Modification of semifluorinated alkanethiolate monolayers by low energy electron irradiation

The low energy electron induced damage in self-assembled monolayers (SAM) f ormed from semifluorinated alkanethiolates (SFAT) of CF3(CF2)(9)(CH2)(n)SH (F10HnSH) with different hydrocarbon chain length (n=2, 11 and 17) on polyc rystalline gold has been monitored in-situ by X-ray photoelectron spectrosc opy and angle resolved near edge X-ray absorption fine structure spectrosco py. All investigated SFAT SAMs exhibit qualitatively similar behavior with respect to low energy electron irradiation. Both the fluorocarbon and hydro carbon parts and the S/Au interface are affected simultaneously. Progressiv e disordering of initially well-ordered, densely packed SAMs, desorption of film constituents, and chemical changes within the residual film are obser ved. Desorption of sulfur-containing fragments, which probably include the complete SFAT chains, was only found for F10H2S/Au. The desorbed carbon-con taining fragments originate almost exclusively from the fluorocarbon part o f the SFAT SAMs. Fluorine desorbs not only as a constituent of the carbon-c ontaining fragments, but through irradiation-induced scission of C-F bonds. The accumulated chemical changes within the residual SFAT films include th e complete disappearance of CF3 tail group, partial transformation of CF2 m oieties into CF entities, appearance of C=C double bonds in the fluorocarbo n and hydrocarbon (predominantly) parts, and transformation of the thiolate head groups into new irradiation-induced sulfur species. Some general tend encies in the reaction of SAMs toward electron-irradiation are noticed in f ull agreement with previous findings for conventional AT SAMs.