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Title: Ultrathin ionic liquid films on single crystal substrates
Author: Foulston, Richard James
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2013
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The adsorption and desorption of two room temperature ionic liquids (ILs), l-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide, [C2Cllm][Tf2N], and l-octyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide, [CsCllm] [Tf2N], on Au(IlO) were studied in the temperature range 100-674 K using ultraviolet photoelectron spectroscopy (UPS), work function measurements, low energy electron diffraction and scanning tunnelling microscopy (STM). The adsorption and desorption of [C2Cdm][T6N] on Cu(111) in the temperature range 173-721 K were also studied, using UPS, work function measurements and X -ray photoelectron spectroscopy (XPS). The ILs were both found to deposit intact, but their adsorption behaviours varied significantly for each IL-substrate combination studied. [C2Cdm][T6N] was found to form a complete first layer during room temperature adsorption on Au(11 0), after which it formed droplets which flattened out with time. The longer alkyl chains of [CsCllm][T6N] resulted in a far more complicated adsorption behaviour, although the formation of droplets was observed after deposition of several layers. [C2Cllm] [T6N] adsorbed quite differently on Cu( 111), where the completion of the first layer was followed by an unidentified growth mode which did not match that of droplet formation or layer-by-Iayer growth. STM images of the first layer of [C2Cllm][T6N] and [CsC1Im][T6N] on Au(IlO) at 100 K indicated the alignment of IL features parallel to the close packed rows of the substrate in the [llO] direction, with a separation matching the x2 spacing of the Au(1l0)-(1x2) clean surface reconstruction in the [001] direction. [C2Cllm][Tf2N] appeared in the STM images as round features, while [CsCllm][Tf2N] appeared in some images as rods exhibiting a double row structure, indicating that the octyl chains of the cation can lie flat on the surface. The desorption behaviours of all IL-substrate combinations were remarkably similar. The IL multilayers desorbed completely by 400 K, after which desorption of the final layer occurred as the IL was annealed to 600-700 K. The Au( 11 0) surface was found to form the Au(ll 0)-(1 x3) reconstruction, which was accompanied by a large decrease in work function, during desorption of the final monolayer for both ILs. A similar decrease in work function at a lower temperature was observed for [C2CtIm] [Tf2N] on CU(lll), but the cause of this work function change has not been identified. ii
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available