim is to obtain a sulfur-terminated self-assembled monolayer (SAM), which is then used for creation of further molecular superstructures with intercalated metal atoms. These metal-molecule self-assembled structures are characterized by high-resolution X-ray photoelectron spectroscopy (XPS) and near edge X-ray adsorption fine structure (NEXAFS) measurements. Formation of a 5,5- bis(mercaptomethyl)-2,20- bipyridine (BPD) SAM on ZnO(0001) is demonstrated using a protocol developed by us earlier for dithiol assembly on gold, allowing production of standing-up SAMs with free SH groups. Thereafter the formation of a metal intercalated dithiol super lattice is achieved by first grafting metal atoms (Ag or Ni) and then attaching a second BPD molecular layer. Metal atoms bind to both sulfur and the pyridine nitrogens within the SAM. Clear changes in the valence band region near the Fermi level are observed, and the highest occupied system orbital positions are determined along with work function evolution. © 2018 American Chemical Society.

The unoccupied electronic structure of tetrakis(phenyl)- and tetrakis(pentafluorophenyl)-porphyrin thick films deposited on SiO2/Si(100) native oxide surfaces has been thoroughly studied by combining the outcomes of near-edge X-ray absorption fine structure spectroscopy at the C, N, and F K-edges with those of scalar relativistic zeroth order regular approximation time-dependent density functional theory calculations carried out on isolated molecules. Both experimental and theoretical results concur to stress the electronic inertness of pristine porphyrin macrocycle based 1sC -> ?* and 1sN -> ?* transitions whose excitation energies are substantially unaffected upon fluorination. The obtained results complement those published by the same group about the occupied states of both molecules, thus providing the missing tile to get a thorough description of the halide decoration effects on the electronic structure of the tetrakis(phenyl)-porphyrin.

International audience; V/Sc multilayer has been developed as a promising candidate for the water window region working near both the Sc-L edge (3.11 nm) and the V-L edge (2.42 nm). To meet the application requirements, its thermal and temporal stability were studied. A series of V/Sc multilayers with a d-spacing ranging from 1.59 to 1.62 nm and a number of bilayers of 100 and 400 was fabricated. Different samples were annealed at temperatures from 100 to 300 °C. Grazing incidence X-ray reflectivity and soft X-ray (SXR) reflectivity measurements showed that the multilayer structure and reflectivity remain mostly unchanged at 100 °C. An obvious deterioration started at 200 °C, while the SXR reflectivity drops close to zero at 250 °C. The multilayer structure completely broke down at 300 °C. Both X-ray diffraction and transmission electron microscopy measurements demonstrated a severe crystallization occurring at 250 °C. Energy dispersive X-ray spectroscopy measurements have further confirmed a significant elemental mixture occurring after 250 °C annealing. The severe intermixing and polycrystallization resulted in the degradation of the multilayer structure. On the other hand, the V/Sc multilayer is relatively stable after half year storage in air environment showing a slight decrease of SXR reflectivity from 18.4% to 16.5%.

V/Sc multilayer is experimentally demonstrated for the first time as a high reflectance mirror for the soft X-ray water window region. It primarily works at above the Sc-L edge (λ = 3.11 nm) under near normal incidence while a second peak appears at above the V-L edge (λ = 2.42 nm) under grazing incidence. The V/Sc multilayer fabricated with a d-spacing of 1.59 nm and 30 bilayers has a smaller interface width (σ = 0.27 and 0.32 nm) than the conventional used Cr/Sc (σ = 0.28 and 0.47 nm). For V/Sc multilayer with 30 bilayers, the introduction of B4C barrier layers has little improvement on the interface structure. As the number of bilayers increasing to 400, the growth morphology and microstructure of the V/Sc layers evolves with slightly increased crystallization. Nevertheless, the surface roughness remains to be 0.25 nm. A maximum soft X-ray reflectance of 18.4% is measured at λ = 3.129 nm at 9° off-normal incidence using the 400-bilayers V/Sc multilayer. According to the fitted model, an s-polarization reflectance of 5.2% can also be expected at λ = 2.425 nm under 40° incidence. Based on the promising experimental results, further improvement of the reflectance can be achieved by using a more stable deposition system, exploring different interface engineering methods and so on.

Self-assembly of dithiol molecules is of interest because these can be used as linkers between metallic or semiconductor entities and thus employed in molecular electronics and plasmonic applications, or for building complex heterostructures. Here we focus on dithiol self-assembly by evaporation in vacuum, a method that could circumvent the dithiol oxidation that can occur in solution. We present a high resolution X-ray photoelectron spectroscopy (XPS) and an ion scattering study of adsorption and desorption of 1,4-benzenedimethanethiol on InP(110) as a function of exposure and sample temperature. Results for InP are compared to those on Au(111) and found to differ due to formation of a thick BDMT layer at room temperature, resulting from extra molecules sticking on top of the self-assembled monolayer. This may play an adverse effect in some afore-mentioned applications as in molecular electronics. We furthermore study the evolution of the dithiol film with sample temperature and the elements remaining at the surface after annealing and delineate initial coverage dependent effects. Fil: Salazar Alarcón, Leonardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Cristina, Lucila Josefina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentina Fil: Jia, Juanjuan. Université Paris Sud; Francia Fil: Chen, Lin. Lanzhou University; China Fil: Giglia, Angelo. Centre National de la Recherche Scientifique; Francia Fil: Pasquali, Luca. Centre National de la Recherche Scientifique; Francia. Università di Modena e Reggio Emilia; Jamaica. University of Johannesburg; Sudáfrica Fil: Sánchez, Esteban Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina Fil: Esaulov, Vladimir A.. Université Paris Sud; Francia Fil: Grizzi, Oscar. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina

Reactive sputtering with a mixture of argon and nitrogen (N

The stability of Cr/C multilayer during irradiation or thermal annealing was investigated using grazing incidence X-ray reflectivity measurement, X-ray photoelectron spectroscopy, X-ray diffraction analysis, small-angle X-ray scattering analysis, and soft X-ray reflectivity measurement. One sample was irradiated with a white beam of synchrotron radiation and five other samples were annealed at various temperatures. The 18-h irradiation treatment caused local surface contaminants but did not affect the buried stacks. The annealing treatment resulted in increased reflectivity at approximately 1.2 keV, and the multilayer remained stable for temperature up to 700 degrees C. Thus, the Cr/C multilayers exhibited excellent stability during irradiation and thermal treatments and can be used for the mirrors and multilayer gratings of third-generation synchrotron radiation systems. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

We combined soft X-ray reflectivity (SXR) and X-ray standing-wave-enhanced fluorescence to study the optical performance and the thermally-induced interface behavior of Co/Mo2C nanometric multilayers, designed to work in the soft X-ray range close to the Co L3 absorption edge. Grazing X-ray reflectivity measurements were performed at 0.154 nm (Cu Kα line) and at two wavelengths in the soft X-ray range, 1.59 and 1.33 nm, close to and far from the Co L3 edge. In the fluorescence experiment the intensity of the Co Lα emission was measured by the standing-wave method within a Co/Mo2C stack. We found that the Co/Mo2C multilayers present good optical performance in the soft X-ray range up to 600 °C annealing temperature. Indeed, the reflectivity value in the soft X-ray range at a grazing angle of 11° is 25% for the as-deposited sample, then slightly varies with annealing and is still 20% after annealing at 600 °C. This demonstrates the good thermal stability of the Co/Mo2C multilayer. We used a simplified two-layer model and modified optical indices of the Co nanofilms to fit the experimental X-ray reflectivity curves. The same modified values of the optical indices are used to fit the X-ray standing-wave curves, confirming the usefulness of the model of the stack.

Small aluminum nanoparticles have the potential to exhibit localized surface plasmon resonances in the deep ultraviolet region of the electromagnetic spectrum, however technical and scientific challenges make it difficult to attain this limit. We report the fabrication of arrays of Al/Al 2O3 core/shell nanoparticles with a metallic-core diameter between 12 and 25 nm that display sharp plasmonic resonances at very high energies, up to 5.8 eV (down to ? = 215 nm). The arrays were fabricated by means of a straightforward self-organization approach. The experimental spectra were compared with theoretical calculations that allow the correlation of each feature to the corresponding plasmon modes.

In multiphase/multilayer solid electrolytes, the composition, reactivity, and structure of interfaces between materials and phases play a fundamental role for fast ion-conduction. Here, the properties of buried interfaces in prototypical fast ion-conducting LaF3/SrF2 epitaxial multilayers are investigated. Photoelectron spectroscopy--both with soft-X and high-energy photons--is applied to separate composition and reactivity of buried interfaces with respect to the outermost surface. X-ray reflectivity, high-energy electron diffraction, X-ray diffraction, atomic force and transmission electron microscopies are used to study morphology, layer crystallinity, epitaxy relations, and buried interface structure. It is found that while the alternated layers present good crystallinity and high lattice matching, with formation of almost ideal sharp interfaces, buried interfaces show a sizeable reduction of the energy barrier for F vacancy formation with respect to bare materials. A density higher by a factor of six of fluorine vacancies is observed at buried interfaces in multilayers with respect to the bare materials. This is correlated to the formation of space charge regions, favoring ion conduction. The formation of F depleted La fluoride regions at interfaces is also promoted by annealing. This is associated to the increase of ion conductivity in annealed heterostructures reported in literature.

Reactive sputtering with a mixture of argon and nitrogen (N2 partial pressure of 4%, 8%, and 15%) as the working gas is used to develop the high reflectance Pd/B4C multilayers for soft X-ray region application. Compared to the pure Ar fabricated sample, the interface roughness of the nitridated multilayer is slightly increased while the compressive stress is essentially relaxed from -623 MPa (pure Ar) to -85 MPa (15% N2). A maximum reflectance of 32% is measured at the wavelength of 9.5 nm for the multilayer fabricated with 15% N2. After storing the multilayers in an air environment for 6-17 months, a distinct aging effect is observed on the nitridated samples. The transmission electron microscopy results indicate that a large part of the top layers of the nitridated samples is deteriorated with severe interdiffusion, essential decrease in d-spacing, and compacted multilayer structure. The deterioration is less pronounced for the multilayers fabricated with a higher ratio of N2. Energy dispersive X-ray spectroscopy reveals that the concentration of nitrogen and boron in the degraded area is much reduced compared to the intact layers. A primitive model of upward diffusion of nitrogen and boron is proposed to explain the aging effects of the nitridated structure.

8 pags., 4 figs., 2 tabs. -- EUV and X-ray Optics: Synergy between Laboratory and Space V. -- SPIE Optics + Optoelectronics, 2017, Prague, Czech Republic, Polarimetry is a valuable technique to help us understand the role played by the magnetic field of the coronal plasma in the energy transfer processes from the inner parts of the Sun to the outer space. Polarimetry in the far ultraviolet (FUV: 100-200 nm), which must be performed from space due to absorption in terrestrial atmosphere, supplies fundamental data of processes that are governed by the Doppler and Hanle effects on resonantly scattered line-emission. To observe these processes there are various key spectral lines in the FUV, from which H I Lyman ¿ (121.6 nm) is the strongest one. Hence some solar physics missions that have been proposed or are under development plan to perform polarimetry at 121.6 nm, like the suborbital missions CLASP I (2015) and CLASP II (2018), and the proposed solar missions SolmeX and COMPASS and stellar mission Arago. Therefore, the development of efficient FUV linear polarizers may benefit these and other possible future missions. C IV (155 nm) and Mg II (280 nm) are other spectral lines relevant for studies of solar and stellar magnetized atmospheres. High performance polarizers can be obtained with optimized coatings. Interference coatings can tune polarizers at the spectral line(s) of interest for solar and stellar physics. Polarizing beamsplitters consist in polarizers that separate one polarization component by reflection and the other by transmission, which enables observing the two polarization components simultaneously with a single polarizer. They involve the benefit of a higher efficiency in collection of polarization data due to the use of a single polarizer for the two polarization components and they may also facilitate a simplified design for a space polarimeter. We present results on polarizing beamsplitters tuned either at 121.6 nm or at the pair of 155 and 280 nm spectral lines., We acknowledge support by the European Community–Research Infrastructure Action under the FP6 ‘Structuring the European Research Area’ Programme (through the Integrated Infrastructure Initiative ‘Integrating Activity on Synchrotron and Free Electron Laser Science’); measurements were performed under ELETTRA proposal numbers 20115134, 20120059, 20125119, 20130201, 20135237, 20140171, 20150344, and 2015497. This work was also supported by the National Programme for Research, Subdirección General de Proyectos de Investigación, Ministerio de Ciencia e Innovación, project numbers AYA2013-42590-P and ESP2016-76591-P. We also acknowledge support by the Italian Ministry of University and Research (MIUR) under the Programmi di Ricerca Scientifica di Rilevante Interesse Nazionale—Bando 2012.

Singlet oxygen has attracted great attention in physical, chemical, as well as biological studies, mainly due to its high reactivity and strong oxidising properties. In this context, hybrid nanosystems comprised of (inorganic) X-ray absorbing nanostructures and (organic) light-sensitive material (photosensitizers) can potentially overcome the limitations of visible light penetration in matter. A deep investigation of the interface of such hybrid nanosystems for X-ray induced generation of singlet oxygen is key to better understand the processes at the hybrid interface, and to control the energy transfer from inorganic to organic counterparts, which ultimately leads to enhanced singlet oxygen generation. Here, we demonstrate that SiC/SiOx core/shell nanowires functionalized with the tetrakis.pentafluorophenyl) porphyrin can act as a highly promising and viable strategy to generate singlet oxygen, making this novel hybrid nanosystem attractive for applications in photocatalysis and nanomedical applications. Using different excitation sources (i. e., electrons, visible light, and X-rays) our findings prove that SiC/SiOx core/shell nanowires show X-ray excited optical luminescence, and that optical emission of the photosensitizer is largely enhanced by the nanowires, yielding an efficient energy transfer. A consequent singlet oxygen production of the functionalized nanowires is demonstrated after X-ray excitation in a clinical linear accelerator. These findings will provide an insight in developing an effective route to the molecular functionalization of SiC/SiOx core/shell nanowires and their potential use as singlet oxygen generators.

In this paper, we present the temperature dependent dispersion model of float zone crystalline silicon. The theoretical background for valence electronic excitations is introduced in the theoretical part of this paper. This model is based on application of sum rules and parametrization of transition strength functions corresponding to the individual elementary phonon and electronic excitations. The parameters of the model are determined by fitting ellipsometric and spectrophotometric experimental data in the spectral range from far infrared (70 cm-1) to extreme ultraviolet (40 eV). The ellipsometric data were measured in the temperature range 5–700 K. The excitations of the valence electrons to the conduction band are divided into the indirect and direct electronic transitions. The indirect transitions are modeled by truncated Lorentzian terms, whereas the direct transitions are modeled using Gaussian broadened piecewise smooth functions representing 3D and 2D van Hove singularities modified by excitonic effects. Since the experimental data up to high energies (40 eV) are available, we are able to determine the value of the effective number of valence electrons. The Tauc–Lorentz dispersion model is used for modeling high energy electron excitations. Two slightly different values of the effective number of valence electrons are obtained for the Jellison–Modine (4.51) and Campi–Coriasso (4.37) parametrization. Our goal is to obtain the model of dielectric response of crystalline silicon which depends only on photon energy, temperature and small number of material parameters, e.g. the concentration of substituted carbon and interstitial oxygen. The model presented in this paper is accurate enough to replace tabulated values of c-Si optical constants used in the optical characterization of thin films diposited on silicon substrates. The spectral dependencies of the optical constants obtained in our work are compared to results obtained by other authors.

α-Sexithiophene (6T) ultrathin films have been grown on CaF2(111)/Si(111) planar surfaces and on CaF2(110)/Si(001) ridged surfaces by molecular beam epitaxy. The growth mode has been studied by means of atomic force microscopy (AFM), photoemission, and near edge X-ray absorption fine structure (NEXAFS). AFM reveals a substantial difference in the film morphology on the two substrates: on CaF2(111) large islands with flat terraces form with no in-plane preferential growth direction; on CaF2(110) narrow and elongated islands develop following the substrate corrugation. Photoemission and X-ray absorption at Ca L2,3 and F K edges indicate that the interaction with the substrate is negligible. Near-edge X-ray absorption (NEXAFS) flanked by DFT calculations of the angular-resolved absorption cross section of 6T at the carbon K-edge reveal that the molecules on both substrates have their long axis vertically oriented with respect to the substrate plane. In addition, in-plane anisotropy of the molecular orientati...

The proper exploitation of the plasmon resonance typical of metallic nanoparticles can allow for the confinement of the electromagnetic field in nanometric volumes, thus creating the so called "hot spots". These nanometric volumes are characterized by high field, remarkably useful characteristic for a huge variety of applications in photonics and optics. The most commonly employed plasmonic metals, Au and Ag, yield resonances only reaching up to the near-UV electromagnetic range, in fact stretching upwards the energy of plasmon resonances requires the use of different materials. Deep-ultraviolet plasmon resonances were indeed predicted exploiting one of the cheapest and most abundant materials available on earth. Aluminium holds the promise of a broadly-tuneable plasmonic response, theoretically extending far into the deep-ultraviolet (DUV). Complex fabrication issues, including the strong Al reactivity, have however stood in the way of achieving this ultimate DUV response. We report the successful realization of 2-dimensional arrays of ultrafine aluminium nanoparticles that exhibit a remarkable plasmonic response up to the DUV electromagnetic range. Careful nanofabrication allowed to maintain the mean NP size below 20 nm, preserving a purely-metallic core. These systems exhibit a striking high-energy plasmon resonance up to 6.8 eV photon energy, and preserve their DUV plasmon response when exposed to atmosphere [1,2]. These observations pave the way to the full exploitation of aluminium plasmonic tunability, hence extending the numerous applications of plasmonics to the high-energy side of the spectral range.