A new method for size estimation of Cu (sub)nano-precipitates in Fe based on a positron quantum-dot-state is developed. Utilizing a unique characteristic of the positron quantum-dot confinement in positron affinitive embedded nano-precipitates, the smearing of the momentum distribution of positron-electron pair around the Fermi momentum in the Cu nano-precipitates is observed by two-dimensional angular correlation of positron annihilation radiation (2D-ACAR) measurements. Due to the uncertainly relation between position and momentum, the size of the Cu nano-precipitates is estimated from the width of the momentum smearing which is inversely proportional to the average size of the precipitates where positrons are confined. Fe–Cu alloys were aged at 475°C for 0.1 to 20 h to form the Cu nano-precipitates with various sizes. The sizes estimated from 2D-ACAR are compared with those by three-dimensional atom probe (3D-AP). Both the results agree with each other. Furthermore, the present method gives the sizes of the Cu subnano-precipitates which are too small to be detected even by the other technique, such as 3D-AP.
