X-Ray Damage to CF3CO2-Terminated Organic Monolayers on Si/Au Supports is due Primarily to X-Ray Induced Electrons

Abstract : X rays damage organic materials. The relative importance of X rays themselves, and of both X ray generated and secondary electrons, in this damage was explored using self-assembled monolayers (SAMs) on multilayer thin film supports. The substrates were prepared by depositing thin films of Si (0, 50, 100 and 200) on thick layers of Au (2000 Angstroms); these systems were supported on chromium-primed silicon wafers. Trifluoroacetyl-terminated SAMs were assembled on these substrates and the samples irradiated with monochromatic A1 Kalpha X-rays. The fluxes of X rays to which the different samples were exposed were the same, but the fluxes and energy distributions of the electrons generated by interactions of the X rays with the substrates differed. The loss of fluorine from the SAMs was followed by XPS and was slower on substrates emitting a lower flux of electrons. This observation indicated that the electrons, and not the X rays themselves, were largely responsible for the damage to the organic monolayer films that resulted in loss of fluorine from them.