The Charge Exchange Of Low Energy Ions Scattering On Metal And Water Adsorbed Cu(110) Surfaces

The interaction between energetic ions and surfaces is of great importance in many fields,such as plasma physics,material science,chemistry and surface science.As an important direction of ion-surface interaction,charge exchange plays an important role both in basic scientific research and in the field of applied technology.We can not only analyze the related physical mechanisms in the charge exchange process,but also indirectly get the information about the solid surface work function and the electronic structure through the distribution of the different charged states of the scattered ions.On the basis of that,many surface analysis technologies,such as low energy ion scattering spectroscopy,secondary ion mass spectroscopy,etc.,can be developed.In this work,the charge exchange processes of low energy positive and negative ions on the surface of a variety of materials are studied.It includes two main parts:the first part is the resonance neutralization of low energy Na~+ions scattering on the surface of Au(111),Pd(111),Cu(111)and Cu(110).The other part is the charge exchange of low energy F~-ions and Cl~-ions grazing scattering on the surface of water adsorbed Cu(110).The first part mainly focuses on the charge exchange process between 0.16-5keV Na~+ions and Au(111),Pd(111),Cu(111),Cu(110)surfaces at different scattering conditions.For high work function surface like Au(111)and Pd(111),the efficient neutralization has been surprisingly observed.With the increase of the work functions of these four surfaces,the nonmonotonic energy dependence of the neutral fraction becomes more and more obvious.For Cu(111)and Cu(110)at the scattering angle of 7°,the energy dependence of the neutral fraction is still nonmonotonic as compared to the scattering angles of 135°and 53°.For the scattering angle of 53°,the nonmonotonic angle dependence has been observed for these surfaces.The essences of the nonmonotonic angle and energy dependence are the same.The BN model calculations reveal that the width and position of the atomic level below the Fermi level at short ion-surface distances are responsible for high neutral fractions at large exit energies,and that the neutral fraction at much smaller exit energies is probably related to the neutralization at large distances.For the exit angle dependence,the competition between neutralization at short and large distances strongly depends on the surface work function.In particular,the neutralization is enhanced by the relatively large parallel velocity.The other part is the charge exchange of 8.5-22.5keV F~-ions and Cl~-ions scattering on the surface of water adsorbed Cu(110)surface.The experimental results show that the positive-ion fraction increases with the increase of perpendicular velocity,which can be well described by the exponential scaling.However,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.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.