Reflection high-energy positron diffraction: the past 15 years and the future

Reflection high-energy positron diffraction (RHEPD) is the positron counterpart of reflection high-energy electron diffraction (RHEED). Owing to the positive charge of the positron, RHEPD provides a powerful tool with which to determine the structure of the first surface layer. We have been investigating important surface systems concerning their unique electric and magnetic properties and also phase transition phenomena using positron beams (flux: 10³~10⁴ e⁺/sec) with ²²Na sources. Currently, we are developing a new RHEPD apparatus with a bright and intense positron beam (flux: 10⁵ e⁺/sec) based on the LINAC at the Slow Positron Facility, KEK. Here, we summarize the past results and the future prospects of the RHEPD study in the surface science.