Positron annihilation in the near surface of room temperature ionic liquids

14th International Workshop on Slow Positron Beam Techniques & Applications

Hirade, T.^1,3 ; O'Rourke, B.E.^2 ; Kobayashi, Y.^2

Nuclear Science and Engineering Center, Japan Atomic Energy Agency, Tokai

319-1195, Japan^1

National Institute of Advanced Industrial Science and Technology, Ibaraki, Tsukuba

305-8568, Japan^2

Graduate School of Science and Engineering, Ibaraki University, 2-1-1, Bunkyo, Ibaraki, Mito

310-8512, Japan^3

关键词: Bis(trifluoromethane sulfonyl)imide;    Layered Structures;    Near surfaces;    Positron lifetime;    Ps formations;    Reaction model;    Room temperature ionic liquids;    Slow positron beam;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/791/1/012029/pdf
DOI  :  10.1088/1742-6596/791/1/012029

来源: IOP

【 摘 要 】

Positronium (Ps; a bound state of an electron and a positron) formation in insulating materials is explained by the spur reaction model. According to the model, electron and/or positron mobility affects the yield of Ps formation. A vertical slow positron beam was used to investigate the surface of a room temperature ionic liquid, N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI). Measurement of positron lifetimes indicated a higher Ps formation probability in near surface of TMPA-TFSI than in the bulk. This result suggests that the electron (and positron) mobility in the near surface may be larger than that in the bulk. Moreover, the longest annihilation lifetime of triplet Ps (ortho-Ps) in the near surface was found to be shorter than that measured in the bulk liquid. Ortho-Ps lifetimes in liquids are well correlated with the surface tension with a shorter lifetime corresponding to higher surface tension. The higher Ps formation yield and the shorter ortho-Ps annihilation lifetime were probably caused by the layered structure in near surface of TMPA-TFSI. A vertical slow positron beam is a strong tool to investigate the surface of room temperature ionic liquids.