Simulation of Intensity Oscillation of Planar Surface-channeling Protons Scattered on KBr Surface Irradiated by Electrons

Abstract

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.

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

“…The convenience our system provides is the use of a ‰uorescent screen to observe the scattering patterns and a commercial digital camera to obtain yield measurements. In this experiment using keV proton beam, the beam current is very stable as compared with that of sub-MeV proton beam from an accelerator 12,13) . This can be attributed to small beam losses during transport in this system.…”

“…The intensity distributions of the scattered patterns were obtained from B values of the RGB color values of the images. It required 13 min to take each distribution set for the irradiation ‰uence 12,13) . Since the numbers of the incident particle to MCP were large compared with the counting rates of MCP that are generally used as particle detection measurements, the bias voltage to the MCP was suppressed.…”

“…At the entrance of the UHV chamber, the electron beam was collimated by a 1.5×10 mm 2 slit and horizontally scanned by a 260-Hz magneticˆeld. The electron beam was also scanned vertically by another 22-Hz magnetiĉ eld to produce uniform irradiation (modulated line scan) 12,13) . The electron beam in front of the sample was spread over 30×30 mm 2 by the scanning magneticˆelds.…”

“…The damping oscillations have also been shown for typical situations but not shown as a systematic compilation. We recently measured re‰ected protons at electronbombarded KBr(001) surfaces with grazing incidence and have observed specular oscillations by the layer-bylayer desorption 12,13) . In previous works we used 550 keV protons from an accelerator.…”

Growth of Au Particles Evaporated on KBr and KCl Substrates Wearing Increased Densities of Surface Steps

“…The acceleration energies for electrons were 5 keV for an irradiation of 3×10 16 cm -2 and 2.5 keV for others. The desorbed surface-atom yield for a 5 keV electrons irradiation is expected to be twice that of a 2.5 keV irradiation 17) . Thus the morphology of the surface may depend on the electron energy and it is possible that the surfaces irradiated by 5 keV electrons are strongly damaged compared with those irradiated by 2.5 keV electrons.…”