Soft X-ray Emission Research Articles

Analytical technique for self-absorption structure of iron L-emission spectra obtained by soft X-ray emission spectrometer.

The method deriving the L self-absorption spectrum from Lα,β emission spectra obtained at different accelerating voltages has been optimized for analyzing the chemical state of Fe in solid materials. Fe Lα,β emission spectra obtained are fitted using Pseudo-Voigt functions and normalized by the integrated intensity of each Fe Ll line, which is not affected by L2,3 absorption edge. The self-absorption spectrum is calculated by dividing the normalized intensity profile collected at low accelerating voltage by that collected at a higher accelerating voltage. The obtained profile is referred to as soft X-ray self-absorption structure (SX-SAS). This method is applied to six Fe-based materials (Fe metal, FeO, Fe3O4, Fe2O3, FeS and FeS2) to observe different chemical states of Fe in those materials. By comparing the self-absorption spectra of iron oxides, one can observe the L3 absorption peak structure shows a shift to the higher energy side as ferric (3+) Fe increases with respect to ferrous (+2) Fe. The intensity profiles of self-absorption spectra of metallic Fe and FeS2 shows shoulder structures between the L3 and L2 absorption peaks, which were not observed in spectra of Fe oxides. These results indicate that the SX-SAS technique is useful to examine X-ray absorption structure as a means to understand the chemical states of transition metal elements.

Characterization of Electronic Properties of Titanium Atom in Heterogeneous Ziegler-Natta Catalyst Analyzed by Soft X-ray Emission Spectrometry (SXES)

Abstract An advanced spectroscopic analysis by Soft X-ray Emission Spectrometry (SXES) was applied for the first time to the characterization of a heterogeneous Ziegler-Natta catalyst, which comprised TiCl4 and dibutylphthalate (DBP) supported on MgCl2. The high energy resolution capability of SXES made it possible to quantitatively detect outermost shell orbit signals of Lα at 452 eV and Lβ at 458 eV of Ti atom. These were assigned to Ti species interacting with DBP and MgCl2, respectively. From the correlation between the signal intensity ratios and the catalytic performances, it was presumed that Ti species interacting with MgCl2 should work as active sites for propylene polymerization.

Solid solubility and site preference of Ti in 3C- and 6H-SiC

Ti is a background impurity in SiC due to its presence in the graphite parts of the SiC production furnace, and it has large impacts on the electrical and magnetic performance of SiC. Herein, the solid solubilities of Ti in 3C- and 6H-SiC were measured at the SiC–TiSi2 thermodynamic equilibrium, and the values of the enthalpy and entropy of dissolution for Ti in 3C- and 6H-SiC were estimated through thermodynamic analysis, which were also confirmed using the formation energy calculation of defects. The soft X-ray emission (SXE) lines of Ti-Lℓ for Ti-doped 3C- and 6H-SiC were explained by the calculated hole transition energies (HTEs) between the L1 and M3 levels in different possible defects, experimentally indicating that Ti prefers the substitution of the Si-site in both 3C- and 6H-SiC. Additionally, the zero-phonon line (ZPL) calculation provided a possible explanation for the origin of the ZPLs in the photoluminescence (PL) spectra of the Ti in 6H-SiC.

One-Minute Quasi-Periodic Pulsations during an M-Class Solar Flare

We study the Quasi-Periodic Pulsations (QPPs) of an M4.4 class solar flare, which occurred in active region NOAA 11165 on 8 March 2011. With the Fast Fourier Transform (FFT) method, we decompose the flare light curve into fast- and slowly-varying components. The 100 s (0.01 Hz) is selected as the cutoff threshold between the fast- and slowly-varying components. One-minute QPPs are found around flare peak at soft X-ray (SXR) and Extreme Ultraviolet (EUV). Using the data from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO), the intermittent jets are detected and the interesting fact is that the jets also display one-minute period. The correlationship between the fast-varying components of SXR or EUV emissions and the jets suggests that the QPPs on light curves and periodic jets could come from the same origination, e.g., the periodic magnetic reconnection in this event.

Radio and X-Ray Observations of the Luminous Fast Blue Optical Transient AT 2020xnd

Abstract We present deep X-ray and radio observations of the fast blue optical transient (FBOT) AT 2020xnd/ZTF 20acigmel at z = 0.2433 from 13 days to 269 days after explosion. AT 2020xnd belongs to the category of optically luminous FBOTs with similarities to the archetypal event AT 2018cow. AT 2020xnd shows luminous radio emission reaching L ν ≈ 8 × 1029 erg s−1 Hz−1 at 20 GHz and 75 days post-explosion, accompanied by luminous and rapidly fading soft X-ray emission peaking at L X ≈ 6 × 1042 erg s−1. Interpreting the radio emission in the context of synchrotron radiation from the explosion’s shock interaction with the environment, we find that AT 2020xnd launched a high-velocity outflow (v ∼ 0.1c–0.2c) propagating into a dense circumstellar medium (effective M ̇ ≈ 10 − 3 M ⊙ yr−1 for an assumed wind velocity of v w = 1000 km s−1). Similar to AT 2018cow, the detected X-ray emission is in excess compared to the extrapolated synchrotron spectrum and constitutes a different emission component, possibly powered by accretion onto a newly formed black hole or neutron star. These properties make AT 2020xnd a high-redshift analog to AT 2018cow, and establish AT 2020xnd as the fourth member of the class of optically luminous FBOTs with luminous multiwavelength counterparts.

Identification of Valence Electronic States Reflecting the Hydrogen Bonding in Liquid Ethanol.

The temperature-dependent X-ray emission spectra of liquid ethanol were calculated theoretically using a semi-classical approximation to the Kramers-Heisenberg formula, which includes the dynamical effects induced by a core-hole. Soft X-ray emission spectroscopic measurements were performed to discern the changes in the hydrogen bonding (h-bonding) structure of liquid ethanol using a temperature-controlled liquid cell at 241 and 313 K. The relative intensities of the peaks at approximately 526.5 and 527.1 eV varied with temperature, and the corresponding behavior was reproduced theoretically, although the variation with temperature in the calculated spectra were more enhanced than that in the experiment. The two peaks can be attributed to the 3a″ + 10a' mixed state and pure 3a″ state, respectively, depending on the behavior of the local h-bonding structure. The splitting of the 3a″ component occurred because of the h-bonding behavior of liquid ethanol. Furthermore, the size of the ethanol cluster decreased with an increase in temperature, mainly due to the breaking of the one-donor/one-acceptor type h-bonding. Our studies suggest that the electronic state of liquid ethanol reflects several types of h-bonding structures, and the ratios of these h-bonding types vary with temperature.

Hydration Mechanism in Blood-Compatible Polymers Undergoing Phase Separation.

Interactions involving intermediate water are crucial for the design of novel blood-compatible materials. Herein, we use a combination of atomic force microscopy, quartz crystal microbalance measurements, and soft X-ray emission spectroscopy to investigate the local hydrogen-bonded configuration of water on blood-compatible poly(2-methoxyethyl acrylate) and non-blood-compatible poly(n-butyl acrylate) grafted on a gold substrate. We find that the initially incorporated water induces polymer-dependent phase separation, facilitating further water uptake. For the blood-compatible polymer, tetrahedrally coordinated water coexists with water adsorbed on C═O groups in low-density regions of the grafted polymer surface, providing a scaffold for the formation of intermediate water. The amount of intermediate water is determined by the type of functional groups, local polymer configuration, and polymer morphology. Thus, blood compatibility is governed by the complex water/polymer interactions.

Pulse duration dependency of the X-ray emission during materials processing with ultrashort laser pulses

The potentially hazardous soft x-ray emission with photon energies of 5 keV and above are part of the emission spectrum during material processing with ultrashort laser pulses. The emission spectrum and the spectral power density are determined by the fraction of the hot electrons in the laser plasma, whose temperature is mainly defined by the irradiance. The interaction of the laser with the plasma intensifies with growing plasma expansion during the laser pulse and the fraction of hot electrons is therefore enhanced with increasing pulse duration. Hence, the pulse duration is one of the predominant parameters, which determine the emission of ionizing radiation. The H(0.07) dose rate was measured to investigate the influence of the pulse duration. In an existing analytical model, the fraction of hot electrons was extended to be a function of the pulse duration. The comparison between experimental data and calculations clearly verify the predictions of the model.

Operando resonant soft X-ray emission spectroscopy of the LiMn2O4 cathode using an aqueous electrolyte solution.

The Mn 3d electronic-structure change of the LiMn2O4 cathode during Li-ion extraction/insertion in an aqueous electrolyte solution was studied by operando resonant soft X-ray emission spectroscopy (RXES). The Mn L3 RXES spectra for the charged state revealed the Mn4+ state with strong charge-transfer from the O 2p to Mn 3d orbitals dominates, while for the open-circuit-voltage and discharged states it is ascribed to the mixture of sites with Mn3+ and Mn4+ states. The degree of charge transfer is significantly different between the Mn3+ and Mn4+ states, indicating that the redox reaction takes place on the strongly-hybridized Mn 3d-O 2p orbital rather than the localized Mn 3d orbital.

Quantitative Analysis of Oxygen in Solution in the Ti-Al-O Ternary Alloys by Soft X-Ray Emission Spectroscopy

Quantitative Analysis of Oxygen in Solution in the Ti-Al-O Ternary Alloys by Soft X-Ray Emission Spectroscopy

Growth mechanism and microstructures of Cu2O/PVP spherulites.

Cu2O spherulites are solvothermaly fabricated by using Cu(NO3)2 as the starting material and polyvinylpyrrolidone (PVP) as a multifunctional growth agent. The specimens at different growth stages are investigated by using X-ray diffraction, electron microscopy, energy dispersive X-ray spectroscopy, soft X-ray emission spectroscopy and infrared spectroscopy. The formation mechanism of Cu2O spherulites is proposed accordingly. Hierarchically, the spherulites are composed of needle-like submicron-rods lying along the radial orientations. The submicron-rods are constructed by piling up of small Cu2O/PVP spheres. The embedded Cu2O nanocrystallites can generate a dipolar field in each along the [100] direction. They deposit at the surface of a negatively charged PVP-containing spherical core, and self-oriented along the radial directions. Therefore, all the Cu2O nanocrystallites would have their positively charged (100) facet facing to the core and their negatively charged (1̄00) facet turning towards to the spherulite surface, leading to a negatively charged surface of spherulites. Unlike randomly oriented nanocrystallites embedded in polymer microspheres, the spherulites would not undergo surface recrystallisation into a single crystal shell due to the restricted potential of local shift and rotation of the nanocrystallites by the Coulomb force from the core. This work provides new perspective towards the formation of spherulites and their structural properties.

The Origin of Time Delays between Sub-Terahertz and Soft X-ray Emission from Solar Flares

The Origin of Time Delays between Sub-Terahertz and Soft X-ray Emission from Solar Flares

Characterization of an X-ray Source Generated by a Portable Low-Current X-Pinch

An X-pinch scheme of a low-current generator (45 kA, 50 ns rise time) is characterized as a potential efficient source of soft X-rays. The X-pinch target consists of wires of 5 μm in diameter—made from either tungsten (W) or gold (Au)-plated W—loaded at two angles of 55° and 98° between the crossed wires. Time-resolved soft X-ray emission measurements are performed to provide a secure correlation with the optical probing results. A reconstruction of the actual photodiode current profile procedure was adopted, capable of overcoming the limits of the slow rising and falling times due to the “slow” response of the diodes and the noise. The pure and Au-plated W deliver an average X-ray yield, which depends only on the angle of the crossed wires, and is measured to be ~50 mJ and ~70 mJ for the 98° and 55° crossed wire angles, respectively. An additional experimental setup was developed to characterize the X-pinch as a source of X-rays with energy higher than ~6 keV, via time-integrated measurements. The X-ray emission spectrum was found to have an upper limit at 13 keV for the Au-plated W configuration at 55°. The portable tabletop X-pinch proved to be ideal for use in X-ray radiography applications, such as the detection of interior defects in biological samples.

Introduction of Soft X-ray Emission Spectrometer and its Applications

Introduction of Soft X-ray Emission Spectrometer and its Applications

Theoretical study of soft X-ray emission and dynamics of laser-induced plasma of double stream gas puff

The double stream gas puff-based laser-produced plasma is studied as a source of soft X-ray radiation in nm wavelength spectral range. Dynamics of plasma induced by Nd:YAG laser beam and its emission is simulated with radiation-magnetohydrodynamic code Zstar. The modeling results for krypton gas stream in an annular helium jet as a circumferential gas for various picosecond and nanosecond laser pulses corresponding to the experiments are presented. The spatial–spectral features and temporal behavior of the soft X-ray and EUV emission are investigated. Under ps pulse, the gas is rapidly ionized in the laser beam channel, but it does not have enough time to shift sensibly during the pulse, and the plasma electron density grows against the background of almost constant ion density during the ionization in the laser radiation field. There is ionization instability only capable to be developed in ps range. At ns pulse, the gas ionization and heating leads to gas pushing out of the channel, and the formation of a divergent compression wave transforming into the shock wave. Behind the compression wave front, conditions arise for the development of Rayleigh–Taylor-type instability. The instability leads to the redistribution of plasma temperature and density, and to the formation of increased soft X-ray emission spots. Time evolution of spatial distributions and spectral characteristics of emitted SXR radiation is analyzed for different laser pulses. Transient effects in multicharged ion plasma are discussed, fundamental understanding of those is required for optimization of plasma radiation source. A conversion efficiency of laser energy into soft X-ray wavebands from krypton plasma is scanned by laser parameters and analyzed.

AGN−Host Interaction in IC 5063. I. Large-scale X-Ray Morphology and Spectral Analysis

Abstract We report the analysis of the deep (∼270 ks) X-ray Chandra data of one of the most radio-loud, Seyfert 2 galaxies in the nearby universe (z = 0.01135), IC 5063. The alignment of the radio structure with the galactic disk and ionized bicone, enables us to study the effects of both radio jet and nuclear irradiation on the interstellar medium (ISM). The nuclear and bicone spectra suggest a low photoionization phase mixed with a more ionized or thermal gas component, while the cross-cone spectrum is dominated by shocked and collisionally ionized gas emission. The clumpy morphology of the soft (<3 keV) X-ray emission along the jet trails, and the large (≃2.4 kpc) filamentary structure perpendicular to the radio jets at softer energies (<1.5 keV), suggest a large contribution of the jet−ISM interaction to the circumnuclear gas emission. The hard X-ray continuum (>3 keV) and the Fe Kα 6.4 keV emission are both extended to kpc size along the bicone direction, suggesting an interaction of nuclear photons with dense clouds in the galaxy disk, as observed in other Compton Thick (CT) active nuclei. The northwest cone spectrum also exhibits an Fe xxv emission line, which appears spatially extended and spatially correlated with the most intense radio hot-spot, suggesting jet−ISM interaction.

Tempered linear and non-linear time series models and their application to heavy-tailed solar flare data.

In this paper, we introduce two tempered linear and non-linear time series models, namely, an autoregressive tempered fractionally integrated moving average (ARTFIMA) with α-stable noise and ARTFIMA with generalized autoregressive conditional heteroskedasticity (GARCH) noise (ARTFIMA-GARCH). We provide estimation procedures for the processes and explain the connection between ARTFIMA and their tempered continuous-time counterparts. Next, we demonstrate an application of the processes to modeling of heavy-tailed data from solar flare soft x-ray emissions. To this end, we study the solar flare data during a period of solar minimum, which occurred most recently in July, August, and September 2017. We use a two-state hidden Markov model to classify the data into two states (lower and higher activity) and to extract stationary trajectories. We do an end-to-end analysis and modeling of the solar flare data using both ARTFIMA and ARTFIMA-GARCH models and their non-tempered counterparts. We show through visual inspection and statistical tests that the ARTFIMA and ARTFIMA-GARCH models describe the data better than the ARFIMA and ARFIMA-GARCH, especially in the second state, which justifies that tempered processes can serve as the state-of-the-art approach to model signals originating from a power-law source with long memory effects.

Deep Chandra observations of diffuse hot plasma in M83

ABSTRACT It is widely believed that galaxy formation and evolution is regulated by stellar mechanical feedback in forms of fast stellar winds and supernova explosions. However, the coupling of this feedback with the interstellar medium remains poorly understood. We examine how the coupling may be traced by diffuse soft X-ray emission in M83 – a nearby face-on spiral galaxy undergoing active star formation, based chiefly on 729 ks Chandra observations. Our main findings are (1) the X-ray emission is enhanced not only along the galaxy’s grand spiral arms, but also clearly in their downstreams; (2) the spectrum of the emission can be well characterized by a supersolar metallicity plasma with a lognormal temperature distribution, plus an X-ray absorption of a lognormal column density distribution; and (3) the intensity of the emission is strongly anticorrelated with the dust obscuration seen in optical images of the galaxy. These findings suggest (A) the morphology of the X-ray emission is likely due to the convolution of the feedback heating of the plasma with its thermal and dynamical evolution; (B) the X-ray emission, accounting for $\sim 10{{\ \rm per\ cent}}$ of the feedback energy input rate, probably traces only the high-energy tail of the radiation from the plasma; (C) a good fraction of the recent star-forming regions seems sufficiently energetic to produce multi-phased outflows, likely responsible for much of the dust obscuration and X-ray absorption. Direct confrontation of the findings with theories/simulations could help to understand the underlying astrophysics of the coupling and how the hot plasma shapes the interstellar medium.

Hydrogen-Bonded Structure of Water in the Loop of Anchored Polyrotaxane Chain Controlled by Anchoring Density.

Hydrogen-bonded network of water surrounding polymers is expected to be one of the most relevant factors affecting biocompatibility, while the specific hydrogen-bonded structure of water responsible for biocompatibility is still under debate. Here we study the hydrogen-bonded structure of water in a loop-shaped poly(ethylene glycol) chain in a polyrotaxane using synchrotron soft X-ray emission spectroscopy. By changing the density of anchoring molecules, hydrogen-bonded structure of water confined in the poly(ethylene glycol) loop was identified. The XES profile of the confined water indicates the absence of the low energy lone-pair peak, probably because the limited space of the polymer loop entropically inhibits the formation of tetrahedrally coordinated water. The volume of the confined water can be changed by the anchoring density, which implies the ability to control the biocompatibility of loop-shaped polymers.

Chemical State Mapping of p/n-Controlled SrB6 Bulk Specimens by Soft X-ray Emission Electron Microscope

Elemental and chemical state maps of p/n-controlled SrB6 bulk specimens are presented by using a soft X-ray emission spectroscopy electron microscope. Those bulk specimens were obtained by sintering powder specimens, prepared by the molten-salt method with different compositions of initial materials. A Sr-map, a chemical shift map of B K-emission, and the spectra of characteristic regions of those materials were compared. It was observed that a local Sr deficiency caused a local hole-doped region, confirmed by a chemical shift in the B K-emission spectrum. n-type SrB6 was rather homogeneous. On the other hand, the p-type SrB6 bulk specimen was a mixture of two different p-type regions. This mixed nature originated, presumably, from an uneven Sr content of SrB6 particles prepared by the molten-salt method using a Sr-deficient starting material. A separation process of the two types of materials will realize a high-quality homogeneous p-type SrB6 bulk specimens.