Jan-Erik Rubensson

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...

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

On the Origin of the Hydrogen‐Bond‐Network Nature of Water: X‐Ray Absorption and Emission Spectra of Water–Acetonitrile Mixtures

A liquid microjet was used to obtain oxygen K-edge X-ray absorption and emission spectra of water–acetonitrile mixtures of various compositions. The observed spectral changes are unambiguously related to the increasing number of broken hydrogen bonds with decreasing water concentration, and the hydrogen-bond network of liquid water can thus be addressed on purely experimental grounds without the need for theoretical modeling.

Unveiling the complex electronic structure of amorphous metal oxides

Amorphous materials represent a large and important emerging area of material’s science. Amorphous oxides are key technological oxides in applications such as a gate dielectric in Complementary metal-oxide semiconductor devices and in Silicon-Oxide-Nitride-Oxide-Silicon and TANOS (TaN-Al2O3-Si3N4-SiO2-Silicon) flash memories. These technologies are required for the high packing density of today’s integrated circuits. Therefore the investigation of defect states in these structures is crucial. In this work we present X-ray synchrotron measurements, with an energy resolution which is about 5–10 times higher than is attainable with standard spectrometers, of amorphous alumina. We demonstrate that our experimental results are in agreement with calculated spectra of amorphous alumina which we have generated by stochastic quenching. This first principles method, which we have recently developed, is found to be superior to molecular dynamics in simulating the rapid gas to solid transition that takes place as this material is deposited for thin film applications. We detect and analyze in detail states in the band gap that originate from oxygen pairs. Similar states were previously found in amorphous alumina by other spectroscopic methods and were assigned to oxygen vacancies claimed to act mutually as electron and hole traps. The oxygen pairs which we probe in this work act as hole traps only and will influence the information retention in electronic devices. In amorphous silica oxygen pairs have already been found, thus they may be a feature which is characteristic also of other amorphous metal oxides.

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).

RIXS dynamics for beginners

Abstract The dynamics in resonant inelastic scattering is reviewed. Simplifying pictures and basic conservation rules are used as starting point for the discussion, rather than a rigorous theoretical framework. It is emphasized that selectivity in terms of energy (and to some extent momentum and angular momentum) of the incoming photon has changed the perspective on core level spectroscopies during the last decade. Dynamics on the femtosecond timescale can be studied by comparing rates of competing processes and analysis of interference effects.

Local Electronic Structure of Functional Groups in Glycine As Anion, Zwitterion, and Cation in Aqueous Solution

Nitrogen and oxygen K emission spectra of glycine in the form of anions, zwitterions, and cations in aqueous solution are presented. It is shown that protonation has a dramatic influence on the local electronic structure and that the functional groups give a distinct spectral fingerprint.

DMSO-Water Clustering in Solution Observed in Soft X-ray Spectra.

The significant deviation from the ideality of dimethyl sulfoxide (DMSO)/water mixtures can be addressed based on the change of the local molecular orbitals of each solvent upon mixing. Oxygen K-edge absorption and emission spectra of DMSO/water solutions were measured using the liquid microjet technique. The spectra demonstrate that the hydrogen bond network in liquid water is already influenced at small DMSO concentrations, and at the molar fraction xDMSO = 0.43 we find strong evidence of DMSO-water clustering reflected by the influence on the occupied molecular orbitals.

Radiative decay of multiply excited core hole states in H2O

A high resolution x‐ray emission spectrum of water vapor has been recorded, using a 7 keV electron beam and a 10 m grazing incidence spectrometer. The spectrum is interpreted in terms of dipole transition moments between CI wave functions built from separately optimized molecular orbitals. The principal features of the spectrum are reproduced considering transitions in the singly and doubly ionized species, giving rise to main lines and Wentzel–Druyvesteyn satellites, respectively.

Competition between decay and dissociation of core-excited carbonyl sulfide studied by x-ray scattering

We show evidence of dissociation during resonant inelastic soft x-ray scattering. Carbon and oxygen K-shell and sulfur L-shell resonant and nonresonant x-ray emission spectra were measured using mo ...