Hydrogen ion scattering from a potassium impurity adsorbed on graphene

Abstract

In this work we study the charge exchange process in the scattering of protons by potassium atoms adsorbed on a graphene surface in a low coverage limit. Both, the projected density of states on the alkaline atom site and the final charge states of the hydrogen projectile are calculated by considering the electronic Coulomb repulsion in the s-valence orbital. The inner 3p and 3s states of potassium are included and the local perturbations of the density matrix on the surrounding C atoms are also considered. The interacting systems are described by an Anderson Hamiltonian whose terms are calculated from the chemical properties of the atoms and the extended features of the graphene surface. The positive and negative ion fractions of hydrogen in the collision process are obtained from Keldysh-Green functions, which are calculated by employing the equation of motion method closed up to a second order in the atom-surface coupling term. It is found that the carbon atoms have no possibility of a direct charge exchange process in a frontal collision of the proton with the K adatom, and that the K-3p band, broadened by the interaction with the graphene surface, provides an important source of electrons for the negative ionization of hydrogen, which is also promoted by the presence of a K-3s core state. The narrow 4s and 3p bands of the adsorbed potassium lead to an oscillatory dependence with the projectile incoming energy, of the probability for the three correlated charge states of hydrogen.

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

“…The ion scattering from metal surfaces covered with alkali atoms has been and continues to be a subject of interest that has motivated many experimental and theoretical works [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. The adsorbates on a metal surface introduce local effects as the change in the density matrix of the adsorbatesurface system, and also nonlocal effects as the change of the surface work function.…”

“…In a previous work [18] we analyzed the frontal collision of protons with a potassium atom adsorbed on a graphene surface. Apart from its technological applications, the interest in graphene is motivated by the singular characteristics of its electronic band structure which gives place to peculiar hybridizations with adsorbed alkaline atoms [19][20][21][22][23][24].…”

“…In Ref. [18] the resonant charge exchange between the proton and the composed surface graphene plus adsorbed potassium was described by an Anderson model that takes into account the three correlated charge states of the hydrogen projectile: positive, neutral, and negative. The surface density matrix includes the electronic repulsion in the valence states of K and also the hybridization of the K-3p states with the graphene band states, together with the local changes in the density matrix on the surrounding C atoms induced by the presence of the K adatom.…”

“…The present work, which can be considered a natural continuation of Ref. [18], is devoted to the analysis of the frontal collision of protons with carbon atoms nearby the K adsorbate. The importance of studying the effects caused by the presence of the potassium on the charge exchange and the electron emission processes when the binary collision is with a carbon atom, resides basically in the ability to identify the signals of a low concentration of impurities in the ion scattering process.…”

“…Both the charge fractions of the projectile and the energy distribution of electrons in the solid after the collision are calculated by using the appropriate Keldysh Green functions and the method of equations of motion (EOM). The electronic correlation in the localized projectile state is also taken into account for calculating the electron distribution in the solid, thus representing an improvement with respect to previous works [18,25,26].…”