We have developed an eXtremely-low-current Low Energy Electron Diffraction (XLEED) apparatus equipped with a micro-channel plate and a position-sensitive detector which reduces electron beam damage and charge-up effects and makes it possible to study the structure of physisorbed films. This XLEED system is combined with the ellipsometer system which monitors the thickness of a physisorbed film. We observed Xe overlayer on Ag (111) and grahpite (0001) surfaces. We found that a thick Xe films on Ag (111) showed a single crystal structure which keeps relative orientation to the substrate.
