Surface characterization of imidazolium ionic liquids by high-resolution Rutherford backscattering spectroscopy and X-ray photoelectron spectroscopy
Surface characterization of imidazolium ionic liquids by high-resolution Rutherford backscattering spectroscopy and X-ray photoelectron spectroscopy
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DOI：
10.1016/j.susc.2009.12.023
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发表时间：
2010-02-15
期刊：
影响因子：
1.9
通讯作者：
Kimura, Kenji
中科院分区：
文献类型：
--
作者：
Hashimoto, Hiroki;Ohno, Atsushi;Kimura, Kenji
采用高分辨率卢瑟福后向散射光谱研究了1-丁基-3-甲基咪唑六氟磷酸盐（[BMIM] [PF6]）和1-丁基-3-甲基咪唑双氰酰胺（[BMIM] [DCA]）的表面组成。虽然[BMIM] [PF6]在最上层的分子层上几乎是化学计量的，但在接近1.5 nm厚度的表面层上观察到[BMIM] [DCA]与理论化学计量有相当大的偏差。氮在这一层几乎完全耗尽，而碳则增加了。此外，在该表面层中还存在类似于3 x 10（14）个原子/cm(2)的氧杂质。借助x射线光电子能谱测量得出结论，[BMIM]] [DCA]的表面覆盖着类似于1.7 x 10（14）分子/cm(2)的酯和/或羧酸。这些污染物分子有一个优先取向，即羰基在[BMIM] [DCA]表面，烷基链指向真空。污染层的起源可能是大块杂质的表面偏析。(C) 2009 Elsevier B.V.版权所有
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 similar to 1.5 nm thickness. Nitrogen is almost completely depleted in this layer while carbon is enhanced. In addition, there are oxygen impurities of similar to 3 x 10(14) atoms/cm(2) 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 similar to 1.7 x 10(14) molecules/cm(2) 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. (C) 2009 Elsevier B.V. All rights reserved.