Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5424152 | Surface Science | 2010 | 6 Pages |
Abstract
The surface composition of 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM] [PF6]) and 1-butyl-3-methylimidazolium dicyanamide ([BMIM] [DCA]) are studied by high-resolution Rutherford backscattering spectroscopy. Although [BMIM] [PF6] is almost stoichiometric up to the topmost molecular layer, considerable deviation from the theoretical stoichiometry is observed for [BMIM] [DCA] in a surface layer of â¼1.5Â nm thickness. Nitrogen is almost completely depleted in this layer while carbon is enhanced. In addition, there are oxygen impurities of â¼3Â ÃÂ 1014Â atoms/cm2 in this surface layer. With the help of X-ray photoelectron spectroscopy measurements it is concluded that the surface of [BMIM] [DCA] is covered by â¼1.7Â ÃÂ 1014Â molecules/cm2 of esters and/or carboxylic acids. These contaminant molecules have a preferred orientation, i.e. the carbonyl groups are on the surface of [BMIM] [DCA] and the alkyl chains are pointing towards vacuum. The origin of the contamination layer could be the surface segregation of bulk impurities.
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Authors
Hiroki Hashimoto, Atsushi Ohno, Kaoru Nakajima, Motofumi Suzuki, Hiroshi Tsuji, Kenji Kimura,