Biomedical subjects

Herbert M Urbassek

Publications and source records attributed to Herbert M Urbassek.

3 recordsLinked to original sources

PubMed2006

Superior regularity in erosion patterns by planar subsurface channeling.

The onset of pattern formation through exposure of Pt(111) with 5 keV Ar(+) ions at grazing incidence has been studied at 550 K by scanning tunneling microscopy and is supplemented by molecular-dynamics simulations of single ion impacts. A consistent description of pattern formation in terms of atomic scale mechanisms is given. Most surprisingly, pattern formation depends crucially on the angle of incidence of the ions. As soon as this angle allows subsurface channeling of the ions, pattern regularity and alignment with respect to the ion beam greatly improves. These effects are traced back to the positionally aligned formation of vacancy islands through the damage created by the ions at dechanneling locations.

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PubMed2004

Step edge sputtering yield at grazing incidence ion bombardment.

The surface morphology of Pt(111) was investigated by scanning tunneling microscopy after 5 keV Ar+ ion bombardment at grazing incidence in dependence of the ion fluence and in the temperature range between 625 and 720 K. The average erosion rate was found to be strongly dependent on the ion fluence and the substrate temperature during bombardment. This dependence is traced back to the variation of step concentration with temperature and fluence. We develop a simple model allowing us to determine separately the constant sputtering yields for terraces and for impact area stripes in front of ascending steps. The experimentally determined yield of these stripes--the step-edge sputtering yield--is in excellent agreement with our molecular dynamics simulations performed for the experimental situation.

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PubMed2004

Parametric study of ion acceleration in a one-dimensional plasma expansion using the particle-in-cell simulation.

The one-dimensional expansion of a plasma off a planar wall into a vacuum is studied using particle-in-cell computer simulation. Particular emphasis is put on the acceleration of ions in the plasma. Energy transfer from the electronic to the ionic subsystem, the energy spectra of the ions, and the center-of-mass motion of the ion cloud are monitored. Various parameters that influence the acceleration process are studied: the presence of several ion charge states, of neutrals, the effects of a binary mixture of ions, and of a thermal nonequilibrium between ions and electrons.

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