Anion and Cation-yield Spectroscopy of Core-excited SF6

We report an extensive study on total and partial-ion-yield spectroscopy around both the S 2p and F 1s thresholds in SF6. All positive and negative single-ion channels have been measured. Below the F 1s threshold we detect a large variation in relative intensity of the resonant structures according to the specific channel monitored, indicating selective fragmentation. Above threshold, at variance with previous cases described by us, we detect high-intensity structures related to shape resonances not only in the cation channels but also for the anions. We discuss the applicability and limits of a model we have developed for the analysis of shape resonances in anion yields as a function of molecular size

Atom-specific identification of adsorbed chiral molecules by photoemission

The study of chiral adsorbed molecules is important for an analysis of enantioselectivity in heterogeneous catalysis. Here we show that such molecules can be identified through circular dichroism in core-level photoemission arising from the chiral carbon atoms in stereoisomers of 2,3-butanediol molecules adsorbed on Si(100), using circularly polarized x rays. The asymmetry in the carbon 1s intensity excited by right and left circularly polarized light is readily observed, and changes sign with the helicity of the radiation or handedness of the enantiomers; it is absent in the achiral form of the molecule. This observation demonstrates the possibility of determining molecular chirality in the adsorbed phase

Unified treatment of recoil and Doppler broadening in molecular high-energy photoemission

Doppler and recoil effects are an integral part of the photoemission process at the high kinetic energies reached in hard x-ray photo-electron spectroscopy (HAXPES) and have a major effect on the observed lineshape, resulting in broadening, energy losses and discrete excitations. These effects can be modeled with a high degree of detail for small systems like diatomic molecules, for larger systems such treatment is often superfluous as the fine spectral features are not observable. We present a united description of the Doppler and recoil effects for arbitrary polyatomic systems and offer an approximate description of the recoil- and Doppler-modified photoemission spectral lineshape as a practical tool in the analysis of HAXPES spectra of core-level photoemission. The approach is tested on the examples of carbon dioxide and pentane molecules. The C and O 1s photoelectron spectra of CO2 in gas phase were also measured at 2.3 and 7.0 keV photon energy at Synchrotron SOLEIL and the spectra were analyzed using the model description. The limitations and applicability of the approach to adsorbates, interfaces and solids is briefly discussed

Roadmap on photonic, electronic and atomic collision physics: I. Light-matter interaction

We publish three Roadmaps on photonic, electronic and atomic collision physics in order to celebrate the 60th anniversary of the ICPEAC conference. In Roadmap I, we focus on the light-matter interaction. In this area, studies of ultrafast electronic and molecular dynamics have been rapidly growing, with the advent of new light sources such as attosecond lasers and x-ray free electron lasers. In parallel, experiments with established synchrotron radiation sources and femtosecond lasers using cutting-edge detection schemes are revealing new scientific insights that have never been exploited. Relevant theories are also being rapidly developed. Target samples for photon-impact experiments are expanding from atoms and small molecules to complex systems such as biomolecules, fullerene, clusters and solids. This Roadmap aims to look back along the road, explaining the development of these fields, and look forward, collecting contributions from twenty leading groups from the field

A high-resolution photoemission study of ethanol adsorption on Si(111)-(7x7)

Ethanol adsorption on Si(111)-(7 x 7) has been investigated by high-resolution photoemission in the valence band and the Si 2p and C Is energy regions. The valence band spectra show that, similarly to methanol adsorption on Si(111)-(7 x 7), ethanol adsorption is dissociative and occurs through O-H bond breakage and Si-O bond formation. However, at variance with a previous study, we find that the adsorption does not proceed selectively on surface rest atoms. The lack of site selectivity is also confirmed by the photoemission spectra of the Si 2p core level line. The possibility of a further fragmentation of the ethoxy species into a methoxy plus a methyl group is discussed. (C) 1998 Elsevier Science B.V. All rights reserved

Effect of the silicon surface step on the acetylene reaction with the Si(111)7x7 reconstructed surface

In this paper we report on a morphological investigation of the growth mechanism of silicon carbide (SiC) on the Si(111)7 x 7 surface. The role of the substrate morphology and temperature during acetylene exposure has been studied with the aim to obtain high quality SiC films. We compared two starting points of silicon substrate: one characterised by step bunching and one by monoatomic terraces of the same width. Our results indicate that a lower density of defects and holes is present in the former case. (C) 2004 Elsevier B.V. All rights reserved