Article ID Journal Published Year Pages File Type
5424152 Surface Science 2010 6 Pages PDF
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 ∼1.5 nm thickness. Nitrogen is almost completely depleted in this layer while carbon is enhanced. In addition, there are oxygen impurities of ∼3 × 1014 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 ∼1.7 × 1014 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.
Related Topics
Physical Sciences and Engineering Chemistry Physical and Theoretical Chemistry
Authors
, , , , , ,