Positrons are very sensitive probes for vacancy-type defects of atomic dimensions, e.g. vacancies, vacancy agglomerates, dislocations or inner surfaces. It is well established that positrons can be trapped at these defects and, because of the locally reduced electron density, the lifetime of the positron localized at the defect increases. This lifetime has characteristic values for each defect type and therefore it is possible to separate out various atomic defect configurations and their relative abundance with very high sensitivity (approx. 1 ppm) and in a nondestructive way. With a pulsed positron beam (approx. 3 mm diameter) of variable energy, lifetime studies can be performed as a function of the positron energy and hence the penetrations depth. Results on silicon and silicon carbide subjected to different treatments will be discussed. For many applications in materials science a positron beam in the micrometer range is desirable. This leads to a scanning positron microscope consisting of a pulsed positron beam of micrometer dimension with a scanning facility. The design and the performance of this first system of its kind will be presented.    «

Positrons are very sensitive probes for vacancy-type defects of atomic dimensions, e.g. vacancies, vacancy agglomerates, dislocations or inner surfaces. It is well established that positrons can be trapped at these defects and, because of the locally reduced electron density, the lifetime of the positron localized at the defect increases. This lifetime has characteristic values for each defect type and therefore it is possible to separate out various atomic defect configurations and their relati...    »