Events in Physics
Paul Coleman, Bath
PROBING MATTER WITH ANTIMATTER: Positron Beam Studies of Semiconductors
Positrons are the most common form of antimatter in our world, and positron beams have featured in some important fundamental experiments, such as the recent production of antihydrogen at CERN. This talk will review what can be learned by the application of beams of positrons as probes of matter on the subatomic scale, and how this relates to modern technological problems. If a positron enters a solid it quickly slows down and annihilates its antiparticle, the electron. By detecting the gamma rays emitted following the annihilation (each having an energy close to mc2) we can learn about the density and momentum distribution of electrons in solids, and in turn gain information on the submicroscopic structure of the material being studied. This is the basis of variable-energy positron annihilation spectroscopy (VEPAS). VEPAS has found applications in structural and electronic analysis of thin films and near-surface layers, nanostructured materials, ion implantation, silicon photonics, and vacancy engineering. Examples will be presented of how useful insights into current problems in semiconductor physics and technology have been gained by combinations of VEPAS and other techniques.