Excitonic instability and athermal halogen atom desorption from NaBr, KBr and RbBr
作者:
K.S. Song,
L.F. Chen,
期刊:
Radiation Effects and Defects in Solids
(Taylor Available online 1994)
卷期:
Volume 128,
issue 1-2
页码: 35-45
ISSN:1042-0150
年代: 1994
DOI:10.1080/10420159408218854
出版商: Taylor & Francis Group
关键词: desorption;halogen atom;alkali halides
数据来源: Taylor
摘要:
Energetic halogen atom desorption observed from certain alkali halide crystals under electron or photon stimulation is being investigated. The relaxed structure of the localized one-center (Frenkel-type free exciton) and two-center (self-trapped exciton: STE) electronic excitations are studied. It is shown that the triplet STE state undergoes an instability on and near the surface (the first and second layer below the surface) similar to that in the bulk and results in the expulsion of neutral Br atom in all three bromides studied. The relaxation energy which could be converted to kinetic energy of the ejecta is estimated to be about 0.5–1.0 eV. From the third layer, only in KBr and RbBr such ejection seems possible. The trajectory of the ejected Br atom is originally along the halogen row in <110> axes. However, as the ejecta approaches the (100) surface, it undergoes a deflection resulting in a trajectory outside the crystal which is found to deviate from the vertical by only about ≌20° at a distance of twice the lattice parameter. It is also observed that a localized hole on the surface and below is efficiently converted into a Vkcenter without leading to a halogen atom desorption. These results are presented within a broader context of the STE relaxation in the alkali halide crystals.
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