Article

Performance of a high resolution, high flux density SGM undulator beamline at the ALS

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Abstract

The performance of ALS beamline 7.0 is described. This is an integrated system for delivering radiation from a 5 cm period undulator to spectroscopy and microscopy experiments across the range of photon energies from 60 to 1200 eV. The beamline is engineered to deliver the highest possible flux, with negligible deformation of the optic surfaces due to heating. Two experiment stations are served with rapid interchangeability. The measured operational parameters, the resolution and flux delivered, and the refocus of the light into a small spot at the experiment are all discussed. © 1995 American Institute of Physics.

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... Similar to Li on other metals [13], we estimate that at this coverage only about 85% of the surface W or Mo atoms will be fully coordinated with Li. Angle-resolved photoemission (ARP) measurements were performed in situ at beam line 7.0 of the Advanced Light Source [14] with photon energy 100.00 eV; other experimental details are described elsewhere [15]. Analysis of surface core level shifts (Mo 3d, W 4f, Li 1s) implies uniform, 2-dimensional growth, and rules out reconstructions, clustering , etc., consistent with growth on many other closepacked surfaces [13].Figure 1(a) shows clean W(110) valence band spectra as a function of polar angle 15 ± , u , 35 ± , from the boundary of the first surface Brillouin zone (SBZ) (S) to the center of the second SBZ (G 1 ). ...
Article
The broken symmetry at surfaces can give rise to a nonzero spin-orbit splitting of valence bands. We observe such a splitting of the d -derived surface state on W(110) and, to a lesser extent, on Mo(110), and follow the evolution of the splitting as monovalent atoms are adsorbed. The observed evolution is directly relevant to recent observations of altered orbital magnetic structure versus adsorbate coverage in magnetic materials. We propose a spin ordering for the associated Fermi contours which has important implications for spin excitations at surfaces. {copyright} {ital 1999} {ital The American Physical Society}
... The experiments were carried out at beamline 7.0 chromatic SR excitation [5]. It is of great interest to at the Advanced Light Source (ALS) at the Lawrence find out how the resonant and non-resonant spectra Berkeley National Laboratory [15]. This undulator show up in more complicated hetero-compounds, beamline includes a spherical-grating monochromator and provides linearly polarized SR of high resolution and high brightness. ...
... The spectral shape of the Cu 2p absorption edge and the chemical shift of the main absorption line served as a tool in monitoring the changes during the reaction. The Cu 2p absorption spectra were measured on beam-line 7.0 [10] at the advanced light source (ALS) at Lawrence Berkeley National Laboratory using a spherical grating monochromator, which gave a resolution of 200 meV at the Cu 2p 3/2 peak of CuO ($931 eV). The Xray absorption spectra were recorded in total fluorescence yield (TFY) mode under high vacuum conditions ($10 À10 torr). ...
Article
This study illustrates how the damage from copper corrosion can be reduced by modifying the chemistry of the copper surface environment. The surface modification of oxidized copper films induced by chemical reaction with Cl− and HCO3- in aqueous solutions was monitored by in situ X-ray absorption spectroscopy. The results show that corrosion of copper can be significantly reduced by adding even a small amount of sodium bicarbonate. The studied copper films corroded quickly in chloride solutions, whereas the same solution containing 1.1mM HCO3- prevented or slowed down the corrosion processes.
... The question that this work seeks to answer is long-standing: what is the molecular-level explanation for the observed entropy of mixing when water and methanol are mixed? The experiments were performed at beamline 7.0 at the Advanced Light Source (ALS), Lawrence Berkeley National Laboratory [5]. A thin window (100 nm silicon nitride), separating the liquid from the surrounding vacuum, is penetrated both by the exciting synchrotron radiation and the secondary X-ray emission. ...
Article
We have examined the influence of the intermolecular interaction on the local electronic structure by using X-ray absorption and emission spectra of liquid methanol, water, and their mixtures (in molar ratios of 9:1 and 7:3). We find a strong involvement of hydrogen bonding in the mixing of water and methanol molecules. The local electronic structure of water and methanol clusters, where water cluster is bridging within a 6-member open-ring structured methanol cluster, is separately determined. The experimental findings suggest an incomplete mixing of water–alcohol systems and a strong self-association between methanol chain and water cluster through hydrogen bonding. The enhancement of joint water–methanol open-ring structure owes the explanation to the loss of entropy of the aqueous solutions.
... [18] The experiments were performed at beamline 7.0 of the Advanced Light Source (ALS) in the Lawrence Berkeley National Laboratory [Warwick et al., 1995]. A spherical grating monochromator incorporated in the beamline can produce an incident photon beam with energies between 80 eV and 1200 eV. ...
Article
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Paleoproterozioc (ca. 1.9 Ga) stromatolites from the Biwabik Iron-Formation (Minnesota, United States) contain fossil forms which in the literature have been attributed to ancient microbes including iron-oxidising bacteria and cyanobacteria. To search for valence state fossils, we measured Fe3+/SigmaFe (SigmaFe = Fe2+ + Fe3+) transverse to the laminae of a Biwabik, probably biogenic stromatolite and compared the results with a scan across the enclosing, likely abiotic sedimentary rock (or interstromatolite fill). To obtain Fe3+/SigmaFe and information about the site symmetry and crystal field strength, we used L3 (2p3/2 -> 3d) soft X-ray absorption spectroscopy and interpreted the measurements using our calculated spectra. We found that Fe3+/SigmaFe is approximately constant at 0.3 within the stromatolite, increases steeply to around 0.6 in the region of the stromatolite-fill boundary, and then reduces significantly in the interstromatolite fill. The crystal field strength for octahedral Fe3+ increased and became more irregular as the scan moved from the stromatolite into the fill. Our results tentatively suggest that a combination of ancient biological and later diagenetic processes can produce steep gradients in Fe3+/SigmaFe and alterations in the crystal field strength across a probable abiotic-biotic boundary. To describe the L3 absorption spectra in the stromatolite-fill region, it was necessary to include a significant Fe3+ tetrahedral component, which suggests the presence of magnetite. At other positions, fits using only octahedral Fe2+ and Fe3+ theoretical curves satisfactorily reproduce the spectra. The search for a possible new type of spatial biosignature in the valence state record for ancient stromatolites might help differentiate between the biogenic stromatolites and abiogenic stromatolite-like structures and could even be relevant to the search for fossil evidence of life in extraterrestrial rocks.
... The experiments were performed at undulator beamline 7.0 of the Advanced Light Source, Lawrence Berkeley National Laboratory, with a spherical grating monochromator. 3 The preparation and characterization of the La 0.5 Ca 0.5 MnO 3 thin film which was used in present measurements is described in Ref. 2. The Mn 2p X-ray absorption spectrum of this film was measured at normal incidence of the photon beam to a sample surface using a total-electron-yield mode. The resolution of the monochromator was set to 0.4 eV. ...
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Resonant soft X-ray scattering spectra of a La0.5Ca0.5MnO3 thin film were measured at varying energies of the incident photon beam across Mn 2p thresholds. The data are analyzed within the framework of the Anderson impurity model and full multiplet theory. The scattering profiles of the film are reasonably well reproduced by model calculations for the Mn3+ system, in contrast to the absorption spectrum at the Mn L2,3 edge for which the contribution of the Mn4+ sublattice is required to be taken into account. The obtained agreement between calculations and experiment indicates that in this case resonant inelastic scattering mainly probes the local electronic structure at the Mn3+ sites in the La0.5Ca0.5MnO3 film. In turn, Mn4+ sites mainly contribute to ordinary Lα,β X-ray emission due to relaxations in the intermediate state of the spectroscopic process. Such a situation can occur when the system favors a phase separation rather than checkerboard charge ordering of Mn3+ and Mn4+ sites.
... The experiments were performed at beamline 7.0.1 [5] at Advanced Light Source, Lawrence Berkeley National Laboratory. ...
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Resonant inelastic x-ray scattering (RIXS) has been applied to the studies of dd excitations in MnO and SrCuO 2 Cl 2 [1,2]. The lowest-lying electronic excitations can be studied most directly by charge neutral spectroscopies, such as electron energy-loss spectroscopy (EELS) and optical absorption. The dd excitations in transition metal compounds are dipole forbidden and therefore very faint in optical spectroscopy. α-Fe 2 O 3 is an antiferromagnetic charge transfer insulator with a bandgap of 2.1 eV. Hematite crystallises in the trigonal system, rhombohedral R-3c group. The crystal structure is the corundum type (Al 2 O 3) and can be described as a hexagonal close packed layering of oxygen with 6-fold co-ordinated iron ions yielding to face and edge-sharing octahedra. In an octahedral symmetry, a d 5 -configuration is found to have well-separated dd-excitations. Optical absorption spectroscopy of α-Fe 2 O 3 has revealed many transitions ranging from infrared to ultraviolet. Using the RIXS process, we probed specifically the dd excitations in α-Fe 2 O 3 by transition sequence 2p 6 3d 5 → 2p 5 3d 6 → 2p 6 3d 5 . These dd transitions become fully allowed, and their intensity can be more easily calculated than that in optical spectroscopy and EELS.
... The experiments were performed at beamline 7.0 of the Advanced Light Source, Lawrence Berkeley National Laboratory with a spherical grating monochromator [5]. The scattering spectra of Ce-based materials were recorded using a grazing-incidence grating spectrometer [6] with a twodimensional detector. ...
Article
INTRODUCTION As previously demonstrated [1], resonant inelastic x-ray scattering spectroscopy at some core thresholds is an efficient tool for probing both intra-atomic neutral and inter-atomic charge-transfer excitations in rare-earth compounds. As a result of creation-annihilation of a core hole there are radiative transition back to the ground and low-lying excited states so that the final states of the spectroscopic process can be described as eigenvalues of the ground state Hamiltonian. For correlated systems with significant configurational mixing in the ground state, resonant x-ray scattering spectra can be interpreted within the framework of a localized, many-body approach based on a single-impurity Anderson model (SIAM). The ground state values of the charge-transfer energy and hybridization strength which are used as model parameters to characterize charge-transfer excitations can be estimated with higher accuracy from analysis of these data. The SIAM is very often used for the description of various transport and spectroscopic properties of Ce-and Yb-based systems with the pronounced heavy fermion behavior [2]. The model predicts a significant temperature dependence of the f occupancy which value is crucial for the interpretation of various physical properties. However, the validity of the SIAM for heavy fermions has been questioned [3] based on the inconsistency of experimental data obtained by electron spectroscopies. In particular, the existence or lack of the Kondo resonance in valence-band photoemission spectra of heavy fermion materials is heavily debated. A large surface contribution to the spectra often complicates the analysis of the bulk component. In this case, the bulk sensitivity and element-specific nature of resonant soft-x-ray scattering spectroscopy is particularly useful. This abstract presents soft-x-ray scattering data recorded at different excitation energies across the Ce 4d absorption edges of CeB 6 , CeAl, γ-Ce, and α-Ce.
... Measurements of XAS and XES at the V L 2,3 -edges and O K-edge were made at beamline 7.0.1 at the Advanced Light Source of Lawrence Berkeley National Laboratory. 21 The XAS spectra were obtained in the total electron yield mode by measuring the sample drain current during the scanning of the photon energy of the incident monochromatic X-ray. The XAS spectra were normalized to the photon current from a clean gold mesh to account for the variations in the intensity of the incident beam, and the energy was calibrated using an NiO single crystal. ...
Article
Gasochromic VO2 thin films were fabricated by the sol-gel spin-coating technique. The results of X-ray absorption spectroscopy and resonant inelastic x-ray scattering spectroscopy reveal that the origin of gasochromic coloration in VO2 is strongly related to the modulation of its structure and the electron-electron correlation. Upon gasochromic coloration, not only does the valence state change with the incorporation of hydrogen, but also the film undergoes the modification of local atomic structure. The structural distortion varies the strength of hybridization of the O 2p - V 3d states and the bond distance of V-O and V-O varies. In the hydric process, the local atomic structure of VO2 changes from that of an un-symmetric to that of a symmetric V-O framework. The incorporated hydrogen adds electrons into the V 3d t2g orbital, enhancing the electron-electron correlation by reducing the V-V distance. This work presents a new physical insight in which modulation of the electron-electron correlation is exploited to control the bleached and colored states, giving rise to the gasochromic phenomenon. The strong correlation among atomic spatial rearrangement, electronic structures, and transmittance supports a cooperative mechanism of the VO2 gasochromic transition. These results reveal a clear correlation between the dynamics of the lattice structure and the electronic properties and suggest a possible pathway to gasochromism and elucidation of its mechanism.
... Beamline10.0.1 at the Advanced Light Source (ALS), Lawrence Berkeley National Laboratory (LBNL), is a high flux high-resolution undulator beamline 1 . Very intense synchrotron radiation generated by the 4.5 m long undulator with 10 cm periodicity (U100) is delivered to various experimental endstations located at three different branchlines. ...
Article
Beamline 10.0.1 delivers the photons from a 4.5 m long 10 cm periodicity undulator (U100) to various endstations in its three branchlines. The beamline uses a spherical grating monochromator (SGM) to produce high energy resolution photon beam, with three gratings to cover the photon energy range from 17 to 340 eV. Typically, angle-resolved photoemission (ARPES) measurements use 30-70 eV photons. The beam size at the High Energy Resolution Spectroscopy (HERS) endstation, designed for ARPES, is measured to be 250 μm (H) by 100 μm (V). Due to grazing incidence geometry in the HERS endstation, the photon beam will have a large projection on the sample surface which could lead to degradation of experimental resolutions. We are in the process of designing and replacing some of the existing mirrors to improve the focus spot at HERS endstation. The detailed design parameters and possible upgrade paths will be presented with verifications using SHADOW ray-tracing program.
... The experiments were performed at undulator beamline 7.0 [57] of the Advanced Light Source (ALS), Lawrence Berkeley National laboratory, employing a spherical grating monochromator and at undulator beamline I511-3 [58] of the Swedish synchrotron facility MAXLAB, which was equipped with plane-grating monochromator SX-700. Resonant ultrasoft X-ray scattering spectra from the samples were recorded using a grazing-incidence grating spectrometer [59] with a two-dimensional detector. ...
Chapter
Resonant inelastic X-ray scattering (RIXS) measurements at the actinide 5d threshold provide an opportunity to study elementary excitations in actinide systems in detail. It has turned out that the technique is very sensitive to the valency and the chemical state of actinide in contrast to X-ray absorption spectroscopy, being hampered by the substantial smearing of spectral structures due to a large core-hole lifetime broadening. In this situation, the virtually unlimited resolution (defined by the response function of the instrument) of the RIXS technique and its ability to enhance transitions to low-lying excited states are especially useful. RIXS spectroscopy provides good signatures in terms of new distinct transitions, representing electronic excitations within the 5f shell and having a characteristic profile. This helps to distinguish between actinide species with different oxidation states, especially in the case when one of the species has a much lower concentration than another. Experimental data for systems of light actinides, such as U, Np, and Pu, are presented and discussed along with the results of model calculations.
... Experiments in the energy range of the U N 4,5 (4d → 5f, 7p transitions) and N 6,7 (4f → 6d, 5g transitions) edges of UO 2 were performed at beamline 7.0.1 of the Advanced Light Source of Lawrence Berkeley National Laboratory, employing a spherical grating monochromator. 22 U 4d and 4f XAS data were measured in the TEY mode using drain current on the sample. The incidence angle of the incoming photons was close to 90°to the surface of the samples. ...
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A systematic x-ray absorption study at the U $3d$, $4d$ and $4f$ edges of UO$_2$ was performed and the data were analyzed within framework of the Anderson impurity model. By applying the high-energy-resolution fluorescence-detection (HERFD) mode of x-ray absorption spectroscopy (XAS) at the U $3d_{3/2}$ edge and conducting the XAS measurements at the shallower U $4f$ levels, fine details of the XAS spectra were resolved resulting from reduced core-hole lifetime broadening. This multi-edge study enabled a far more effective analysis of the electronic structure at the U sites and characterization of the chemical bonding and degree of the $5f$ localization in UO$_2$. The results support the covalent character of UO$_2$ and do not agree with the suggestions of rather ionic bonding in this compound as expressed in some publications.
... The soft x-ray absorption and emission measurements were performed at beamline I511-3 [36], of MAX-Lab, Lund, Sweden and beamline 7.0.1 [37] at the Advanced Light Source (ALS), Berkeley, CA, USA. Beamline 7.0.1 employs a spherical-grating monochromator with fixed entrance slit and sliding exit slit while beamline I511-3 is equipped with a SX-700 plane-grating monochromator. ...
Article
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Soft x-ray emission and absorption spectroscopic data are reported for the O 1s region of a single crystal of UO2, a polycrystalline NpO2 sample, and a single crystal of PuO2. The experimental data are interpreted using first-principles correlated-electron calculations within the framework of the density functional theory with added Coulomb U interaction (DFT+U). A detailed analysis regarding the origin of different structures in the x-ray emission and x-ray absorption spectra is given and the effect of varying the intra-atomic Coulomb interaction-U for the 5 f electrons is investigated. Our data indicate that O 1s x-ray absorption and emission spectroscopies can, in combination with DFT+U calculations, successfully be used to study 5 f -shell Coulomb correlation effects in dioxides of light actinides. The values for the Coulomb U parameter in these dioxides are derived to be in the range of 4-5 eV.
... Experiments at the Ce M 4,5 edges (3d → 4f , 6p transitions) of CeO 2 were performed at beamline 7.0.1 of the Advanced Light Source, Lawrence Berkeley National Laboratory (20). The data were measured in the total electron yield (TEY) mode, using drain current from the sample. ...
Article
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Significance This work is to our knowledge the first illustration of the ability of the high-energy resolution fluorescence-detection X-ray absorption spectroscopy (HERFD-XAS) technique to directly probe the crystal-field splitting in the 5 f shell of actinides. This is a breakthrough for actinide science, allowing for the easy extraction of desired information from the spectroscopic method, which is easy to interpret and to calculate. Furthermore, the HERFD-XAS technique allows us to resolve the charge-transfer satellites in actinide spectra that were hidden before, thus enhancing the sensitivity to the covalent character of the chemical bonding. Using ThO 2 as an example, we show that other common techniques underestimate the crystal-field strength and that ThO 2 is not an anionic compound as previously believed.
... Experimental RIXS experiments were conducted on beamline 7.0.1 [14] at the Advanced Light Source. The photon energy resolution was set to 0.2 eV for XAS measurements at the Fe L-edge. ...
Article
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The problem of resolving molecular components of the electronic structure of complex, organic solids with respect to their chemical and orbital character has been approached using core-level photon spectroscopies. Specifically, the bulk C 2poccupied and unoccupied partial densities of states (PDOS) of the organic superconductorsκ-ET2Cu(SCN)2andκ-ET2Cu[N(CN)2]Br were measured using a combination of high-resolution soft X-ray absorption (SXA) and soft X-ray emission (SXE). The PDOS was also calculated using a tight binding model, and the measured spectra compared directly to that predicted by the calculations. The emission and absorption spectra from both materials were found to be quite similar, reflecting mostly contributions from the common conductive ET layers. The presence of two nonequivalent carbon sites of the ET molecule was identified in the SXA spectra. Contributions from theπandσstates were identified in the emission spectra. The occupied C 2pbandwidth was found to be approximately 17eV. An observed dependence of the SXE spectra on the excitation energy is partly accounted for by a simple model that considers the presence of the two nonequivalent ET carbon sites. We also find evidence in the SXE spectra for a high degree of localization in the lowest unoccupied states.
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This is a mini-review about the development of various cells built over the years for in situ electronic structure study of gas molecules, molecular liquids, gas/solid and liquid/solid interfaces. In the study of gas molecules, the role of the parity selection rule in the case of homonuclear diatomic molecules (N2 and O2) is revealed and illustrated by the resonant X-ray emission spectra, while the occurrence of forbidden transitions in CO2 is explained in terms of dynamical symmetry breaking due to vibronic coupling. X-ray emission spectroscopy has been used to elucidate the molecular structure of liquid water, liquid methanol, methanol–water mixtures, as well as cation–water solutions, and to reveal the influence of the intermolecular interaction on the local electronic structure of water molecules. The in situ soft X-ray spectroscopy experimental studies of electrochemical reactions were also performed under ambient conditions.
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The dynamic physiochemical response of a functioning graphene-based aerogel supercapacitor is monitored in operando with soft X-ray spectroscopy and interpreted through ab initio atomistic simulations. Unanticipated changes in the electronic structure of the electrode as a function of applied voltage bias indicate structural modifications across multiple length scales via independent pseudocapacitive and electric double layer charge storage channels. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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Nitrogen-doped TiO2 nanoparticles with visible-light absorption properties were investigated with x-ray absorption and emission spectroscopy. The results indicate the substitution of nitrogen on the oxygen sites which are bonded to titanium atoms in the TiO2 host. The nitrogen dopant does not apparently change the crystal field nor the contribution of the O orbitals to the electronic structure of the TiO2 host, but alters slightly the Ti component of the electronic structure of the TiO2 host. Such a doping effect is likely to be the explanation for the visible-light absorption properties of the nitrogen-doped TiO2 nanoparticles.
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Both synchrotron radiation based soft-X-ray absorption spectroscopy (XAS) and resonant soft-X-ray emission spectroscopy (XES) on a variety of nano-structured systems has yielded characteristic fingerprints. With high-resolution monochromatized synchrotron radiation excitation, resonant inelastic X-ray scattering (RIXS) has emerged as a new source of information about electronic structure and excitation dynamics of nanomaterials. The selectivity of the excitation, in terms of energy and polarization, has also facilitated studies of emission anisotropy. Various features observed in resonant emission spectra have been identified and studied.
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We have synthesized core/shell/shell (CSS) CdSe/ZnSe/ZnS quantum dots (QDs) and investigated their exciton dynamics using time correlated single photon counting (TCSPC). The unique synthetic method combines hot injection with successive injection of precursors in one pot. Transmission electron microscopy (TEM) shows that CSS QDs were 6 ± 2 nm in diameter. The elemental composition, determined by energy dispersive X-ray spectroscopy, was 3.3% cadmium, 8.6% selenium, 42.3% sulfur, and 45.8% zinc by mole. Photoluminescence spectroscopy (PL) showed that the PL quantum yield is increased from 0.9% for CdSe to 25% for CSS. Global fitting was used for the analysis of exciton dynamics for CdSe, CdSe/ZnS core/shell, and CSS QDs. The decays of the PL spectra for CdSe and CdSe/ZnS were fit with triple exponentials with lifetimes of 0.7, 8, and 30 ns and 0.7, 10, and 30 ns respectively, while the CSS spectrum was fit with a double exponential with lifetimes of 12 and 30 ns. We attribute the 0.7 ns component to nonradiative recombination through dangling bonds at the CdSe surface or at crystal lattice dislocations at the CdSe/ZnS interface. This study clearly demonstrates that the CSS approach can be used to substantially improve the optical properties of QDs desired for various applications.
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The authors show an experimental setup to carry out soft-x-ray fluorescence spectroscopy of liquids under an ultrahigh vacuum (UHV) condition. The flow liquid cell has a window to attain compatibility with UHV conditions of the fluorescence spectrometer and synchrotron radiation beamline. The soft-x-ray photons enter the liquid cell through a 100 nm thick silicon nitride window, and the emitted soft x rays exit through the same window to be detected by photon diode and microchannel plate detectors. This setup allows liquids and, in particular, liquid-solid interfaces to be studied. Such a liquid cell has been used to study the electronic structure of a variety of systems ranging from water solutions of inorganic salts and nanomaterials under wet conditions.
Performance of future generations of integrated circuits will be limited by the RC delay caused by on-chip interconnections. Overcoming this limitation requires the deployment of new high conductivity metals such as copper and low dielectric constant intermetal dielectrics (IMD). Fluorinated amorphous carbon (a-CFx) is a promising candidate for replacing SiO2 as the IMD. In this paper we investigated the structure and electronic properties of a-CFx thin films using high-resolution x-ray absorption, emission, and photoelectron spectroscopy. The composition and local bonding information were obtained and correlated with deposition conditions. The data suggest that the structure of the a-CFx is mostly of carbon rings and CF2 chains cross-linked with C atoms. The effects of growth temperature on the structure and the thermal stability of the film are discussed.
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ZnSn1-x Gex N2 direct bandgap semiconductor alloys, with a crystal structure and electronic structure similar to InGaN, are earth-abundant alternatives for efficient, high-quality optoelectronic devices and solar energy conversion. The bandgap is tunable almost monotonically from 2 eV (ZnSnN2 ) to 3.1 eV (ZnGeN2 ) by control of the Sn/Ge ratio.
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We present a novel in situ reaction cell for heterogeneous catalysis monitored in situ by x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS). The reaction can be carried out at a total pressure up to 1 atm, a regime that has not been accessible to comparable in situ techniques and thus closes the pressure gap to many industrial standard conditions. Two alternate catalyst geometries were tested: (A) a thin film evaporated directly onto an x-ray transparent membrane with a flowing reaction gas mixture behind it or (B) a powder placed behind both the membrane and a gap of flowing reaction gas mixture. To illustrate the working principle and feasibility of our reaction cell setup we have chosen ethylene epoxidation over a silver catalyst as a test case. The evolution of incorporated oxygen species was monitored by total electron/fluorescence yield O K-XAS as well as O K-RIXS, which is a powerful method to separate contributions from inequivalent sites. We find that our method can reliably detect transient species that exist during catalytic reaction conditions that are hardly accessible using other spectroscopic methods.
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The electronic structure of single-crystal PuO2 is studied using O 1s x-ray absorption (XA) and x-ray emission. Interpretation of the experimental data is supported by extensive first-principles calculations on the basis of the densityfunctionaltheory+U approach. The measured XA spectra show a significant difference in intensity for the first two peaks between different spots or areas on the single crystal. Our theoretical simulations show that the first peak, at ~531 eV, can be attributed to O 2p-Pu 5f hybridization, while the second peak, at ~533.4 eV, is due to hybridization of O 2p with Pu d states. The reasons for the observed differences in the O 1s XA spectra are explored by calculating a number of defect structures PuO2±x as well as by simulating the existence of Pu(V) sites. Our results indicate the presence of oxidation states higher than Pu(IV) in some areas of the single crystal. The findings also suggest that plutonium oxide with a Pu fraction in an oxidation state higher than Pu(IV) consists of inequivalent Pu sites with Pu(IV)O2 and Pu(V)O2 rather than representing a system where the Pu oxidation state is constantly fluctuating between Pu(IV) and Pu(V).
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The study addresses the possibilities of immobilizing the mobile species of actinides in the geosphere using metallic iron. Sorption on corroding iron is well known, but there have been uncertainties as to the possibilities of reducing the actinyl species to sparingly soluble oxides and, thereby, permanently immobilizing them. Resonant inelastic x-ray scattering (RIXS) measurements at the actinide 5d edges on Fe foils exposed to U(VI) and Np(V) solutions in ground water unambigiously indicate reduction of actinides to respectively U(IV) and Np(IV) on iron surfaces. The reduction manifests itself in an appearance of distinct specific signatures of U(IV) and Np(IV) in the RIXS profile of 5f-5f excitations. Such signatures and RIXS intensity/cross-section behaviour with varying energy of incident photons can be reproduced by model atomic-multiplet calculations of the RIXS spectra. By normalizing the RIXS signal of corresponding 5f-5f excitations to core-to-core 6p-to-5d characteristic fluorescence transitions of actinides, their reduction rates on Fe samples with different exposure to actinide solutions can be estimated. Observed reduction implies similar processes in the nuclear waste canister thus suggesting reduced probability of nuclear waste release with ground waters from the canister.
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An overview is presented of the theory of X-ray Raman scattering. Second-order perturbation theory for the interaction between matter and light is used as a common starting point, and the consequences of this theory are analytically and numerically analyzed for a variety of experimental situations. The review focuses on results from radiative and nonradiative scattering experiments conducted with 2nd and 3rd generation synchrotron radiation sources during the last couple of years, dealing with atomic, molecular, solid state and surface adsorbate targets. After giving a brief synopsis of relevant experimental techniques, some basic theoretical concepts and principles of X-ray Raman scattering are described, followed by a presentation of the various particular aspects associated with the resonant X-ray scattering process. That is: polarization – interference – role of symmetry – symmetry breaking and energy dependence – dissociation and time dependent interpretations – duration time and frequency detuning – formation of band profiles – Doppler effects – screening and chemical shifts – elastic scattering – solid state theory – application to surface adsorbates – absorption in the Raman mode – direct processes versus resonant X-ray scattering – many channel theory. Each aspect is described by a qualitative picture, a mathematical analysis, and by illustrative examples from experiment combined in some cases with results from simulations. Simple systems are chosen to demonstrate the consequences of various aspects of the theory.
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We demonstrate how X-ray emission spectroscopy can be used to elucidate the molecular structure of liquid water, liquid methanol, methanol–water mixtures, as well as cation-water solutions, and to reveal the influence of the intermolecular interaction on the local electronic structure of water molecules. By comparing X-ray emission spectra of the water molecule and liquid water, a strong involvement of the total-symmetric valence-orbital is found in the hydrogen bonding. The local electronic structure of water molecules under different broken hydrogen bonding situations can be separately determined. We find that molecules in the pure liquid methanol in a confined sample cell predominantly persist as hydrogen-bonded chains and rings with six and/or eight molecules of equal abundance. For water methanol solutions the evidence of incomplete mixing is observed at the microscopic level, which provides a new explanation for a smaller entropy increase in the solution due to water molecules bridging methanol chains to form rings. Further, the influences of cations on the water molecular structure have been studied by the X-ray absorption and emission spectra.
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Covalent chemical modification is a powerful strategy for endowing low-cost graphitic carbon substrates with designer functionality. However, the surface chemistry of carbon is complex, making it difficult to tailor carbon materials with molecular level precision. Herein, we establish a new chemical modification strategy that generates strong aromatic linkages to carbon surfaces. In particular, we show that condensation of amidine-containing molecules with oxidic edge defects on carbon surfaces generates well-defined pyrimidine and imidazole linkages. X-ray photoelectron and nitrogen K-edge X-ray absorption near-edge structure spectroscopies along with time-of-flight secondary ion mass spectrometry tandem MS analysis establish the molecular structures of the surface linkages. We find that the ring structure and nucleophilicity of the precursor molecule guides the selectivity of the surface condensation reaction, with 5-5 ring strain driving selective condensation to form pyrimidine linkages on zigzag edges. This work establishes new methods for functionalizing and analyzing carbon surfaces at the molecular level.
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The design of VUV beamlines for the Advanced Light Source is discussed. Features of the design serve to illustrate the careful attention required in order to preserve the performance of the low emittance ``third generation`` storage ring, operating with insertion devices. 11 refs.
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The Advanced Light Source (ALS), which is currently being commissioned at Lawrence Berkeley Laboratory, is a third generation light source designed to produce XUV radiation of unprecedented brightness. To meet the high brightness goal the storage ring has been designed for very small electron beam emittance and the undulators installed in the ALS are built to a high degree of precision. The allowable magnetic field errors are driven by electron beam and radiation requirements. Detailed magnetic measurements and adjustments are performed on each undulator to qualify it for installation in the ALS. The first two ALS undulators, IDA and IDB, have been installed. This paper describes the program of measurements, data analysis, and adjustments carried out for these two devices. Calculations of the radiation spectrum, based upon magnetic measurements, are included. Final field integral distributions are also shown. Good field integral uniformity has been achieved using a novel correction scheme, which is also described.
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Key technical and strategic choices are reviewed, leading to the fabrication method of ion-milled grating grooves for the monochromators at the Advanced Light Source (ALS) at Lawrence Berkeley Laboratory (LBL), and for other synchrotrons. Several laboratories and their industrial partners have joined to manufacture gratings with close to theoretical performance. Metrology data and theoretical comparisons are given for square wave profile grating samples ion-milled into electroless nickel surfaces. The extensive capabilities in mirror and grating manufacture and metrology made available in recent years at laboratory and industrial facilities are reviewed.
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In order to facilitate the accurate calculation of diffraction grating efficiencies in the soft x-ray region, we have implemented the differential method of Neviere and Vincent in Mathematica [1]. This simplifies the programming to maximize the transparency of the theory for the user. We alleviate some of the overhead burden of the Mathematica program by coding the time-consuming numerical integration in C subprograms. We recall the differential method directly from Maxwell`s equations. The pseudo-periodicity of the grating profile and the electromagnetic fields allows us to use their Fourier series expansions to formulate an infinite set of coupled differential equations. A finite subset of the equations are then numerically integrated using the Numerov method for the transverse electric (TE) case and a fourth-order Runge-Kutta algorithm for the transverse magnetic (TM) case. We have tested our program by comparisons with the scalar theory and with published theoretical results for the blazed, sinusoidal and square wave profiles. The Reciprocity Theorem has also been used as a means to verify the method. We have found it to be verified for several cases to within the computational accuracy of the method.
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Design analyses using finite-elements methods are presented for thermal distortion of water-cooled diffraction grating substrates for a potential application at the LBL Advanced Light Source, demonstrating that refinements in cooling channel configuration and heat flux distribution can significantly reduce optical surface distortion with high heat loads. Using an existing grating substrate design, sensitivity of tangential slope errors due to thermal distortion is evaluated for a variety of thermal boundary conditions, including coolant flow rate and heat transfer film coefficients, surface illumination area and heat distribution profile, and location of the convection cooling surface adjacent to the heated region.
Article
A 55 meter spherical grating monochromator has been completed at the Stanford Synchrotron Radiation Laboratory (SSRL). The monochromator includes a unique capability for water cooled gratings, and is presently operating with a fused silica grating from 180 to 820 eV. A resolution of 60 meV has been achieved at 400 eV, inferred from the linewidths of the nitrogen 1s-pi* resonance. A photon flux of 4 × 1010 photon/s has been observed at 440 eV and 40 mA ring current (and with 0.5 eV resolution). It is expected that this flux value will improve by a factor of approximately 10-30 when a full-performance condensing system is installed later this year. The optical and mechanical systems design of the Rowland Circle monochromator with moving entrance and exit slits is reviewed. The details of the laser interferometer encoded wavelength drive, the mounting of the water cooled gratings, and the mechanical design features which improve the stability and accuracy of the system are described. The alignment of the gratings, grating chamber, and slits is discussed.
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The vibrational structure of the (1s)−1(π2p)1Π inner shell excited state of N2 has been observed, enabling the decay width and the shape of the potential function of the state to be deduced. The validity of the equivalent core model is discussed.
Conference Paper
Over the last several years the long trace profiler (LTP) has been evolving into a sophisticated machine capable of measuring surface profiles of very long dimensions. This report explains improvements, both hardware and software, that have helped to achieve accuracies and ranges in surface profiling that have been unobtainable until now. A comparison made by measuring standard optical surfaces on other instruments corroborates these accuracies.
Conference Paper
The recent development in gracing incidence grating monochromator design is discussed and the performance limiting for such instruments are examined. Especially the aberrations of toroidal and spherical gratings are investigated using the optical path function concept. It is shown that large radius spherical gratings, which can be produced with better slope tolerances than aspherics, also yield smaller overall line curvature than toroids. Therefore, a new simple spherical grating monochromator design is proposed and its performance is analyzed.
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The X1 undulator on the X-ray ring of the NSLS at Brookhaven is an extremely bright source of soft X-ray photons. On the recently completed spectroscopy beamline X1B we have attempted to utilise the intrinsically narrow beam size and divergence to maximise the intensity throughput in a spherical grating monochromator (SGM). The high power density of the undulator radiation requires the use of water cooled mirrors, entrance slit and grating. Calculations predict that simple side cooled copper pads attached to optical elements will be sufficiently effective that resolution degradation due to thermal deformation of figure error will be negligible in the SGM design. This is confirmed by attainment of resolution superior to other SGMs and the BESSY SX700-II monochromator over the energy range 300–540 eV (C1s−1, N1s−1 and Ols−1). At a resolution comparable to the best so far obtained for the nitrogen N 1s π∗ excitation (401 eV) on other monochromators we have demonstrated an intensity increase, at the sample, of more than three orders of magnitude. The design consideration upon which beamline X1B is based are highly relevant to the construction of soft X-ray monochromators at future synchrotron radiation sources such as the ALS (Berkeley). Elettra (Trieste) and BESSYII (Berlin).
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Photodiodes with x‐ray sensitive photocathodes are commonly used as broadband x‐ray detectors in fusion plasma diagnostics. We have measured the photocathode quantum efficiency between 1–500 Å of common photocathode materials including aluminum, copper, nickel, gold, three forms of carbon, chromium, and cesium iodide. We have also studied the effects of the experimental environment and long‐term cathode aging on the measured quantum efficiencies. In addition, we have measured the x‐ray mass‐absorption coefficients of x‐ray filter windows of Kimfoil, aluminum, polypropylene, and Formvar in energy regions where data were previously unavailable. Measurements between 1–50 Å were performed at the Los Alamos Scientific Laboratory’s low‐energy x‐ray calibration facility, while the measurements between 50–500 Å were performed at the National Bureau of Standard’s synchrotron ultraviolet radiation facility.
Article
We report on the performance of a newly constructed synchrotron radiation soft x‐ray beamline. This beamline, dubbed Dragon, is a spherical version of the cylindrical element monochromator design proposed previously. By measuring the K‐edge absorption spectra of condensed nitrogen, it is determined that this monochromator has achieved resolving power 10<sup>4</sup> at 400‐eV photon energy, using its full 15 by 1 mrad angular acceptance. The ideas and advantages contained in the CEM design have also been experimentally confirmed.
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This paper discusses general thermal engineering problems and two specific categories of thermal design issues for high-photon-flux beam lines at the LBL Advanced Light Source: thermal distortion of optical surfaces and elevated temperatures of thermal absorbers receiving synchrotron radiation. A generic design for water-cooled heat absorbers is described for use with ALS photon shutters, beam-defining apertures, and heat-absorbing masks. Also, results of in situ measurements of thermal distortion of a water-cooled mirror in a synchrotron radiation beam line are compared with calculated performance estimates.