Evidence for pore surface dependent positronium thermalization in mesoporous silica/hybrid silica films

In this paper, we report the thermalization process of positronium (Ps) in various mesoporous silica/hybrid silica films with pore surfaces decorated by different groups, such as -OH, -H, and -CH₃, studied by Ps time-of-flight measurement. Thermalization of Ps in pores with -OH and -H was found to be more efficient than in pores decorated with -CH₃. This can be understood from the point of view that Ps thermalization rates upon collisions with these groups are different due to their different effective masses. Therefore, our observation shows that Ps slowing down in mesoporous silica/hybrid silica films is strongly dependent on the pore surface chemistry.