jeudi 23 mars
Mise à jour
jeudi 23 mars
Accueil du site > Équipes scientifiques > Surfaces, Interfaces : Réactivité et Nanostructuration (SIREN) > Interactions atomes-surfaces
Probing surface cristallographic structure
Probing surface defects
Probing dynamics of surface atoms and electrons, a surface can also be investigated by how it reacts, what sort of excitations can we trigger ?
Probing surface growth
When exposed to molecular or atomic vapor, successive layers start to build up, this is particularly well controlled inside Molecular Beam Epitaxy vessel. Our diffraction technique is able to count the number of deposited layer as well as their quality [more].
How we do it ?
we shoot a well defined beam of fast atoms or ions at grazing incidence so that they cannot penetrate below the surface and we observe the scattered particles on a position sensitive detector placed downstream. Here we call fast all projectiles above 100 eV and we use such energies to be able to detect them with high efficiency with microchannelplates, the kind of device used to in high end night vision systems.
what for ? one simple answer is to investigated fondamental processes. For instance it was previously unclear why, upon impact of atoms or ions, most insulators emit more electrons than metal whereas they are known to bind more strongly their electrons ??? [more] Here, the answer was that part of this large energy needed to extract an electron can be bypassed when the projectile goes negative before loosing its electron. this was demonstrated by using measurement where emitted electron were detected in coincidence with the scattered projectiles. more generally, when large effects are understood, smaller effects become visible etc. This is exactly what happened, after electron capture and loss we investigated discrete electronic excitations then quasi continuous excitation of electron hole pair, then the excitation of phonons until we discovered elastic diffraction, i.e. conditions were no energy is exchanged with the surface !!