Accession Number:

ADP007936

Title:

Excitonic Mechanism of Photon-Simulated Desorption of Excited Alkali Atoms from Alkali Halides,

Descriptive Note:

Corporate Author:

VANDERBILT UNIV NASHVILLE TN DEPT OF PHYSICS AND ASTRONOMY

Personal Author(s):

• Bunton, Patrick H.
• Haglund, Richard F., Jr.
• Liu, Dengfa
• Tolk, Norman H.

Report Date:

1992-05-22

Pagination or Media Count:

4.0

Abstract:

The mechanism leading to photon-stimulated desorption PSD of excited atoms from the surfaces of alkali halides has been a subject of controversy since it was first discussed a decade ago. We have recently carried out a systematic experimental study of PSD from alkali halides under both valence-band and core-level excitation. Our data demonstrate that the desorption yields for excited alkali atoms track the excitonic optical response of these crystals even at photon energies below the bulk band gap. Secondary electron measurements, taken simultaneously, implicate the formation of excess metal in the time and dose dependence of PSD yields. These results suggest a unified picture of PSD in which the ion motion initiating desorption is pictured as the decay of a localized, highly deformed vibrational mode of the crystal. Plausible mechanisms for creation of the excited atomic state include relaxation of excited F-centers and resonant neutralization into the excited state on metallic microclusters.

Descriptors:

• *DESORPTION
• *HALIDES
• *ALKALI METAL COMPOUNDS
• *EXCITONS
• ATOMS
• COLOR CENTERS
• CORES
• CRYSTALS
• DECAY
• ELECTRONS
• EXCITATION
• IONS
• MEASUREMENT
• METALS
• MOTION
• NEUTRALIZATION
• PHOTONS
• RELAXATION
• SECONDARY
• SURFACES
• TRACKS
• VALENCE
• VALENCE BANDS

Subject Categories:

• Physical Chemistry

Distribution Statement:

APPROVED FOR PUBLIC RELEASE