Size-dependent momentum smearing effect of positron annihilation radiation in embedded nano Cu clusters

Momentum density distributions determined by the analysis of positron annihilation radiation in embedded nano Cu clusters in iron were studied by using a first-principles method. A momentum smearing effect originated from the positron localization in the embedded clusters is observed. The smearing effect is found to scale linearly with the cube root of the cluster's volume, indicating that the momentum density techniques of positron annihilation can be employed to explore the atomic-scaled microscopic structures of a variety of impurity aggregations in materials.