Wave packet propagation study of the charge transfer interaction in the F^- -Cu(111) and -Ag(111) systems

The electron transfer between an $F^{-}$ ion and $Cu(111)$ and $Ag(111)$ surfaces is studied by the wave packet propagation method in order to determine specifics of the charge transfer interaction between the negative ion and the metal surface due to the projected band gap. A new modeling of the $F^{-}$ ion is developed that allows one to take into account the six quasi-equivalent electrons of $F^{-}$ which are {\it a priori} active in the charge transfer process. The new model invokes methods of constrained quantum dynamics. The six-electron problem is transformed to two one-electron problems linked via a constraint. The projection method is used to develop a wave packet propagation subject to the modeling constraint. The characteristics (energy and width) of the ion $F^{-}$ ion level interacting with the two surfaces are determined and discussed in connection with the surface projected band gap.Comment: 34 pages, Revtex, 9 figures (postscript

The sequence to hydrogenate coronene cations:A journey guided by magic numbers

The understanding of hydrogen attachment to carbonaceous surfaces is essential to a wide variety of research fields and technologies such as hydrogen storage for transportation, precise localization of hydrogen in electronic devices and the formation of cosmic H2. For coronene cations as prototypical Polycyclic Aromatic Hydrocarbon (PAH) molecules, the existence of magic numbers upon hydrogenation was uncovered experimentally. Quantum chemistry calculations show that hydrogenation follows a site-specific sequence leading to the appearance of cations having 5, 11, or 17 hydrogen atoms attached, exactly the magic numbers found in the experiments. For these closed-shell cations, further hydrogenation requires appreciable structural changes associated with a high transition barrier. Controlling specific hydrogenation pathways would provide the possibility to tune the location of hydrogen attachment and the stability of the system. The sequence to hydrogenate PAHs, leading to PAHs with magic numbers of H atoms attached, provides clues to understand that carbon in space is mostly aromatic and partially aliphatic in PAHs. PAH hydrogenation is fundamental to assess the contribution of PAHs to the formation of cosmic H2.</p

Excitation of local magnetic moments by tunnelling electrons

The advent of milli-kelvin scanning tunneling microscopes (STM) with inbuilt magnetic fields has opened access to the study of magnetic phenomena with atomic resolution at surfaces. In the case of single atoms adsorbed on a surface, the existence of different magnetic energy levels localized on the adsorbate is due to the breaking of the rotational invariance of the adsorbate spin by the interaction with its environment, leading to energy terms in the meV range. These structures were revealed by STM experiments in IBM Almaden in the early 2000's for atomic adsorbates on CuN surfaces. The experiments consisted in the study of the changes in conductance caused by inelastic tunnelling of electrons (IETS, Inelastic Electron Tunnelling Spectroscopy). Manganese and Iron adatoms were shown to have different magnetic anisotropies induced by the substrate. More experiments by other groups followed up, showing that magnetic excitations could be detected in a variety of systems: e.g. complex organic molecules showed that their magnetic anistropy was dependent on the molecular environment, piles of magnetic molecules showed that they interact via intermolecular exchange interaction, spin waves were excited on ferromagnetic surfaces and in Mn chains, and magnetic impurities have been analyzed on semiconductors. These experiments brought up some intriguing questions: the efficiency of magnetic excitations was very high, the excitations could or could not involve spin flip of the exciting electron and singular-like behavior was sometimes found at the excitation thresholds. These facts called for extended theoretical analysis; perturbation theories, sudden-approximation approaches and a strong coupling scheme successfully explained most of the magnetic inelastic processes. In addition, many-body approaches were also used to decipher the interplay between inelasComment: Review article to appear in Progress of Surface Scienc

Lymphoepithelioma-like carcinoma of the vulva, an underrecognized entity? Case report with a single inguinal micrometastasis detected by sentinel node technique

This report describes an unusual EBV-negative lymphoepithelioma-like carcinoma of the vulva in a 73-year-old patient. The lesion was localised at the right minor labium and was resected by partial vulvectomy. A synchronous sentinel lymph node biopsy revealed a single micrometastasis in the right inguinal region, which prompted local radiotherapy. Follow-up nine months later showed only slight vulvar atrophy, without signs of local recurrence or distant metastases

Attachement et bombardement électronique

Parmi les processus induits par impact d'électron sur une molécule, le processus d'attachement contrôle les transferts d'énergie entre l'électron et la molécule et produit des ions négatifs par fragmentation de l'ion négatif moléculaire intermédiaire formé. L'article porte essentiellement sur les mécanismes de formation d'ions négatifs par attachement dissociatif, en présentant les approches théoriques à la base de ces mécanismes et en les illustrant par quelques exemples (HCl, SF6

Low energy electron impact on gas phase 5-nitrouracil

Excitation of the first electronic states, vibrational excitation between 1 and 3 eV, and negative ion formation (0–2 eV) in gas phase 5-nitrouracil are presented. Five singlet states are clearly identified at 4.76; 5.72; 6.82; 7.82 and 9.2 eV. A band at 3.7 eV could be assigned to a triplet state. The vibrational modes observed indicate resonant states having both p* and r* character. The most intense anions (MNO2), (MH) appear at zero energy with huge cross sections (P1018 m2). Anion cross sections versus electron energy reveal structures interpreted using the anion energy thresholds found by DFT calculations. 2008 Elsevier B.V. All rights reserved

Dynamique d'états électroniques excités à la surface d'un film ultra-mince d'Ar condensé sur un métal

Ce travail de thèse porte sur l'étude de la dynamique d'états électroniques excités à la surface d'un métal recouvert d'une couche ordonnée ultra-mince de diélectrique (Ar). On s'est intéressé à la façon dont cette couche adsorbée modifie les propriétés des deux types d'états excités en surface : états délocalisés (comme états image, résonances image, résonances de puits quantique) et états localisés sur un adsorbat moléculaire (ion négatif transitoire). Pour décrire l'interaction entre l'électron excité et la couche d'Ar on a développé un modèle microscopique tridimensionnel sans paramètre ajustable, qui intègre la structure électronique et géométrique de la couche adsorbée sur métal. Les propriétés des états électroniques délocalisés (énergie, durée de vie, masse effective) sont discutées en fonction de l'épaisseur de la couche d'Ar (entre 1 et 4 mono-couches). Le caractère isolant d'une couche d'Ar très mince, même une seule mono-couche, est mis en évidence. Les résultats théoriques concernant les états image sur Cu(100) recouvert d'Ar sont comparés à des résultats expérimentaux et l'accord est très bon. Sur le même système, on a mis en évidence des résonances de puits quantique qui ont été par la suite confirmées expérimentalement. L'existence et les propriétés des résonances image sur un métal à électrons libres recouvert d'Ar sont aussi discutées.Les propriétés (énergie et largeur) de la résonance N2-(2?g) de la molécule d'azote adsorbée sur une mono-couche d'Ar déposée sur métal sont calculées et discutées en termes d'effets locaux(site d'adsorption) et globaux (réflectivité à l'interface Ar-vide).The present work concerns the dynamics of electronic excited states at the surface of a metal covered by a very thin dielectric ordered layer (Ar). We have studied how this layer modifies the properties of two types of excited states at surface: delocalised states (image states, image resonances, quantum well resonances) and localised states on molecular adsorbates at the surface. In order to describe the interaction between the excited electron and the Ar layer we have developed a parameter free microscopic model. This model takes into account the electronic and geometrical structures of the adsorbed layer on the metal. The properties of the delocalised electronic states (energy, lifetime, effective mass) as a function of the Ar layer thickness (from 1 to 4 monolayers) are discussed. We have shown that a very thin Ar layer exhibits an insulating character. The theoretical results concerning the image states on Cu(100) covered by Ar are compared to experimental results and the agreement between them is very good. We have observed quantum well resonances on the same system. These resonances have been confirmed experimentally afterwards. The existence and properties of image resonances on a free electron metal covered by an Ar layer are also discussed.The properties (energy and width) of the N2-(2?g) resonance of the nitrogen molecule adsorbed on an Ar monolayer deposited on a metal are calculated and discussed in terms of local (adsorption sites) and global (reflectivity of the Ar-vacuum interface) effects.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Influence of a graphene surface on the first steps of the hydrogenation of a coronene molecule

International audienc