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Charge transfer during oxygen negative ion surface scattering is performed to investigate the electronic interaction for the water/Cu system as a function of incident velocity. We find that both positive and negative ion fractions increase with incident velocity for the specular scattering condition. The positive ions produced close to the surface can be understood by the mechanisms of collision-induced ionization and Auger ionization, and they finally survive from the resonant and/or Auger neutralization, which are well described by the exponential scaling. The negative ions are formed through the resonant charge transfer, and the velocity dependence has been explained by the kinematically parallel velocity effect and the surface work function. The modified rate equation taking into account these two factors is in rough agreement with the experimental result. [ABSTRACT FROM AUTHOR]

In this work, we present negative-ion fractions as a function of exit velocity and angle after keV-energy negative oxygen and carbon ions scattering on a highly oriented pyrolytic graphite (HOPG) surface, at a scattering angle of 38°. The negative-ion fractions increase monotonously with the increase of exit velocity for specular scattering, while negative-ion fractions present a bell-shaped dependence on exit angle. In order to gain further insight into the nature of charge transfer on HOPG, a modified charge transfer model involving the contribution of positive ions has been proposed and roughly reproduced the velocity and angle dependences of negative-ion fractions. [ABSTRACT FROM AUTHOR]

Doping has significantly affected the characteristics and performance of semiconductor electronic devices. In this work, we study the charge transfer processes for 8.5–22.5 keV C − and F − ions scattering on H 2 O-terminated p-type Si(100) surfaces with two different doping concentrations. We find that doping has no influence on negative-ion formation for fast collisions in this relatively high energy range. Moreover, we build a model to calculate negative ion fractions including the contribution from positive ions. The calculations support the nonadiabatic feature of charge transfer. [ABSTRACT FROM AUTHOR]

Shifted Fermi sphere model and parallel velocity effects on clean metals have been verified by a number of previous studies. However, for fast F − and Cl − ions scattering on dissociated water covered Cu(110) at grazing incidence, the negative-ion fraction is projectile dependent and monotonically increases with the increase of impact velocity, which cannot be explained by the conventional parallel velocity effect. The positive-ion fraction increases with the increase of perpendicular velocity, which can be well described by the exponential scaling. Positive ions efficiently formed at large perpendicular velocities strongly suppress the negative ion yield at short distances from the surface, so that negative ions are only formed at large distances. In addition, the large surface work function further promotes a transition between two kinds of parallel velocity effects. The calculation taking into account these contributions is in rough agreement with the experimental data. [ABSTRACT FROM AUTHOR]

The experiment of 6.5–22.5 keV C − , O − and F − ions scattering on water covered Si(111) surface has been performed. It is found that the positive-ion fraction is very low and increases monotonically as a function of perpendicular exit velocity and exit angle. In particular, the negative-ion fraction increases monotonically with perpendicular exit velocity for specular scattering, and for a given incident energy the angle dependence of the fraction is nonmonotonic. We interpret the observed positive ions in terms of inelastic binary collision, and adopt a modified resonant charge transfer model to calculate the bell-shaped negative-ion fraction. We find that the neutral yield at short ion-surface distance is nonzero and obeys well an exponential dependence. It strongly indicates that a dynamical equilibrium for negative ion formation is never achieved at short distances, and the band gap effect on charge transfer can be neglected to a large extent in this relatively high energy region. [ABSTRACT FROM AUTHOR]