Analysis of Clean Transition Metal Surfaces by Core Level Spectroscopy

The shifts in the binding energy of core electrons detected by high resolution X-ray photoelectron spectroscopy are a very sensitive probe of the chemical bonding of the excited atom. Since the surface atoms have their geometrical environment perturbed, their core levels are shifted from their bulk positions. A very large number of experiments have been performed on the 4f core level positions of tantalum and tungsten for various orientations of the surface plane. Systematic trends have been put forward and explained by theoretical models. Furthermore, the analysis of the angular variation of the core level line intensities gives structural information when compared with theoretical calculations. In the case of W(100) a single scattering theory is sufficient to reproduce experimental data. Finally we show that, in some particular cases, the core level lineshapes may differ strongly from a Doniach Sunjic model. The temperature dependence of their widths due to core hole-phonon coupling can be reproduced within the independent boson theory

Maternal exposure to ambient black carbon particles and their presence in maternal and fetal circulation and organs : an analysis of two independent population-based observational studies

Funding European Research Council, Flemish Scientific Research Foundation, Kom op Tegen Kanker, UK Medical Research Council, and EU Horizon 2020. Acknowledgments The ENVIRONAGE birth cohort was initiated by the European Research Council (ERC-2012-StG 310898) and received additional funding from the Flemish Scientific Research Foundation and Kom op Tegen Kanker (KoTK). The detection equipment was funded by the METHUSALEM Program and the INCALO project (ERC-PoC). We acknowledge the Flemish Scientific Research Foundation (FWO; 1150920N to EB and G082317N). The SAFeR study was funded by the UK Medical Research Council (MR/L010011/1 and MR/P011535/1) and the EU's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie project PROTECTED (grant agreement number 722634) and FREIA project (grant agreement number 825100) as well as by NHS Grampian Endowments grants (16/11/056, 17/034, 18/14, 19/029, and 20/031) to PAF. We thank the midwives from the maternity ward of the East-Limburg Hospital in Genk, Belgium, for coordinating and supporting the study at the ward. We thank the Advanced Optical Microscopy Centre for the maintenance of the microscopic instruments. Moreover, we thank our colleagues from the Centre for Environmental Sciences for their hard work in collecting and processing the samples for the ENVIRONAGE birth cohort. Additionally, we thank the NHS Grampian Research Nurses and NHS Grampian R&D for their tireless recruitment work for the SAFeR study. We thank the past and present SAFeR team for their hard work with the fetuses and placentae. Finally, we thank the NHS Grampian Biorepository for their oversight role in SAFeR and assistance in processing and preparation of tissue sections.Peer reviewedPublisher PD

PROPRIETES ELECTRONIQUES DES PHASES ADSORBEES ET DES SURFACES DES METAUX ET SEMI-CONDUCTEURS

Cet article présente quelques progrès récents obtenus dans les études expérimentales des propriétés électroniques des adsorbats et des surfaces métalliques propres. La spectroscopie d'électrons et plus particulièrement la photoémission angulaire apparaît comme un moyen puissant pour obtenir des informations sur les niveaux électroniques des adsorbats ou des surfaces propres. Cette technique peut également donner des informations sur la géométrie des atomes de surface. Des études expérimentales sur les plasmons de surface, les états de surface et les déplacements de niveaux de coeur sont présentées pour des surfaces propres. A titre d'exemples de surfaces couvertes d'adsorbats, deux cas typiques sont choisis : la structure de bande bidimensionnelle et la molécule orientée. Enfin il est montré que la diffraction des photoélectrons peut-être utilisée pour la détermination des structures atomiques, que ce soit dans le cas des adsorbats ou des surfaces propres.This paper surveys recent progress in experimental studies on electronic properties of adsorbates and clean metal surfaces. Electron spectroscopy and particularly angle resolved photoelectron spectroscopy appears to be a very powerful tool to get informations on electronic levels of adsorbates or clean surfaces. Moreover this technique may also give informations about the atomic geometry of the surface. Experimental investigation about surface plasmons, surface states, core level shifts are presented for clean surfaces. As examples of adsorbate covered surfaces two typical cases are chosen : two dimensional band structure and oriented molecules. Finally the photoelectron diffraction may be used for surface structure determination either in the case of an adsorbate or a clean metal surface

Spectroscopie de pertes d'énergie d'électrons. Application a l'étude de la chimisorption de l'oxygène sur la face (100) du molybdène

We describe results of a study of the adsorption of oxygen on the (100) molybdenum face by électron energy loss spectroscopy. New transitions appear which confirm the values obtained by photoemission from the same system. The comparison between the two techniques is extended to other metal-adsorbed gas systems and there is a fair agreement.Les résultats d'une étude de l'adsorption d'oxygène sur la face (100) du molybdène par spectroscopie de pertes d'énergie d'électrons sont décrits. De nouvelles transitions apparaissent confirmant les valeurs obtenues par photoémission sur le même système. La comparaison des deux techniques est étendue à d'autres couples métal-gaz adsorbé et montre la bonne concordance des résultats

PERTES CARACTÉRISTIQUES DES ÉLECTRONS RÉFLÉCHIS SUR LE MOLYBDÈNE (100)

La rétrodiffusion des électrons de 250 eV en incidence normale sur la face (100) de Mo présente un spectre assez complexe pour les pertes d'énergie comprises entre 5 et 25 eV. Ce spectre est notablement altéré par CO et H2 chimisorbés sur le molybdène.The energy spectrum of back scattered 250 eV electrons impinging normally onto (100) Mo is rather complex for energy losses less than 25 eV. This spectrum is definitely altered when CO and H2 are chemisorbed on the molybdenum surface

Substrate-dependent valency of Yb chemisorbed onto Si(111)7×7, Si(100)2×1, and a-Si surfaces

Yb chemisorption at monolayer coverages onto Si substrates is the precursor stage of Yb/Si interface formation. Ytterbium is divalent as a metal but forms mixed-valent intermetallic compounds with silicon. L-edge x-ray-absorption resonance measurements show that at the early stage of the Yb/Si interface formation the Yb-Si chemisorption on different Si substrates induces mixed valency in the Yb atoms chemisorbed on the a-Si surface sites and a lower mixed valency in those on the Si(100) sites, but leaves purely divalent Yb ions on the Si(111) surface. This has direct consequences on the kinetics of the interface formation that develops for higher Yb coverages. Delocalization of Yb 4f electrons appears to be a unique electron probe of the bonding at semiconductor surfaces, and the Yb/Si interface can be viewed as a prototype case for understanding the kinetics of metal-semiconductor interface formation