N. Leclercq

New high luminosity “double toroidal” electron spectrometer

In this article we describe the design and the operation of an original, high transmission, electrostatic “double toroidal” electron energy analyzer. The double toroidal analyzer allows the high resolution and high luminosity simultaneous measurement of the kinetic energy, and angular distribution of electrons, using a two-dimensional position sensitive detector. The exact shape of the electrodes is deduced from both analytical and numerical electron trajectory calculations. The electron detector is based on a charge analysis and optimized to attain a 100 kHz counting rate. The actual performances of the analyzer are illustrated with spectra obtained after resonant Auger decay of N2O excited around the nitrogen K shell (hν=401 eV), and of Kr after 3d5/2→5p excitation at hν=91.2 eV. A “etendue” of 15% of the pass energy, as well as a resolving power (Ep/δE) of 100 were measured.

Development of a four-element conical electron lens dedicated to high resolution Auger electron–ion(s) coincidence experiments

A four-element conical electron lens has been developed in view of its integration to a double toroidal electron energy analyzer (DTA) dedicated to Auger electron–ion coincidence measurements. The lens design, using electron trajectory numerical simulations, was entirely guided by the perspective of analyzing energetic electrons with high resolution in the multicoincidence regime. The design, construction, and experimental characterization stages of this electron optics system are described in this article. Emphasis is put on the importance of third generation synchrotron radiation sources when performing such multicoincidence experiments.

High spatial resolution two-dimensional position sensitive detector for the performance of coincidence experiments

A position sensitive detector (PSD) adapted to the technical and mechanical specifications of our angle and energy resolved electron-ion(s) coincidence experiments is described in this article. The device, whose principle is very similar to the one detailed by J. H. D. Eland [Meas. Sci. Technol. 5, 1501 (1994)], is composed by a set of microchannel plates and a delay line anode. The originality comes from the addition in front of the encoding surface of a ceramic disk covered by a resistive surface. The capacitive coupling between the anode and the resistive plane has the double advantage of eliminating the spatial modulations due to the lattice of the anode and also of sensitizing a greater number of electrodes, increasing thus considerably the accuracy of the position measurements. The tests carried out with a time to digital conversion module of 250 ps resolution showed that a spatial resolution better than 50μm and a dead time of 160 ns can be achieved. Typical images obtained with the help of the EPI...

Resonant Auger spectroscopy on SiF4 and SiCl4 molecules excited around the silicon 2p edge

Abstract We describe in this paper very recent results obtained by mean of resonant Auger spectroscopy experiments on SiF 4 and SiCl 4 molecules excited around the silicon 2p edge. Both molecules exhibit participator resonant Auger decay paths never observed in previous measurements. The enhancement of photoelectron lines is interpreted by the silicon character versus the halogeno lone pairs parentage. In contrast with the SiF 4 molecule, the SiCl 4 molecule reveals a continuous electron background when exciting the two first core to anti-bonding discrete resonances. A possible explanation of the origin of this electron background in terms of an Auger emission perturbed by the nuclear motion is also given.

New setup for angular distribution measurements of Auger electrons from fixed in space molecules

A new experimental setup for measurement of the angular distributions of energy selected Auger electrons emitted from fixed in space molecules is presented. The system is based on two identical ion detectors with a small angular acceptance placed at 0° and 90° relative to the polarization axis of the incident radiation, and a high luminosity double-toroidal electron analyzer combined with position sensitive detection. This setup allows selection of the molecular alignment for σ and π ionization channels simultaneously and provides an energy and ejection angle measurement of the outgoing electron. The performance in terms of energy and angular resolution, as well as the calibration procedure, are discussed. Sample results obtained on the carbon monoxide ionized above the C 1s threshold are presented.

Dynamical effects and selective fragmentation after inner shell excitation

We have studied the fragmentation of core excited molecules probed by the Auger electron-ion coincidence technique. Our results illustrate site selective fragmentation by hexamethyldisiloxane ionized at the Si 2p and the C 1s thresholds. By combining high resolution electron spectroscopy with resonant Auger electron-ion coincidence, we reveal the role played by nuclear motion in the fragmentation of core excited CO2 and CF4 molecules.