Radiation-induced surface smoothing and structural relaxation in electron-irradiated ZnS and ZnSe crystals

The evolution of surface morphology and structural parameters in ZnS and ZnSe crystals under highenergy electron irradiation was investigated using a phenomenological modeling approach based on experimentally obtained irradiation-dependent structural and morphological data. The analysis focused on the fluence dependence of the surface roughness parameters Ra and Rz, coherent-domain size, and lattice parameter in the electron fluence range of (0−2.5) · 1017 electrons/cm2. It was found that the surface roughness parameters Ra and Rz decrease according to an exponential law, indicating the occurrence of radiation-induced surface smoothing. A phenomenological kinetic equation describing roughness relaxation as a function of electron fluence was proposed and solved analytically. The obtained model demonstrates that the smoothing rate is proportional to the excess surface roughness relative to the limiting relaxed state. In contrast, the coherent-domain size generally increases with increasing fluence, whereas the lattice parameter decreases nearly linearly, indicating radiation-induced structural relaxation, lattice compaction, and defect rearrangement processes. Comparative analysis of ZnS and ZnSe crystals revealed differences in the smoothing kinetics and structural evolution parameters, which may be associated with differences in defect mobility and irradiation-assisted relaxation processes. Correlations were observed between the fluence-dependent evolution of surface roughness and bulk structural parameters, indicating concurrent morphological and structural changes under electron irradiation. The proposed phenomenological description provides a framework for comparing these irradiation-induced responses in ZnS and ZnSe crystals.

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