Surface composition of binary ionic crystals: Correlation between evaporation and electronic processes

The impact of annealing and evaporation of crystals on their surface composition

“…Thus the congruent evaporation of LN seems to be impossible. This is in contrast to the behaviour of binary A I I B V I compounds such as BaO, SrO, CdS, CdTe and CdSe [7]. There is a mechanism of self-regulation for these compounds which provides the congruence of their evaporation via adapting their surface composition (this being in the general case nonstoichiometric) to the temperature, electrical field, illumination and other external factors.…”

“…With respect to vacuum evaporation, the negative surface appears to be considerably more stable. To interpret this finding, one can draw on some regularities established for the evaporation of A I I B V I binary ionic compounds [7]. The A I I B V I results show that the evaporation rate of the electropositive component is enhanced by any factor which increases the concentration of free electrons at the surface.…”

“…Therefore V i − ϕ is positive and the neutral Li atoms should evaporate with a lower activation energy than that of ions and thus determine the kinetics of Li evaporation from LN. Applying to LN the results obtained for binary compounds [7], one can predict a faster evaporation of Li atoms for the LN surface enriched by free electrons, namely for the positive surface. This is just what is observed experimentally.…”

“…The problem becomes especially serious when one needs to obtain and exploit thin compound films with properties approaching those of the bulk crystal [4][5][6]. The interrelation between the surface composition and vacuum evaporation has been investigated in detail for polar binary compounds of A I I B V I type [7]. For ternary compounds, among which LN belongs, this issue is much more intricate and less well understood.…”