X-ray Spectra Produced By The Interaction Of Slow Highly Charged Ions With Cu Surface

Physical phenomena such as the generation and de-excitation of hollow atoms and the ionization of inner shells during the incident of highly charged ions(HCI)on the solid surface are of special significance,and it is fundamental in the research of material processing and surface analyzation.The study of these special physical processes can be facilitated by measuring the X-rays emission during the interaction,such as,neutralization prosess,kinetic energy and potential energy transfer mechanism.In the past few decades,due to the special physical process of highly charged ions interacting with solid surfaces,many groups had done experiments to study X-ray emission generated by slow highly charged ions impinging on solid surfaces.With the development of the research on the interaction between highly charged ions with solids,people found that the researches play an important role in astrophysics,atomic and molecular physics,nanomaterial preparation or other research fields.In astrophysical research,it was found that many stars in the universe include highly charged ions.Especially in the process of exploring the properties and laws of astrophysics,people found that X-rays generated by the highly charged ions collide with the surrounding particles.The internal composition and activity process of the stars can be analyzed through the collected X-ray information.In this work,we used the Electron Cyclotron Resonance Ion Source to get the N^q+(q=3,5,6)and O^q+(q=3,5,6,7)beams.After the beams were focused and deflected,the ions were extracted to interact with the Cu target in the vacuum chamber.Through measuring and analyzing the X-ray spectra,the influence of the kinetic energy and charge state of the ions on the X-rays generated during the interaction was analyzed.We obtained the following research results:(1)We discuss the emission mechanism of K-shell X-rays produced by the impact of the low-velocity N^q+(q=3,5,6)and O^q+(q=3,5,6,7)ions on Cu surface.N^q+(q=3,5)and O^q+(q=3,5,6)ions without K-shell vacancy emitted X-rays through direct coulomb collision with Cu atoms.Therefore,the K-shell X-ray yields increase with the increase of the charge state and kinetic energy of the incident ions.While for N⁶⁺and O⁷⁺ions,they have one vacancy in the K shell,when the incident ions are close to the surface,it will form hollow atoms above the surface,and emit X-rays through de-excitation of hollow atoms.The X-ray yields decrease with the increase of the kinetic energy.However,the experimental results show that the X-ray yields of N⁶⁺do not obviously decrease with the increase of the kinetic energy of the incident ions,but the X-ray yields of O⁷⁺have an obvious decreasing trend with the increase of the kinetic energy of the ions.(2)Based on the X-ray yields data,we calculated the ionization cross-sections of N and O,and found that the experimental ionization cross-sections increase significantly with the increase of the kinetic energy of the incident ions.However,the charge state of incident particles has no obvious effect on the ionization cross-sections.It shows that the K-shell ionization of the incident ions is caused by the close collisions with the target atoms.The theoretical value of the ionization cross-sections was calculated by the BEA theoretical model to compare with the experimental value.The results show that the experimental value of the ionization cross-sections is close to the theoretical value,and they both increase with the increase of the kinetic energy of the incident ions.We also calculated the kinetic energy threshold for the emission of the K-shell X-ray of O^q+(q=3,5,6)ions impinging on the Cu surface.(3)Analyzing the K-shell X-ray spectra collected by the Silicon drift detector,we found that the O^q+(q=3,5,6,7)ions with different kinetic energies and the same charge state have not obvious doppler shift of K-shell X-ray peak positions.After fitting the K-shell X-ray data of the O^q+(q=3,5,6)ions with the kinetic energy of 10 ke V/q,we found that the K-shell X-ray peak positions shift to the high-energy direction with the increase of the charge state of the incident ions.In a word,this work has important significance for the de-excitation process of hollow atoms formed in the interaction between the incident ions and the surface.