High-resolution X-ray Spectroscopy Research Articles

Simultaneous X-ray and optical spectroscopy of the Oef supergiantλCephei

Probing the structures of stellar winds is of prime importance for the understanding of massive stars. Based on their optical spectral morphology and variability, the stars of the Oef class have been suggested to feature large-scale structures in their wind. High-resolution X-ray spectroscopy and time-series of X-ray observations of presumably-single O-type stars can help us understand the physics of their stellar winds. We have collected XMM-Newton observations and coordinated optical spectroscopy of the O6Ief star lambda Cep to study its X-ray and optical variability and to analyse its high-resolution X-ray spectrum. We investigate the line profile variability of the He II 4686 and H-alpha emission lines in our time series of optical spectra, including a search for periodicities. We further discuss the variability of the broadband X-ray flux and analyse the high-resolution spectrum of lambda Cep using line-by-line fits as well as a code designed to fit the full high-resolution X-ray spectrum consistently. During our observing campaign, the He II 4686 line varies on a timescale of ~18 hours. On the contrary, the H-alpha line profile displays a modulation on a timescale of 4.1 days which is likely the rotation period of the star. The X-ray flux varies on time-scales of days and could in fact be modulated by the same 4.1 days period as H-alpha, although both variations are shifted in phase. The high-resolution X-ray spectrum reveals broad and skewed emission lines as expected for the X-ray emission from a distribution of wind-embedded shocks. Most of the X-ray emission arises within less than 2R* above the photosphere.

Resonant inelastic X-ray spectroscopy of atoms and simple molecules: Satellite features and dependence on energy detuning and photon polarization

We summarize recent results dealing with high resolution (resonant) X-ray spectroscopy of atomic and molecular targets in the tender X-ray energy region. We comment on advantages, new possibilities and problems related to RIXS spectroscopy with respect to the standard photoabsorption technique, where scanning the probe energy is the only option. In particular, three research areas are covered: X-ray emission mediated by energy dependent photoabsorption to multi-electron excited states, the Cl K core-hole clock studies exemplified by systematic study of chloro(fluoro)-hydrocarbon targets and the polarization dependent X-ray emission studies. Due to its spectral selectivity and simultaneous detection capability, high resolution wavelength dispersive X-ray spectroscopy has the capability to resolve structural and dynamical properties of matter within new instrumentation frontiers.

Time-dependent electric field in Al/CdTe/Pt detectors

Al/CdTe/Pt detectors are very attractive devices for high-resolution X-ray spectroscopy, even though they suffer from bias-induced time instability (polarization). Polarization phenomena cause a progressive time-degradation of the spectroscopic performance of the detectors, due to hole trapping and detrapping from deep acceptor levels that directly control the electric field distribution. In this work we present experimental investigations on the electric field profile of planar Al/CdTe/Pt detectors by means of Pockels effect measurements. The time/temperature dependence of the electric field was investigated in a long time window (up to 10h) and the correlation with the reverse current transients was also studied. Two energy levels (0.62eV and 1.16eV) of the deep hole traps were measured, in agreement with our previous results obtained through electrical and spectroscopic approaches.

Reactive transport benchmarks for subsurface environmental simulation

Over the last 20 years, we have seen firsthand the evolution of multicomponent reactive transport modeling and the expanding range and increasing complexity of subsurface applications it is being used to address. There is a growing reliance on reactive transport modeling (RTM) to address some of the most compelling issues facing our planet: climate change, nuclear waste management, contaminant remediation, and pollution prevention. While these issues are motivating the development of new and improved capabilities for subsurface environmental modeling using RTM (e.g., biogeochemistry from cell-scale physiology to continental-scale terrestrial ecosystems, nonisothermal multiphase conditions, coupled geomechanics), there remain longstanding challenges in characterizing the natural variability of hydrological, biological, and geochemical properties in subsurface environments and limited success in transferring models between sites and across scales. An equally important trend over the last 20 years is the evolution of modeling from a service sought out after data has been collected to a multifaceted research approach that provides (1) an organizing principle for characterization and monitoring activities; (2) a systematic framework for identifying knowledge gaps, developing and integrating new knowledge; and (3) a mechanistic understanding that represents the collective wisdom of the participating scientists and engineers. There are now large multidisciplinary projects wheremore » the research approach is model-driven, and the principal product is a holistic predictive simulation capability that can be used as a test bed for alternative conceptualizations of processes, properties, and conditions. Much of the future growth and expanded role for RTM will depend on its continued ability to exploit technological advancements in the earth and environmental sciences. Advances in measurement technology, particularly in molecular biology (genomics), isotope fractionation, and high-resolution X-ray spectroscopy, have created new lines of research that can be used to inform the conceptualization of reactions and rate laws and validate mechanistic models. For example, spectroscopy has identified the oxidation states of key components and elemental distributions at increasingly smaller scales and lower concentrations; molecular biology has progressed from identifying the presence of microbes to characterization of which microbial communities are active and what they are doing (i.e., microbial function), which has led in turn to the identification of active processes under conditions beyond what analytical chemistry can discern; isotope ratios in pore water and solid phases that can be used to distinguish between biotic from abiotic processes, sorption from precipitation, and origin and age of groundwater. The other noteworthy development that is expanding the role of RTM in subsurface environmental modeling is he advance in computational technology that is enabling the simulation of more coupled processes with increasing mechanistic detail. In some cases, this involves the inclusion of more reactive species and/or microbial populations in the simulations; in other cases, the impact is through the ability to achieve high resolution of property distributions over longer simulated times. To achieve these ambitious objectives for subsurface reactive transport simulation, the subsurface science and engineering community is being driven to provide accurate assessments of engineering performance and risk for important issues with far-reaching consequences. As a result, the complexity and detail of subsurface processes, properties, and conditions that can be simulated have significantly expanded. This expansion was enabled, in part, by advances in measurement technology, computing technology, and numerical techniques.« less

High-resolution x-ray spectroscopy to probe quantum dynamics in collisions of Ar17+,18+ ions with atoms and solids, towards clusters

We report on studies of projectile excited states produced by electron capture in both low and high velocity regimes, and when highly charged ions (HCIs) collide either with dilute or dense matter. Quantum effects in the interaction dynamics are probed via high-resolution x-ray spectroscopy for Ar17+ at 7 keV u−1 and for Ar18+ at 13.6 MeV u−1 on Ar, N2 or CH4 gas targets and on carbon solid foils. Relevant comparison between those two collision velocity regimes, and between gaseous and solid targets reveal specific features. In particular, the effect of multiple capture process occurring within a single-collision with gaseous target can be compared with the consequence of multistep collisions arising at surfaces and in solid-bulk at low velocity. At high velocity, beside evidence for collective response of the target electrons due to the wake field induced by HCI passing through the solid-bulk, we demonstrate that excitation and ionization collision processes damp the populations of projectile excited states for long ion transit times. The evolution of the np population as a function of n in solid is at variance from the 1/n3 law found in gas, and the disagreement increases with solid target thickness. We have also tackled studies of HCIs in collision with clusters showing that x-ray spectroscopy provides a powerful tool to sign the presence of clusters in a supersonic gas jet.

Synthesis and Characterization of Gold Nanoparticles Grafted on Nanoporous Anodic Aluminum Oxide (AAO) Membrane

Gold nanoparticles (Au NPs) supported on nanoporous anodic aluminium oxide (AAO) membrane has been successfully prepared by direct anionic exchange for further application in catalysis. The nanoporous AAO membrane is immersed in HAuCl4 solution at different pH to achieve gold nanoparticles grafted on AAO (Au-AAO). It was found that the pH of the HAuCl4 solution played an important role for controlling the size of Au NPs as well as the amount of Au depositing on the surface of AAO membrane. The prepared Au-AAO membranes were characterized by diffuse reflectance UV-Vis spectroscopy, high-resolution scanning electron microscopy (SEM) and energy dispersive x-ray (EDX) spectroscopy.

Improved resistive switching phenomena and mechanism using Cu-Al alloy in a new Cu:AlOx/TaOx/TiN structure

Improved resistive switching phenomena such as device-to-device uniformity, lower formation voltage (2.8V) and RESET current, >500 program/erase cycles, longer read endurance of >106 cycles with a program/erase pulse width of 1μs, and data retention of >225h under a low current compliance of 300μA have been discussed by using Cu-Al alloy in Cu:AlOx/TaOx/TiN conductive bridging resistive random access memory (CBRAM) device for the first time. The switching mechanism is based on a thinner with dense Cu filament formation/dissolution through the defects in the Cu:AlOx/TaOx/TiN structure owing to enhance memory characteristics. These characteristics have been confirmed by measuring randomly picked 100 devices having via-hole size of 0.4×0.4μm2. The Cu-Al alloy becomes Cu:AlOx buffer layer and Ta2O5 becomes TaOx switching layer owing to Gibbs free energy dependency. All layers and elements are observed by high-resolution transmission electron microscope (HRTEM) image and energy dispersive X-ray spectroscopy (EDX). By developing a numerical equation in between RESET current and formation voltage, it is found that a higher rate of Cu migration is observed owing to both the defective switching layer and larger size, which results a lower formation voltage and RESET current of the Cu:AlOx/TaOx/TiN structure, as compared to Cu/Ta2O5/TiN under external positive bias on the Cu electrode. This simple Cu:AlOx/TaOx/TiN CBRAM device is useful for future nanoscale non-volatile memory application.

Band structure measurement and analysis of the Bi2Te3/CdTe (111)B heterojunction

The band alignments of the Bi2Te3/CdTe (111)B (Te-terminated) heterojunction were investigated using high-resolution x-ray and ultraviolet photoemission spectroscopy. The measured valence band offset and the conduction band offset of the Bi2Te3/CdTe were 0.22 ± 0.05 and 1.12 ± 0.05 eV, respectively, and indicated that the Bi2Te3/CdTe heterojunction had a type I band structure.

Control of the intermolecular coupling of dibromotetracene on Cu(110) by the sequential activation of C-Br and C-H bonds.

Dibromotetracene molecules are deposited on the Cu(110) surface at room temperature. The complex evolution of this system has been monitored at different temperatures (i.e., 298, 523, 673, and 723 K) by means of a variety of complementary techniques that range from STM and temperature-programmed desorption (TPD) to high-resolution X-ray spectroscopy (XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS). State-of-the-art density-functional calculations were used to determine the chemical processes that take place on the surface. After deposition at room temperature, the organic molecules are transformed into organometallic monomers through debromination and carbon-radical binding to copper adatoms. Organometallic dimers, trimers, or small oligomers, which present copper-bridged molecules, are formed by increasing the temperature. Surprisingly, further heating to 673 K causes the formation of elongated chains along the Cu(110) close-packed rows as a consequence of radical-site migration to the thermodynamically more stable molecule heads. Finally, massive dehydrogenation occurs at the highest temperature followed by ring condensation to nanographenic patches. This study is a paradigmatic example of how intermolecular coupling can be modulated by the stepwise control of a simple parameter, such as temperature, through a sequence of domino reactions.

Analytical studies of the Alexandrovo Thracian tomb wall paintings

A profound study of samples obtained from Thracian tomb wall paintings at Alexandrovo, Bulgaria (dating back to the fourth century BC) were carried out by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and Attenuated Total Reflectance Fourier transform infrared spectroscopy (ATR FTIR), high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS). The current work provides a glimpse of the ingenious construction and painting techniques used in Thracian tomb at Alexandrovo. The results suggest that beeswax was used as a paint binder and also revealed presence of various nano-materials.

Evidence of locally enhanced target heating due to instabilities of counter-streaming fast electron beams

The high-current fast electron beams generated in high-intensity laser-solid interactions require the onset of a balancing return current in order to propagate in the target material. Such a system of counter-streaming electron currents is unstable to a variety of instabilities such as the current-filamentation instability and the two-stream instability. An experimental study aimed at investigating the role of instabilities in a system of symmetrical counter-propagating fast electron beams is presented here for the first time. The fast electron beams are generated by double-sided laser-irradiation of a layered target foil at laser intensities above 1019 W/cm2. High-resolution X-ray spectroscopy of the emission from the central Ti layer shows that locally enhanced energy deposition is indeed achieved in the case of counter-propagating fast electron beams.

Silicon Drift Detectors and CUBE Preamplifiers for High-Resolution X-ray Spectroscopy

In this work we present the results of the experimental characterization of Silicon Drift Detectors (SDDs) readout by CUBE preamplifiers for X-ray spectroscopy measurements. One specific goal of the work was to characterize SDDs of different sizes cooled at low temperature in view of their use in the upgrade of the SIDDHARTA nuclear physics experiment. Beside the target application, the results of this work are also of interest for a more extended use of the SDDs in other X-ray spectroscopy applications. The SDDs have been designed as single units with square shape of different areas, $64$ mm $^{2}$ ( $8~\hbox{mm} \times 8~\hbox{mm}$ ) and $144 $ mm $^{2}$ ( $12~\hbox{mm} \times 12~\hbox{mm}$ ), and also as monolithic array of $3 \times 3$ elements of the $8~\hbox{mm} \times 8~\hbox{mm}$ unit (total area $26~\hbox{mm} \times 26~\hbox{mm}$ ). The read-out of the SDDs is based on a CMOS (Complementary Metal Oxide Semiconductor) preamplifier (CUBE) both for the single unit and for the $3 \times 3$ array. For the readout of the array, an Application Specific Integrated Circuit (ASIC) has been used. An energy resolution better than 124 eV at the ${\rm Mn} - {\rm K}\alpha $ line has been measured with a $64 $ mm $^{2}$ SDD cooled at the temperature of 50 K. The energy resolution remains good ( $ eV) also at short shaping time (250 ns) thanks to the noise feature of the CUBE preamplifier. Results of measurements on SDDs of different format and also on arrays of SDDs are presented in this work.

Multi-element readout of structured HPGe-detectors for high-resolution x-ray spectroscopy using CUBE-preamplifiers

Very recently we have shown that CUBE-preamplifiers developed by XGLab s.r.l. can be used for the readout of single elements of thick structured planar HPGe- and Si(Li)-detectors produced by SEMIKON [1]. In this paper we will present the results of a simultaneous multi-element readout of structured detectors using the same preamplifiers for measuring high-energy x-rays (more than 100 keV) with a comparable energy resolution as for the single-element readout. Several high-purity germanium detectors (HPGe-detectors) with different position sensitive structures on one detector contact have been used for the first tests. In addition to that we have modified an existing 16-pixel HPGe-polarimeter from GSI-Darmstadt with the new readout. The detector elements (7 mm × 7 mm each, arranged in a 4 × 4 matrix) are connected to CUBE-preamplifiers used in pulse-reset mode. The technological progress achieved with this detector system resulting in a significant improved energy resolution will contribute a lot to much more precise polarization measurements of x-rays emitted from atom-ion collisions which are part of the physics program of the SPARC collaboration (Stored Particles Atomic Physics Research Collaboration) at GSI and the future FAIR accelerator facility (Facility for Antiproton and Ion Research).

Degradation of methylene blue using porous WO3, SiO2-WO3, and their Au-loaded analogs: adsorption and photocatalytic studies.

A facile sonochemical approach was used to deposit 3-5 nm monodisperse gold nanoparticles on porous SiO2-WO3 composite spheres, as confirmed by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). High-resolution TEM (HR-TEM) and energy dispersive X-ray spectroscopy (EDS) further characterized the supported Au nanoparticles within the Au-SiO2-WO3 composite. These analyses showed isolated Au nanoparticles within both SiO2- and WO3-containing regions. Selective etching of the SiO2 matrix from Au-SiO2-WO3 yielded a pure Au-WO3 material with well-dispersed 10 nm Au nanoparticles and moderate porosity. This combined sonochemical-nanocasting technique has not been previously used to synthesize Au-WO3 photocatalysts. Methylene blue (MB) served as a probe for the adsorption capacity and visible light photocatalytic activity of these WO3-containing catalysts. Extensive MB demethylation (azures A, B, C, and thionine) and polymerization of these products occurred over WO3 under dark conditions, as confirmed by electrospray ionization mass spectrometry (ESI-MS). Photoirradiation of these suspensions led to further degradation primarily through demethylation and polymerization pathways, regardless of the presence of Au nanoparticles. Ring-opening sulfur oxidation to the sulfone was a secondary photocatalytic pathway. According to UV-vis spectroscopy, pure WO3 materials showed superior MB adsorption compared to SiO2-WO3 composites. Compared to their respective nonloaded catalysts, Au-SiO2-WO3 and Au-WO3 catalysts exhibited enhanced visible light photocatalytic activity toward the degradation of MB. Specifically, the rates of MB degradation over Au-WO3 and Au-SiO2-WO3 during 300 min of irradiation were faster than those over their nonloaded counterparts (WO3 and SiO2-WO3). These studies highlight the ability of Au-WO3 to serve as an excellent adsorbant and photodegradation catalyst toward MB.

Preparation and exchange bias effects of Bi0.8Ba0.2FeO3/La0.7Sr0.3MnO3 heterostructures

Bi0.8Ba0.2FeO3/La0.7Sr0.3MnO3 multiferroic heterostructures are successfully synthesized on single crystal LaAlO3(100) substrates by pulsed laser deposition via adjusting the parameters of laser energy, laser frequency, substrate temperature, oxygen pressure, distance between substrate and target, etc. The pure phase with perovskite structure is confirmed by the X-ray diffraction measurements. Using high-resolution transmission electron microscopy and energy dispersive X-Ray spectroscopy, we find that all the layers show preferential (00l) orientation, suggesting the epitaxial growth of the multilayered structure. Isothermal (7 K) M-H curves measured on sample after cooling the sample down to lower than ± 1 T fields reveal a shift in M-H loop. The strong temperature dependence of HEB is likely to be directly related to an electronic orbital reconstruction at the interface and complex interplay between orbital and spin degrees of freedom.

X-ray High-resolution Spectroscopy for Laser-produced Plasma

The study of the emission spectrum gives information about the material generating the spectrum itself and the condition in which this is generated. The wavelength spectra lines are linked to the specific element and plasma conditions (electron temperature, density), while their shape is influenced by several physical effects like Stark and Doppler ones.In this work we study the X-ray emission spectra of a copper laser-produced plasma by using a spherical bent crystal spectrometer to measure the electron temperature. The facility used is the laser TVLPS, at the Tor Vergata University in Rome. It consists of a Nd:Glass source (in first harmonic - 1064nm) whose pulse parameters are: 8J in energy, time duration of 15ns and a focal spot diameter of 200μm. The adopted spectrometer is based on a spherical bent crystal of muscovite. The device combines the focusing property of a spherical mirror with the Bragg's law. This allows to obtain a great power resolution but a limited range of analysis. In our case the resolution is on average 80eV. As it is well-known, the position of the detector on the Rowland's circle is linked to the specific spectral range which has been studied. To select the area to be investigated, we acquired spectra by means of a flat spectrometer. The selected area is centered on 8.88Å. To calibrate the spectrum we wrote a ray-tracing MATLAB code, which calculates the detector alignment parameters and calibration curve. We used the method of line ratio to measure the electron temperature. This is possible because we assumed the plasma to be in LTE condition. The temperature value was obtained comparing the experimental one, given by the line ratio, with the theoretical one, preceded by FLYCHK simulations.

Diagnostics of warm dense matter by high-resolution X-ray spectroscopy of hollow ions

AbstractThe short review on the possible applications of the hollow ion spectra for the diagnostics of the high-temperature plasma created by intensive laser and particle beams is presented. Because of the hollow ion spectra features are defined mainly by the mechanisms of their excitation, we consider the various types of the high-temperature plasma where different excitation processes are important. It is shown that like ordinary spectral lines, spectra of the hollow ions offer considerable diagnostic opportunities. At the present time, hollow ion spectra are used mainly to investigate plasma heated by X-ray radiation, but the hollow ions must be generated when plasma is heated by fast heavy ion beams too. In this case, the resultant substance state will be also characterized by solid-state density, and some spatial regions of targets will have relatively low temperatures, i.e., will be a nonideal plasma. It is emphasized that hollow ion spectra are promising diagnostic tool for both nonideal plasma and warm dense matter.

High-resolution spectroscopy of X-rays emitted from electron bombarded surfaces

The investigations of a compact 6-crystal Johann/Johansson diffraction X-ray spectrometer, covering a wide range (70eV–15keV) of photon energies, applied to observe the X-rays emitted from electron bombarded surfaces are discussed in terms of its focusing properties and achievable energy resolution. In the present study the X-ray spectra of Si-Kα1,2 and Al-Kα1,2 X-ray lines excited by 5keV electron beam were measured using PET and TAP crystal, respectively, in the “out-of-focus” geometry which will be used to study the electron/ion surface interactions at the electron beam ion source (EBIS) facility. The measured X-ray spectra were interpreted in terms of the performed ray-tracing simulations which demonstrate the key features of the “out-of-focus” geometry. It was demonstrated that in this case the energy resolution in the range 1–3eV for photon energy 1–2keV can be achieved with an increased acceptance for the extension of X-ray source, of about 1mm, which is important feature for practical applications. Additionally, a dependence of the X-ray intensity and energy resolution on slit opening was studied in details. The results are important for investigations of surfaces with electron and ion impact, in particular, for the future high-resolution X-ray spectroscopy experiments at the EBIS facility.

High-Resolution X-Ray Spectroscopy of Galactic Supernova Remnants

High-resolution X-ray spectroscopy of Galactic supernova remnants (SNRs), based on grating spectrometers onboard XMM-Newton and Chandra, has been revealing a variety of new astrophysical phenomena. Broadened oxygen lines for a northwestern compact knot in SN 1006 clearly show a high oxygen temperature of ~300 keV. The high temperature together with a lower electron temperature (<em>kT<sub>e</sub></em> ~ 1 keV) can be reasonably interpreted as temperature non-equilibration between electrons and oxygen behind a collisionless shock. An ejecta knot in the Puppis A SNR shows blueshifted line emission by ~ 1500kms<sup>-1</sup>. The line widths are fairly narrow in contrast to the SN 1006's knot; an upper limit of 0.9 eV is obtained for O VIII Lyα, which translates to an oxygen temperature of <em>kT<sub>O</sub></em> < 30 keV. The low temperature suggests that the knot was heated by a reverse shock whose velocity is 4 times slower than that of a forward shock. Anomalous intensity ratios in O VII Heα lines, i.e., a stronger forbidden line than a resonance line, is found in a cloud-shock interaction region in Puppis A. The line ratio can be best explained by the charge-exchange emission that should arise at interfaces between the cold/warm clouds and the hot plasma. There are several other targets for which we plan to analyze high-quality grating data prior to the operation of the soft X-ray spectrometer onboard Astro-H.

Synthesis and characterization of multimetallic-core and siliceous-shell Au/Pt/Ag@SiO2 sol–gel derived nanocomposites

Trimetallic Au/Pt/Ag nanocomposite loaded amine functionalized silica nanopowder (Au/Pt/Ag@SiO2 nanopowder) is prepared through sol–gel route. Surface morphology and bulk composition of the composite were obtained using atomic force microscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy and energy dispersive X-ray spectroscopy. Brunauer–Emmett–Teller (BET) surface area, the pore volume and pore radius of the composite particles are calculated by applying the BET equation to the sorption isotherms. In addition to that, UV–Vis-diffuse reflectance spectrum was analyzed for the synthesized composite. The synthesized composite is proposed as the promising photocatalyst for the decolouration of methyl violet dye. We have successfully reported the syntheses and photocatalytic decolouration activity of MV dye in aqueous solution under UV-A light irradiation by SiO2 and Au/Pt/Ag@SiO2 nanopowder. The sol–gel synthesized Au/Pt/Ag@SiO2 nanopowder is proposed as a promising photocatalyst for the decolouration of MV dye. The metallic core and siliceous shell enhance the photocatalytic decolouration activity.