Soft X-ray Emission Spectra Research Articles

Simple derivation of L-absorption spectra of 3d transition metal elements by the self-absorption effect observed in soft X-ray emission spectra.

This study proposes a simple evaluation method for deriving L-absorption information from two L-emission spectra of 3d transition metal (TM) elements obtained at two different accelerating voltages. This method realizes a spatial identity for X-ray emission and absorption spectroscopies. This method was evaluated for the Fe L-emission spectra of Fe and its oxides and was applied to the TM L-emission spectra of MnO, Co, CoO and NiO. The derived absorption peak positions were consistent with those obtained previously at synchrotron orbital radiation facilities, which considered the core-hole effect. This simple derivation method could be useful for obtaining X-ray absorption spectroscopy distribution images from X-ray emission spectroscopy mapping data obtained by scanning electron microscopy.

Chemistry of zipping reactions in mesoporous carbon consisting of minimally stacked graphene layers.

The structural evolution of highly mesoporous templated carbons is examined from temperatures of 1173 to 2873 K to elucidate the optimal conditions for facilitating graphene-zipping reactions whilst minimizing graphene stacking processes. Mesoporous carbons comprising a few-layer graphene wall display excellent thermal stability up to 2073 K coupled with a nanoporous structure and three-dimensional framework. Nevertheless, advanced temperature-programmed desorption (TPD), X-ray diffraction, and Raman spectroscopy show graphene-zipping reactions occur at temperatures between 1173 and 1873 K. TPD analysis estimates zipping reactions lead to a 1100 fold increase in the average graphene-domain, affording the structure a superior chemical stability, electrochemical stability, and electrical conductivity, while increasing the bulk modulus of the framework. At above 2073 K, the carbon framework shows a loss of porosity due to the development of graphene-stacking structures. Thus, a temperature range between 1873 and 2073 K is preferable to balance the developed graphene domain size and high porosity. Utilizing a neutron pair distribution function and soft X-ray emission spectra, we prove that these highly mesoporous carbons already consist of a well-developed sp2-carbon network, and the property evolution is governed by the changes in the edge sites and stacked structures.

Electron transfer in LiMn1.5Ni0.5O4 during charging studied with soft X-ray spectrometry.

This is the first report on analyzing the chemical state of Li-ion battery electrodes at different states of charge by using a wavelength-dispersive spectrometer, which has a two-order improved energy resolution in the soft X-ray energy region compared with that of a conventional energy-dispersive X-ray analyzer. Electrodes containing LiMn1.5Ni0.5O4 were charged to prepare Li0.5Mn1.5Ni0.5O4 and λ-Mn0.75Ni0.25O2. The soft X-ray emission spectra obtained from those materials show that the O-K emission signal was drastically decreased throughout the charging process. This suggests that O-2p electron contributed to the electrochemical oxidation. The density of states and Bader charge evaluated from ab initio calculation support this result.

Soft X-ray absorption and emission spectra of nanographene prepared from pentacene with hot mesh deposition and soft X-ray irradiation

The molecular orientation and partial density of states were evaluated using NewSUBARU by soft X-ray absorption spectroscopy (XAS) and soft X-ray emission spectroscopy measurements. The degree of molecular alignment was degraded by increasing mesh temperature in hot mesh deposition (HMD), in other words, was changed from pentacene (Pn) to 6,13-dihydropentacene (DHP). At a mesh temperature of 1450 °C, the different XAS was obtained due to the mixing effect of Pn and DHP, and presence of Pn oligomer. The HMD carbon film transformed into the graphite-like film and the graphene on the quartz substrate and the Ni/quartz substrate after soft X-ray irradiation, respectively. The HMD carbon film after soft X-ray irradiation showed the peaks due to terminal carbon such as CH n and COOH in comparison with the reported large graphene sheet. It indicates that the flake size of the graphene on the Ni/quartz substrate was small and had many edges.

Hydration of the Zwitterionic and Protonated Forms of Glycine Betaine Probed by Soft X-ray Emission Spectroscopy Coupled with Chemometrics.

Soft X-ray absorption and emission spectra of glycine betaine (GB) have been measured at the O K-edge in neutral and strongly acidic solutions. The absorption spectra of the neutral solutions have a resonance peak at 532.6 eV, assigned to the transition to the π* orbital, whereas in the acidic solutions, the peak is shifted by -0.3 eV. The emission spectra taken as a function of the GB concentration have been analyzed by means of a modified classical least-squares regression method to obtain the hydration number of the solute. The analysis is successful when the emission spectra have been acquired at the energy of a slightly detuned resonance, giving 28 and 24 as the minimum values for the zwitterionic and protonated GB, respectively. The number of 28 accords with the reported values for the number of water molecules in the first hydration layer of the zwitterion and is greater than that obtained by other experimental techniques. The obtained numbers are used to discuss the hydration structure of GB with the aid of ab initio molecular orbital calculations. The hydration structure of the protonated form of GB is explored for the first time.

Soft X-ray and EUV emission spectra of beryllium plasma produced by neodymium-glass laser radiation with broad frequency and angular spectra

We present the results of an experimental study of soft X-ray (SXR) and extreme ultraviolet emission spectra of the plasma produced by exposing a plane solid beryllium target to laser radiation with broad frequency and angular spectra. SXR lines up to 1s – 9p of Be IV as well as the plasma continuum are recorded for a laser focal-spot intensity of 5.3 × 1013 W cm−2. To model the SXR beryllium plasma spectra, simulations are carried out using the INDHAUS programme and the FLYCHK code in the framework of local thermodynamic equilibrium model, which agree nicely with experimentally obtained results.

Soft X-Ray and Cathodoluminescence Examination of a Tanzanian Graphite Deposit.

Hyperspectral soft X-ray emission (SXE) and cathodoluminescence (CL) spectrometry have been used to investigate a carbonaceous-rich geological deposit to understand the crystallinity and morphology of the carbon and the associated quartz. Panchromatic CL maps show both the growth of the quartz and the evidence of recrystallization. A fitted CL map reveals the distribution of Ti4+ within the grains and shows subtle growth zoning, together with radiation halos from 238U decay. The sensitivity of the SXE spectrometer to carbon, together with the anisotropic X-ray emission from highly orientated pyrolytic graphite, has enabled the C Kα peak shape to be used to measure the crystal orientation of individual graphite regions. Mapping has revealed that most grains are predominantly of a single orientation, and a number of graphite grains have been investigated to demonstrate the application of this new SXE technique. A peak fitting approach to analyzing the SXE spectra was developed to project the C Kα 2pz and 2p(x+y) orbital components of the graphite. The shape of these two end-member components is comparable to those produced by electron density of states calculations. The angular sensitivity of the SXE spectrometer has been shown to be comparable to that of electron backscatter diffraction.

Multiple Temperature Components of the Hot Circumgalactic Medium of the Milky Way

Abstract We present a deep XMM-Newton observation of the Galactic halo emission in the direction of the blazar 1ES 1553+113. In order to extract the Galactic halo component from the diffuse soft X-ray emission spectrum, accurately modeling the foreground components is crucial. Here we present complex modeling of the foregrounds with unprecedented details. A careful analysis of the spectrum yields two-temperature components of the halo gas ( T 1 em = 10 6.25 − 6.42 K, T 2 em = 10 6.68 − 6.92 K). We find that these temperatures obtained from the emission spectrum are not consistent with those from the absorption spectrum ( T 1 ab = 10 6.07 − 6.13 K, T 2 ab = 10 6.96 − 7.15 K), unlike the previous studies that found only one-temperature component of the Milky Way circumgalactic medium. This provides us with interesting insights into the nature of emitting and absorbing systems. We discuss several possibilities objectively, and conclude that most likely we are observing multiple (3–4) discrete temperatures between 10 5.5 K and ≥ 10 7 K in the Milky Way circumgalactic medium.

On the uniqueness of the solution of the problem of reconstructing a continuous soft X-ray emission spectrum by the iterative method

Abstract The question on the uniqueness of the solution of the problem of reconstructing a continuous soft X-ray emission spectrum by the iterative method [Nuclear Inst. and Methods in Physics Research A, 916 (2019) 313–321] from spectrograms obtained with a transmission diffraction grating is considered. It is shown that, despite the presence of a potentially infinite number of solutions of this problem, only one of them has the physical sense.

Spectroscopic studies on the enhanced radiation with high Z rare gas seeding for mitigating divertor heat loads in LHD plasmas

Abstract We have measured extreme ultraviolet (EUV) and soft X-ray emission spectra of krypton (Kr) ions in the Large Helical Device (LHD) plasmas with Kr gas seeding intended for mitigating divertor heat loads. Several isolated lines or quasi-continuum bands from ion stages in the range of Kr5+–Kr25+ have been identified in a variety of wavelength ranges. The time trends of the line intensities indicate major contributions of ions with M-shell (n = 3) outermost electrons to the enhanced total radiation in the region closer to the core plasma. A line intensity ratio analysis for Kr25+ implies an unignorable contribution of the recombining component for the emissivity from this ion stage. A difference between the trends of neon (Ne) and Kr is also observed in a discharge with a combination of Kr and Ne seedings intended for more effective radiation enhancement.

Method for recovering soft X-ray emission spectra of plasmas from spectrograms recorded with a transmission diffraction grating

An iterative method was developed for recovering soft X-ray emission spectra from spectrograms obtained using a transmission diffraction grating. The method was compared with another one that was previously used. In the case of a linear radiation detector, both these methods are almost equivalent. In the case of a nonlinear detector, the method used previously could not be used, whereas the new method provides high-quality recovery of X-ray spectra.

Electronic Structure of Boron Doped HOPG: Selective Observation of Carbon and Trace Dope Boron by Means of X-ray Emission and Absorption Spectroscopy

We have measured the soft X-ray absorption and emission spectra of near B-K and C-K absorption edges of highly oriented pyrolytic graphite (HOPG) doped with a small amount (0.32 at.%) of boron (B), including incident/takeoff angle dependence.The main peak intensities at the B-K edge around 182 eV were almost independent on the change of takeoff angle. On the other hand, the satellite peak around 185 eV becomes larger as the takeoff angle becomes smaller. Based on this result, unlike the previous assignment of the main peak predicted from the quantum chemical calculation (π orbitals), it is reasonable to attribute the main peak to the σ orbitals. The takeoff angle dependence of the B-K emission is similar to the angle dependency of the C-K emission of undoped HOPG. Based on this and the theoretical consideration, it is presumable that the doped B atom does not intercalate between the layers of HOPG; it replaces the C atom of the hexagonal network structure and has a wave function similar to that of C atoms (sp2 type hybridized orbital). (Less)

High ionization states observed in soft x-ray spectra from plasmas of second row transition elements produced by femtosecond laser pulses

The soft x-ray emission spectra of femtosecond-laser-produced plasmas from 2nd row transition elements from yttrium (Z = 39) to palladium (Z = 46), with the exception of technetium (Z = 43), were measured in the 1–5 nm region. Plasmas were produced by shining pulses from a titanium–sapphire laser with 65 fs pulse duration and an energy per pulse of 4.5 mJ focused to an intensity of 3 × 1015 W cm−2 onto bulk targets. While the emission spectra from yttrium to molybdenum (Z = 42) contain only the unresolved transition arrays (UTA) already observed in nanosecond and picosecond laser-target interactions described in our previous paper (Lokasani et al 2015 J. Phys. B: At. Mol. Opt. Phys. 48 245009), transitions from higher ionization states are clearly demonstrated in the spectra emitted from ruthenium (Z = 44), rhodium (Z = 45) and palladium targets heated by the femtosecond laser. These UTAs are interpreted by comparing the experimental spectra to calculated results, obtained using the Cowan suite of codes, the flexible atomic code as well as previous predictions of isoelectronic trends. The 3d–4f transitions arrays emitted from Ru XXI-XXIII, Rh XXI-XXIII and Pd XXI-XXIII ions are clearly seen in the observed spectra. To our knowledge, such high ionization states are demonstrated for the first time at such moderate laser energies.

Analysis of soft x-ray emission spectra of laser-produced dysprosium, erbium and thulium plasmas

Soft x-ray emission spectra of dysprosium, erbium and thulium ions created in laser-produced plasmas were recorded with a flat-field grazing-incidence spectrometer in the 2.5–8 nm spectral range. The ions were produced using an Nd:YAG laser of 7 ns pulse duration and the spectra were recorded at various power densities. The experimental spectra were interpreted with the aid of the Cowan suite of atomic structure codes and the flexible atomic code. At wavelengths above 5.5 nm the spectra are dominated by overlapping n = 4 − n = 4 unresolved transition arrays from adjacent ion stages. Below 6 nm, n = 4 − n = 5 transitions also give rise to a series of interesting overlapping spectral features.

The multielectron character of the S 2p → 4eg shape resonance in the SF6 molecule studied via detection of soft X-ray emission and neutral high-Rydberg fragments

We have studied the nature of the S 2p→4eg shape resonance in the SF6 molecule by performing two different experiments. Soft X-ray emission spectra measured at the 4eg shape resonance reveal features that do not originate from the S 2p−1 states. One of the features can be assigned to the 6a1g→S 2p transition. The 6a1g orbital, which is empty in the molecular ground state, can be populated either in core–valence double excitations or in S 2p shake-up transitions. Both these channels are considered. We have also studied the fragmentation of SF6 molecule after the decay of the S 2p core-hole states by observing neutral fragments in high-Rydberg states, where an electron occupies an orbital with n≥20 (n is the principal quantum number). Such neutral fragments become, in relative terms, more abundant at the S 2p→4eg shape resonance with respect to the S 2p→2t2g shape resonance, which is a pure one-electron phenomenon.

Obtaining Soft X-ray Emission and Absorption Spectra Using SR from the VEPP-4 Storage Ring on the Metrology Station “Cosmos”

The experimental equipment of the metrology station “Cosmos” was adjusted for obtaining soft X-ray emission (XES) and absorption (XANES) spectra of reference samples. In the present work were used two different optical schemes: flat (Bragg-scheme) and cylindrically bent crystals (Johann scheme). Experimental XES and XANES spectra were compared with the spectra obtained on a laboratory X-ray spectrometer and the results of the quantum-chemical calculations.

New parallel wavelength-dispersive spectrometer based on scanning electron microscope.

A new wavelength - dispersive X-ray spectrometer for scanning electron microscopy (SEM) has been developed. This spectrometer can cover an energy range from 50 eV to 1120 eV by using an array made of seventeen reflection zone plates. Soft X-ray emission spectra of simple elements of Li, Be, B, C, N, Ti, V, O, Cr, Mn, Fe, Co, Ni, Cu, Zn and Ga were measured. The overall energy resolving power on the order of E/ΔE ~80 to 160 has been demonstrated. Spectrometer with 200 reflection zone plates has been used as a multi-channel analyser in the energy range of 100 - 1000 eV for quasi - continuous spectra measurements. The predicted energy-resolving power on the order of E/ΔE = 50 has been achieved in the entire energy range.

イオン液体の電子構造

This article shows our recent study on electronic structure of several typical ionic liquids. Ultraviolet photoemission spectroscopy, inverse photoemission spectroscopy and soft x-ray emission spectroscopy (SXES) were used for elucidating the electronic structure of ionic liquids based on methylbutylimidazolium ([Cn mim]+) cation. Non-resonant SXES spectra measured above N, O, and F 1s edges selectively probed the partial density of states of the cation and anion. They give a clear evidence that the highest occupied molecular orbital of the [C4 mim]+ cation contributes to the topmost occupied states of the ionic liquids [C4 mim]+PF6−. Resonant soft x-ray emission spectra at the N 1s edge of these ionic liquids revealed that the energy gap of [C4 mim]+PF6− is solely determined by the [C4 mim]+ cation, in contrast to usual ionic crystals like NaCl and NaBr. The ionic liquids composed of fluoride anions PF6− and BF4− have anomalous electronic structure. Such basic knowledge about the electronic structure of ionic liquid must be helpful for new molecular design of ionic liquids.

In situremoval of carbon contamination from optics in a vacuum ultraviolet and soft X-ray undulator beamline using oxygen activated by zeroth-order synchrotron radiation

Carbon contamination of optics is a serious issue in all soft X-ray beamlines because it decreases the quality of experimental data, such as near-edge X-ray absorption fine structure, resonant photoemission and resonant soft X-ray emission spectra in the carbon K-edge region. Here an in situ method involving the use of oxygen activated by zeroth-order synchrotron radiation was used to clean the optics in a vacuum ultraviolet and soft X-ray undulator beamline, BL-13A at the Photon Factory in Tsukuba, Japan. The carbon contamination of the optics was removed by exposing them to oxygen at a pressure of 10(-1)-10(-4) Pa for 17-20 h and simultaneously irradiating them with zeroth-order synchrotron radiation. After the cleaning, the decrease in the photon intensity in the carbon K-edge region reduced to 2-5%. The base pressure of the beamline recovered to 10(-7)-10(-8) Pa in one day without baking. The beamline can be used without additional commissioning.

Soft X-ray Emission Spectra of Mn-doped ZnO Thin Films

The local electronic structures of Zn0.97Mn0.03O和Zn0.67Mn0.33O thin films prepared by a molecular beam epitaxy(MBE) at 200 ℃ were investigated by soft X-ray fluorescence spectrometer of beamline 8.0.1 of the Advanced Light Source(ALS).The special interest can be given to find the relationship between the electronic structure of Mn and magnetic properties of our samples.Analysis of the integral intensity ratio of Mn L2 to L3 emission lines(I(L2)/I(L3)) from resonant and nonresonant Mn L2,3 X-ray emission spectra(XES) indicates that ferromagnetism(FM) is related to the free d charge carriers in the film.For ferromagnetic Zn0.97Mn0.03O sample,the majority of Mn atoms are incorporated at Zn substitutional sites and the film shows strong Coster-Kronig(C-K) transitions due to a large amount of free charge carriers available around Mn atoms.Both non-localized d charge carriers as itinerant electrons and 4s electrons from interstitial Mn obtained by Ruderman-Kittel-Kasuya-Yosid(RKKY) calculations can induce the ferromagnetic exchange interaction.However,the disappearance of FM in Zn0.67Mn0.33O sample can be explained in terms of the existence of MnO clusters leading to a reduction in the number of free charge carriers.