| Budget Amount *help |
¥11,300,000 (Direct Cost: ¥11,300,000)
Fiscal Year 1987: ¥4,700,000 (Direct Cost: ¥4,700,000)
Fiscal Year 1986: ¥6,600,000 (Direct Cost: ¥6,600,000)
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| Research Abstract |
As surface analysis technique, LEED was frequently used at an early stage. At present, RHEED is efficiently used because og the difficulty in the theoretical treatment of LEED data. In the present ptoject, We aimed to develop a ultra-low energy positron diffraction apparatus, which seems to be easily treated by theoretical aspects and be more sensitive to surface strcutures than LEED. As compared with LEED, ULEPD is superior in the following points; low multiple scatteting, no exchange interaction, nearly zero inner potential and so on. In this project, we manufactured trially a ulta-low energy positron diffraction apparatus. At an initial stage, we calculated the trajectory of positrons for various conditions and designed electrostatic docussing lens system. This focussing lens system was composed of two-tube lenses with cylindtrical electrostatic rings, symmetric Einzel lenses and anti-symmetric Einzel lenses. For the extraction of positrons, we utilized the lens system developed by
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Soa. This Soa gun showed an excellent focussing property in a very wide range. Trajectory calculations were made by the method of transformation matrices which is widely used in the electron optics. We calculated trajectories from the first Soa gum to the entrance to CMA, from the exit fo CMA to the first remoderatoe crystal, from the secong Soa gun to the second remoderator crystal, the third Soa gun to the final zoom lens, and from the exist of zoom lens to teh specimen position, respectively. From this calculation, we determined the optimum values of applied voltages for 35 electrostatic rings. For this arrangement, the beam diameter of 1.7mm at lev, 0.5mm at 10eV and 0.17mm at 100V was obtained at the dispersed angle og 1.15 degree. as a preliminaly measurement of ultra-low positron diffraction, we measured the counting rate of gamma rays from annihilation of positrons in the Cu (100) surface by an assembly of BaF2 scintillator and a photomultiplier tube as a function of incident positron energy. The counting rate showed minima at energies correpsonding to Bragg conditions. This garanteed the efficient operation of this apparatus. Less
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