Molecular-dynamics simulation of positive-ion and neutral halogen desorption following Na K-shell Auger cascades in the NaF crystal
A Na K-shell Auger cascade in NaF can produce either four to six neighboring valence holes, or two to four neighboring valence holes and a F/sup +/ ion. If the holes remain localized as neutral atoms where they are created, they will assist the F/sup +/ ion to desorb, or assist in the desorption of Na/sup +/ ions. The neutral atoms themselves may also desorb. We use molecular-dynamics calculations to investigate whether the F/sup +/ ion and neutral F atoms produced by the Na K-shell Auger cascade in NaF can in fact lead to the desorption of positive ions and/or neutral F atoms. Simple fits to the Gordon-Kim potentials are used for the ionic interactions. Ab initio two-body potentials are developed to describe the interaction between a neutral F atom just outside of the crystal surface and a Na or F ion in the surface plane. The potentials exhibit a repulsive inner wall similar to that found for the diatomic molecules, and a shallow well. The integration time required for a satisfactory simulation of positive-ion desorption by the Knotek-Feibelman mechanism is shown to be 1--2 ps. Using 2-ps simulations, it is shown that only when the F/sup +/ ion is accompanied by four neighboring F atoms from the same Auger cascade does positive-ion desorption occur from the perfect (100) surface. Analogous results are obtained in simulations designed to relate to the imperfect (100) surface. It is concluded that the neutral atoms assist positive ions to desorb only in configurations which appear to be too rare to be of experimental significance. It is shown that crystal temperature, near room temperature, is not a factor in determining whether positive-ion desorption occurs by the Knotek-Feibelman mechanism.
- Research Organization:
- Sandia National Laboratories, P.O. Box 5800, Albuquerque, New Mexico 87185-5800
- OSTI ID:
- 6358282
- Journal Information:
- Phys. Rev. B: Condens. Matter; (United States), Journal Name: Phys. Rev. B: Condens. Matter; (United States) Vol. 39:8; ISSN PRBMD
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360603* -- Materials-- Properties
ALKALI METAL COMPOUNDS
ATOM COLLISIONS
AUGER EFFECT
BAND THEORY
BINDING ENERGY
CHARGED PARTICLES
COLLISIONS
DESORPTION
EFFECTIVE MASS
ELECTRONIC STRUCTURE
ELEMENTS
ENERGY
FLUORIDES
FLUORINE
FLUORINE COMPOUNDS
FLUORINE IONS
HALIDES
HALOGEN COMPOUNDS
HALOGENS
HOLES
INNER-SHELL IONIZATION
ION COLLISIONS
ION-ATOM COLLISIONS
IONIZATION
IONS
MASS
MEDIUM TEMPERATURE
NONMETALS
SODIUM COMPOUNDS
SODIUM FLUORIDES
SODIUM IONS
TEMPERATURE DEPENDENCE
VALENCE