Charge exchange in H-Cu(111) low energy collisions

R. VIDAL; M. TACCA; E. C. GOLDBERG; QUINTERO RIASCOS, VANESSA; F. BONETTO

Buzios

Encuentro; XL Meeting of the Brazilian Physical Society; 2017

The formation of positive and negative ions in the scattering of protons by a Cu(111) surface is theoretically andexperimentally analyzed for a large scattering angle in a backscattering geometric con¯guration. Low EnergyIon Scattering (LEIS) technique was used to measure the ion fractions in the collision, where a peculiarly highyield of negative ions are detected for the whole energy range analyzed (from 2 to 8keV) A ¯rst principlesquantum-mechanical formalism is applied to describe the charge transfer produced in low energy collisionsbetween a H+ incident ion and the Cu(111) metallic surface. All the physical ingredients involved on thedynamic problem analyzed, such as the crossed terms of the density matrix of the surface solid, the number ofsurface atoms considered, and the change in the energy level and its width relative to the target surface Fermilevel are discriminated and its in°uence on the partial and ¯nal charge states are thoroughly examined. Thecontrast between theoretical and experimental data allows us to infer how relevant are the di®erent physicalingredients included in the model and the energy range where they play a signi¯cant role. According to our¯ndings we can conclude that: i) the projectile charge state is mainly de¯ned on the exit trajectory, beingthe ¯nal part of the trajectory specially relevant for lower energies; ii) the inclusion of the crossed terms ofthe density matrix introduces a signi¯cant change on the projectile energy level and width, leading to relevantchanges in the neutralization curve on the whole range of incoming energies and iii) the introduction of a largenumber of surface atoms to describe the solid target is crucial to explain the the large negative ion fractionexperimentally observed.