Surface Characterization of the Plasmaionic Liquid Interface Using X-Ray Photoelectron Spectroscopy

Room temperature ionic liquids (IL) are salts that are liquid below 100°C and are typically chemically stable and nonvolatile, making them useful solvents for a variety of applications.
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As a result of their low vapor pressure, ILs have been used with low-pressure plasmas to produce metal nanoparticles through the reduction of dissolved metal salts.
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In this work, we use X-ray photoelectron spectroscopy (XPS) to characterize the plasma-IL interface before and after plasma exposure. XPS is a surface-sensitive technique that uses soft X-rays to liberate core electrons from a sample material. These core electrons are then energy-analyzed to determine chemical composition. The IL used here is 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]) and is exposed to a low-pressure (100–500 mTorr) DC discharge with one stainless steel electrode and a second electrode immersed in the IL. XPS spectra will be presented for [BMIm][BF4] before and after plasma exposure. The results are important for understanding the processes occurring at the IL surface that ultimately enable nanoparticle production in ILs with dissolved metal salts.