Synchrotron Radiation Experiments Research Articles

Reaction pathways of iron-sulfide mineral formation: an in situ X-ray diffraction study

Iron sulfides were synthesized via a co-precipitation method. In addition, synchrotron-radiation experiments were performed under a range of pH and temperature conditions (up to 100 °C) to compare the results of in situ and ex situ crystal growth investigation of iron sulfides. In acidic environments, H 2 S acts as an oxidant, oxidizing Fe 2+ to Fe 3+ and allowing formation of greigite from mackinawite. However, under neutral conditions, due to very low H 2 S concentrations, the oxidant may be S (instead of H 2 S), allowing mackinawite to transform into greigite. Both mackinawite and magnetite were present under alkaline conditions, with possible transitions of Fe 2+ +2OH − →Fe(OH) 2 , followed by 3Fe(OH) 2 →Fe 3 O 4 +2H 2 O+H 2 . In situ X-ray diffraction results indicate that the mineral transformation rate under acidic conditions is faster than under neutral and alkaline conditions. This means that acid environments can enhance rapid phase transformation of iron sulfides. The results under different experimental conditions suggest that there is a variety of formation pathways for iron-sulfide minerals owing to the presence of different oxidants in different geochemical environments.

Electron Correlation in the Ionization Continuum of Molecules: Photoionization of N2 in the Vicinity of the Hopfield Series of Autoionizing States.

Direct measurement of autoionization lifetimes by using time-resolved experimental techniques is a promising approach when energy-resolved spectroscopic methods do not work. Attosecond time-resolved experiments have recently provided the first quantitative determination of autoionization lifetimes of the lowest members of the well-known Hopfield series of resonances in N2. In this work, we have used the recently developed XCHEM approach to study photoionization of the N2 molecule in the vicinity of these resonances. The XCHEM approach allows us to describe electron correlation in the molecular electronic continuum at a level similar to that provided by multireference configuration interaction methods in bound state calculations, a necessary condition to accurately describe autoionization, shakeup, and interchannel couplings occurring in this range of photon energies. Our results show that electron correlation leading to interchannel mixing is the main factor that determines the magnitude and shape of the N2 photoionization cross sections, as well as the lifetimes of the Hopfield resonances. At variance with recent speculations, nonadiabatic effects do not seem to play a significant role. These conclusions are supported by the very good agreement between the calculated cross sections and those determined in synchrotron radiation and attosecond experiments.

Structures of Atomically Designed PtCo Alloy Catalysts and Durability/Activity Towards Oxygen Reduction Reaction

For polymer electrolyte fuel cells, Pt-based alloy catalysts have been widely studied. We have developed a novel nanocapsule method1,2 for the synthesis of controlled PtCo alloy nanoparticles (PtCo/GCB, graphitized carbon black support to mitigate carbon corrosion), and modified the method3for covering hydrogen-treated PtCo/GCB (H-PtCo/GCB) with Pt-skin layers. Figure 1 shows images obtained with a transmission electron microscope (TEM) of PtCo/GCB, H-PtCo/GCB, and Pt-skin coated PtCo catalyst (PtxAL-PtCo/GCB) with the histograms of the particle-size distributions. Particle sizes were very uniform with the diameters of 2.5±0.2 nm for PtCo/GCB and H-PtCo/GCB, and of 3.0±0.3 nm for PtxAL-PtCo/GCB. By the electron diffraction (Table 1), the lattice of PtCo/GCB was determined as fcc. After the hydrogen treatment at 400 oC,3 the lattice became fct for H-PtCo/GCB. After the addition of a Pt-skin on H-PtCo/GCB, the lattice was mostly (ca. 97%) fct and partially (ca. 3%) fcc, presumably due to the addition of a Pt-skin. By X-ray absorption fine structure (XAFS) measurements, Pt and Co atoms were found to be very uniformly distributed in PtCo/GCB. For H-PtCo/GCB, neither the atomic distances nor the coordination numbers showed a large change, whereas for PtxAL-PtCo/GCB, the Pt-Pt coordination number increased showing the formation of a Pt-skin layer. The effect of the Pt-skin layers was examined in a 0.1-M HClO4 solution at 65 oC with a multi-channel flow double-electrode cell2 on the activity towards the oxygen reduction reaction and the durability examined by the accelerated durability test according to the protocol for load-change cycles4 recommended by the Fuel Cell Commercialization Conference of Japan (FCCJ) (Fig. 2). Both the durability and the mass activity evaluated at 0.85 V vs. the reversible hydrogen electrode were the highest at PtxAL-PtCo/GCB followed by H-PtCo/GCB. By in situ XAFS measurements, the layers of Pt skins were indicated to exist at the surface of the alloy particles in 0.1 M HClO4. After 30,000 cycles, the initial high activity at PtCo/GCB was lost and became almost identical to that at a commercial Pt catalyst supported on carbon black (c-Pt/CB) because of Co leaching out.5,6 The efficiency/usefulness of the atomically-controlled Pt-skin layers was clearly demonstrated. Detailed structural analysis during the durability test is now in progress. Acknowledgements This work was carried out under the “HiPer-FC” and “SPer-FC” projects, NEDO, Japan. The synchrotron radiation experiments were performed at BL14B2 and BL16B2 of SPring-8 (Proposal No. 2015B1851, 2015B1852, 2015B3388, 2015B5390, 2016A5390). References 1) H.Yano, M. Kataoka, H. Yamashita, H. Uchida, M. Watanabe, Langmuir, 23, 6438 (2007). 2) H. Yano, J. M. Song, H. Uchida, M. Watanabe, J. Phys. Chem. C, 112, 8372 (2008). 3) M. Watanabe, H. Yano, D. A. Tryk, H. Uchida, J. Electrochem. Soc., 163, F455 (2016). 4) http://fccj.jp/pdf/23_01_kt.pdf in Japanese. 5) M. Watanabe, D. A. Tryk, M. Wakisaka, H. Yano, H. Uchida, Electrochim. Acta, 84, 187 (2012). 6) K. Okaya, H. Yano, K. Kakinuma, H. Uchida M. Watanabe, ACS Appl. Mater. Interfaces, 4, 6982 (2012). Figure 1

(Invited) Analyses of CO Tolerance at Stabilized Pt-Skin/Ptfe and PtCo Hydrogen Anode Catalysts with High Activity and Robustness for Residential PEFCs

For residential polymer electrolyte fuel cells (PEFCs) operated with H2-rich (reformate) fuel gas, the hydrogen oxidation reaction (HOR) at Pt catalysts is severely poisoned even by trace amounts of CO contained in the reformate due to a strong blocking of active sites. So far, Pt-Ru alloy catalysts have been used to mitigate such CO poisoning. However, the HOR mass activity at Pt-Ru alloys is not sufficiently high, so that a large amount of precious metals (Pt and Ru) must be used. In addition, since Ru is not stable at high potentials (≥ 0.8 V), leaching into the acidic electrolyte membrane, the anode must be protected so as not to be oxidized by air. Recently, we have developed a Ru-free hydrogen anode catalyst by forming a stabilized Pt-skin (one to two atomic layers: xAL) on PtM-alloy (M = Fe, Co, and Ni) nanoparticles supported on carbon black (PtxAL‒PtM/C).1,2 These new catalysts exhibited a high HOR activity, in both the presence and absence of CO, as well as a robustness.3,4 The apparent values of mass activity (MA app) for the HOR on PtxAL‒PtFe/C at 20 mV vs. RHE in H2-saturated 0.1 M HClO4 solution were 2‒3 times larger than those for a commercial Pt2Ru3/C (c-Pt2Ru3/C) catalyst in the absence and presence of adsorbed CO (COad) at 70 °C as shown in Fig. 1. The retention of MA app on these PtxAL-PtM/C catalysts after an accelerated durability test (ADT) simulating daily start-stop cycles repeated exposure to the reformate gas and air (2,500 potential cycles between 0.02 V and 0.95 V) in N2 purged-0.1 M HClO4 solution at 70 oC was as high as ca. 80 % as shown in Fig. 2. The apparent area-specific activity values at the PtxAL‒PtM/C remained unchanged during ADT. This suggests that the dealloying of the M component in the PtxAL‒PtM/C was suppressed by the stabilized Pt-skin layer. To clarify the mechanism of such an enhancement of HOR activity and CO-tolerance for the PtxAL‒PtM/C, we performed multilateral-analyses, by in-situ attenuated total reflection Fourier transform infrared reflection-adsorption spectroscopy (ATR-FTIRAS), density functional theory (DFT) calculations, and in-situ X-ray absorption spectroscopy (XAS) techniques. It was found that the adsorption energy of CO on terrace sites on the PtxAL skin covering the PtM alloy was weakened by the modified electronic structure. The HOR activity of PtxAL‒PtFe/C with pre-adsorbed CO was found to recover appreciably after bubbling with CO-free pure H2. Such a recovery can be ascribed to an increase in the number of active sites by a transfer of linearly adsorbed COad at terrace sites (COL, terrace) to step/edge sites (COL, step/edge) on the surface of the Pt-skin layer, without removal of COad from the surface.4,5 We will also discuss possible mechanisms for the CO-tolerant HOR. This work was supported by funds for the “Superlative, Stable, and Scalable Performance Fuel Cells (SPer-FC)” project from the New Energy and Industrial Technology Development Organization (NEDO) of Japan. The synchrotron radiation experiments were performed at BL14B2 (Proposal Nos. 2015B3388 and 2016A1805) and BL16B2 (2016A5390 and 2016B5390) of SPring-8 in cooperation with the Device-Functional Analysis Department of NISSAN ARC Ltd. Figure 1

Time-Resolved Nanostructural Analysis of Catalyst Layer Formation Process by Synchrotron X-ray Scattering

Polymer electrolyte membrane fuel cell (PEMFC) has been considered as a highly efficient electrochemical power converter with zero emissions of CO2. The oxygen reduction reaction (ORR) occurs at the interface between platinum (Pt) catalyst nanoparticle and ionomer in the catalyst layer of membrane electrode assembly (MEA). The catalyst layer is fabricated by coating of the catalyst ink containing the carbon-supported platinum (Pt/C) catalyst, ionomer, and solvents. In the catalyst layers, ionomer provided an ultra-thin film, coating the Pt catalyst nanoparticles and the carbon support surfaces. These ultra-thin films have a significant influence on the electrochemical activity and transport phenomena that determine the whole cell performances. Recently, precise structural analyses of catalyst inks and catalyst layers have been reported. To the best of our knowledge, however, the dynamics of the catalyst layer formation process remain unclear. Herein, we performed in-situmeasurements of synchrotron radiation grazing-incidence small-angle X-ray scattering (GISAXS) of a catalyst ink during drying process. The ink was coated on a silicone (Si) wafer with a film applicator and the scattering images of the film were acquired as a function of the elapsed time. The catalyst ink was prepared by blending a Pt/C catalyst, ionomer (Nafion®) and solvents (water/1-propanol (NPA) =1:1 in volume ratio). The solid content of the catalyst ink was 10 wt%, and the weight ratio of ionomer to carbon ratio was 1:1. The catalyst ink was coated on a Si wafer using a film applicator and X-ray beam (wavelength λ = 0.100 nm) was irradiated on the film at a small grazing angle (0.15 °) and the scattering images were measured using a photon counting detector (PILATUS3X 2M, DECTRIS Ltd.) at a distance of 2700 mm from the film (BL45XU/SPring-8). Selected 2D GISAXS patterns during catalyst layer formation process are shown in Fig. 1. The 2D GISAXS pattern significantly change with the elapsed time, in particular for the out-of-plane direction. Several scattering peaks appear immediately after the ink coating. With time elapsed, the peak intensities increase and their peak positions shift toward smaller qz . The intensity profiles on the out-of-plane q z axis of GISAXS patterns measured during catalyst layer formation process as a function of the elapsed time (t) are shown in Fig. 2. From t = 0 s, the peak at around q z ~ 0.2 nm−1 shift toward smaller q z with increasing t. Furthermore, at t ~ 50 s, two peaks around q z ~ 0.5 nm−1 appear and combine into one peak. Thereafter, this peak shifts toward smaller q z with increasing t. These results demonstrate that nanostructural evolution of catalyst layer formation process can be traced by utilizing synchrotron X-ray scattering. The peak shifts would be due to the growth of Pt/C agglomeration induced by solvent evaporation. For the precise assignment of scattering peaks, further investigations based on direct observations of the catalyst ink using cryogenic transmission electron microscopy are now in progress. This presentation is based on results obtained from the PEMFC Research and Development Program for “Highly‐Coupled Analysis of Phenomena in MEA and its Constituents and Evaluation of Cell Performance” commissioned by the New Energy and Industrial Technology Development Organization (NEDO). The synchrotron radiation experiments were performed at BL45XU in SPring-8 with the approval of JASRI (Proposal No.2016A1194 and, No.2016B1004). Figure 1

Design and fabrication of a preamplifier to be used with a MWPC at the ILSF

The Iranian Light Source Facility (ILSF) is a new 3 GeV third generation synchrotron radiation facility in Middle East, which at the time being is in its design stage. For day one operation of the ILSF a custom made two-dimensional multiwire position sensitive detector with delay line readout will be used in small/wide angle scattering and diffraction experiments with synchrotron radiation. For many years such X-ray detectors have played an important role in these synchrotron radiation experiments and owing to their robustness they are still in use in many places. Paired with state of the art read-out electronics they are serious low cost competitors to other solutions based on solid-state hybrid pixel detectors. To achieve minimum dead time and high global count rates these detectors will require preamplifiers with certain characteristics, which involve low noise, good signal/noise ratio (better than 20 dB), high gain, short rise time (lower than 10 ns) and pulse duration shorter than 120 ns. In this paper, we present the design and first results of the evaluation of a voltage preamplifier developed at ILSF within a collaboration agreement between ILSF, Iran and the Italian Synchrotron Radiation Facility (Elettra), Italy. The application of this preamplifier in an in-house multiwire detector is discussed and results are presented.

Effect of Pre-annealing on Sintering of Stainless Steel Fiber Felt

Stainless steel fiber felt is a class of unique porous metal materials. This study investigates the effect of pre-annealing on the sintering of stainless steel fiber felt through quantitative characterization of sintered joints based on synchrotron radiation experiments. The sintered joint size was found to follow a marked normal distribution in fiber felt samples sintered with and without pre-annealing. However, pre-annealing prior to sintering led to a significant reduction in the total number of sintered joints as well as a reduction in the percentage of large sintered joints. Consequently, fiber felt samples sintered with pre-annealing achieved less than half the tensile strength of those sintered without pre-annealing. Delamination through fracture of sintered joints was pronounced in fiber felt samples sintered with pre-annealing, while failure occurred mainly through fracture of individual fibers in those sintered without pre-annealing. It was concluded that sintering without pre-annealing is necessary for the fabrication of high-strength fiber felt products and the reasons are briefly discussed.

Nano-channels in the spider fang for the transport of Zn ions to cross-link His-rich proteins pre-deposited in the cuticle matrix

We identify the presence of multiple vascular channels within the spider fang. These channels seem to serve the transport of zinc to the tip of the fang to cross-link the protein matrix by binding to histidine residues. According to amino acid and elemental analysis of fangs extracted shortly after ecdysis, His-rich proteins are deposited before Zn is incorporated into the cuticle. Microscopic and spectroscopic investigations in the electron microscope and synchrotron radiation experiments suggest that Zn ions are transported through these channels in a liable (yet unidentified) form, and then form stable complexes upon His binding. The resulting cross-linking through the Zn–His complexes is conferring hardness to the fang. Our observations of nano-channels serving the Zn-transport within the His-rich protein matrix of the fibre reinforced spider fang may also support recent bio-inspired attempts to design artificial polymeric vascular materials for self-healing and in-situ curing.

Time-Resolved Nanostructural Analysis of Thin-Film Formation Process from Nafion Solution by Synchrotron X-Ray Scattering

Perfluorosulfonate ionomers such as Nafion consist of a polytetrafluoroethylene backbone having pendant side chains terminating with sulfonic acid groups. These materials have attracted much attention as proton-conducting materials in polymer electrolyte membrane fuel cells (PEMFCs), due to their excellent chemical stability and high proton conductivity. The catalyst layer is fabricated by deposition of catalyst ink containing catalyst, ionomer, and solvents. In the catalyst layers, ionomer provided an ultra-thin film, coating the catalyst and the catalyst support surfaces. These ultra-thin films have a significant influence on the electrochemical activity and transport phenomena that determine the whole cell performances. Recently, precise structural analyses of ionomer in the solutions and solid-state thin films have been reported. To the best of our knowledge, however, the dynamics of ionomer thin-film formation process remain unclear.Herein, time-resolved measurements of grazing-incidence small- and wide-angle X-ray scattering (GISAXS/GIWAXS) utilizing synchrotron radiation at BL45XU/SPring-8 were carried out to observe the nanostructural evolution of thin film during solidification processes (i.e., spin-coating) from the Nafion solution. GISAXS and GIWAXS are synchrotron-based X-ray techniques that have been used extensively to provide nanostructural insight of polymeric thin films. In the present study, effects of solvent evaporation and centrifugal force on the structural formation behaviors of Nafion were observed for water/1-propranol (NPA) solution of Nafion (3.5 wt% Nafion in water/NPA (1/1 in volume ratio)). The wavelength of the X-ray beam was 0.1 nm, and camera length was 270 mm and 2503 mm for GIWAXS and GISAXS measurements, respectively. The scattering intensity at a certain scattering vector q was measured as a function of time after deposition of Nafion solution on the rotated Si substrate (2000 rpm). The 2D-scattering image was acquired using a photon counting detector (PILATUS3X 2M, DECTRIS Ltd.). In the first stage from t = 0 to 20 s, the 2D GIWAXS profile showed strong solvent peak and crystalline peak arising from the packing of the Nafion backbone (q z ~ 11.7 nm-1, d-spacing is defined as 2π/qz , d ~ 0.5 nm) quickly appeared. After 180 s, the solvent peak disappeared, and only the crystalline peak was observed. This supports that fine crystallites were contained in Nafion solution. The 2D GISAXS profile, on the other hand, significantly changed with time. Selected GISAXS patterns during thin-film formation process are shown in Fig. 1. In the first stage (from t = 0 to 110 s), an interaction peak was observed at q > 0.1 nm-1, the position of which is related to the main first neighbor distance D between the scatter structures in Nafion solution, and the peak position shifted towards larger q values with time. This indicates that solvent evaporation decreases the distance between the scatter structures in Nafion solution. At the second stage (from t = 110 to 135 s), the new peak of q z ~ 1.9 nm-1 (d ~ 3.3 nm) corresponding to so-called ionomer peak appeared. At the third stage (form t = 135 to 180 s), the interaction peak disappeared, and only the peak of qz ~ 1.9 nm-1 was observed, indicating that the ordered structure were fixed in solid-state thin film after the solvent evaporation. This work clearly indicates that second-scale nanostructural evolution of Nafion during the film forming process can be traced by utilizing synchrotron GISAXS/GIWAXS measurements. Further investigations on the effects of process parameters during film forming with a film applicator on nanostructural formation behaviors of Nafion are now in progress.This presentation is based on results obtained from the PEMFC Research and Development Program for “Highly‐Coupled Analysis of Phenomena in MEA and its Constituents and Evaluation of Cell Performance” commissioned by the New Energy and Industrial Technology Development Organization (NEDO). The synchrotron radiation experiments were performed at BL45XU in SPring-8 with the approval of JASRI (Proposal No.2015B1105). Figure 1

Analysis of Microscopic Strain and Crystalline Structure in Ge/Ge1−X Sn x Fine Structures by Using Synchrotron X-ray Microdiffraction

The strain engineering is a promising technology not only for low-power CMOS but also for optoelectronic applications of germanium (Ge) devices compatible with the conventional silicon (Si) process technology [1]. In terms of CMOS applications, a uniaxial compressive strained Ge has drawn attention as high-mobility channel material in p-MOSFET which is expected to transcend that of conventional strained Si channel [2]. We are focusing on germanium-tin (Ge1−x Sn x ) as a source/drain (S/D) stressors to apply a uniaxial compressive strain into Ge in analogy with Si1−x Ge x S/D for strained Si channel. However, there are few reports of the local epitaxial growth of Ge1−x Sn x on patterned Ge substrate and the local strain technology of the Ge/Ge1−x Sn x heterostructures. Since the recent device dimensions of Si CMOS devices have reached the sub-100 nm scale in accordance with Moore’s law, the investigation of the microscopic crystalline and the strain structures for various next generation semiconductor materials has grown increasingly important. In this study, we experimentally characterized the local strain structure in Ge/Ge1−x Sn x fine heterostructures by using synchrotron x-ray microdiffraction method [3,4]. We prepared Ge stripe structures with various line widths (25–100 nm) sandwiched with Ge1−x Sn x stressors. Patterned Ge(001) substrate with a SiO­ 2 cap layer was formed by anisotropic wet/dry etching as lines parallel along to the <110> direction. The pitch of a Ge stripe is 500 nm. The Ge1−x Sn x layers were grown with solid-source molecular beam epitaxy (MBE) system and metal-organic chemical vapor deposition (MOCVD) system [5]. The Sn content in the Ge1−x Sn x was 2.9–6.5%. The x-ray microdiffraction measurement was performed at the beamline BL13XU in SPring-8 to analyze the local strain distribution and crystalline structure in Ge/Ge1−x Sn x samples. A synchrotron radiation light with an energy of 8 keV (λ=0.155 nm) was used. The cross-section size of an incident x-ray microbeam was estimated to be 0.16×0.20–0.82×0.26 μm2 in preliminary experiments. Transmission electron microscope observations revealed that Ge1−x Sn x were epitaxially grown on both sides of a Ge line, while the crystalline structure of Ge1−x Sn x on SiO2 on the top of Ge line was polycrystalline. We consider that the stressors of locally grown epitaxial Ge1−x Sn x can induce a local strain into the Ge line. In order to directly characterize the in-plane strain status in strained Ge region, we examined two-dimensional reciprocal space mapping (2DRSM) around the Ge1—1—3 asymmetric Bragg reflection with step scans of the microbeam position across the Ge lines with a step of 50 nm. Three diffraction peaks related to the bulk Ge, the epitaxial Ge1−x Sn x stressors, and the strained Ge are clearly observed in 2DRSM results. The intensity of diffraction peak of the strained Ge periodically varied corresponds to the stripe pitches. The diffraction peak position of the strained Ge in 2DRSM indicates an in-plane compressive strain is induced into a Ge line sandwiched with Ge1−x Sn x stressors. From the 2DRSM results for various Ge stripe widths, an in-plane strain value can be estimated from the lattice spacing with respect to that of bulk Ge. The in-plane compressive strain value in the Ge increases with narrowing the Ge line width and increasing the Sn content in the Ge1−x Sn x stressors, which is consistent with the simulated results of finite element method calculations. For the Ge0.943Sn0.057 stressors, the in-plane compressive strains were estimated to be 0.84%, 0.46% and 0.38% for 30, 60, and 100 nm-wide Ge lines, respectively. In summary, the formation of Ge/Ge1−x Sn x fine heterostructures were achieved by MBE and MOCVD, and experimentally characterized the local strain distribution in the Ge/Ge1−x Sn x by synchrotron radiation microdiffraction method. The microdiffraction enables a quantitative analysis of strain and an investigation of local crystalline structure in sub-100 nm-scale Ge lines sandwiched with Ge1−x Sn x stressors. This work was partly supported by the JSPS through the FIRST Program initiated by the CSTP, a Grant-in-Aid for Scientific Research (S) (Grant No. 26220605) and Core-to-Core Program ICRC-ACP4ULSI from the JSPS in Japan. The synchrotron radiation experiments were performed at SPring-8 with the approval of JASRI (Nos. 2012B1783, 2013A1682, 2013B1779, 2015A1874, and 2015B1813/BL13XU). [1] S. Zaima et al., Sci. Technol. Adv. Mater. 16, 043502 (2015). [2] T. Krishnamohan et al., IEDM Proc., 899 (2008). [3] S. Takeda et al., Jpn. J. Appl. Phys. 45, L1054 (2006). [4] Y. Imai et al., AIP Conf. Proc. 1221, 30 (2010). [5] Y. Inuzuka et al., Thin Solid Films 602, 7 (2016).

Operando soft X-Ray Absorption and Raman Spectroscopic Study on Magnesium Deposition By Using Ether-Based Electrolyte

Magnesium rechargeable battery, which uses magnesium metal anode, is one of the candidates for the next generation batteries. The magnesium metal anode has a high theoretical volumetric capacity (3832 mAh/cm3), and relative low reduction potential (-2.356 V vs. standard hydrogen potential). However, conventional electrolytes consisting of inorganic salts and ester solvents, as widely used in lithium ion batteries, do not occur reversible deposition/dissolution of magnesium metal. This is because a passivation layer is formed at the magnesium metal anode surface that blocks both magnesium ions and electron transport. The limitation of available electrolytes prevents the magnesium battery from being used in a practical application.Recently, it has been reported that reversible magnesium deposition/dissolution reactions can occur in inorganic magnesium salts dissolved in glyme-based solvents electrolytes 2, 3. However, the reaction mechanism of magnesium metal anode has not been clearly understood. To clarify the reaction mechanism, it is necessary to investigate the interfacial structure of magnesium ion at anode/electrolyte interface. In this study, we investigated the bulk structure of the glyme-based electrolyte using Raman spectroscopy, X-ray absorption spectroscopy (XAS) and the theoretical calculation. Furthermore, we observed the electronic and local structure of the electrolyte at the interface during magnesium deposition using operando soft x-ray absorption spectroscopy.0.5 M Mg(TFSA)2/triglyme and 0.5 M Mg(TFSA)2/2-MeTHF electrolytes were prepared by stirring Mg(TFSA)2 with triglyme or 2-MeTHF in an Ar-filled glove box. Raman spectroscopic measurements were carried out using LabRAM HR-800 equipped with He-Ne laser (633 nm) at room temperature. operando XAS measurements at Mg K-edge were conducted at the beam line BL27SU at SPring-8 (Japan). XAS spectra were obtained at different potential during magnesium deposition. Magnesium deposition/dissolution occurred in Mg(TFSA)2/triglyme as observed in previous report3. In contrast to Mg(TFSA)2/triglyme, magnesium metal deposition did not observe in Mg(TFSA)2/2-MeTHF. Raman spectroscopy showed that TFSA anion exists as uncoordinated state with magnesium ion in the Mg(TFSA)2/triglyme, while TFSA anion strongly coordinates with magnesium ion in the 2-MeTHF-based electrolyte. operando Mg K-edge XAS observed that the local structure attributed to first coordination shell changed more smaller with decreasing potential in the Mg(TFSA)2/triglyme than in the Mg(TFSA)2/2-MeTHF at anode/electrolyte interface. In the Mg(TFSA)2/triglyme, the solvation structure of magnesium ion without coordination of TFSA anion, may suppress its local structure change during approaching the anode/electrolyte interface, resulting in the reversible magnesium deposition/dissolution. ACKNOWLEDGMENTS This study was partially supported by Synchrotron radiation experiment was performed at BL27SU of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI). REFERENCES [1] Aurbach, D.; Lu, Z.; Schechter, A.; Gofer, Y.; Gizbar, H.; Turgeman, R.; Cohen, Y.; Moshkovich M.; Levi, E., Nature, 2000, 407, 724-727.[2] Ha, S.-Y.; Lee, Y.-W.; Woo, S. W.; Koo, B.; Kim, J.-S.; Cho, J.; Lee, K. T.; Choi, N.-S., ACS Appl. Mater. Interfaces, 2014, 6, 4063-4073.[3] Orikasa, Y.; Masese, T.; Koyama, Y.; Mori, T.; Hattori, M.; Yamamoto, K.; Okado, T.; Huang, Z. -D.; Minato, T.; Tassel, C.; Kim, J.; Kobayashi, Y.; Abe, T.; Kageyama, H.; Uchimoto, Y., Sci. Rep., 2014, 4, 5622.

Electronic structure, Dirac points and Fermi arc surface states in three-dimensional Dirac semimetal Na3Bi from angle-resolved photoemission spectroscopy**Project supported by the National Natural Science Foundation of China (Grant No. 11574367), the National Basic Research Program of China (Grant Nos. 2013CB921700, 2013CB921904, and 2015CB921300), and the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant No. XDB07020300). The

The three-dimensional (3D) Dirac semimetals have linearly dispersive 3D Dirac nodes where the conduction band and valence band are connected. They have isolated 3D Dirac nodes in the whole Brillouin zone and can be viewed as a 3D counterpart of graphene. Recent theoretical calculations and experimental results indicate that the 3D Dirac semimetal state can be realized in a simple stoichiometric compound A3Bi (A = Na, K, Rb). Here we report comprehensive high-resolution angle-resolved photoemission (ARPES) measurements on the two cleaved surfaces, (001) and (100), of Na3Bi. On the (001) surface, by comparison with theoretical calculations, we provide a proper assignment of the observed bands, and in particular, pinpoint the band that is responsible for the formation of the three-dimensional Dirac cones. We observe clear evidence of 3D Dirac cones in the three-dimensional momentum space by directly measuring on the kx–ky plane and by varying the photon energy to get access to different out-of-plane kzs. In addition, we reveal new features around the Brillouin zone corners that may be related with surface reconstruction. On the (100) surface, our ARPES measurements over a large momentum space raise an issue on the selection of the basic Brillouin zone in the (100) plane. We directly observe two isolated 3D Dirac nodes on the (100) surface. We observe the signature of the Fermi-arc surface states connecting the two 3D Dirac nodes that extend to a binding energy of ∼150 meV before merging into the bulk band. Our observations constitute strong evidence on the existence of the Dirac semimetal state in Na3Bi that are consistent with previous theoretical and experimental work. In addition, our results provide new information to clarify on the nature of the band that forms the 3D Dirac cones, on the possible formation of surface reconstruction of the (001) surface, and on the issue of basic Brillouin zone selection for the (100) surface.

Study on Reaction Magnesium Deposition Mechanism By Operando Soft X-Ray Absorption Spectroscopy

Magnesium rechargeable batteries have much attention for next generation batteries because of the high theoretical volumetric capacity, safety, and abundance of magnesium metal anode. In order to improve the efficiency of magnesium metal anode, it is required to develop the electrolyte that enables magnesium deposition and dissolution reversibly. Although Grignard reagents have been widely known as the electrolyte for magnesium deposition/dissolution[1], the stability of the electrolytes in high potential and their corrosive nature are major problems. In recent years, magnesium deposition/dissolution in magnesium inorganic salts with triglyme solvents have been reported[2,3]. For the further development of electrolyte for magnesium batteries, the reaction mechanism at electrolyte/magnesium metal interface should be elucidated. In this study, we have developed operando soft X-ray measurement system and apply to the analysis of electronic and local structure of electrolyte during magnesium deposition. Furthermore, bulk structure of electrolyte is investigated by Raman spectroscopy, X-ray absorption spectroscopy (XAS) and the theoretical calculation. 0.5 M Mg(TFSA)2/triglyme and 0.5 M Mg(TFSA)2/2-MeTHF electrolytes were prepared by mixing Mg(TFSA)2 (KISHIDA CHEMICAL Co., Ltd., 99.9%>) with triglyme (KISHIDA CHEMICAL Co., Ltd. 99%>) or 2-MeTHF (Merck, 98%>) in an Ar-filled glove box. Electrochemical properties of the electrolyte were investigated by cyclic voltammetry (CV) with the three-electrode cell. Platinum plate and magnesium rod were used as working electrode and counter electrode, respectively. Operando XAS measurements at Mg K-edge were carried out at the beam line BL27SU at SPring-8 (Japan). XAS spectra were obtained at different potential during magnesium deposition. Raman spectroscopic measurements were carried out using LabRAM HR-800 (HORIBA, Ltd.) equipped with He-Ne laser (633 nm) at room temperature. While magnesium deposition/dissolution is observed in Mg(TFSA)2/triglyme and Grignard system, magnesium is not deposited in Mg(TFSA)2/2-MeTHF. From the results of Raman spectroscopy, TFSA anion exists as uncoordinated state with magnesium ion in the triglyme system, while TFSA anion coordinates with magnesium ion in the 2-MeTHF system. Fourier transform from Mg K-edge EXAFS oscillation measured at different potentials in 0.5 M Mg(TFSA)2/triglyme and 0.5 M Mg(TFSA)2/2-MeTHF indicate that peak intensity of Mg-O bond decreases with decreasing potential.The decreases of peak intensity reflect the desolvation process of triglyme and 2-MeTHF from magnesium ion. These results suggested that reason of high overpotential in 0.5 M Mg(TFSA)2/2-MeTHF is specific adsorption of TFSA anion. The specific adsorped TFSA anion may inhibits charge transfer raction of magnesium ion. ACKNOWLEDGMENTS This study was partially supported by the Research and Development Initiative for Scientific Innovation of New Generation Battery (RISING) Project under the auspices of New Energy and Industrial Technology Development Organization (NEDO), Japan. Synchrotron radiation experiment was performed at BL27SU of SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI). REFERENCES [1] Aurbach, D.; Lu, Z.; Schechter, A.; Gofer, Y.; Gizbar, H.; Turgeman, R.; Cohen, Y.; Moshkovich M.; Levi, E., Nature, 407, 724 (2000). [2] Ha, S.-Y.; Lee, Y.-W.; Woo, S.W.; Koo, B.; Kim, J.-S.; Cho, J.; Lee, K.T.; Choi, N.-S., ACS Appl. Mater. Interfaces 6, 4063 (2014). [3] Orikasa, Y.; Masese, T.; Koyama, Y.; Mori, T.; Hattori, M.; Yamamoto, K.; Okado, T.; Huang, Z. -D.; Minato, T.; Tassel, C.; Kim, J.; Kobayashi, Y.; Abe, T.; Kageyama, H.; Uchimoto, Y., Sci. Rep., 4, 5622 (2014).

(Invited) Chalcopyrites and III-V Semiconductors for Solar Water Splitting--a Detailed Look at the Electronic and Chemical Surface Structure

This presentation will discuss the chemical and electronic surface properties of Cu(In,Ga)(S,Se)2- and GaInP2-based materials in view of their use in solar water-splitting devices. Many of the primary requirements for photoelectrochemistry (such as efficiency and stability) are directly related to such properties, but it is generally quite difficult to paint a comprehensive surface picture, in particular in operando environments. The talk will focus on results obtained with a tool chest of soft x-ray and electron spectroscopies, with primary emphasis on high-brilliance synchrotron radiation experiments. It will be shown how photoelectron spectroscopy (PES), also under “ambient pressure” conditions, inverse photoemission (IPES), x-ray emission spectroscopy (XES), and x-ray absorption spectroscopy (XAS) can be suitably combined to derive surface electronic band gaps, study local chemical bonding and electronic level alignment, and gain insights into chemical stability.

Structural Origin of the Enhanced Glass-Forming Ability Induced by Microalloying Y in the ZrCuAl Alloy

In this work, the structural origin of the enhanced glass-forming ability induced by microalloying Y in a ZrCuAl multicomponent system is studied by performing synchrotron radiation experiments combined with simulations. It is revealed that the addition of Y leads to the optimization of local structures, including: (1) more Zr-centered and Y-centered icosahedral-like clusters occur in the microstructure; (2) the atomic packing efficiency inside clusters and the regularity of clusters are both enhanced. These structural optimizations help to stabilize the amorphous structure in the ZrCuAlY system, and lead to a high glass-forming ability (GFA). The present work provides an understanding of GFAs in multicomponent alloys and will shed light on the development of more metallic glasses with high GFAs.

An insulating-conductive transition driven by partial crystallization of amorphous Zn–Sn–O alloy

An insulating-conductive transition of Zn–Sn–O alloy is succeeded in this work driven by the partial crystallization out of the amorphous surrounding. The optimized room temperature mobility of 48 cm 2 V −1 s −1 and surface roughness of 0.3 nm are achieved in a 125-nm-thick film with a Sn cation composition of 0.44. To our knowledge, the mobility is superior to typical values of transparent conductive oxides under the criterion of a surface roughness less than 1 nm. Moreover, a proper mechanism that an oxygen-deficient amorphous surrounding with a strong ns -orbital overlapping of cations induced by the partial crystallization is the origin of the insulating-conductive transition has been demonstrated through synchrotron radiation experiments. In brief, the mechanism revealed in this work could provide effective information for new potentialities of fabricating transparent electrodes.

Fabrication of High Strength and Ductile Stainless Steel Fiber Felts by Sintering

Stainless steel fiber felts are important porous stainless steel products for a variety of industry applications. A systematic study of the sintering of 28-µm stainless steel fibers has been conducted for the first time, assisted with synchrotron radiation experiments to understand the evolution of the sintered joints. The critical sintering conditions for the formation of bamboo-like grain structures in the fiber ligaments were identified. The evolution of the number density of the sintered joints and the average sintered neck radius during sintering was assessed based on synchrotron radiation experiments. The optimum sintering condition for the fabrication of high strength and ductile 28-µm-diameter stainless steel fiber felts was determined to be sintering at 1000°C for 900 s. Sintering under this optimum condition increased the tensile strength of the as-sintered stainless steel fiber felts by 50% compared to conventional sintering (1200°C for 7200 s), in addition to much reduced sintering cycle and energy consumption.

Detecting Structural Features in Metallic Glass via Synchrotron Radiation Experiments Combined with Simulations

Revealing the essential structural features of metallic glasses (MGs) will enhance the understanding of glass-forming mechanisms. In this work, a feasible scheme is provided where we performed the state-of-the-art synchrotron-radiation based experiments combined with simulations to investigate the microstructures of ZrCu amorphous compositions. It is revealed that in order to stabilize the amorphous state and optimize the topological and chemical distribution, besides the icosahedral or icosahedral-like clusters, other types of clusters also participate in the formation of the microstructure in MGs. This cluster-level co-existing feature may be popular in this class of glassy materials.

Automated exploration of isomerization and dissociation pathways of ethylene sulfide cation by the global reaction route mapping method

Isomerization and dissociation reaction pathways of C2H4S+ associated with photoionization of c-C2H4S have been explored on the potential energy surfaces by the global reaction route mapping (GRRM) method. Reaction channels yielding C2H3S+, HCS+, H2S+, C2H3+, and C2H2S+ were disclosed. Calculated values of energy barriers to transition states and direct dissociation energies gave theoretical supports to recent synchrotron radiation experiments generating HCS+ and C2H3S+.

A device for the application of uniaxial strain to single crystal samples for use in synchrotron radiation experiments.

We present the design, construction, and testing of a straining device compatible with many different synchrotron radiation techniques, in a wide range of experimental environments (including low temperature, high field and ultra-high vacuum). The device has been tested by X-ray diffraction on single crystal samples of quasi-one-dimensional Cs2Mo6Se6 and K2Mo6Se6, in which microscopic strains up to a Δc/c = 0.12% ± 0.01% change in the c lattice parameters have been achieved. We have also used the device in an inelastic X-ray scattering experiment, to probe the strain-dependent speed of sound ν along the c axis. A reduction Δν/ν of up to -3.8% was obtained at a strain of Δc/c = 0.25% in K2Mo6Se6.