Muonium emission into vacuum from mesoporous thin films at cryogenic temperatures

TL;DR

This study demonstrates efficient Muonium emission from mesoporous SiO2 films into vacuum at cryogenic temperatures, with detailed analysis of diffusion mechanisms and potential barriers, advancing Mu spectroscopy applications.

Contribution

It provides the first quantitative analysis of Muonium diffusion and vacuum emission from mesoporous films at cryogenic temperatures, including diffusion constants and tunneling models.

Findings

Muonium vacuum yield of 38% at 250 K and 20% at 100 K.

Diffusion constants D250KMu = 1.6×10^-4 cm^2/s, D100KMu = 4.2×10^-5 cm^2/s.

Diffusion described by quantum tunneling with a potential barrier of -0.3 eV.

Abstract

We report on Muonium (Mu) emission into vacuum following {\mu}+ implantation in mesoporous thin SiO2 films. We obtain a yield of Mu into vacuum of (38\pm4)% at 250 K temperature and (20\pm4)% at 100 K for 5 keV {\mu}+ implantation energy. From the implantation energy dependence of the Mu vacuum yield we determine the Mu diffusion constants in these films: D250KMu = (1.6 \pm 0.1) \times 10-4 cm2/s and D100KMu = (4.2\pm0.5)\times10-5 cm2/s. Describing the diffusion process as quantum mechanical tunneling from pore-to-pore, we reproduce the measured temperature dependence T^3/2 of the diffusion constant. We extract a potential barrier of (-0.3 \pm 0.1) eV which is consistent with our computed Mu work-function in SiO2 of [-0.3,-0.9] eV. The high Mu vacuum yield even at low temperatures represents an important step towards next generation Mu spectroscopy experiments.