Trajectories of fast (0.55 MeV) protons impinging under planar surface channeling conditions with an angle of incidence of several mrad are calculated on KBr(001) surfaces decorated by electron stimulated desorption (ESD). Two-dimensional angular distributions of protons scattered on the surface are obtained. In order to calculate trajectories, a computational technique is needed to form a set of morphologies of the surfaces according to the electron ‰uence. In our method, an assumption is made that the topmost atoms on the low coordinate sites are easily emitted by the ESD processes 5) . By choosing parameters introduced in the method, the oscillatory behavior of the desorption yields demonstrated by other groups is reproduced 2) . The resulting peak intensity of the re‰ected protons from the trajectory on the ensemble of surfaces with varying electron ‰uence oscillates as the electron ‰uence increases. Corresponding angular distributions of re‰ected protons have been measured on the electron irradiated KBr(001) surfaces, and a similar oscillation can be seen on the scattered yields with weak amplitudes.

Surfaces of KCl crystals irradiated uniformly by scanning of 5 keV beam of electrons collimated with one direction are observed by an atomic force microscope (AFM). The irradiation doses are in the range up to 10 16 cm-2. The surfaces remain many overlapped terraces of sub-micron with random orientations. They are hard to be associated with the square pits observed in well known layer by layer desorption measurements in the dose range of 10 14 cm-2. The desorption process is simulated by a model based on the assumption that the low-coordinated sites act as the precursors for desorption. We have introduced parameters into this model to reproduce the oscillating structure of the particle-yields of the layer by layer desorption. The resultingˆnal morphology in the dose range of 10 16 cm-2 shows that many overlapped terraces are created with random orientations, whose terrace-lengths are small compared with that observed. The morphologies show that the process assumed to reproduce the layer by layer desorption can lead the multi-layer steps on the surface.

To observe specular oscillations in ion-surface scattering originating from layer-by-layer desorption of an electron stimulated desorbed (ESD) surface, a 15 keV proton beam was impinged on the surface with an angle of incidence less than 1°. We prepared an experimental system to examine the scattering yields of re‰ecting protons by conveniently employing a ‰uorescent screen to view scattering yields (scattering patterns) and a commercial digital camera for yield measurements. Because the present energy of the proton beam was too low to illuminate the screen, a micro-channel plate was inserted in front of the screen. Measurements with electron irradiation show obvious damping specular oscillations; the widths of angular distributions of scattered protons simultaneously oscillated with increasing electron ‰uence. From the measured periods of the oscillations, the ESD rates of thermal desorption from KBr(001) at 1.5 keV electrons irradiation were obtained for sample temperatures.

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