Joseph Nordgren

Soft x-ray emission spectroscopy using monochromatized synchrotron radiation (invited)

Soft x‐ray emission spectroscopy is a common tool for the study of the electronic structure of molecules and solids. However, the interpretation of spectra is sometimes made difficult by overlaying lines due to satellite transitions or close‐lying core holes. Also, irrelevant inner core transitions may accidentally fall in the wavelength region under study. These problems, which often arise for spectra excited with electrons or broadband photon sources can be removed by using monochromatized synchrotron radiation. In addition, one achieves other advantages as well, such as the ability to study resonant behavior. Another important aspect is the softness of this excitation agent, which allows chemically fragile compounds to be investigated. In this work we demonstrate the feasibility of using monochromatized synchrotron radiation to excite soft x‐ray spectra. We also show new results which have been accomplished as a result of the selectivity of the excitation. The work has been carried out using the Flippe...

A soft X-ray monochromator for the MAX synchrotron radiation facility☆

A high resolution soft X-ray monochromator for the 550 MeV MAX storage ring is described. The instrument combines a plane elliptical premirror collecting a large (10 mrad) horizontal angle of radiation and a modified version of the well-known SX-700 plane grating monochromator (PGM). The modification consists of changing the original ellipsoidal focussing mirror to a plane elliptical mirror. Thereby the horizontal and vertical focussing are decoupled and good imaging properties are obtained irrespective of the large horizontal acceptance angle. The MAX-PGM will be part of an experimental station for photoelectron, photoabsorption and photon stimulated ion desorption spectroscopy.

Nitrogen bonding structure in carbon nitride thin films studied by soft x-ray spectroscopy

Soft x-ray absorption (SXAS) and emission (SXES) spectroscopies were applied to study the nitrogen bonding structure in magnetron sputtered CNx thin films. By comparing with calculated spectra of N in different model systems, N in three main bonding environments can be identified: (i) C≡N bonds, with a sharp SXAS peak at 399.5 eV, (ii) pyridine-like N (i.e., N bonded to two C atoms), with an x-ray absorption resonance at ∼398.5 eV, and (iii) N substituted in graphite, possibly with one sp3 carbon as a neighbor (SXAS energy ∼401 eV). These bondings are present in all CNx films analyzed; however, as shown earlier, the relative intensities between the peaks may vary with the growth conditions. Differences in the coordination of the nearest or second nearest C neighbors only cause slight changes in the peak positions and spectrum shape.

Beamline I511 at MAX II, capabilities and performance

The new undulator beamline I511 at MAX-lab, now under commissioning, has been optimized for X-ray emission and photoelectron spectroscopies. Using an SX-700 high flux monochromator the accessible photon energy range is from 90 eV to about 1500 eV. The per

Structural and electronic properties of low dielectric constant fluorinated amorphous carbon films

Fluorinated amorphous carbon (a-CFx) films were studied by high-resolution x-ray absorption, emission, and photoelectron spectroscopy. The composition and local bonding information were obtained and correlated with substrate temperature during deposition. The data suggest that the structure of the a-CFx is mostly of carbon rings connected by CF2 groups. The cross linking increases with substrate temperature.

Polarization-dependent soft-x-ray absorption of highly oriented ZnO microrod arrays

Polarization-dependent x-ray absorption measurements were performed on crystalline ZnO three-dimensional arrays consisting of highly oriented microrods as well as on particulate thin films consisting of monodisperse spherical nanoparticles. Strong anisotropic effects have been observed for the highly oriented ZnO rods, but not for the isotropic spherical nanoparticles. Full-potential calculations of the orbital-resolved x-ray absorption of a ZnO wurtzite periodic crystal, including Zn 3d among the valence states, show very good agreement with the experimental findings. Comprehensive fundamental knowledge of the electronic structure of ZnO is obtained by probing and demonstrating the orbital symmetry of oxygen and its contribution to the conduction band of this important II–VI semiconductor.

Design of a portable large spectral range grazing incidence instrument

A design of a small size grazing incidence instrument is presented, which offers large spectral range and high resolution without sacrificing luminosity. The instrument is particularly suited for use at synchrotron radiation sources since it can be conveniently attached to existing experiment chambers. The basic idea of the design is the use of fixed mounted gratings of diffent radii and groove densities and a big two-dimensional position sensitive detector mounted on a x-y angle table. The design is discussed in some detail and performance is presented.

Instrumentation for soft X-ray emission spectroscopy

Abstract An account is presented of developments in instrumentation for soft X-ray emission spectroscopy (SXES) based on synchrotron radiation. An account for grating spectrometers for soft X-ray emission spectroscopy is given, and some considerations regarding synchrotron radiation applications of the spectroscopy are presented. A few points that relate to the new features of resonant SXES and polarization dependent studies are discussed in some detail. A brief discussion on future developments in SXES instrumentation is included.

Solid electrolyte interphase on graphite Li-ion battery anodes studied by soft X-ray spectroscopy

We have measured X-ray absorption and emission near the C 1s edge of graphite electrodes cycled in lithium-ion battery cells. Resonantly excited emission spectra of graphite electrodes exhibit features characteristic of both highly oriented pyrolytic graphite as well as polycrystalline graphite. Spectra of three electrodes cycled in two different electrolytes are presented and compared with spectra of the pristine electrode. A solid electrolyte interphase (SEI) was detected on the electrochemically cycled electrodes. By the use of selective excitation, resonant X-ray emission spectra of the SEI-species were obtained and compared to spectra of reference compounds. The SEI on the cycled graphite anode was shown to comprise lithium oxalate (Li2C2O4), lithium succinate (LiO2CCH2CH2CO2Li) and lithium methoxide (LiOCH3).

First results from the SpectroMicroscopy Beamline at the Advanced Light Source

The SpectroMicroscopy Facility at the Advanced Light Source is based on a high brightness, high‐resolution beamline, and includes a collection of projects designed to exploit the unique characteristics of the soft x‐ray beam. The beamline itself is comprised of a 5‐m long, 5‐cm‐period undulator, a spherical‐grating monochromator with water‐cooled gratings. Adaptive optics refocus the monochromatic beam to two ‘‘microfocus’’ experimental stations with spot sizes less than 50 μm diameter and a third ‘‘nanofocus’’ station uses a zone‐plate lens to further demagnify the microfocus spot. Experimental stations include an ‘‘ultraESCA’’ spectrometer for small‐area spectroscopy and photoelectron diffraction, a scanning transmission x‐ray microscope, and photoelectron microscopes. Commissioning experiments of microscopic actinide photoemission, surface‐core‐level photoelectron diffraction, and high‐resolution soft x‐ray fluorescence demonstrate dramatic improvements in sensitivity due to the high brightness and sma...