Field-enhanced evaporation of cleaved (100) surfaces of alkali halides

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Abstract
The application of an electric field parallel to cleaved (100) faces of NaCl and KCl was found to increase the evaporation rates from these surfaces in vacuum. With a field gradient of 0·17 MVm−1 applied along the [100] direction after an initial field-free evaporation, the rate of evaporation of NaCl increased by 30–38% at 809 K. Significantly higher evaporation enhancement was observed if the field was applied at the start of the isothermal evaporation. Qualitatively similar results were observed in the case of KCl. However, the application of a field on Ca-doped KCl resulted in a much higher increase in the evaporation rate. For both materials enhancement is only measurable above a threshold value. These results are interpreted in terms of field influence on the disconnection of ions from ledges in a manner consistent with the Terrace-Ledge-Kink (TLK) model of evaporation.