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Weinstein RD, Richards J, Thai SD, Omiatek DM, Bessel CA, Faulkner CJ, Othman S, Jennings GK: Characterization of self-assembled monolayers from lithium dialkyldithiocarbamate salts. Langmuir. 2007 Feb 27;23(5):2887-91. Epub 2007 Jan 30.
We report the formation of self-assembled monolayers (SAMs) onto gold substrates by exposure to lithium dialkyldithiocarbamate salts [(Li+(R2DTC-), where R = n-propyl, n-butyl, n-octyl, n-decyl, n-dodecyl, or n-octadecyl] in ethanol or methylene chloride. The crystallinity and composition of the monolayers were assessed by polarized modulation infrared reflection absorption spectroscopy (PM-IRRAS), wettability was characterized by contact angles of water and hexadecane, thickness was measured by spectroscopic ellipsometry, and barrier properties determined by electrochemical impedance spectroscopy. While the shorter R2DTC-s formed monolayers with liquid-like packing, monolayers prepared from the longest R2DTC- (where R = n-octadecyl) exhibit similar thickness, crystallinity, wettability, and capacitance as monolayers prepared from n-octadecanethiol. The hydrocarbon chains within the monolayers prepared from (C18) 2DTC- are less canted on average than those prepared from n-octadecanethiol. Nonetheless, the (C18) 2DTC- SAM exhibits an order of magnitude lower resistance against the penetration of redox probes, which is attributed to a higher density of pinhole defect sites. |
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