University of Groningen. Hollow-atom probing of surfaces Limburg, Johannes

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1 University of Groningen Hollow-atom probing of surfaces Limburg, Johannes IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below. Document Version Publisher's PDF, also known as Version of record Publication date: 1996 Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Limburg, J. (1996). Hollow-atom probing of surfaces Groningen: s.n. Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons). Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Downloaded from the University of Groningen/UMCG research database (Pure): For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Download date:

2 Contents Preface v 1 Objectives 1 2 Fundamentals Introduction Charge exchange One-electron transitions Auger transitions Collective excitations Radiative decay The classical over-the-barrier model Capture distance and image charge acceleration Hollow atom formation and deexcitation Experimental approaches Scattered projectiles Sputtered material Electron emission Photon emission Computer simulations Experiment ECR ion source Sir Collimator and deceleration system Electrostatic analyzer Time of ight system Targets xi

3 xii Contents 4 KLL Auger spectra of hydrogenic ions Introduction Targets Electron spectra Identication of the peaks Atomic structure calculations Introduction Limited observation time Calculations for hollow atoms Coster-Kronig transitions in hollow atoms Introduction Experimental results Coster-Kronig transitions and rate equations Discussion An L-shell lling model Introduction Experiment Ion trajectory simulations Modelling KLL Auger emission Discussion Hollow atom formation on an insulator surface Introduction Experiments The N 6+ series The N, O, Ne series Discussion Ion scattering: He on Al(110) Introduction Experiment Energy loss experiments Measurement ofcharge state fractions Trajectory simulations Charge exchange He ++ projectiles He + projectiles Modelling charge state fractions Discussion Energy loss...102

4 xiii Modelling energy loss Discussion Results Stopping power Ion scattering: O q+ on Al(110) Introduction Scattered charge state fractions Energy loss Negative ion formation Introduction Experiment A simple model Results and discussion Conclusions and outlook Timescales of hollow atom deexcitation Target eects The evolution of hollow atoms Hollow-atom probing of surfaces Appendices 136 A Atomic Units 137 B Chopper pulse width 139 B.1 Bunching eects B.2 Lens system B.3 Geometry eect C Solution of Coster-Kronig rate equations 143 Bibliography 147 List of publications 159 Samenvatting 161 Dankwoord 165

5 List of Tables 4.1 Measured and calculated K 1 LL Auger energies for C up to F He KLL Auger transition energies and rates Calculated KLL-Auger transition rates for Li-like systems Calculated KLL Auger transition energies for Li-like systems Simulated trajectory data N 6+ hollow atom congurations, rates, energies Comparison of AN rates A C, O and F ionizaton and anity energies Electron conguration of O 0 3 P, 1 D and 1 S states Fit results using v? (1) Fit results using v? (z c ) Fit results for and f;s xv

6 List of Figures 2.1 Charge exchange processes Ion-surface distances Ion-surface potential curve Atomic physics hall Electron Cyclotron Resonance Ion Source ECRIS Photograph of Sir set-up Schematic of the Sir set-up Lens system, target manipulator and ESA Beam prole Time of ight tube Chopper-sweeper system TOF spectra for contaminated and clean Al Auger spectrum of hydrogenic N on Ni(110) KLL Auger spectra of O 7+ on Si(100) Doppler shift of sharp KLL peaks Intensity of sharp Auger peaks versus velocity Auger spectra of hydrogenic C,N,O,F and Ne on Si(100) KLL Auger spectra of hydrogenic C, N and O on Ni(110) KLL Auger spectra of hydrogenic C,N,O and Ne on W Auger spectra of O 7+ onw,niandsi Calculated and measured He KLL Auger spectra He KLL-Auger peak intensities vs. observation time Calculated spectra for Li-like and hollow atom congurations Calculated carbon KLL spectra Relative energy shift of KLL-Auger peaks KLL Auger spectrum for O 7+ on Si(100) Auger spectra of hydrogenic and helium-like ions on Si(100) KLL Auger and Coster-Kronig transitions Solutions of rate equations, O xvii

7 xviii List of Figures 6.4 Solutions of rate equations, O Calculated and measured spectra, O 7+ and O KLL Auger spectra of N 6+ on Si(100), constant v? Auger spectra of N 6+ on Al(110), constant v? Auger spectra of N 6+ on Al(110), specular reection Doppler shifts of sharp peaks and of FWHM Simulated trajectories for constant v? Simulated trajectories for specular reection Calculations of Auger energies and lifetimes for hollow atoms Calculated KLL Emission probability KLL Auger spectra of N 6+ on LiF(100) KLL Auger spectra of N 6+ on Si(100) KLL Auger spectra of N 6+,O 7+ and Ne 9+ on LiF(100) L and M electron binding energies for N, O and Ne hollow atoms Energy spectra of He scattered o Al(110) Fractions He + /(He + +He 0 ) vs. v Simulated trajectory lengths He +,He 2+ neutralization scheme Experimental and calculated loss curves Fit results from the energyloss model Stopping power versus v Scattered charge state fractions O q+ /O tot Energy loss distributions of scattered O r+ r = 1; 1; 2; Negative ion fractions for C 4+ and C + scattered on Al(110) Negative ion fractions for O 6+ and O Negative ion fraction for F Position of C, O, F anity and ionization levels A hydrogenic ion approaches a conducting surface Hydrogenic ion approaching an insulating surface diabatic vs. adiabatic picture of hollow-atom evolution Ion-surface potential V t (z), diabatic and adiabatic picture B.1 Pulse width and time spread of chopper-sweeper system