Secondary Electron Emission Measurements of Ionic Liquids

We present measurements of the secondary electron emission (SEE) yields of ionic liquids for primary electron beam energies of 50 to 1000 eV. Ionic liquids are salts that consist of an organic cation and polyatomic anion and are liquid below 100°C and thermally stable up to 450°C. As a result of their low vapor pressure, ionic liquids can be combined with low-pressure plasmas to produce metal nanoparticles through the reduction of dissolved metal salts by the reactive species produced in the plasma. Nanoparticles have been created with DC discharges using a pair of electrodes with one immersed in an ionic liquid containing dissolved metal precursors.^1,2 In typical DC discharges, the plasma is sustained by SEE from the cathode and electron-impact ionization of the gas. For discharges operating with a liquid cathode, the processes leading to electron emission from the liquid are likely very different than from metal cathodes. In this work, we exploit the low vapor pressure of ionic liquids to make direct measurements of the SEE yield under vacuum by bombarding liquid samples of 1-butyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium acetate with electrons and measuring the resulting currents.

 

[1] K. Baba, T. Kaneko, and R. Hatakeyama, Appl. Phys. Express 2 (2009) 035006.

[2] Y. Hatakeyama, S. Takahashi, and K. Nishikawa, J. Phys. Chem. C 114 (2010) 11098-11102.