Negative ion formation by neutral hydrogen atom grazing scattering from a LiF(100) surface

Abstract

We present a theoretical description of negative ion conversion of the grazing scattering of neutral hydrogen atoms on LiF(100) surface. Here, in addition to the capture of a valence band electron near a surface F⁻ site by an incident H atom, the Coulomb repulsive barrier tunneling behavior is also considered to treat the detachment of the affinity electron from the formed H⁻ ion to vacuum through its interaction with the surface F⁻ site. With incorporation of the image-attraction-induced increase on the vertical component of the projectile energy and the collective dielectric screening effect of surrounding anions and cations on the charge of surface F⁻ site which participates in the electron detachment, the image attractive interaction was revealed to obviously increase the electron detachment probability, in turn obviously decreasing the final negative ion yield. Moreover, the sub-eV order of the energy defect between the H⁻ affinity level and the unoccupied image state induced by the potential field of the H⁻ image charge in LiF leads to an additional H⁻ destruction channel in which H⁻ affinity electron transfers to the unoccupied image state without electron emission by a nearly resonant charge transfer manner. A clear picture of this electron loss process is also presented. Our present results well reproduce the experimental observation in the whole velocity range and the high fraction of H⁻ ion yield as an alternative solution can be used on the implantation of ITER device.