Surface Topography Dependent Desorption of Alkali Halides

Abstract

Electron-stimulated desorption of the (100)KBr surface has been investigated in vacuum with noncontact atomic force microscopy and mass spectroscopy. It has been found that both desorption components (K and Br) show oscillatory dependence on the electron dose with the oscillation amplitude decaying gradually. These results correspond with periodically varying, as a result of a layer-by-layer desorption, surface topography. It is proposed that the surface terrace edges act as traps for excited F centers diffusing in the crystal. The oscillating density of terrace edges varies surface recombination/reflection rates for the F centers and modulates the balance between surface and bulk deexcitation of the crystal.

Dynamics of the defect-mediated desorption of alkali halide surfaces

“…After a few periods of oscillations, the process does not follow the layer-by-layer mode anymore, and the oscillations are damped. The connection between the desorption yield changes and the surface topography has been confirmed previously by the AFM measurements [11,12].…”

“…Consequently, when the desorption signal passes through its maximum, the concentration of excited, mobile F-centers in the vicinity of the surface is high. At the minimum of the desorption signal majority of beam generated F-centers is reflected from the relatively undefected surface [11] accumulating in the bulk as immobile, ground state defects. Consequently, the recombination of H-centers with the accumulated ground state F-centers is nonradiative.…”

“…The study of time dependence of the yield of emitted particles, and the atomic force microscopy (AFM) measurements have demonstrated that electron-stimulated de-sorption from alkali halide surfaces proceeds in a layer-bylayer mode by growth and linking of pits (of monoatomic depth) on the (100) crystal surface [11,12]. It was also demonstrated, that the flux of emitted atoms is anticorrelated with the concentration of F-centers at the surface, or in the subsurface region.…”

“…Using the AFM technique, it was for the first time possible to study not only what already left the surface but to examine the atomic structure of the crystal right after the desorption process without exposing it to the reactive ambient environment [11,17]. This atomistic approach to processes leading to surface modification allowed for establishing a consistent theoretical model describing both the particle emission from bombarded alkali halides, and the surface topography changes due to beam-induced electronic excitation/ionisation [9,18].…”

Detection System for KeV Proton Beam Scattered from an ESD-surface with Monolayer Pits of Alkali Halide Crystal

“…At the end of the 1990s, Szymonski et al observed damping oscillations of the yields of thermally desorbed alkali and halogen atoms (thermal component), which provided evidence of layerby-layer desorption of the ESD surface 8,9) . Both Hoche et al and Szymonski et al respectively showed that rectangular pits grow on the surfaces by using methods of decoration carbon replica and atomic force microscope measurements [7][8][9] . These recent measurements reveal the following scenario [8][9][10] :…”