[en] In this thesis electron transfer between atoms and metal surfaces in general is discussed and the negative ionization of hydrogen by scattering protons at a cesiated crystalline tungsten (110) surface in particular. Experimental results and a novel theoretical analysis are presented. In Chapter I a theoretical overview of resonant electron transitions between atoms and metals is given. In the first part of chapter II atom-metal electron transitions at a fixed atom-metal distance are described on the basis of a model developed by Gadzuk. In the second part the influence of the motion of the atom on the atomic charge state is incorporated. Measurements presented in chapter III show a strong dependence of the fraction of negatively charged H atoms scattered at cesiated tungsten, on the normal as well as the parallel velocity component. In chapter IV the proposed mechanism for the parallel velocity effect is incorporated in the amplitude method. The scattering process of protons incident under grazing angles on a cesium covered surface is studied in chapter V. (Auth.)

[en] Resonant charge exchange in atom-metal surface scattering has been the subject of many theoretical and experimental studies. Atoms which easily surface ionize like the alkalis when adsorbed at a metal surface form ionic bonds between adsorbate and substrate resulting in a surface dipole. A surface coverage of about half a monolayer then results in a dipole layer, by virtue of which the work function of the metal is decreased by a factor of three. A theoretical description and calculation of this effect from first principles has previously been formulated. These theoretical considerations also offer the possibility of a quantitative prediction of surface ionization. Recently the possibility of surface ionization - positive as well as negative ionization - by scattering ions or neutrals from a metal surface has been explored very intensively. This large interest is mainly due to the possibilities of forming intense H^- and possibly Li^- ion beams by scattering the respective positive ions from low work function metal surfaces, like cesium covered tungsten. The intense negative ion beams after neutralization will be needed for heating plasmas in connection with fusion. This paper is concerned with the theoretical and experimental progress in the field of surface ionization. (Auth.)

[en] The fundamental ionisation process of negative surface ionisation is described and two applications are discussed. One is in the so called surface-plasma sources which enable the production of intense negative ion beams. The second application is in the passive diagnosis of the charge exchange of neutrals emitted from hydrogen plasmas. (C.F.)

[en] H^- and D^- formation is studied by scattering H⁺ and D⁺ from a cesiated W(110) surface. The conversion efficiencies are measured as a function of the angle of incidence and of the incident energy of the H⁺ and D⁺ ions. Conversion efficiencies up to 40% are measured. The results can be qualitatively explained by a semi-classical model. (orig.)

No abstract available

[en] When an atom or ion is scattered from a metal or other surface the scattered particle may be found in a distribution of charge states. He⁺ scattering is normally assumed to be dominated by Auger neutralisation for which the simple semiclassical theory is discussed. Many charge exchange phenomena actually occur via the direct or resonant electron transfer process of which examples are given. The correct theory of this process is a quantum mechanical or amplitude one. A simple account of this theory is given and the limiting formulae which can be obtained under simple physical assumptions are emphasized. A detailed application to the neutral fraction of Na scattered from W(110) is given and compared with experiment. Up to now the effect of parallel velocity has not been taken into account. The authors show how this can be done on a jellium surface by a displacement of the Fermi sphere in momentum space. The results are applied to the H^- fraction in H⁺ scattering from cesiated W(110) which shows a strong parallel velocity effect. (Auth.)

[en] The efficiency of converting H⁺, H⁺₂, H⁺₃ and Li⁺ ions into H^- and Li^- by scattering the ions from cesiated single crystal and polycrystalline tungsten has been determined experimentally as well as theoretically. The ions were reflected under grazing angles of incidence. Maximum efficiencies for hydrogen and lithium were measured of 40% and 23%, respectively. By determining the negative ion fraction of the reflected particles as a function of the angle of reflection, theoretical predictions on conversion are tested without the need to correct for the reflection probability. It was found that at particle velocities > or approx. = 3 x 10⁵ m/sec the conversion efficiency depends strongly on the magnitude of the velocity component parallel to the surface. In general, the experimental data show a good agreement with the theoretical predictions