M. Huttula

The Normal Incidence Monochromator Beamline I3 on MAX III

On the 700 MeV MAX III ring at MAX‐lab, a 6.65 m off‐axis eagle type monochromator beamline has recently been commissioned. The beamline is sourced by an apple type variable polarization undulator. The energy range of the beamline is 4.6–50 eV and the resolving power achieved is more than 100,000. There are two branch lines, one for angle and spin resolved photoemission studies from solids and the other for gas phase and luminescence experiments. We present the design and performance of the beamline.

Auger cascade satellites following 3d ionization in xenon

The electron spectra of xenon have been measured at the kinetic energy region of 8–40 eV using synchrotron radiation excitation below and above the 3d ionization threshold. The hole in the 3d orbital leads to the cascade of Auger transitions, the final steps of which give rise to pronounced satellite structures at the low kinetic energy region. In order to estimate the satellite production, the average kinetic energies and transition probabilities of Auger transitions after 3d ionization have been calculated using the method of global characteristics. Furthermore, the fine structure of the most intense satellite Auger transitions has been calculated using the pseudorelativistic Hartree–Fock method, and the results have been used to assign the main satellite peaks. In addition, the production of multi-charged Xe ions has been investigated and the role of electron–electron interaction in explaining the remaining differences between experiment and theory has also been discussed.

Solvation at nanoscale: Alkali-halides in water clusters

The solvation of alkali-halides in water clusters at nanoscale is studied by photoelectron spectroscopy using synchrotron radiation. The Na 2p, K 3p, Cl 2p, Br 3d, and I 4d core level binding energies have been measured for salt-containing water clusters. The results have been compared to those of alkali halide clusters and the dilute aqueous salt solutions. It is found that the alkali halides dissolve in small water clusters as ions.

Limitations of the ionic model in describing core-hole decay: molecular versus crystalline KCl

Normal Auger decay spectra of the 2p core hole in potassium have been measured both for molecular gas-phase and crystalline solid-state samples of KCl. While the spectrum for the latter is easily interpreted using a strictly ionic approach, the molecular spectrum gives evidence of strong additional effects. The observed differences between the two phases are discussed from the viewpoint of the ionic model, considering also the perturbation by the different environments and symmetries. The uniquely molecular effects seen in the Auger electron spectra are attributed to the sudden change in character of the valence (Cl 3p) orbital upon core-hole decay, accompanied by dynamic relaxation processes.

A multipurpose electron–ion spectrometer for measurements with synchrotron radiation

Abstract A multipurpose system has been constructed for ion and electron measurements. The system can be used as a time of flight ion mass spectrometer, conventional electron spectrometer or threshold electron spectrometer. In the future it is planned to use the system as a coincidence spectrometer between ions and electrons with selected kinetic energies. The construction of the system is described and some measured spectra are presented.

Photoelectron spectroscopy of unsupported bismuth clusters: Size related effects of metallic properties

Evolution of metallic properties of free and initially neutral nanoscale Bi clusters has been studied using synchrotron radiation excited photoelectron spectroscopy. The 4f and 5d core as well as the valence levels have been probed. The cross-level analysis indicates metallic properties in Bi clusters in the observed size range from 0.5 nm to 1.4 nm. The behavior of the core-level and valence binding energies as a function of cluster size has been observed to be smooth and relatively consistent. Valence responses for the largest clusters have their shape and width similar to those of the polycrystalline solid Bi.

Ionic bonding in free nanoscale NaCl clusters as seen by photoelectron spectroscopy

The free neutral nanoscale NaCl clusters have been produced in a beam and studied with x-ray photoelectron spectroscopy. High resolution spectra simultaneously containing cluster and molecular-monomer, featuring in both the valence and core-level Na 2p and Cl 2p regions, have been obtained. Cluster-level energy shifts of around 3 eV toward lower binding energy for Na 2p and ≈1 eV toward higher binding energy for Cl 2p relative to the monomer levels have been unambiguously established. To rationalize the core-level energy shifts of the nanoscale NaCl clusters, the ionic model taking into account all charge-charge and polarization interactions has been developed and implemented. A satisfactory agreement between the experimental and model results has been obtained. The model calculations have also shed additional light on the size- and site-specific cluster responses.

Vacuum ultraviolet excitation luminescence spectroscopy of few-layered MoS2

We report on vacuum ultraviolet (VUV) excited photoluminescence (PL) spectra emitted from a chemical vapor deposited MoS2 few-layered film. The excitation spectrum was recorded by monitoring intensities of PL spectra at ~1.9 eV. A strong wide excitation band peaking at 7 eV was found in the excitation. The PL excitation band is most intensive at liquid helium temperature and completely quenched at 100 K. Through first-principles calculations of photoabsorption in MoS2, the excitation was explicated and attributed to transitions of electrons from p- and d- type states in the valence band to the d- and p-type states in the conduction band. The obtained photon-in/photon-out results clarify the excitation and emission behavior of the low dimensional MoS2 when interacting with the VUV light sources.

The gas phase L2,3VV Auger electron spectra of chlorine in XCl (X=H, D, Li, Na, K) molecules

The Auger electron spectra (AES) following the chlorine 2p ionization in the gas phase alkali-chlorides as well as in the HCl and DCl molecules were studied theoretically and experimentally. Nonrelativistic ab initio calculations based on quantum chemical methods and the one-center approximation were used to compute the Cl L2,3VV AES. The vibrational band structure in the AES was simulated by full life time vibrational interference (LVI) theory and a more approximate moment method. Calculations were compared with the corresponding experimental electron or photon impact excited spectra. Overall features and changes in the series of the experimental AES are correctly predicted by the theory. For the most intense transitions in these spectra a qualitative explanation of the energies is given on the basis of a model that includes electrostatic interactions, Pauli repulsion, and polarization. This explains that the substantial changes of the spectra with X are due to a R−3 dependence of the electrostatic inter...

Valence photoionization of free, neutral, and size-varied alkali metal clusters

The valence photoelectron spectra of free, neutral, and size-varied K and Rb alkali metal clusters are studied. The experimental spectra are simulated with jellium model-based calculations with and without inclusion of dipole matrix elements and continuum wavefunctions. The simple jellium model used is found to provide good qualitative correspondence with the experimental results. It is shown that the dipole matrix elements provide a remarkable improvement to the standard density of states approach in understanding the photoelectron spectra of small to medium size metal clusters.