title: Characterization of self-assembled monolayers from lithium dialkyldithiocarbamate salts.
abstract: 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.
authors.affiliation: Department of Chemical Engineering, Villanova University, Villanova, PA 19085, USA. randy.weinstein@villanova.edu
authors.forename: Randy D
authors.initials: RD
authors.lastname: Weinstein
authors.forename: Joshua
authors.initials: J
authors.lastname: Richards
authors.forename: Susan D
authors.initials: SD
authors.lastname: Thai
authors.forename: Donna M
authors.initials: DM
authors.lastname: Omiatek
authors.forename: Carol A
authors.initials: CA
authors.lastname: Bessel
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Faulkner
authors.forename: Siti
authors.initials: S
authors.lastname: Othman
authors.forename: G Kane
authors.initials: GK
authors.lastname: Jennings
mesh_terms: D000327:Adsorption; D002219:Carbamates / Q000737:chemistry*; D002627:Chemistry, Physical / Q000379:methods*; D017097:Electric Impedance; D004563:Electrochemistry; D000431:Ethanol / Q000737:chemistry; D006838:Hydrocarbons / Q000737:chemistry; D008094:Lithium / Q000737:chemistry*; D008752:Methylene Chloride / Q000737:chemistry; D008956:Models, Chemical; D010084:Oxidation-Reduction; D012492:Salts / Q000737:chemistry*; D013053:Spectrophotometry; D013055:Spectrophotometry, Infrared / Q000379:methods; D013859:Thiocarbamates / Q000737:chemistry*
chemical_list: D002219:Carbamates; D006838:Hydrocarbons; D012492:Salts; D013859:Thiocarbamates; D000431:Ethanol; D008752:Methylene Chloride; D008094:Lithium