Academic literature on the topic 'Resonant Auger scattering'

The angular distribution and spin polarisation of the resonantly photoexcited Xe¤(4d–15/2 6p3/2 ) N5O2,3O2,3 Auger spectrum is investigated. The two-step model has been used which allows us to independently determine the dynamic parameters of the primary excitation and the Auger emission process. Assuming either a fully circularly or linearly polarised photon beam the dynamic parameters determining the primary photoexcitation become constant numbers independent of the matrix elements. Applying a relativistic distorted wave approximation the relevant numbers describing the Auger decay dynamics, i.e. relative intensities, angular distribution and spin polarisation parameters have been calculated, and are compared with experimental and other theoretical data. With this, predictions for the spin polarisation vector are possible. A large degree of dynamic spin polarisation has been found for all Auger transitions to a final state with Jf = ½ . This is in contrast to earlier calculations for diagram Auger transitions. Recently, we have given an explanation for this deriving propensity rules for resonant Auger transitions. The propensity rules allow for predictions for which Auger line a large dynamic spin polarisation can be expected. The predictions are in accord with our multiconfigurational Dirac–Fock calculations for the resonant Xe N5O2,3O2,3 and Ar L3M2,3M2,3 Auger multiplets. It is demonstrated that the effect of a large spin polarisation is caused by a large shift of the scattering phase of the emitted ?s1/2 partial waves, whereas a small spin polarisation is due to a cancellation between the Coulomb and scattering phases of the partial waves.

We propose a new Auger-like mechanism for energy relaxation in quantum dots (QD) driven by resonant scattering of delocalized wetting layer (WL) carriers. It is demonstrated that resonant scattering leads to a considerable increase in the relaxation rate that can explain experimentally obtained relaxation rates. Analytical results for the relaxation rate are obtained for rectangular dots revealing a weak logarithmic dependence on the dot depth and level density. Comparing results for a rectangular and a parabolic QD model we conclude that the relaxation rate is not very sensitive to a chosen model.

We study steady states of semiconductor nanowires subjected to strong resonant time-periodic drives. The steady states arise from the balance between electron-phonon scattering, electron-hole recombination via photoemission, and Auger scattering processes. We show that tuning the strength of the driving field drives a transition between an electron-hole metal (EHM) phase and a Floquet insulator (FI) phase. We study the critical point controlling this transition. The EHM-to-FI transition can be observed by monitoring the presence of peaks in the density-density response function, which are associated with the Fermi momentum of the EHM phase and are absent in the FI phase. Our results may help guide future studies toward inducing exotic nonequilibrium phases of matter by periodic driving.

In this article, the mechanism of electronic transitions during scattering and stimulated desorption of ions from solid surfaces is discussed. Reactive ions such as H + and O + experience transient chemisorption during scattering from solid surfaces. These ions are neutralized almost completely on metal and semiconductor surfaces due to the band effect on resonance neutralization. The neutralization probability of H + is suppressed considerably on highly ionic compound surfaces and is dependent on the target species due to the formation of the bound state (on cations) or the surface molecule (on anions). Because of this, the H - ion is formed preferentially on the cationic site rather than on the anionic site. The noble-gas ions are neutralized via the Auger process so that the neutralization probability is basically independent of the band effect. The stimulated desorption of secondary O + and F + ions does not exhibit the band effect. This is because the desorption is initiated by the core hole state, which is followed by ionization via the intra-atomic Auger decay after breakage of the chemisorptive bond. The stimulated desorption of H + might occur from the valence holes but is more likely to be caused by the core-excited OH species via the interatomic Auger decay. The core hole is created not only by the electron and photon irradiation but also by the energetic ion bombardment due to the nonadiabatic transition of the primary ion/s core hole. Also presented are some applications of ion scattering and ion stimulated desorption for the analysis of the diffusion/segregation dynamics of oxygen and hydrogen on solid surfaces.

The present thesis is devoted to theoretical studies of resonant X-ray scattering and propagation of strong X-ray pulses. In the first part of the thesis the nuclear dynamics of different molecules is studied using resonant X-ray Raman and resonant Auger scattering techniques. We show that the shortening of the scattering duration by the detuning results in a purification of the Raman spectra from overtones and soft vibrational modes. The simulations are in a good agreement with measurements, performed at the MAX-II and the Swiss Light Source with vibrational resolution. We explain why the scattering to the ground state nicely displays the vibrational structure of liquid acetone in contrast to excited final state. Theory of resonant X-ray scattering by liquids is developed. We show that, contrary to aqueous acetone, the environmental broadening in pure liquid acetone is twice smaller than the broadening by soft vibrational modes significantly populated at room temperature. Similar to acetone, the "elastic" band of X-ray Raman spectra of molecular oxygen is strongly affected by the Thomson scattering. The Raman spectrum demonstrates spatial quantum beats caused by two interfering wave packets with different momenta as the oxygen atoms separate. It is found that the vibrational scattering anisotropy caused by the interference of the "inelastic" Thomson and resonant scattering channels in O2. A new spin selection rule is established in inelastic X-ray Raman spectra of O2. It is shown that the breakdown of the symmetry selection rule based on the parity of the core hole, as the core hole and excited electron swap parity. Multimode calculations explain the two thresholds of formation of the resonant Auger spectra of the ethene molecule by the double-edge structure of absorption spectrum caused by the out-of- and in-plane modes. We predict the rotational Doppler effect and related broadening of X-ray photoelectron and resonant Auger spectra, which has the same magnitude as its counterpart-the translational Doppler effect. The second part of the thesis explores the interaction of the medium with strong X-ray free-electron laser (XFEL) fields. We perform simulations of nonlinear propagation of femtosecond XFEL pulses in atomic vapors by solving coupled Maxwell's and density matrix equations. We show that self-seeded stimulated X-ray Raman scattering strongly influences the temporal and spectral structure of the XFEL pulse. The generation of Stokes and four-wave mixing fields starts from the seed field created during pulse propagation due to the formation of extensive ringing pattern with long spectral tail. We demonstrate a compression into the attosecond region and a slowdown of the XFEL pulse up to two orders of magnitude. In the course of pulse propagation, the Auger yield is strongly suppressed due to the competitive channel of stimulated emission. We predict a strong X-ray fluorescence from the two-core-hole states of Ne created in the course of the two-photon X-ray absorption.
QC 20110426