Hydrogen ion scattering from alkali/graphene surface: Alkali core states effects

M. A. ROMERO; ADALBERTO IGLESIAS-GARCÍA; GARCÍA E.

SURFACE SCIENCE

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2022 vol. 721

0039-6028

We present a theoretical study of the frontal collision of protons with a graphene surface to which an alkaliadatomis added. Na and Cs adsorbates are studied in a low coverage limit. We analyze how the presence ofadsorbates affects the charge exchange when the binary collision between the H+ protons and the adatoms ordifferent carbon atoms close to the impurity occurs. The charge transfer process in the scattering of protons in theK and C atoms of a graphene surface to which a K adatom is added has already been analyzed and discussed inour previous works. We find that the inner states of the alkali atoms adsorbed on graphene introduce importantdifferences in the charge transfer depending on their positions with respect to the valence band of graphene. Fora better grasp of this, in this work we select Cs and Na as adatoms due to Cs has core levels that can resonate withthe valence band of graphene, while Na does not. The interacting system is described by the Anderson Hamiltonianwhich takes into account the electronic repulsion at the projectile site; the ion charge fractions after thecollision are calculated by using the non-equilibrium Green-Keldysh functions formalism. Also, we describe theadsorption of the alkali atom on the surface using the single impurity Anderson model and introduce the Green?sfunctions required to calculate the adatom spectral density. In the scattering of H+ from Cs, the charge fractionsas a function of the incident energy, behave similarly to the scattering from K. For the Na adatom, the dependenceis different, showing a monotonous increase in the high energy regime. The results of this work allow us toinfer the signals in the charge exchange, from the localized features of the density of states on the alkalineadsorbate during the scattering process, due to the peculiarities of the electronic band structure of graphene.