Interaction of molecular beams of RbCl with (100) surfaces of NaCl

Abstract

The interaction of molecular beams of RbCl with (100) surfaces of NaCl is studied for crystal temperatures between 561 and 669 K and for molecular beam fluxes between 5 × 10 9 and 3.9 × 10 13 [cm −2 s −1] by measurements of transient desorption fluxes, by SIMS and by electron microscopy. A very fast ion exchange Rb + ⇋ Na + between admolecules and the crystal surface is observed. The results for undersaturation are interpreted by a model which considers this ion exchange and a maximum capacity of the surface for Rb + ions which results in 2.3 × 10 13 cm −2. Additional adsorption of RbCl at the steps is discussed. The resulting desorption times obey Arrhenius equations. At supersaturation for a saturation ratio of S = 3.5 at 595 K layer growth is found up to a deposition of ≈ 10 ML, then ramp-like crystallites with orientations parallel to the [100] directions are formed. For S = 10 the resulting surface topographies are interpreted by the Stranski-Krastanov mode. The formation of RbClNaCl solid solutions in very thin surface layers is discussed.