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EELS study of the dynamics of clean Ni(100): Surface phonos and surface resonances
A309 Surface Science 171 (1986) 615 631 North-Holland, Amsterdam
615
CROSS-CORRELATION FUNCTIONS FLUCTUATIONS FROM POTASSIUM
ACROSS W(II2) OF CURRENT SUBMONOLAYERS:
SURFACE
PROPAGATION
DIFFUSION
R. B L A S Z C Z Y S Z Y N
OR SOLITON
MECHANISM?
* and Ch. K L E I N T
Department of Plo'sics. Karl-Marx-Uni~ersio', Linn~strasse 5, DDR-7010 Leipzig, German Dem. Rep. Received 21 June 1985: accepted for publication 14 January 1986 Field emission current cross-correlation functions (CCFs) of flicker noise from potassium submonolayers in the tungsten (1t2) region are presented and discussed. They were determined for two different orientations by the two-collector technique described recently using two probes with constant distance. With increasing time delay the CCFs show a broad maximum centered at "rm,,x. It reflects the anisotropy of the substrate and in addition "rm~,x is Arrhenius-like temperatureand also strongly coverage-dependent. While at lower coverages surface diffusion should explain the CCF properties, a soliton or domain propagation mechanism is proposed for medium and higher coverages based on results of the adlayer soliton theory by Pokrovsky and coworkers.
632
Surface Science 171 (1986) 632 642 North-Holland, Amsterdam
EELS STUDY OF THE DYNAMICS SURFACE M. R O C C A
PHONONS
O F C L E A N Ni(100):
AND SURFACE
*, S. L E H W A L D
RESONANCES
a n d H. I B A C H
Institut ff~r Grenzfli~ehenforschung und Vakuumphysik, Kernforschungsanlage Jfilich, "Postfach 1913, D-5170 JVdich, Fed. Rep. of German)' and T a l a t S. R A H M A N
Department of Pt~vsics, Cardwell Hall, Kansas State University, Manhattan, Kansas 66506, USA Received 16 October 1985; accepted for publication 30 January 1986 A systematic EELS study of the phonon spectrum of Ni(100) has been performed along the high symmetry directions F - X and F - M. The inelastically scattered electrons were investigated for different scattering geometries and different impact energies in order to look for optimum scattering conditions for each mode. Apart from surface phonons we observed various other energy losses due to surface resonances inside the bulk phonon bands. The experimental data are compared to the results of lattice dynamical calculations using the Green function technique. The phonon spectrum can be reproduced by allowing a 20% increase of the force constant between first and second layer nickel atoms in accord with former results.
615
CROSS-CORRELATION FUNCTIONS FLUCTUATIONS FROM POTASSIUM
ACROSS W(II2) OF CURRENT SUBMONOLAYERS:
SURFACE
PROPAGATION
DIFFUSION
R. B L A S Z C Z Y S Z Y N
OR SOLITON
MECHANISM?
* and Ch. K L E I N T
Department of Plo'sics. Karl-Marx-Uni~ersio', Linn~strasse 5, DDR-7010 Leipzig, German Dem. Rep. Received 21 June 1985: accepted for publication 14 January 1986 Field emission current cross-correlation functions (CCFs) of flicker noise from potassium submonolayers in the tungsten (1t2) region are presented and discussed. They were determined for two different orientations by the two-collector technique described recently using two probes with constant distance. With increasing time delay the CCFs show a broad maximum centered at "rm,,x. It reflects the anisotropy of the substrate and in addition "rm~,x is Arrhenius-like temperatureand also strongly coverage-dependent. While at lower coverages surface diffusion should explain the CCF properties, a soliton or domain propagation mechanism is proposed for medium and higher coverages based on results of the adlayer soliton theory by Pokrovsky and coworkers.
632
Surface Science 171 (1986) 632 642 North-Holland, Amsterdam
EELS STUDY OF THE DYNAMICS SURFACE M. R O C C A
PHONONS
O F C L E A N Ni(100):
AND SURFACE
*, S. L E H W A L D
RESONANCES
a n d H. I B A C H
Institut ff~r Grenzfli~ehenforschung und Vakuumphysik, Kernforschungsanlage Jfilich, "Postfach 1913, D-5170 JVdich, Fed. Rep. of German)' and T a l a t S. R A H M A N
Department of Pt~vsics, Cardwell Hall, Kansas State University, Manhattan, Kansas 66506, USA Received 16 October 1985; accepted for publication 30 January 1986 A systematic EELS study of the phonon spectrum of Ni(100) has been performed along the high symmetry directions F - X and F - M. The inelastically scattered electrons were investigated for different scattering geometries and different impact energies in order to look for optimum scattering conditions for each mode. Apart from surface phonons we observed various other energy losses due to surface resonances inside the bulk phonon bands. The experimental data are compared to the results of lattice dynamical calculations using the Green function technique. The phonon spectrum can be reproduced by allowing a 20% increase of the force constant between first and second layer nickel atoms in accord with former results.