Collision of protons with carbon atoms of a graphene surface in the presence of adsorbed potassium

ADALBERTO IGLESIAS-GARCÍA; M. A. ROMERO; GARCIA E.; E. C. GOLDBERG

PHYSICAL REVIEW B

AMER PHYSICAL SOC

Lugar: New York; Año: 2020 vol. 102

1098-0121

In this work we study the frontal collision of protons with the carbon atoms of a graphenesurface with a low coverage of adsorbed potassium. It is aimed at the analysis of the effect ofthe adsorbates in both charge exchange and electron emission processes, when the binary collisionoccurs between the proton and a carbon atom of the surface. The frontal collision with the Kadsorbate, already analyzed and discussed in a previous work, is compared with the frontal collisionwith different carbon neighbors. In the present work we studied the signals, due to the localizedstructures in the density matrix of the composed graphene plus potassium surface, that can bedistinguished when the collision occurs either with the adsorbate, a nearby carbon atom or a carbonatom that does not feel the presence of the adsorbate. The interacting system is described by theAnderson Hamiltonian which takes into account the electronic repulsion on the projectile site; thecharge fractions, the energy distribution of electrons in the solid, and the electron emission after thecollision are calculated by using the nonequilibrium Green-Keldysh functions formalism solved bythe equation of motion method. In the binary collision with a carbon atom, the extended featuresof the band structure of graphene smooth the dependence of the projectile charge fractions on theincoming energy and notably decrease the negative ions formation. The localized structures of thedensity of matrix caused by the presence of the adsorbate are perceptible for scatter carbon atomsclose to K. The intense emission of low energy electrons obtained in the case of the scattering bypotassium is fundamentally associated with the very localized K-4s empty band. This characteristic,although less marked, remain in the scattering by nearby carbon atoms, due to both, the interactionwith K along the projectile trajectory and the perturbed local density of states on the carbon atomsdue to the adsorbate presence. In addition, the extended nature of the electronic structure ofgraphene allows for the emission of more energetic electrons.