Linear magnetic and alignment dichroism in Auger photoelectron coincidence spectroscopy (original) (raw)
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Electron–electron coincidence study of double Auger processes in atoms
Journal of Electron Spectroscopy and Related Phenomena, 2004
The double Auger process after Ar 2p and Ne 1s inner-shell photoionization is investigated by means of angle resolved time-of-flight electronelectron coincidence spectroscopy. This method allows to disentangle direct double Auger from cascade Auger processes. Information about the energy sharing as well as the angular correlation of the two emitted electrons is obtained. Circular dichroism in the double Auger emission produced by circularly polarized light is discussed.
Dichroic effects in Auger photoelectron coincidence spectroscopy of solids
The Sn M 5 N 45 N 45 Auger spectrum from the ͑ ͱ 3 ϫ ͱ 3͒R30°-Sn/ Ge͑111͒ surface has been measured in coincidence with the corresponding 3d 5/2 photoelectron. By detecting this pair at appropriate emission angles, the contribution from spin-symmetric ͑triplet͒ and spin-antisymmetric ͑singlet͒ final states can be selectively enhanced or suppressed. This dichroic effect in the Auger photoelectron coincidence spectroscopy of solids provides a probe of the local valence electronic structure with element, chemical states, emission depth, and spin selectivity. The consequences and applications of this dichroic effect are discussed.
Photoelectron–Auger electron coincidence spectroscopy of free molecules: New experiments
Journal of Electron Spectroscopy and Related Phenomena, 2011
Photoelectron-Auger electron coincidence spectroscopy probes the dicationic states produced by Auger decay following the photoionization of core or inner valence levels in atoms, molecules or clusters. Moreover, the technique provides valuable insight into the dynamics of core hole decay. This paper serves the dual purpose of demonstrating the additional information obtained by this technique compared to Auger spectroscopy alone as well as of describing the new IPP/FHI apparatus at the BESSY II synchrotron radiation source. The distinguishing feature of the latter is the capability to record both the photoelectron and Auger electron with good energy and angle resolution, for which purpose a large hemispherical electrostatic analyser is combined with several linear time-of-flight spectrometers. Results are reported for the K-shell photoionization of oxygen (O 2 ) and the subsequent K-VV Auger decay. Calculations in the literature for non-coincident O 2 Auger spectra are found to be in moderately good agreement with the new data.
Photoelectron-Auger Electron Coincidence Spectroscopy of Free Molecules
fhi-berlin.mpg.de
Photoelectron-Auger electron coincidence spectroscopy probes the dicationic states produced by Auger decay following the photoionization of core or inner valence levels in atoms, molecules or clusters. Moreover, the technique provides valuable insight into the dynamics of core hole decay. This paper serves the dual purpose of demonstrating the additional information obtained by this technique compared to Auger spectroscopy alone as well as of describing the new IPP/FHI apparatus at the BESSY II synchrotron radiation source. The distinguishing feature of the latter is the capability to record both the photoelectron and Auger electron with good energy and angle resolution, for which purpose a large hemispherical electrostatic analyser is combined with several linear time-of-flight spectrometers. New results are reported for the K-shell photoionization of oxygen (O 2) and the subsequent K-VV Auger decay. Calculations in the literature for non-coincident O 2 Auger spectra are found to be in moderately good agreement with the new data.
Auger photoelectron coincidence spectroscopy
Journal of Electron Spectroscopy and Related Phenomena, 1999
Auger photoelectron coincidence spectroscopy (APECS) is a technique that provides us with unique information and a chance to gain insight into the significance of processes in the Auger spectra of atoms in solids. Hence it is a great aid in our understanding of the Auger process in atoms where electron correlations are strong. Despite the first demonstration of the technique more than 20 years ago, there are still very few working experiments. The reasons why, and the ways forward are discussed.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1994
The Auger electron spectrum associated with decay of a core-hole on the terminal nitrogen and that associated with the central nitrogen of nitrous oxide, N20, are obtained individually through the use of a coincidence technique. Specifically, each of the two Auger electron spectra is obtained by detection of Auger electrons in coincidence with near zero energy (threshold) photoelectrons at the respective ionization thresholds. These zero energy electrons serve to identify the core-ionization continuum associated with the different Auger electrons. The salient features of the experimental spectra are in good agreement with theoretical calculations. The low counting rate generally associated with coincidence experiments, especially in the gas phase, is not encountered because the low energy electrons are collected over a 4-rr solid angle. Also, velocity discrimination is accomplished by a spatial filter rather than by time-of-flight to utilize the maximum duty cycle of the synchrotron source. These data are believed to be the first examples of chemical-site-selective molecular Auger spectra .
Spin selectivity by Auger Photoelectron coincidence spectroscopy
The M 3 M 4,5 M 4,5 Auger transition from a Cu(111) surface is studied using Angular Resolved Auger-PhotoElectron Coincidence Spectroscopy (AR-APECS). In the experiment two different geometrical configurations of the electron analyzers allow us to sample different emission angles of the ejected electrons leading to different weights of the singlet and triplet contributions in the studied transition. The experimental spectra are modeled within a two-step approach using the Cini theory for the closed band case so as to properly consider the spin-orbit interaction and the hole-hole correlation energy. Ingredients for the theory, like density of states, are obtained fully ab-initio in the framework of density functional theory by performing all-electron calculations. The obtained results confirm the recently discovered selectivity of AR-APECS in the final spin-state.
Photoelectron–Auger electron coincidence study for condensed matter
Journal of Electron Spectroscopy and Related Phenomena, 2004
Advances in materials science have produced a wide array of new solid-state systems with tunable properties and previously unattainable combinations of phenomena that hold the promise of entirely new approaches to technological applications. Invariably, these new materials are increasingly complex and include a large number of constituents in a variety of chemical states. Entirely new theoretical and experimental approaches are needed to gain the insights necessary for intelligent engineering of these materials. In the past 20 years, a steadily increasing number of electron-electron coincidence experiments on atoms and molecules have demonstrated the capability of investigating complicated systems with sensitivity and specificity well beyond the limits imposed by conventional electron spectroscopies. Over the past decade or so, Auger-photoelectron coincidence spectroscopy (APECS) has emerged as a powerful technique for obtaining detailed information about complex materials systems. Moreover, the recent advent of angle-resolved (AR)-APECS has introduced a new level of discrimination in studying the distribution of electrons photoemitted from complex systems. In this review, we describe the basic ideas behind APECS and discuss a study of the SiO 2 system as an example of the unique information this technique can provide. We then introduce the concept of AR-APECS, explain its novel state and angular momentum selectivity that can be used to disentangle information about complex systems that is hidden to conventional spectroscopies. Examples of AR-APECS measurements from Cu, Ge, and graphite that exemplify the capabilities of this technique are presented.
Physical Review Letters, 2011
The absence of sharp structures in the Auger line shapes of partially filled bands has severely limited the use of electron spectroscopy in magnetic crystals and other correlated materials. By a novel interplay of experimental and theoretical techniques we achieve a combined understanding of the photoelectron, Auger, and Auger-photoelectron coincidence spectra (APECS) of the antiferromagnetic CoO. A recently discovered dichroic effect in angle resolved (DEAR) APECS reveals a complex pattern in the Auger line shape, which is here explained in detail, labeling the final states by their total spin. Since the dichroic effect exists in the antiferromagnetic state but vanishes at the Néel temperature, the DEAR-APECS technique detects the phase transition from its local effects, thus providing a unique tool to observe and understand magnetic correlations where the usual methods are not applicable.
Non-dipole effects in magnetic dichroism in atomic photoionization
Journal of Physics B: Atomic, Molecular and Optical Physics, 2001
Expressions for the angular distribution of photoelectrons from polarized atoms and for the magnetic dichroism in the angular distribution are obtained taking into account a full multipole expansion of radiation in electric and magnetic moments. Non-dipole effects in circular and linear magnetic dichroism in the angular distribution are analysed within the first-order corrections. An experimental arrangement is proposed to observe the non-dipole effects in the magnetic dichroism in the angular distribution and, for the first time, calculations of these effects are performed. Pronounced non-dipole effects are predicted for the photoionization of the sodium atom in the 3p state in the region of the Cooper minimum at photon energies as low as 10 eV.