Positron Annihilation Studies of Materials

This chapter gives a concise overview of the probe techniques of positron annihilation and their use for studying the electronic structure and open volume defects in a wide range of materials. The first part introduces the behavior of positrons in solids, in particular the trapping and annihilation of positrons at defect sites. In this context, the focus is on the interrelations between the annihilation characteristics observed and the type, concentration, and electronic structure of defects. The three basic techniques of positron lifetime spectroscopy as well as Doppler broadening and angular correlation of the positron-electron annihilation radiation are discussed in detail together with practical aspects such as positron sources, sample preparation, and instrumentation. Special attention is given to novel developments such as coincident Doppler broadening measurements with chemical sensitivity, and advances in positron beam techniques. Studies of near-surface defects and depth profiling with monoenergetic beams of low-energy positrons are described. The versatility of positron annihilation techniques is demonstrated by selected examples of vacancy studies in ordered intermetallic alloys and semiconductors and free volumes in highly disordered materials. Keywords: vacancies; crystal defects; open-volume defects; electron momentum; doppler broadening; positron lifetime spectroscopy; angular correlation of annihilation radiation (ACAR); positron beam techniques