Behavior of adsorbed hydrogen on Ni(1 1 1) surface with reemitted slow-positron spectroscopy

We have measured reemitted slow-positrons from hydrogen-adsorbed Ni(1 1 1) surface on different adsorbing conditions. It is seem that the reemitted slow-positron yield is maximum in the (2 × 2)-2H superstructure on Ni(1 1 1) surface. The origin of the change in reemitted slow-positron due to different adsorbing conditions will be discussed.