Positron Annihilation Study of Irradiated HOPG-type Graphite

概要

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Positron annihilation angular correlation measurements (ACAR : angular correlation of annihilation radiation) were made for HOPG (highly oriented pyrolytic graphite) and PGCCL (HOPG-type graphite, Le Carbone-Lorraine) irradiated by various particles, such as electrons, neutrons and deuterium particles. The ACAR measurements made under the condition of P_Z//c-axis for unirradiated specimens showed a clear minimum at θ=0°, but P_Z⊥c-axis measurement did not show this minimum. This minimum is considered to be due to the annihilation of positrons with π electrons the momentum distribution of which is extended to the direction parallel to c-axis. On the other hand, by neutron irradiation this minimum disappeared, which suggests that positrons are trapped at radiation-induced defects, probably vacancy sites, and the probability of the annihilation with π electrons was decreased to the large extent. But, in the case of hydrogen irradiation the minimum was not affected so much, which suggests hydrogen atoms do not disturb the π electrons, probably because hydrogen atoms are trapped at boundary regions, such as those between adjacent crystallites or region of stacking disorder.positron annihilationangular correlationHOPGneutron irradiationelectron irradiationhydrogen irradiation
東北大学の論文
1997-03-28