S. Svensson

Thermochromism in poly(3‐hexylthiophene) in the solid state: A spectroscopic study of temperature‐dependent conformational defects

Reversible thermochromism in thin solid films of poly(3‐hexylthiophene), or P3HT, has been studied using ultraviolet and x‐ray photoelectron spectroscopies (UPS and XPS, respectively). The UPS and XPS spectra, as well as previously published optical absorption spectra, are analyzed using the results of valence effective Hamiltonian (VEH) quantum chemical calculations of the electronic structure of isolated polymer chains. The analysis of the spectra indicates that at elevated temperatures thermally induced electronic localization occurs as a consequence of thermally induced conformational disorder.

Large Tunable Rashba Spin Splitting of a Two-Dimensional Electron Gas in Bi2Se3

We report a Rashba spin splitting of a two-dimensional electron gas in the topological insulator Bi(2)Se(3) from angle-resolved photoemission spectroscopy. We further demonstrate its electrostatic control, and show that spin splittings can be achieved which are at least an order-of-magnitude larger than in other semiconductors. Together these results show promise for the miniaturization of spintronic devices to the nanoscale and their operation at room temperature.

Vibrational and lifetime line broadenings in ESCA

Abstract The line profile of the narrow, symmetric 1s line from neon, recorded with the new ESCA instrument with X-ray monochromatization, is analyzed. The natural linewidth of this line is found to be 0.23 ± 0.02 eV, in good agreement with theoretical calculations of the oscillator strengths for Auger transitions and X-ray emission. Spectra from molecules show frequently asymmetric core electron lines under high resolution. This rules out previous explanations based on a chemical influence on the natural lifetime. Contrary to earlier assumptions, vibrational excitations are shown to be important in core electron spectra. For methane, the vibrational energy spacing is large enough to allow the vibrational lines to be partly resolved. Recent results from accurate PNO CI calculations on methane agree well with the experimental findings. The Franck-Condon transitions in the C1s and N1s lines from CO and N2 are shown to be well described in the harmonic approximation and approximating the potential curves of the highly excited core hole states with the potential curve for the ground state of NO+, X1 Σ+. Knowledge of vibrational excitations in core electron spectra is shown to be valuable in the analysis of high resolution X-ray emission spectra of free molecules.

Beam line I411 at MAX II - Performance and first results

We report on the characteristics and first results from the soft X-ray beam line I411, based on an undulator at the third generation synchrotron facility MAX II, Sweden. The beam line is designed for high-resolution, angle-resolved electron spectroscopy on gases, liquids and solids. Main components are the modified SX700 monochromator and the end station, both of which were previously used at beam line 51 at MAX I. The end station is equipped with a rotatable SES-200 hemispherical electron-analyser. Before the end station, a one-metre section is reserved for exchangeable experimental set-ups. The usable photon energy range is 50-1500 eV and the photon flux is two orders of magnitudes higher compared to beam line 51. At 400 eV a resolving power of about 5700 in the first order of the monochromator grating could be obtained. In gas phase, a total electron energy resolution of 16 meV has been achieved. Detailed results on the undulator performance, flux, photon and electron energy resolution as well as some technical details are presented here. As an example of the capabilities of the beam line I411, we present the fully vibrationally resolved Auger resonant Raman electron spectrum of gas-phase N 2.

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.

Soft X-ray undulator beam line I411 at MAX-II for gases, liquids and solid samples

We report on the build-up of the new undulator beam line 1411 at the third-generation synchrotron radiation facility MAX II in Lund, Sweden. This beam line is based on an upgraded version of the modified SX700-monochromator and the end station which were installed previously at beam line 51 at MAX I. The end station is equipped with a rotatable Scienta hemispherical electron-analyser making angle-resolved high resolution electron spectroscopy possible for various kinds of samples. The beam line performance will be considerably improved on MAX II due to a new undulator and the superior light source properties, e.g. the small vertical electron beam size. Undulator spectra have been measured and estimates of the photon flux at the experiment and the expected energy resolution are presented. The parameters for a new refocusing mirror were defined by ray tracing using the beam waist of the undulator. The beam line length was extended by 1 m to offer additional space for exchangeable experimental chambers.

SCF and limited CI calculations for assignment of the Auger spectrum and of the satellites in the soft X-ray spectrum of H2O

Abstract SCF and limited CI calculations have been performed for a number of excited states of doubly ionized water. The calculations allowed an assignment of both the Auger spectrum and most of the satellites in the soft X-ray spectrum. The assignment for the two highest peaks in the Auger spectrum was ambiguous. SCF calculations of the K emission spectrum of H 2 O were also performed. It was found that limited CI calculations were of importance for some states with two open shells in one symmetry. Such effects are caused by large off-diagonal lagrangian multiplies connecting the open shells in the reference configuration.

Electron shake-up and correlation satellites and continuum shake-off distributions in X-Ray photoelectron spectra of the rare gas atoms

Abstract The rare gases H, He, Ne, Ar, Kr and Xe have been studied in the gas phase at low pressure by means of high resolution photoelectron Spectroscopy. Monochromatized Al Kα radiation at 90° was used to excite the photoelectrons. Extended energy regions of all valence electron spectra and the most interesting core electron spectra have been recorded. The spectra contain a large number of correlation satellites and shake-up as well as double shake-up satellites which originate from unknown highly excited, singly ionized states. The energies and intensities of these discrete satellites have been determined and several states are identified. The assignments rely partly on results from relativistic MCSCF calculations, and partly on comparisons with optical data and recent Auger electron data. Relativistic MCSCF energies for a large number of excited states in Kr + and Xe + are reported. Extended shake-off continua in both the valence region and in the core electron regions have been recorded. The shake-off continua of Ne and Ar reveal several Fano-like resonance states. The resonances occur when shake-up photoionization channels, involving inner valence electron excitation or multiple valence excitation, have the same energies and symmetries as photoionization channels for outer valence electron shake-off. A theoretical model for this type of resonance is presented and some numerical results are obtained and compared with experimentally determined Fano parameters for the most prominent resonance in the Nels shake-off spectrum.

Lifetime Broadening and CI-Resonances Observed in ESCA

The electron spectrum of the M2 and M3 levels in bromine and krypton have been studied by high resolution ESCA. The M1M2,3M2,3 super Coster-Kronig transitions become energetically forbidden for Zless than sim-36 (Kr) and recent calculations therefore predict a decrease in the M2 and M3 natural linewidths around krypton in the periodic system. The experiment shows that the 3p3/2 linewidth is smaller in Kr than in Br. It is, however, also found that this decrease in linewidth is followed by configuration interaction (CI) between 3p2P and 3d2nl*2P states. Several descrete CI resonances are observed in the Kr 3p spectrum. Such resonances are also studied in the N shell for the elements from Te (Z = 52) to Ba (Z = 56). For these elements the effect is found to be much larger due to the strong collective character of 4d-nf* excitations.

A new method for ESCA studies of liquid-phase samples

Abstract A new technique is described for obtaining ESCA spectra from liquid-phase samples. It combines temperature regulation of the liquid samples, which are continuously created as thin films on a metal backing, with the use of monochromatized A1 Kα radiation for excitation. The technique is simple to implement and can be used routinely over essentially unlimited periods of recording time in the spectrometer. The results show substantially increased quality with respect to earlier measurements in terms of signal-to-background ratio and resolution. The technique also implies a vast increase in the number of solvents usable for future liquid-phase ESCA work.