In the present Contribution, an overview of the technique of positron annihilation spectroscopy utilizing variable energy positron beams will be given. This technique is often called as the slow-positron implantation spectroscopy (SPIS).
A possible impact of SPIS for research on ultra fine-grained and nanocrystalline materials will be illustrated by an example of results obtained within the Prague - Dresden collaboration. An information on a slow-positron beam, being under construction at Charles University, Prague, Faculty of Mathematics and Physics, will be given.