Measurement of the ortho-positronium confinement energy in mesoporous thin films
Abstract
In this paper, we present measurements of the ortho-positronium emission energy in vacuum from mesoporous films using the time of flight technique. We show evidence of quantum mechanical confinement in the mesopores that defines the minimal energy of the emitted Ps. Two samples with different effective pore sizes, measured with positron annihilation lifetime spectroscopy, are compared for the data collected in the temperature range 50-400 K. The sample with smaller pore size exhibits a higher minimal energy (735 meV), compared to the sample with bigger pores (485 meV), due to the stronger confinement. The dependence of the emission energy with the temperature of the target is modeled as ortho-positronium being confined in rectangular boxes in thermodynamic equilibrium with the sample. We also measured that the yield of positronium emitted in vacuum is not affected by the temperature of the target.