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.

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e 1 600346@eng. oi t .ac .j p It is known that even if insulators are covered with conductive layer, an electric charging-up takes place within the insulator below the surface. Such sub-surface charging phenomenon should be clearly understood for a quantitative discussion on electron beam (EB) analyses with backscattered, secondary, Auger electrons and the characteristic X-rays. Several simulations which represent charging process of materials under EB irradiation have been reported.[ 1-41 The most important mechanism of such simulation is the electron beam induced conduction (EBIC) for the quantitative discussion, In the present study the EBIC is calculated based on the energy deposited, which has introduced by Tanaka et al, [ 13 and it is expressed by where A = 0.89 and k = 7 . 7~ 10 The parameter D ( z ) is the energy deposited by the primary EB, and it is obtained by a Monte Carlo simulation of electron trajectories in a sample.Under the assumption of the EBIC, the continuity equation of the charge accumulation during EB irradiation is formulated as follows;-18 A s / ( Q -c m . rad*) for a red-PMMA.The Poisson equation and the Ohm's law taken into account in a sample are expressed as: and respectively, where N is the number of electrons accumulated, G(z) is the number of electrons deposited by EB, J is the current density, V is the potential, E is the dielectric constant of the material, q is the electron charge, 0 is the conductivity and E is the electric field. The spatial distribution of G(z) is also obtained by the Monte Carlo simulation. Here, EB exposure area is assumed to be large, and only depth distributions of electric charge, the potential, the field and so on are obtained. Here, a sample is assumed to be PMMA. 116