Search

Non-dipole 3p → 2p x-ray emission was observed for the first time after resonant and non-resonant production of a 2p core hole in solid cobalt, nickel, copper and copper oxide. In all the materials studied, this emission follows a resonant Raman scattering behaviour. Its emission energy and its intensity relative to the 3s → 2p3/2 transition are compared with a free ion Hartree–Fock calculation. The emission energy for the non-dipole transition is in good agreement with the calculations, but the measured intensity is about one order of magnitude larger than the calculations predict. A compression or distortion of the 3p orbital in the solid is suggested as the cause for the intensity enhancement.

The planned construction of an X-ray free-electron laser (XFEL) will provide new opportunities for research in various areas of physics, chemistry and biology. The proposed design of the XFELs at DESY (Deutsches Elektronen-Synchrotron) and SLAC (Stanford Linear Accelerator Center) is built on the concept of a fourth-generation synchrotron source and will provide an intense pulse (I(0) approximately 10(16) W cm(-2), tau(gamma) approximately 100 fs) for photon wavelengths down to 1 A. Some guidelines for applications of these sources pertaining to atomic physics are presented here. Issues such as the onset of strong photon-field effects, multiple ionization and hollow-atom formation are analyzed. Attention is especially given to studying the interaction with rare-gas atoms, for which some numerical estimates are provided.

Understanding the atomic bonding properties at the interface between thin films is crucial to a number of key modern technical devices, including semiconductor integrated circuits, magnetic recording media, batteries, and even solar cells. Semiconducting materials such as titanium nitride (TiNx) are widely used in the manufacturing of modern electronic devices, requiring a wealth of information about its electronic structure. We present data from soft x-ray emission, soft x-ray absorption, and Rutherford backscattering spectroscopy experiments involving a sample consisting of a 40 nm TiN layer on top of an aluminum film 600 nm thick. Soft x-ray emission spectroscopy and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy are tools that provide a nondestructive, atomic site-specific probe of the interface, where the electronic structure of the material can be mapped out element by element. Rutherford backscattering spectroscopy (RBS) measurements supply data on the elemental composition and dep...

金沢大学ナノマテリアル研究所 / 金沢大学理工研究域数物科学系 / 金沢大学大学院自然科学研究科物質情報解析, Soft-x-ray fluorescence measurements have been performed on a single crystal of the organic antiferromagnet 2,4,6-triphenylverdazyl. Resonant and nonresonant C Ka and N Ka (2p!1s transition! x-ray emission spectra ~XES! were measured and compared with x-ray photoelectron valence band spectra and deMon density-functional theory calculations. It is shown that intramolecular interactions are much stronger than intermolecular ones and give the main contribution to the formation of C 2p density of states. We present evidence of a delocalization of unpaired N 2p electrons over the verdazyl ring. The excitation energy dependence of C Ka and N Ka XES observed below the C 1s and N 1s thresholds, respectively, is discussed in terms of symmetry selective resonant inelastic x-ray scattering.

First principles calculations of Zn11X1S12 supercells in the zincblende structure, where X is a magnetic ion, show that when X=Cr, Fe, and Ni the materials are calculated to be half metallic and ferromagnetic, i.e., the densities of states of these bulk materials at the Fermi energy is calculated to be 100% spin polarized and the exchange interaction is ferromagnetic. This behavior persists even when on-site Coulomb “Hubbard U” potentials are applied.

Soft-x-ray emission spectra for the La {ital N}{sub 4,5}{ital O}{sub 2,3} transitions in lanthanum aluminate LaAlO{sub 3} include contributions from several relatively intense multiplet lines near 80 eV. The appearance of this spectrum contrasts sharply with the three diagram lines observed for the {ital N}{sub 4,5}{ital O}{sub 2,3} emission spectrum of Ba in BaF{sub 2}. An atomic model of the La {ital N}{sub 4,5}{ital O}{sub 2,3} transition, assuming single occupancy of the 4{ital f} shell by a spectator electron, provides a good approximation of the measured spectrum. Emission features due to the low-energy {sup 3}{ital P}{sup {ital o}} and {sup 3}{ital D}{sup {ital o}} terms of the 4{ital d}{sup 9}4{ital f} configuration are also apparent in the LaAlO{sub 3} emission spectra, but not in emission spectra from BaF{sub 2}. Reflection measurements indicate that the 4{ital f} level is not occupied in the ground state in LaAlO{sub 3}. The data suggest that charge transfer from ligand orbitals following creation of a 4{ital d} vacancy prior to the emission process is the predominant mechanism giving rise to the required 4{ital f} occupancy.

Boron carbide thin films of several B/C ratios have been deposited on Si(111) using plasma‐enhanced chemical vapor deposition from nido‐pentaborane(9) (B5H9) and methane (CH4). X‐ray diffraction studies of boron carbide thin films on Si(111) exhibited characteristic microcrystalline diffraction lines. Soft x‐ray emission spectroscopy was used to verify that the local electronic structure and composition of each sample corresponded to a homogeneous solid solution boron carbide phase.

Soft-x-ray emission (SXE) and soft-x-ray absorption (SXA) are used to investigate the electronic structure of \ensuremath{\alpha}-${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$, anodized ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$, MgO, and ${\mathrm{MgAl}}_{2}$${\mathrm{O}}_{4}$. It is found that both SXE and SXA are sensitive to the crystal phase, suggesting their use as a structural probe. Comparison of the Al ${\mathit{L}}_{2,3}$ SXE of \ensuremath{\alpha}-${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ and the Mg ${\mathit{L}}_{2,3}$ SXE of MgO with local-density-approximation (LDA) density-of-states calculations shows that the agreement is good, and suggests that the final-state rule is valid for the SXE of these oxides. On the other hand, comparisons show that results of the SXA and LDA calculations are not in good agreement. A model based on atomiclike excitations explains a portion of the MgO SXA spectrum well. Evidence which suggests that the remaining features are due to band structure is given.

The VUV ring at the National Synchrotron Light Source (NSLS, Brookhaven national Laboratory) is a source of nanosecond-duration, high-brightness, broadband IR pulses. The authors are developing several measurement techniques for characterizing Hg1-xCdxTe and other IR detector materials using this source. For example, the broadband IR pulses can be used to study transient photoconductive decay at various photon energies near the bandgap. A particularly novel technique they have developed is far-infrared photoinduced nanosecond spectroscopy (FIR-PINS). In this all-optical (contactless) measurement, a short laser pulse generates photocarriers which are subsequently sensed by a far-infrared pulse from the synchrotron. Spectroscopic analysis of the far-infrared yields the free carrier plasma frequency, providing information on the photocarrier density. By varying the delay time of the far-infrared pulse (relative to the laser pulse), the photocarrier relaxation is determined with nanosecond resolution. In addition to being contactless, the technique offers other potential advantages over electrical measurements. Results for MBE-grown Hg1-xCdxTe are presented.

Radiometric transfer standards consisting of windowless diodes with cathodes made of anodized aluminum oxide on aluminum are now available from the National Bureau of Standards with calibrations in the 200-600-A wavelength range. This extends the previously existing range of calibration for these diodes (600-1200 A). For wavelengths shorter than 600 A, synchrotron radiation at NBS-SURF is used as the source of radiant energy. A noble gas double ionization chamber is used to calibrate a secondary standard diode that is then intercompared with the transfer standards. Monitors take into account variations in the intensity of synchrotron radiation and in beam position. Methods of accounting for the effects of second-order radiation in the incident flux and secondary ionization in the double ionization chamber are discussed. Calibration uncertainties are about 10%.

Electron synchrotrons are becoming increasingly important as sources of extreme uv radiation for physical experiments. The NBS 180-MeV machine has been utilized for gas absorption studies over a four-year period, during which a 3-m grazing incidence spectrograph and monochromator have been designed, constructed and put into operation. The instruments are extremely stable to vibration and temperature variation, and are operating with a slit limited resolution of the order of 0.06 A. The design principles and features of these instruments are described, and a highly successful prealignment procedure for grazing incidence spectrometers is outlined. The effect of the unusual characteristics of this light source on the illumination and performance of the spectroscopic instruments is discussed.

The Al ${\mathit{L}}_{2,3}$ soft-x-ray reflection and emission spectra of ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As have been measured for x between 0.17 and 1.0. The valence-band maximum was monitored via the emission spectra using a fit based on band-structure parameters. The dominant features in the reflection spectra are produced by the ${\mathit{L}}_{2,3}$ core excitons. Since both the reflection spectra and emission spectra were obtained using the same soft-x-ray spectrometer, the energies of the excitons above the valence-band maximum are accurately obtained. The known values of the optical band gap, as a function of x, are then used to determine the core exciton binding energy. The core excitons are found to follow and lie above the conduction-band minimum by 0.3 eV as the Al composition changes. Our results are compared to various core exciton theories and to previous experiments.

Photon-excited soft x-ray emission spectra for CuO, Cu{sub 2}O, and bismuth cuprate in the region of the Cu 3{ital d}{r arrow}3{ital p} transitions were measured to obtain bulk-sensitive electronic partial density-of-states information. For CuO and Cu{sub 2}O transitions from the valence levels into the {ital M}{sub II} and {ital M}{sub III} levels were clearly resolved. The emission features were separated by the 2.3-eV spin-orbit interaction of the copper 3{ital p}{sub 1/2} and 3{ital p}{sub 3/2} states and appeared in the statistical intensity ratio. The copper {ital M}{sub III} emission spectrum of the superconductor is broader than the spectra of CuO and Cu{sub 2}O. For all three compounds the shape of the {ital M}{sub III} emission spectrum extracted from the data is qualitatively similar to calculations of the copper single-particle local density of states. No evidence of multiplet structure was observed in the emission spectrum of CuO in spite of the open {ital d} shell in the ground state. The measurements are compared with published copper {ital L} emission data and photoemission results.

Bulk iron silicides and implanted iron silicides have been studied by soft-x-ray emission (SXE) spectroscopy. The Si {ital L}{sub 2,3} emission spectra of these materials are measured. For bulk silicides, these spectra provide a measure of {ital s}- and {ital d}-type partial density of states (PDOS) localized on the Si sites. We compare them with available band-structure calculations and also with photoemission measurements. For implanted systems, the Si {ital L}{sub 2,3} emission spectra provide useful information about the silicide formation process with the variation of implant doses.

In this paper, we present and analyze an improved spectrometer design that has evolved from studies of the focal properties of transmission gratings in converging ligid beams. This design uses a variable line space grating at a fixed angle of incidence to focus the diffracted light in one dimension, producing resolutions in excess of 1000 over a large wavelength region. Attractive features of this concept include high throughout, simple wavelenght scanning, simple optical elements (plane gratings and plane and toroidal mirrors), and relatively inexpensive realizations. After presenting a mathematical analysis of the primary design features, we discuss implementations of this design both as a spectrometer and as two versions of beamline monochromators. Design parameters for the two monochromators will be given.

In this paper we present the preliminary results from a new experimental technique to synchronize the pulses from a mode-locked Nd-YAG laser to the light pulses in the VUV storage ring at the National Synchrotron Light Source (NSLS). We describe a method to electronically change the delay time between the laser pulses and the synchrotron pulses. We also illustrate a method to overlap the synchrotron pulses with the laser pulses in space and time. Preliminary results will be presented for two experiments.

We present temperature-dependent soft-x-ray emission and soft-x-ray absorption measurements on MgO, \ensuremath{\alpha}-${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$, and \ensuremath{\alpha}-${\mathrm{SiO}}_{2}$. The measurements show in detail the final-state effect on phonon broadening for transitions involving the Mg 2P core state in MgO. In addition, we report the temperature dependence of emission and absorption features for MgO, \ensuremath{\alpha}-${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$, and \ensuremath{\alpha}-${\mathrm{SiO}}_{2}$. The temperature dependence of the transitions involving the valence- and conduction-band states should be an important check on band-structure calculations. These results are compared to published temperature-dependent optical-reflectivity measurements.

The Al {ital L}{sub 2,3} and O {ital K} thresholds for single-crystal {alpha}-Al{sub 2}O{sub 3} have been studied by photoemission. Energy-distribution curves, constant-initial-state (CIS), and constant-final-state (CFS) spectra are reported and compared to the absorption spectrum reported previously. An exciton appears as a doublet at threshold in the Al {ital L}{sub 2,3} CFS, CIS, and absorption spectra. The details of the Al {ital L}{sub 2,3} CFS spectrum and absorption spectrum are similar, while the exciton is the only feature present in the CIS spectrum. Comparisons of the various Al {ital L}{sub 2,3} spectra allow the probabilities of different exciton decay channels to be determined. The probability for nonradiative direct recombination of the exciton is found to be (8{plus minus}1)% and the probability for Auger decay of the exciton is found to be (72{plus minus}20)%. Comparisons of the O {ital K} CIS and CFS spectra suggest that no O {ital K} exciton is formed.

A determination of the alignment of ${\mathrm{He}}^{+}$(2p) between the n=2 and 3 levels was carried out by measuring the angular distribution of the 304-\AA{} fluorescence that follows photoionization with synchrotron radiation. The alignment ${\mathit{A}}_{\mathit{c}}^{0}$ is related to the cross-section ratio \ensuremath{\zeta}=${\mathrm{\ensuremath{\sigma}}}_{2\mathit{p}\mathit{k}\mathit{d}}$/${\mathrm{\ensuremath{\sigma}}}_{2\mathit{p}}$ and thus provides a means of separating the kd and ks partial-wave contributions to the 2p ion production. The partial-cross-section ratio R=${\mathrm{\ensuremath{\sigma}}}_{2\mathit{p}}$/${\mathrm{\ensuremath{\sigma}}}_{2\mathit{s}}$ was also determined by measuring the fluorescence signal at the magic angle with and without an external electric field that quenches the 2s ions. With these data a partition of the n=2 cross section into the partial cross sections ${\mathrm{\ensuremath{\sigma}}}_{2\mathit{s}\mathit{k}\mathit{p}}$, ${\mathrm{\ensuremath{\sigma}}}_{2\mathit{p}\mathit{k}\mathit{s}}$, and ${\mathrm{\ensuremath{\sigma}}}_{2\mathit{p}\mathit{k}\mathit{d}}$ was carried out. The effect of the broad ${1}_{3}$ autoionizing resonance in these partial cross sections was determined. A comparison with the results of a many-body-perturbation-theory calculation shows good agreement for the alignment, as well as for R, ${\mathrm{\ensuremath{\sigma}}}_{2\mathit{s}\mathit{k}\mathit{p}}$, and ${\mathrm{\ensuremath{\sigma}}}_{2\mathit{p}\mathit{k}\mathit{s}}$, but somewhat of a discrepancy for ${\mathrm{\ensuremath{\sigma}}}_{2\mathit{p}\mathit{k}\mathit{d}}$.

The ${\mathit{L}}_{23}$ reflection spectra for single-crystal MgO, \ensuremath{\alpha}-${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$, and \ensuremath{\alpha}-${\mathrm{SiO}}_{2}$ are measured. These reflection spectra are used to generate absorption spectra that agree well with electron-total-yield and electron-energy-loss measurements. Exciton features are shown to exist in the band gap by comparing the valence-band maximum plus optical band gap to the observed transition energies. The energy splitting of the ${\mathit{L}}_{2\mathrm{\ensuremath{-}}}$${\mathit{L}}_{3}$ excitons, as seen in reflection, is clearly resolved for ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ and ${\mathrm{SiO}}_{2}$, while in electron-total-yield measurements the doublets are not resolved for ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$. This resolution allows the calculation of the exchange energy using intermediate-coupling theory.

The Si L2,3 emission spectra of silicon crystals implanted with Co at doses of (1–8) × 1017 Co/cm2 have been examined using soft‐x‐ray‐emission (SXE) spectroscopy. At the lowest dose, the spectra are little modified from that of crystalline Si, indicating that only a small fraction of Si is in the form of silicides within the probe depth of SXE spectroscopy. For higher doses and implant profiles with Co extending to the surface, there is clear evidence for ordered CoSi2 combined with richer Co phases, but little evidence for pure Si or for ordered regions of CoSi.

We have compared the Al L23 and Si L23 emission and reflection spectra of Al2O3 and SiO2 to obtain information on the nature of the excited states in the presence of the L23 holes. A 5 m Rowland spectrometer, using a 600 l/mm grating mounted in grazing incidence was used to detect both electron excited soft X-ray emission and near normal soft X-ray reflection. We report fine structure in the emission spectra above the L23 edges which coincides with structure in the reflection spectra. These features appear both in the bandgap and in the conduction band. Such features within the bandgap are typically identified as excitons, while those in the conduction band must be localized excited states. Therefore, measurements of ϵ2, for SiO2 and Al2O3 above the L23 edge should be interpreted in terms of localized excitations in the presence of a core hole, rather than interband transitions.

The Ni and Co monosilicides and disilicides are studied by soft-x-ray-emission spectroscopy. The Si {ital L}{sub 2,3} spectra, which provide a measure of the partial densities of states of {ital s} and {ital d} angular momentum symmetry (({ital s}+{ital d}) PDOS) localized on the Si site, are compared with available theoretical calculations, and discussed in terms of the contribution of {ital s} electrons to the bonding. The Ni and Co {ital M}{sub 2,3} emission spectra are also obtained, and analyzed to provide information about the {ital d} PDOS localized at the metal site. These spectra are discussed in terms of {ital p}-{ital d} bonding in the silicides.

The photon excitation of soft X-ray emission spectra using monochromatized radiation from a synchrotron light source provides important advantages compared with electron excitation. The equipment used for such studies on beamline U-10 at the National Synchrotron Light Source (NSLS) is described. With data obtained from this beamline and elsewhere, we discuss and illustrate the elimination of bremsstrahlung, the reduction in damage produced by energy deposition, the elimination of overlapping spectra made possible by selective excitation of particular core levels, and the interactions between excitation and emission processes observed using photon excitation near threshold.

The {ital L}{sub 2,3} emission spectrum of {ital c}-Si, excited by monochromatized synchrotron radiation, has been recorded with a 5-m Rowland spectrometer. Dramatic spectral changes are observed as the excitation energy is varied from the 2{ital p} binding energy up to 144 eV. It is proposed that a spectator electron, close to the bottom of the conduction band, influences the emission spectrum. The observations suggest that intraband shakeup is important in the excitation process, and that a population of low-lying levels, via initial-state shakeup, influences the high-energy-excited Si {ital L} emission spectrum.

Tunable, polarized, microfocused x-ray pulses were used to record x-ray absorption spectra across the K edges of Kr{sup +} and Kr{sup 2+} produced by laser ionization of Kr. Prominent 1s {yields} 4p and 5p excitations are observed below the 1s ionization thresholds in accord with calculated transition energies and probabilities. Due to alignment of 4p hole states in the laser-ionization process, the Kr{sup +} 1s {yields} 4p cross section varies with respect to the angle between the laser and x-ray polarization vectors. This effect is used to determine the Kr{sup +} 4p{sub 3/2} and 4p{sub 1/2} quantum state populations, and these are compared with results of an adiabatic strong-field ionization theory that includes spin-orbit coupling.

This is a construction project for an end station at the ALS, which is optimized for measuring NEXAFS of nanostructures with fluorescence detection. Compared to the usual electron yield detection, fluorescence is able to probe buried structures and is sensitive to dilute species, such as nanostructures supported on a substrate. Since the quantum yield for fluorescence is 10{sup -4}-10{sup -5} times smaller than for electrons in the soft x-ray regime, such an end station requires bright undulator beamlines at the ALS. In order to optimize the setup for a wide range of applications, two end stations were built: (1) A simple, mobile chamber with efficient photon detection (>10{sup 4} times the solid angle collection of fluorescence spectrographs) and a built-in magnet for MCD measurements at EPU beamlines (Fig. 1 left). It allows rapid mapping the electronic states of nanostructures (nanocrystals, nanowires, tailored magnetic materials, buried interfaces, biologically-functionalized surfaces). It was used with BL 8.0 (linear polarized undulator) and BL 4.0 (variable polarization). (2) A sophisticated, stationary end station operating at Beamline 8.0 (Fig. 1 right). It contains an array of surface characterization instruments and a micro-focus capability for scanning across graded samples (wedges for thickness variation, stoichiometry gradients, and generalmore » variations of the sample preparation conditions for optimizing nanostructures).« less

Using site-specific soft x-ray emission and absorption spectroscopy in conjunction with site-specific x-ray photoelectron spectroscopy, we present measurements of the valence and conduction band states of NiO. Significant hybridization between the Ni and the O electronic states near the Fermi energy is observed throughout both the valence and conduction bands, in accordance with density-functional theory calculations also presented. The relationship between our emission and absorption measurements also shows direct similarities to other techniques used to measure the non-dipole-allowed $d\text{\penalty1000-\hskip0pt}d$ transitions within NiO, addressing questions concerning the character of the insulating band gap of this system. NiO has previously been described as a large-gap, charge-transfer insulator, while our data show the valence and conduction states at the Fermi energy to be primarily of Ni $d$--character hybridized with a small amount of O $p$--character states, suggesting a mixture of charge-transfer and Mott-Hubbard character as described by the Zaanen-Sawatzky-Allen model.

Double K-shell photoionization of Ne at 5000 eV was observed by recording the KK-KLL Auger-electron hypersatellite spectrum. The measured Auger spectrum is compared with the results of multiconfiguration Dirac-Fock calculations. Shake calculations are used to identify likely multivacancy states produced by photoexcitation or ionization in addition to double-K vacancies, and their calculated Auger spectra are compared with the measured spectrum. The measured relative intensities of hypersatellite and diagram Auger lines are combined with experimental and theoretical determinations of branching ratios from single- and double-K vacancies into final states to determine the ratio of double-to-single K-shell photoionization cross sections to be 0.32(4)%. This ratio is much larger than the calculated high-energy-limit ratio and indicates a large contribution of dynamic electron correlation.

We have studied double K‐shell photoionization of Ne and Mo (Z = 10 and 42) at the Advanced Photon Source. Double K‐vacancy production in Ne was observed by recording the KK‐KLL Auger hypersatellite spectrum. Comparison is made with calculations using the multiconfiguration Dirac‐Fock method. For Mo, double K‐vacancy production was observed by recording the Kα, β fluorescence hypersatellite and satellite x rays in coincidence. From the intensities of the Auger or x‐ray hypersatellites relative to diagram lines, the probabilities for double K‐vacancy production relative to single K‐vacancies were determined. These results, along with reported measurements on other atoms, are compared with Z‐scaling calculations of the high‐energy limits of the double‐to‐single K‐shell photoionization ratio.

Si L 2.3 x-ray emission stimulated with narrow-band synchrotron radiation has been studied as a function of excitation energy. In strong contrast to crystalline silicon, amorphous silicon yields emission spectra that are independent of the excitation energy, thereby demonstrating that long-range order plays a necessary role in the excitation-energy dependence of the crystalline emission

Understanding the atomic bonding properties at the interface between thin films is crucial to a number of key modern technical devices, including integrated circuits, magnetic disk read/write heads, batteries, and solar cells. Semi-conducting materials such as titanium nitride (TiNx) are widely used in the manufacturing of modern electronics, requiring a wealth of information about its electronic structure. We present data from soft x-ray emission and absorption experiments involving a sample consisting of a 40 nm TiN layer on top of an aluminum film 550 nm thick. Soft x-ray emission spectroscopy (XES) and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy are tools that provide a non-destructive, atomic site-specific probe of the interface, where the electronic structure of the material can be mapped out element by element. From these measurements, we show that the Ti and the N diffuse into the Al film to form an equivalent material depth of about 4.5 nm, and the NEXAF structure reveals that...

The results of x-ray fluorescence measurements of the molecular superconductors (ET)[(HO)Fe(CO) ]·CHCN (T = 8.5 K) and (ET)[(HO)Cr(CO) ]·CHCN (T ∼ 6 K) and molecular conductor (ET)[(HO)Fe(CO) ]·CHN containing paramagnetic 3d ions are presented. The following transition of the x-ray emission valence spectra are monitored: C K α, N K α (2p→1s transition) and Fe L, Cr L (3d4s→2p transition). It is found that the electronic structure of the solvents (benzonitrile, pyridine) that occupy the hexagonal cavities formed by the anionic layer is close to that of the neutral molecule. The ratio of the emission intensities of the peaks L to L for Fe and Cr is found to be 2.8-3.1 times higher for (ET)[(HO)Fe(CO) ]·CHCN and (ET)[(HO)Cr(CO) ]·CHCN than for pure metals. This indicates that the paramagnetic 3d ions are situated in highly insulating anionic layers. We did not find any changes in the C K α emission for different solvent molecules.

Absolute inclusive and exclusive cross sections for ionization of H and He by Compton scattering are presented and analyzed. The exclusive cross section for ionization of one electron, leaving the second electron in the ground state, is 20% smaller for H than for He. Furthermore, the exclusive cross section for ionization with excitation to the first excited state is seven times larger for H than for He. However, at high energies the inclusive Compton cross sections for both H and He are within 1% of two times the Thomson cross section for elastic scattering of a free electron, even when ground-state correlation is accurately included. A general analysis based on quasielastic scattering is applied to both shake and correlated calculations.

We investigate the excitation energy dependence of the boron [ital K] soft-x-ray emission of B[sub 2]O[sub 3] and hexagonal-BN using synchrotron radiation. When exciting into the core exciton state the spectra are shifted to lower energy by 1.5 and 1.8 eV, respectively. This shift is found to be a result of phonon relaxation and differences in initial-and final-state electronic screening.

In response to the needs of the emerging field of normal incidence soft x-ray optics, a field with applications ranging from extreme ultraviolet (XUV) solar imaging to x-ray lithography, the National Institute of Standards and Technology (NIST) has initiated an XUV multilayer and optical substrate characterization program. In this paper, we give an overview of the present capabilities of the NIST facility and discuss some of the proposed improvements, concentrating on the new soft x-ray reflectometry facility being built at SURF.

We present the first soft x-ray-emission spectra for solid Kr (4{ital p}-3{ital d}) and Xe (5{ital p}-4{ital d}) that are free of complicating satellite spectra. Monochromatic synchrotron-radiation excitation is used to suppress the satellites. The data are analyzed to determine the {ital P}{sub 3/2} bandwidth for both elements; these results are compared with both photoemission data and available theoretical calculations. Bandwidths are found to be larger than those predicted by most electronic structure calculations.

We characterize the time evolution of ion spatial distributions in a laser-produced plasma. Krypton ions are produced in strong, linearly and circularly polarized optical laser fields (1014–1015 W/cm2). The Kr+ ions are preferentially detected by resonant x-ray absorption. Using microfocused, tunable x rays from Argonne’s Advanced Photon Source, we measure ion densities as a function of time with 10 μm spatial resolution for times ≤50 ns. For plasma densities of the order of 1014 cm−3, we observe a systematic expansion of the ions outward from the laser focus. We find the expansion timescale to be independent of the plasma density though strongly dependent on the plasma shape and electron temperature. The former is defined by the laser focus, while the latter is controlled by the laser polarization state. We have developed a fluid description assuming a collisionless quasineutral plasma, which is modeled using a particle-in-cell approach. This simulation provides a quantitative description of the observed...

New beamline development on SURF features toroidal grating instruments for Surface Science studies and Far UV photodiode calibration. The progress and capabilities of these lines will be discussed along with the developments on the high resolution normal incidence spectrometer beam line under construction by the University of Maryland. The ongoing programs in Surface Science and Photoelectron Spectroscopy will be briefly reviewed with a more detailed discussion of the latest results in calibration efforts using electron counting and the calculable spectral distribution of synchrotron radiation.

We have begun a program to measure oscillator strengths of autoionizing resonances that result from a transition in the VUV between a laser excited initial state and a final state in which a core electron is promoted. These measurements demonstrate a new technique to combine synchrotron radiation, laser pumping, and photoelectron spectroscopy.Measurements of the energy positions of autoionizing resonances have been honed to a fine art over the past 50 years. Total cross section measurements and the parameters that describe autoionizing resonances have been determined. Most of these studies have been made from the dipole allowed ground state. Recently autoionizing resonances have been observed from excited initial states and from ion initial states. We have heard several talks, at this meeting which described some of this type of research. In the measurements to be described in this paper, laser radiation is combined with synchrotron radiation, as shown schematicaly in Figure 1, to study the photoionization from excited initial states to continuum final states or to autoionizing final states. Continuum radiation from the Aneau de Collisions d’Orsay (ACO), which is installed at the Universite de Paris-Sud, in Orsay France, is monochromatized by a toroidal grating monochromator (TGM) and is focused by a toroidal output mirror on to a weakly collimated sodium beam emanating from a furnace mounted on the axis of a cylinderical mirror analyzer (CMA). This electron spectrometer is used to study the kinetic energy distribution of the ejected photoelectrons produced by the interaction of the photon beam with the focused synchrotron radiation.

The effects of electric fields of intensity up to about 10 kVcm-1 on the autoionising resonances buying between the 2P3/2 and 2P1/2 ionisation limits in Xe have been studied in absorption. Fields of this strength produce pronounced effects on series members for n>11 The major effects are a decrease in transmission in the neighbourhood of the resonances and a lowering of the classical field ionisation potential.

Collisional ionization of sodium and barium vapors resonantly excited with c.w. or pulsed laser sources, and subsequent electron-atom energy transfers, are studied by electron spectroscopy. Cross sections for associative and Penning ionization of sodium in excited states, are obtained.

A sodium atomic beam with density ${10}^{13}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ was illuminated by cw dye laser radiation (a few watts per square centimeter) tuned to the ${D}_{2}$ resonance line. In the energy spectrum of the emitted electrons, several lines were observed between 4 and 7 eV. Their positions and intensities indicate that seed electrons are produced either via associative ionization or via collisional ionization from excited states populated by energy-pooling collisions. These electrons are then heated through successive superelastic collisions with excited $3p$ atoms.

The first observation, by electron spectrometry, is reported in laser-excited sodium vapor of the primary low energy electrons produced by associative ionization and by Penning ionization of sodium atoms in highly excited n1 states. The sequential heating of these primary electrons has been observed in 1, 2 or 3 superelastic collisions with Na(3p) atoms. The variation of associative ionization was measured as a function of the excited state density by using inner-shell photoionization produced by synchrotron radiation. Finally, an associative ionization cross section of 3.8 X 10-17 cm2 and a Penning ionization cross section for the 5s state of 1.1 X 10-12 cm2 were found (within 50% uncertainty) for an oven temperature of 520 K.

The soft x-ray emission spectra of single-crystal LiF excited with synchrotron radiation are presented. The radiative decay of the lithium 1s core exciton is observed. Radiative transitions between the valence band and the core hole are also observed in undamaged samples. Spectra obtained with broadband synchrotron-light excitation are shown to be dominated by diffuse scattering from damaged sample surfaces. Excitation with photon energies between 100 and 150 eV generates true emission spectra. An important result is that electrons excited into the conduction band are frequently trapped in an exciton state before recombining with the core hole.

Photoelectron studies of molecular autoionization resolved into position within the resonance profile, photoelectron ejection angle, and final vibrational state are reported. By using the first members of prominent window and absorption series converging to N/sub 2//sup ts+/ B/sup 2/..sigma../sub u//sup +/ as an example, striking variations of vibrational branching ratios and photoelectron asymmetry parameters within autoionizing profiles are demonstrated. Such triply differential data represent a very detailed characterization of the rovibronic interactions governing molecular autoionization.

The high intrinsic brightness of the circulating electron beam at SURF-II is used as the entrance slit for a two-meter normal incidence monochromator. A typical beam size for the electron beam is 100 μ high by 2 mm wide yielding an observed resolution of 0.4 A with a 200 μm exit slit and a 2400 lines/mm grating. The instrument accepts a beam with a 65 mrad horizontal divergence and a 10 mrad vertical divergence. A plane pre-mirror used near normal incidence reflects the incoming radiation onto the 2 m grating; this combination provides a horizontal exit beam, and enables the experiment to be located three meters from the orbit tangent point. With magnesium fluoride coated aluminum optics a flux of 2×10″ photons/s·A at 1200 A is observed with a 10 mA circulating current. A flux of 5×10 10 photons/sdA at 600 A is observed with an osmium coated grating and a 10 mA circulating current. Sample spectra of the angle-resolved photoelectron spectrum of CO are presented.

A variable wavelength angle resolving photoelectron spectrometer has been used to study the effects of autoionization and shape resonances upon molecular photoionization. Such resonance phenomena produce non-Franck-Condon effects in the vibrational intensity distributions and significant variations in the asymmetry parameters. Results are presented for C 2 N 2 and CO 2 . Constant Photoelectron Energy (CPE) spectroscopy has been performed on C 2 H 2 and spectra are shown at four kinetic energies. The information concerning energy absorption in molecules gained from these studies is discussed.