Matrix effects on secondary ion emission from a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis[trifluoromethanesulfonyl]imide.
The ionization mechanism of room-temperature ionic liquids has been investigated using time-of-flight secondary ion mass spectrometry in the temperature range of 15-300 K. Analyses of 1-ethyl-3-methylimidazolium bis[trifluoromethanesulfonyl]imide ([emim][Tf(2)N]) deposited on a Ni(111) substrate revealed that the [emim](+) and [Tf(2)N](-) yields increase together with the Ni(+) yield at monolayer coverage; no such increase was observed for the films deposited on a D(2)O spacer layer. Results indicated that the [emim][Tf(2)N] molecule is not perfectly ionized; the Ni(111) surface accepts (for [emim](+)) or donates (for [Tf(2)N](-)) an electron with higher efficiency than the counterion because of the metal band effect. This phenomenon might be induced by electrostatic interactions between the separated cation and anion during sputtering. It is also suggested that the sputtered Ni atom can be ionized nonadiabatically by the formation of a quasimolecule with adspecies. The multilayer of [emim][Tf(2)N] deposited at 15 K has a porous structure, resembling that of polar molecules, because of nonionic intermolecular interactions. The phase transition is identifiable, together with the morphological change in the crystalline film, from temperature evolutions of the secondary ion yields.
Souda
Ryutaro
R
International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan. souda.ryutaro@nims.go.jp
D003460:Crystallization; D004583:Electrons; D007093:Imidazoles / Q000737:chemistry*; D052578:Ionic Liquids / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D009532:Nickel / Q000737:chemistry*; D044367:Phase Transition; D018629:Spectrometry, Mass, Secondary Ion; D013449:Sulfonamides / Q000737:chemistry*; D013696:Temperature
C517865:1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide; D007093:Imidazoles; D052578:Ionic Liquids; D007477:Ions; D013449:Sulfonamides; D009532:Nickel; C518739:1-ethyl-3-methylimidazolium