Interface bonding of a ferromagnetic/semiconductor junction : a photoemission study of Fe/ZnSe(001)

We have probed the interface of a ferromagnetic/semiconductor (FM/SC) heterojunction by a combined high resolution photoemission spectroscopy and x-ray photoelectron diffraction study. Fe/ZnSe(001) is considered as an example of a very low reactivity interface system and it expected to constitute large Tunnel Magnetoresistance devices. We focus on the interface atomic environment, on the microscopic processes of the interface formation and on the iron valence-band. We show that the Fe contact with ZnSe induces a chemical conversion of the ZnSe outermost atomic layers. The main driving force that induces this rearrangement is the requirement for a stable Fe-Se bonding at the interface and a Se monolayer that floats at the Fe growth front. The released Zn atoms are incorporated in substitution in the Fe lattice position. This formation process is independent of the ZnSe surface termination (Zn or Se). The Fe valence-band evolution indicates that the d-states at the Fermi level show up even at submonolayer Fe coverage but that the Fe bulk character is only recovered above 10 monolayers. Indeed, the Fe 1-band states, theoretically predicted to dominate the tunneling conductance of Fe/ZnSe/Fe junctions, are strongly modified at the FM/SC interface.Comment: 23 pages, 5 figures, submitted to Physical review

Ozone synthesis induced by electron bombardment of a dioxygen matrix

L'irradiation d'un film d'oxygène moléculaire par des électrons conduit à la production d'ozone. O3 a été mis en évidence par spectroscopie de perte d'énergie d'électrons (HREELS) qui permet d'observer les modes d'excitation vibrationnelle des molécules. L'identification de O3 est confirmée par l'étude de l'effet isotopique. Le seuil énergétique de formation est de l'ordre de 3,5 eV. Il correspond à la dissociation de O2 par attachement d'un électron : O2+e-↦(3P)+O-(2P), suivi de la réaction spontanée de recombinaison : O+O2+O2↦O3+O2. A des énergies supérieures à 5,1 eV, l'excitation de O2 vers des états de Rydberg et du continuum de Schumann-Runge est la principale source d'oxygène atomique et donc d'ozone. Des mesures en fonction du temps d'irradiation montrent que la quantité d'ozone formé sature

Synthèse d'ozone induite par bombardement électronique d'une matrice d'oxygène

L'irradiation d'un film d'oxygène moléculaire par des électrons conduit à la production d'ozone. O3 a été mis en évidence par spectroscopie de perte d'énergie d'électrons (HREELS) qui permet d'observer les modes d'excitation vibrationnelle des molécules. L'identification de O3 est confirmée par l'étude de l'effet isotopique. Le seuil énergétique de formation est de l'ordre de 3,5 eV. Il correspond à la dissociation de O2 par attachement d'un électron : O2+e-↦(3P)+O-(2P), suivi de la réaction spontanée de recombinaison : O+O2+O2↦O3+O2. A des énergies supérieures à 5,1 eV, l'excitation de O2 vers des états de Rydberg et du continuum de Schumann-Runge est la principale source d'oxygène atomique et donc d'ozone. Des mesures en fonction du temps d'irradiation montrent que la quantité d'ozone formé sature

Electron capture and loss in the scattering of oxygen atoms and ions on Mg, Al and Ag surfaces

We present the results of a study of collisions of 1 to 4 keV oxygen ions and atoms with Mg, Al and Ag surfaces. Formation of O- is in particular investigated. This is an interesting multichannel problem, since the ground state electronic configuration of oxygen 2p(4) corresponds to three states and electron capture processes involve three atom (P-3, D-1 and S-1)-metal continua. We report scattered ion fractions, measured in an angular range extending from 2 degrees to 40 degrees with respect to the surface plane. This allowed us to investigate the characteristics of the resonant charge transfer process for a large range of collision velocities normal to the surface, thus probing the charge transfer process in different atom-surface distance ranges. The ion fractions are found to increase with increasing angle and increasing energy. Similar fractions are obtained for Al and Ag, but significantly higher ones for Mg. Ionisation processes in hard collisions with surface atoms are observed. An electron spectroscopy study was performed and did not reveal any signs of autoionising state (O**2p(2)3s(2)) production

Electron capture and loss in the scattering of oxygen atoms and ions on Mg, Al and Ag surfaces

We present the results of a study of collisions of 1 to 4 keV oxygen ions and atoms with Mg, Al and Ag surfaces. Formation of O- is in particular investigated. This is an interesting multichannel problem, since the ground state electronic configuration of oxygen 2p(4) corresponds to three states and electron capture processes involve three atom (P-3, D-1 and S-1)-metal continua. We report scattered ion fractions, measured in an angular range extending from 2 degrees to 40 degrees with respect to the surface plane. This allowed us to investigate the characteristics of the resonant charge transfer process for a large range of collision velocities normal to the surface, thus probing the charge transfer process in different atom-surface distance ranges. The ion fractions are found to increase with increasing angle and increasing energy. Similar fractions are obtained for Al and Ag, but significantly higher ones for Mg. Ionisation processes in hard collisions with surface atoms are observed. An electron spectroscopy study was performed and did not reveal any signs of autoionising state (O**2p(2)3s(2)) production

Local effects in electron capture processes of fluorine atoms interacting with an oxidised Mg surface

Changes in electron capture rates during the oxidation of metal surfaces are investigated on the example of $\rm F^-$ formation in fluorine ion/atom scattering on a Mg surface exposed to $\rm O_2$ and also for MgO(100). In the low-coverage, chemisorption range, $\rm F^-$ formation decreases in spite of a decrease in the surface work function. This is assigned to a local effect due to specifics of the electronic structure at the adsorbate site, which is akin to surface poisoning effects. At high exposures corresponding to oxide formation electron capture is very efficient and can be understood in terms of a quasi-resonant localised charge exchange mechanism between a F atom and a MgO lattice O anion