Charge Exchange Of Low Energy Alkali-metal Na~+ Ions Grazing Scattering On Metal Surfaces

Charge exchange is a ubiquitous physical phenomenon in the interaction between ions and surfaces,which has attracted extensive attention from researchers.Its essence is the quantum transition behavior of active electrons within the instantaneous Coulomb barrier constructed by the ion-surface in femtosecond time,which is applicated in many disciplines such as surface science,plasma physics,atomic and molecular physics,material science.It plays an important role and is of great significance to the development of thin film growth,surface catalysis,ion etching and other research fields.Based on charge exchange,many surface analysis techniques have been derived,such as secondary ion mass spectrometry,low-energy ion scattering spectroscopy,Auger electron spectroscopy,etc.In recent years,researchers have paid special attention to the phenomenon of charge exchange between alkali metal ions and metal surfaces,especially on the mental surfaces with high work function,the neutral fraction shows a high non-monotonic trend.This phenomenon cannot be explained by existing theoretical models,and it deserves further study.In this thesis,using the ultra-high vacuum ion-surface collision experiment platform,under the condition of 7° scattering angle,0.2～5keV Na+ ions scatter on the surfaces of Au(111),Pd(lll)and Cu(111)in grazing incidence.The dependences of the neutral fraction on the incident energy and exit angle were studied.Under the condition of specular scattering,it is found that the neutral fraction of Cu(111)and Pd(111)surfaces showed a non-monotonic trend of decreasing first and then increasing with the increase of incident energy.For Au(111),the fraction first decreases close to 0%with the increase of incident energy,and then does not increase significantly.For 0.3keV and 5keV,it is found that the neutral fraction of Pd(111)surface shows a non-monotonic trend of decreasing first and then increasing as the exit angle increased.For Au(111),the neutral fraction at 0.3 keV has the same trend to Pd(111)as a function of exit angle,but at 5 keV,it first decreases to close to 0%as the exit angle increases,and then does not increase significantly.The traditional Jellium model cannot explain the above experimental phenomena.This thesis considers the effects of energy level downshift and parallel velocity,and uses the Brako-News theoretical model for qualitative analysis.During close-range interaction,the Na atom 3 s energy level will move below the Fermi level,resulting in an increase in the neutral fraction at larger incident energies.The neutralization fraction at low incident energy is related to long-distance interaction and depends on the relative position of the Na atom 3s energy level and the surface Fermi energy level.The increase in parallel velocity will increase the neutral fraction.Angle dependence is essentially the same as energy dependence.In addition,on the Au(111)surface,at a higher incidence energy and a larger exit angle of 5keV energy,the neutral fraction always approaches 0%without a significant increase.This phenomenon may be due to the small angle of Na+ ion,where the interaction time is relatively long.