The velocity of dislocation-related evaporation steps on (100) surfaces of NaCl

Abstract

The velocity of steps in dislocation-related evaporation lamellae on (100) surfaces of NaCl was investigated using the double-decoration technique. Velocities showed a dependence on step separation which was consistent with the Burton, Cabrera and Frank (1951) (BCF) theory. Steady-state velocities of monatomic steps (a₀/2 high) were the same for edge- and screw-dislocation-generated lamellae. The activation energy for evaporation calculated from the temperature dependence of the velocity at infinite separation, 228·1 kj mol⁻¹, is in good agreement with values calculated from thermogravimetric studies. Externally imposed electric fields with gradients of up to 0·1 MV m ⁻¹ had no effect on the velocities or their dependence on step separation. These observations are discussed in terms of a previously reported threshold effect in field-enhanced evaporation