摘要:

We investigate the neutralization of fast protons (4 to 200 keV) after the interaction with a clean AI(111)-surface at grazing incidence (Φ < 1°). At projectile velocities of about 0.4v0(v0= Bohr velocity) we observe almost total neutralization, while the neutral fraction decreases down to 2% at about 3v0. Model calculations in the framework of resonant electron transfer, which describe the charge exchange of alkali–ions at an aluminum surface fairly well, predict a much stronger decrease of neutralization with increasing projectile velocity than observed. We interpret this discrepancy by the presence of further electron capture mechanisms like Auger-neutralization, etc. The yield of negative ions is lower than 1% at all velocities and is satisfactorily reproduced by theory of resonant electron transfer.

ISSN:1042-0150    

DOI:10.1080/10420158908220514

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

We have studied the neutralization of fast Na+- and K+-ions after the interaction with clean and flat Al(111)- and Ni(111)-surfaces at grazing incidence Φ < 1°. The neutral fractions of specularly reflected projectiles show two different classes of dependences on projectile velocity which can be referred to the difference between work function of the target and binding energy of the atomic ground term. Model calculations in the framework of resonance tunneling between metal surface and atom which incorporate the parallel velocity of the projectile by Galilean-transformation and the electronic spin degree of freedom reproduce our experimental data fairly well.

ISSN:1042-0150    

DOI:10.1080/10420158908220515

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Transient adsorption or skipping motion of 200–2000 eV silicon ions scattered under specular conditions from a Cu(111) surface is reported. The phenomena are identified on the basis of the observation of discrete energy loss peaks in the scattered Si+and Si−ion kinetic energy distributions, together with their behaviour upon variation of the crystal azimuth, incidence angle of the beam to the surface, and scattering angular distributions. Up to five reflections, with a total energy loss of 20% of the incident beam energy, could be identified. We propose that the beam is trapped following energy loss, by electron-hole pair and plasmon excitation, which exceeds the incident beam energy component normal to the surface. Trajectory calculations which include this coupling of the energy loss and interaction potential satisfactorily reproduce the experimental observations.

ISSN:1042-0150    

DOI:10.1080/10420158908220516

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

We have measured the energy loss of 200–2000 eV silicon ions which have undergone both direct scattering and skipping motion on a Cu(111) surface. The inelastic energy losses associated with 1,2,…, 5 surface reflections for both positive and negative final charge states are identified. The energy loss is approximately proportional to the projectile energy and is independent of the crystal azimuth. A final charge state dependence is observed, as are extrapolated non-zero energy losses for Si−and Si+production at zero beam energy. These latter losses agree quantitatively with the energy required to promote an electron from the Fermi level of Cu(111) to the affinity level of Si, and the energy required to reionize Si, respectively, thus providing direct information on the charge state during scattering. Comparison with theoretical calculations shows that energy loss theory must be extended to include charge redistributions characteristic of chemical bonding.

ISSN:1042-0150    

DOI:10.1080/10420158908220517

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

ISSN:1042-0150    

DOI:10.1080/10420158908220518

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

We have scattered 3–30 keV H+-, H2+-, Na+-, K+-ions from clean Al(111)- and Ni(111)-surfaces at grazing angles Φ < 1° and studied electron transfer to excited projectile states by means of optical spectrometry. We observe in general a rapid decrease in level excitation probability with increasing level excitation energy. For Na+-Al scattering we find a rather strong variation of relative level excitation probabilities with projectile energy, whereas this variation for the interaction with the nickel target is poor. The data are discusseed in the framework of a two-step model: close encounter collisions in the vicinity of the surface and population of excited terms of receding ions via resonant electron transfer.

ISSN:1042-0150    

DOI:10.1080/10420158908220519

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The features of electron exchange between secondary excited Si ions and the (111) Si surface are studied experimentally and theoretically. An oscillating character of the Si+* energy spectrum due to the charge-exchange process has been found in the case when the energy of the excited state of the ion is located near the maximum in the density of the surface electron states. The oscillations found experimentally have been shown to be explainable if the electron exchange inside a solid occurs prior to ion transition through the surface.

ISSN:1042-0150    

DOI:10.1080/10420158908220520

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

We have measured the charged fraction of scattered Ne during the 170° scattering of kilovolt Ne+by a two-dimensional lattice of arsenic atoms grown on a Si(111) surface template. We found that the charged fraction increases with the incident energy to reach values above 0.25 which is significantly higher than that for He+scattered from As. The charged fraction is not sensitive to the azimuthal direction of incidence, but it is strongly dependent on the elevation angle with respect to the sample surface. We found that the collisions between the Ne+ions and the As atoms are not purely atomic in nature. Our result directly indicates the importance of the delocalized valence band electrons in the charge exchange process.

ISSN:1042-0150    

DOI:10.1080/10420158908220521

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Electronic excitation during impact scattering of He+ions with a kinetic energy ranging from 0.1 to 1 keV from solid surfaces has been studied. The ionization probability of He0is strongly dependent on the species of target elements; the probability for Zn or Cd is estimated to be about three orders of magnitude smaller than that for Ca at a kinetic energy of 1 keV. The excitation of surface valence electrons in the course of He+scattering also shows a remarkable target-material dependence, which has been confirmed at a surface of ionic compounds having a large band-gap energy: the excitation of surface p-electrons to the conduction band has been explicitly observed for a certain He+-target combination which yields sufficient promotion of the He 1s orbital in the quasimolecular state.

ISSN:1042-0150    

DOI:10.1080/10420158908220522

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The energy loss of neutralized He in the energy range below 5 keV increases approximately linear with the primary energy. The losses are of the order of 100 eV. The magnitude of the loss depends on the crystallographic orientation. These experimental findings are found to be in qualitative agreement with theoretical estimates based on the non linear stopping power theory.

ISSN:1042-0150    

DOI:10.1080/10420158908220523

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor