Total Electron Yield Spectra Research Articles

Influence of Anions on the Electrolyte/Electrode Interfacial Dynamics Probed By in-Situ/Operando Soft X-Ray Absorption Spectroscopy

Since the demonstration of room temperature plating and stripping of calcium with high capacities and low polarization using Ca(BH4)2 as the electrolyte, there is considerable interest in the study of electrochemical processes in calcium batteries in addition to the conventional magnesium batteries. The greater polarizability of Ca2+ over Mg2+represents greater configurational flexibility, facilitating ionic cluster formation and rapid delivery of Ca2+ ions to the electrode interface. With such motivation in calcium batteries, a critical question to address is the probing of the solvation and charge transfer mechanism at the electrode/electrolyte interface. In this work, the solvation and charge transfer mechanisms of two calcium electrolytes, Ca(BH4)2 and calcium hexafluoroisopropoxyborate (Ca(BHFIP)2), with different types of anions, are compared under operando conditions. It has been reported that when BH4 - is substituted by the more weakly coordinated BHFIP-, the electrolyte ionic conductivity will increase by an order of magnitude, which demonstrates the strong coordination of BH4 - to Ca2+ in THF. To probe the Ca2+ coordination chemistry difference at this electrolyte/electrode interface as a function of the type of anions, total electron yield (TEY) mode soft X-ray absorption spectra (XAS) sensitive to the interfacial speciation have been employed under operando electrochemical conditions. It was observed that the Ca(BHFIP)2 in THF shows a small shoulder on the right side of the L2-edge and a pre-edge peak on the left side of the L2-edge peak. A less prominent pre-edge peak is also observed on the left side of the L3-edge peak. These signatures become more prominent when the potential is swept negatively and are not reversible when the potential is swept positively in a cyclic voltammetry cycle. On the other hand, the Ca(BH4)2 in THF is more reversible, and no shoulder peak on the right side of the L2-edge peak was observed. The TEY spectra indicate their differences in the Ca2+coordination chemistry at the electrode/electrolyte interface as a result of the interacted anions and it will guide future development of electrolytes for calcium batteries. The detailed solvation structure of the calcium is to be resolved with the DFT calculations. Such operando soft XAS studies of the interfacial dynamics reveal the transient processes in the solvation at the electrolyte/electrode interface and will pave the way for the development of calcium electrolytes in batteries.

Mechanism of Mn incorporation into hydroxyapatite: Insights from SR-XRD, Raman, XAS, and DFT calculation

Hydroxyapatite (HAp) is ubiquitous in soils, sediments, and rocks in nature and also found to be the main mineral component of biological bones and teeth. HAp is structurally robust and chemically diverse with substitution by cations and/or anions, contributing to its important geological, environmental, and technological applications. Incorporation of Manganese (Mn), one of the common impurities in HAp, generally alters the physicochemical properties of HAp. It is thus fundamentally important to understand the incorporation mechanism of Mn in the HAp structure, as well as induced structural changes. In this study, HAps with various Mn contents have been synthesized by a co-precipitation method and then characterized with various techniques. It is indicated that as high as 10 mol% Mn can be successfully incorporated into HAp, and Mn incorporation decreases particle sizes of HAps. The interplanar spacing of (002) decreases linearly with increasing Mn content. The decrease in the crystallinity with Mn incorporation has been disclosed by the linear redshift and broadening of the ν1(PO4) in Raman spectra. Fourier Transform Infrared Spectroscopy (FTIR) analysis suggests significant covalent character of Mn-OH. Total electron yield (TEY) spectra and X-ray absorption near edge structure (XANES) analysis confirm that the incorporated Mn is in the oxidation state of Mn2+. Extended X-ray absorption fine structure (EXAFS) analyses of Ca and Mn in HAp suggest that Mn prefers to occupy the Ca2 site over the Ca1 site. Furthermore, density function theory (DFT) calculations show that the Ca2 site is more energetically favored for Mn2+ incorporation.

Atomistic mechanism of cadmium incorporation into hydroxyapatite

Abstract Hydroxyapatite (HAp) has been widely used to remove cadmium (Cd) in contaminated water and soils via Cd-Ca substitution. The Cd incorporation into HAp affects its structure; however, the detailed mechanism remains unclear. In this study, a series of Cd-substituted hydroxyapatites were synthesized and characterized with various techniques. Cd incorporation causes a decrease in a- and c-lattice parameters due to the radius of Cd2+ being slightly smaller than that of Ca2+. As the Cd content increases, the particle sizes of the synthesized samples decrease and their specific surface areas increase. Raman bands shift linearly and the ν1(PO4) peak at 961 cm−1 becomes broadened with increasing Cd content. Change in X-ray absorption near edge structure (XANES) spectra of the P K-edge indicates distortion of phosphate with Cd incorporation. Total electron yield (TEY) spectra of the Ca L2,3-edge show a decrease in the octahedral symmetry, suggesting preferential occupancy of Cd over the Ca2 site. Extended X-ray absorption fine structure (EXAFS) analysis of the Ca K-edge reveals no obvious change in the local environment of Ca induced by Cd incorporation. However, EXAFS analysis of the Cd K-edge indicates that the substituted Cd occupies one Ca2 site in hexagonal Ca2 positions at low-Cd contents [<10 mol% of Cd/(Cd+Ca)], while both Ca1 and Ca2 sites are occupied at higher Cd contents. This study provides atomistic insight into the mechanism for Cd incorporation in HAp, which will help develop an approach for effective Cd removal using HAp for environmental remediation.

Friction-condition-dependent sulfide and sulfate evolution on dialkylpentasulfide tribofilm studied by XANES

The effects of friction conditions, such as rotational speed, frictional time, and applied load, on the evolution mechanism of sulfide and sulfate on the top and bottom layers of tribofilm were investigated by total electron yield (TEY) and fluorescence yield (FY) mode X-ray absorption near-edge structure (XANES) spectra in the same beam line (4B7A). The results demonstrated that the top and bottom layers of tribofilms were covered by sulfide and sulfate. The addition of dialkylpentasulfide (DPS) could form complex nonuniform tribofilm. In addition, the friction condition (speed, load, or time) has its unique role in the generation of sulfide and sulfate at a specific depth on the tribofilm surface. The enhancement of friction conditions could promote the sulfur tribochemical reaction in a comparatively large range and alter the relative intensity of sulfurization and the sulfur-oxidizing process.

Soft X‐ray spectromicroscopy studies of pitting corrosion of reinforcing steel bar

Pitting corrosion of reinforcing steel bar (rebar) imbedded in concrete by chloride ions can cause concrete degradation. It is thus necessary to develop methods to mitigate concrete corrosion which could include using a protective polymer rebar coating. Corrosion studies of polyvinyl butyral‐carbon black polymer‐coated rebar using soft X‐ray fluorescence (XRF) microprobe and micro‐X‐ray absorption near edge spectroscopy (μ‐XANES) are reported in this study. After removal of the polyvinyl butyral‐carbon black polymer coating, Fe Lα1, Mn Lα1, and O Kα1 XRF maps were collected as well as Fe and Mn L3‐edge μ‐XANES spectra from different regions across the whole rebar surface by collection of total electron yield (TEY) and partial XRF yield (PFY) spectra. The distribution of metallic Fe and Fe corrosion products was determined by analysis of the Fe XRF map. The μ‐XANES spectra indicated a higher fraction of Fe (III) phases on the corroded rebar surface, while Fe (II/III) phases were the major corrosion products beneath the surface region. In addition, Mn (II) and Mn (III) were determined as the valence states of the manganese corrosion products.

1]Benzothieno[3,2-b]benzothiophene (BTBT) derivatives: Influence in the molecular orientation and charge delocalization dynamics

Abstract Using near-edge X-ray absorption fine structure (NEXAFS) and resonant Auger spectroscopy (RAS) in conjunction with the core-hole clock methodology the electronic structure, molecular ordering and orientation and charge transfer dynamics in the femtosecond time scale of 2,7-di-tert-pentyl[1]benzothieno[3,2-b]benzothiophene (di(Me)2Pr-BTBT), 2,7-di-iso-propyl[1]benzothieno[3,2-b]benzothiophene (diiPr-BTBT) and 2,7-di-tert butyl[1]benzothieno[3,2-b]benzothiophene (ditBu-BTBT) films were investigated. Total electron yield (TEY) and fluorescence yield (FY) NEXAFS spectra were recorded with the aim of determining the preferred molecular orientation of the oligomers at the surface and in the bulk. Angular dependent sulfur 1s NEXAFS spectra for diiPr-BTBT and ditBu-BTBT films deposited onto FTO (fluorine doped tin oxide) point to well-organized films with a preferred edge-on geometry, while for the di(Me)2Pr-BTBT film little variation is seen, indicating that the film matches its herringbone crystal packing. Films prepared on ITO (indium tin oxide) and silicon were also investigated by TEY and FY NEXAFS. Greater film ordering is observed in the bulk. The electron charge transfer time following sulfur K-edge main resonance was calculated. The ditBu-BTBT films showed the lowest charge transfer time as well as greater molecular organization, pointing to an increased coupling, as compared to the other oligomers.

Polarization-Dependent Ti 2p-Resonant X-ray Raman Scattering from Ti2O3

Detailed resonant X-ray emission spectra (XES) and these polarization dependences of Ti2O3 were obtained by excitation at the Ti 2p absorption edge. About 100 XES spectra were observed in different polarization configurations. X-ray Raman scattering spectra showed two types of crystal field (dd) excitations as well as charge-transfer (CT) excitations. Bulk states of the powder sample were obtained by the XES measurement, which is the photon-in/photon-out method. Partial photon yields (PPYs) of some elementary excitations were extracted from the XES spectra. The CT excitations were hidden in total electron yield spectra, but these were revealed by PPY measurements. Symmetry information of these excitations was acquired on the basis of polarization dependences.

Ramsey interferometry for resonant Auger decay through core-excited states

We theoretically investigate the electron dynamics in Ne atoms involving core-excited states through the Ramsey scheme with a pair of time-delayed x-ray pulses. Irradiation of Ne atoms by the $\ensuremath{\sim}1$ femtosecond x-ray pulse simultaneously populates two core-excited states, and an identical but time-delayed x-ray pulse probes the dynamics of the core-excited electron wave packet which is subject to the resonant Auger decay. The energy-integrated total Auger electron yield and energy-resolved Auger electron spectra in the time domain show periodic structures due to the temporal evolution of the wave packet, from which we can obtain the counterpart in the frequency domain through the Fourier transformation. The Auger electron energy spectra in the time as well as frequency domains show the interference patterns between the two Auger electron wave packets released into the continuum from the superposition of two core-excited states at different times. These spectra are important to clarify the individual contribution of the different Auger decay channels upon core excitation by the x-ray pulse.

Non‐destructive depth analysis of the surface oxide layer on Mg2Si with XPS and XAS

Depth analysis of the surface oxide layer on a Mg2Si crystal was performed with X‐ray photoelectron spectroscopy (XPS) and X‐ray absorption spectroscopy (XAS). In XPS, X‐rays from synchrotron radiation with the energies between 2100 and 3300 eV were used as the excitation sources for depth analysis. The Si 1s and Mg 1s XPS spectra show the formation of a thinner SiO2‐X layer at outermost surface and a thicker MgO layer at lower surface on the Mg2Si. In XAS, total electron yield and partial electron yield (PEY) acquisition modes were used for the measurement of Si K‐edge. The PEY spectrum was obtained by detecting electrons with a fixed kinetic energy of 5, 10, 20, 30, 40, or 50 eV. Although the PEY spectrum with electrons of 5 eV shows similar features with the total electron yield spectrum, detection of electrons with 50 eV gives an increase in the ratio of a peak at 1843.7 eV to the peak assigned to Mg2Si. The peak at 1843.7 eV can be assigned to the formation of SiO2‐X on the Mg2Si. From XPS and XAS results, it is indicated that a thinner SiO2‐X layer at outermost surface and a thicker MgO layer at lower surface are formed at initial oxidation of the Mg2Si. Copyright © 2016 John Wiley & Sons, Ltd.

Development of a XEOL detection system for the scanning transmission X-ray microscopy beamline at the Shanghai Synchrotron Radiation Facility

We describe the design and capabilities of the x-ray excited optical luminescence (XEOL) technique at the scanning transmission x-ray microscopy beamline (BL08U1A) of the Shanghai Synchrotron Radiation Facility. The detection system is a functional expanding of the original end station, making full use of its precision positioning stages. The simultaneous collection of XEOL and total electron yield spectra is realized using homemade software when the excitation energy is scanned. The setup is validated by the 2D near-edge x-ray absorption spectroscopy (NEXAFS) XEOL mapping across the O K-edge of a nanostructured ZnO sample. The ability to detect the signal of very weak light-emitting material is verified by using TiO2 nanopowder.

Pt-Mediated Reversible Reduction and Expansion of CeO2 in Pt Nanoparticle/Mesoporous CeO2 Catalyst: In Situ X-ray Spectroscopy and Diffraction Studies under Redox (H2 and O2) Atmospheres

Here, we report the Pt nanoparticle mediated reduction (oxidation) and lattice expansion (contraction) of mesoporous CeO2 under H2 (O2) atmospheres and in the temperature range of 50–350 °C. We found that CeO2 in the Pt/CeO2 catalyst was partially reduced in H2 (and fully oxidized back in O2) as demonstrated by several in situ techniques: APXPS spectra (4d core levels) for the topmost surface, NEXAFS total electron yield spectra (at the M5,4 edges) in the near surface regions, and (N)EXAFS fluorescence spectra (at the L3 edge) in the bulk. Moreover, XRD and EXAFS showed the reversible expansion and contraction of the CeO2 unit cell in H2 and O2 environments, respectively. The expansion of the CeO2 cell was mainly associated with the formation of oxygen vacancies as a result of the Pt-mediated reduction of Ce4+ to Ce3+. We also found that pure mesoporous CeO2 can not be reduced in H2 under identical conditions but can be partially reduced at above 450 °C as revealed by APXPS. The role of Pt in H2 was ident...

Molecular orientation and composition at the surface of spin‐coated polyfluorene:Fullerene blend films

AbstractThe surface composition in spin‐coated films of polyfluorene:fullerene blends was determined quantitatively by near‐edge X‐ray absorption fine structure (NEXAFS) spectroscopy. By comparing partial and total electron yield spectra, we found vertical compositional differences in the surface region. Furthermore, the orientation of the polymer chains was investigated by variable‐angle NEXAFS. Blend films of poly[(9,9‐dioctylfluorenyl‐2,7‐diyl)‐co‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole] with [6,6]‐phenyl‐C61‐butyric acid methyl ester in two different blend ratios were studied. Results showed polymer enrichment of the surfaces for films with a polymer:fullerene weight ratio of 20:80 and of 50:50, spin‐coated from both chlorobenzene and chloroform solutions. The angular dependence of the NEXAFS spectra of the pure polymer films showed a preferential plane‐on orientation, which was slightly stronger in the subsurface region than at the surface. In blend films, this orientational preference was less pronounced and the difference between surface and subsurface vanished. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013

Imide Photodissociation Investigated by X-ray Absorption Spectroscopy

X-ray absorption spectroscopy is used to investigate the photodissociation of the imides PMDI (pyromellitic diimide) and SSMCC (sulfosuccinimidyl 4-(N-maleimidomethyl) cyclohexane-1-carboxylate). PMDI contains only one type of imide, and its photodissociation can be explained by a simple conversion from imide to a mix of imine and nitrile after desorption of the oxygens from the imide. SSMCC contains two different imides. One reacts like PMDI, the other in a more complex multistep process. Eventually, N(2) is formed in the bulk of the sample at high radiation density. The sequence of reactions is inferred from the π* peaks in total electron yield and fluorescence yield absorption spectra at the N 1s and O 1s edges. First-order rate equations are used to model the evolution of the peak areas versus radiation dose.

Charge-transfer induced ferromagnetism in nanostructured ZnO/Al powders: An x-ray absorption near edge structure study

The correlation between the x-ray absorption spectra and the magnetic properties for Al doped ZnO nanostructures prepared by mechanical alloying has been studied in order to clarify the origin of the room-temperature ferromagnetism in the Al doped ZnO nanostructures. Room-temperature ferromagnetism is induced in nanostructured ZnO-Al powders by milling without any ferromagnetic dopant. The O and Al K-edge x-ray absorption spectra acquired from the ferromagnetic ZnO-Al powders indicate a clear sign of a charge transfer from Al to O on ZnO. The comparison of the florescence yield and total electron yield spectra suggests that this charge transfer takes place mostly at the surface of ZnO particles. Our results show that the surface charge transfer between Al and O plays an important role in the induction of spontaneous magnetization in the Al doped ZnO.

Monochromatic soft-x-ray-induced reactions of CF2Cl2 adsorbed on Si(111)-7 × 7 studied by continuous-time photon-stimulated desorption spectroscopy near the F(1s) edge

Continuous-time core-level photon-stimulated desorption (PSD) spectroscopy was used to investigate the monochromatic soft x-ray photoreactions of CF2Cl2 adsorbed on Si(111)-7 × 7 near the F(1s) edge (681–704 eV). Sequential F+ PSD spectra were observed as a function of photon exposure at the CF2Cl2-covered surface (dose = 2.0 × 1014 molecules cm−2, ∼0.75 monolayer). The F+ PSD and total electron yield (TEY) spectra of solid CF2Cl2 near the F(1s) edge were also measured. Both F+ PSD and TEY spectra depict three features in the energy range of 687–695 eV, and are assigned to the excitations of F(1s) to (13a1 + 9b2)[(C–Cl)∗], (7b1 + 14a1)[(C–F)∗] antibonding and 5p Rydberg orbitals, respectively. Following the Auger decay process, two holes are created in the C–F bonding orbitals producing the 2h1e final state which results in the F+ desorption. This PSD mechanism, responsible for the F+ PSD of solid CF2Cl2, is used to explain the first F+ PSD spectrum in the sequential F+ PSD spectra. The variation of spectral shapes in the sequential F+ PSD spectra shows the consumption of adsorbed CF2Cl2 molecules and the production of surface SiF species as a function of photon exposure. The photolysis cross section of the adsorbed CF2Cl2 molecules by photons with varying energy (681–704 eV) is deduced from the sequential F+ PSD spectra and found to be ∼6.0 × 10−18 cm2.

Communication: Near edge x-ray absorption fine structure spectroscopy of aqueous adenosine triphosphate at the carbon and nitrogen K-edges

Near edge x-ray absorption fine structure (NEXAFS) spectroscopy at the nitrogen and carbon K-edges was used to study the hydration of adenosine triphosphate in liquid microjets. The total electron yield spectra were recorded as a function of concentration, pH, and the presence of sodium, magnesium, and copper ions (Na(+)/Mg(2+)/Cu(2+)). Significant spectral changes were observed upon protonation of the adenine ring, but not under conditions that promote π-stacking, such as high concentration or presence of Mg(2+), indicating that NEXAFS is insensitive to the phenomenon. Intramolecular inner-sphere association of Cu(2+) did create observable broadening of the nitrogen spectrum, whereas outer-sphere association with Mg(2+) did not.

Inner‐shell photoabsorption spectroscopy of push–pull nitroanilines—Theoretical and experimental studies at N 1s region

AbstractOscillator strengths for N 1s excitation spectra of the gas‐phase aniline and nitrobenzene, and the solid‐phase meta‐ and para‐nitroanilines have been derived from the total electron yield and total ion yield spectra acquired by tunable synchrotron radiation. Ab initio calculations carried out within the improved virtual orbital method and equivalent ionic core virtual orbital model have been used to aid spectral interpretation. The Rydberg‐valency mixture has also been evaluated for all compounds. These results are compared to those acquired with the extended hückel molecular orbital method [Goeta et al., Chem Mater, 2000, 12, 3342]. The building block model has been used to simulate the nitroanilines spectra. The sensitivity of core excitation spectroscopy to intramolecular nitroanilines charge transfer and the N 1s → π* spectral features dependence upon the substitution pattern (meta or para) have been confirmed, as already verified for the gas‐phase inner‐shell energy loss spectra for the same molecules [Turci et al., Can J Chem, 1996, 74, 851]. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008

Soft x-ray photoreactions of CF3Cl adsorbed on Si(111)-7×7 studied by continuous-time photon-stimulated desorption spectroscopy near F(1s) edge

The continuous-time core-level photon-stimulated desorption (PSD) spectroscopy was employed to monitor the monochromatic soft x-ray-induced reactions of CF3Cl adsorbed on Si(111)-7x7 near the F(1s) edge (681-704 eV). Sequential F+ PSD spectra were measured as a function of photon exposure at the CF3Cl-covered surface (dose=0.3x10(15) molecules/cm2, approximately 0.75 ML). The F+ PSD and total electron yield (TEY) spectra of molecular solid CF3Cl near the F(1s) edge were also measured. Both F+ PSD and TEY spectra show two features at the energy positions of 690.2 and 692.6 eV, and are attributed to the excitations of F(1s) to 11a1[(C-Cl)*] and (8e+12a1)[(C-F)*] antibonding orbitals, respectively. Following Auger decay, two holes are created in the F(2p) lone pair and/or C-F bonding orbitals forming the 2h1e final state which leads to the F+ desorption. This PSD mechanism, which is responsible for the F+ PSD of solid CF3Cl, is employed to interpret the first F+ PSD spectrum in the sequential F+ PSD spectra. The variation of spectrum shapes in the sequential F+ PSD spectra indicates the dissipation of adsorbed CF3Cl molecules and the formation of surface SiF species as a function of photon exposure. From the sequential F+ PSD spectra the photolysis cross section of the adsorbed CF3Cl molecules by photons with varying energy (681-704 eV) is determined to be approximately 1.0x10(-17) cm2.

Phase change observation in reflection multilayers by total electron yield and reflection spectra

Precise optical elements for use in the extreme ultraviolet region are necessary for controlling both the uppermost layer thickness and the reflection phase in a reflection multilayer system. In this study, a phase value corresponding to both the uppermost layer thickness and the reflection phase was derived from the reflectance and total electron yield (TEY) intensity. Mo∕Si multilayers were fabricated on a silicon wafer with various thicknesses of the uppermost Mo layer. Phase values obtained from the reflection and TEY measurements were found to change in accordance with increases in the thickness of the uppermost Mo layer and a concomitant change in the reflection phase.

How well does total electron yield measure x-ray absorption in nanoparticles?

The possibility to quantitatively analyze total electron yield (TEY) spectra as a measure of the x-ray absorption cross section from supported magnetic nanoparticles is explored by a combination of experiments and Monte Carlo simulations. Unless the particles are very small, it is found that saturation effects are important and can lead to a severe underestimation of the magnetic moments, when the magneto-optical sum rules are straightforwardly applied to experimental data. However, unlike for planar samples the possibility to examine and correct the saturation effects by varying the x-ray angle of incidence is not given, the absorption profiles are largely unaffected in their shape. The Monte Carlo simulations, appropriately conducted for the material under investigation, provide an estimate of the saturation effects occurring in nanoparticle TEY data.