Modification of semifluorinated alkanethiolate monolayers by low energy electron irradiation

The low energy electron induced damage in self-assembled monolayers (SAM) formed from semifluorinated alkanethiolates (SFAT) of CF3(CF2)9(CH2)nSH (F10HnSH) with different hydrocarbon chain length (n=2, 11 and 17) on polycrystalline gold has been monitored in-situ by X-ray photoelectron spectroscopy and angle resolved near edge X-ray absorption fine structure spectroscopy. All investigated SFAT SAMs exhibit qualitatively similar behavior with respect to low energy electron irradiation. Both the fluorocarbon and hydrocarbon parts and the S/Au interface are affected simultaneously. Progressive disordering of initially well-ordered, densely packed SAMs, desorption of film constituents, and chemical changes within the residual film are observed. Desorption of sulfur-containing fragments, which probably include the complete SFAT chains, was only found for F10H2S/Au. The desorbed carbon-containing fragments originate almost exclusively from the fluorocarbon part of the SFAT SAMs. Fluorine desorbs not only as a constituent of the carbon-containing fragments, but through irradiation-induced scission of C–F bonds. The accumulated chemical changes within the residual SFAT films include the complete disappearance of CF3 tail group, partial transformation of CF2 moieties into CF entities, appearance of C[double bond, length half m-dash]C double bonds in the fluorocarbon and hydrocarbon (predominantly) parts, and transformation of the thiolate head groups into new irradiation-induced sulfur species. Some general tendencies in the reaction of SAMs toward electron-irradiation are noticed in full agreement with previous findings for conventional AT SAMs