Do alkanethiols adsorb onto the surfaces of TI-Ba-Ca-Cu-O-based high-temperature superconductors? The critical role of H₂O content on the adsorption process

The reactivity of Tl_1.4Ba₂CaCu₂O_7.0, a high-temperature superconductor (HTSC), toward a redox-active adsorbate molecule with thiol functionality has been investigated as a function of solvent type and H₂O content. Previously it had been reported that alkanethiols do not stably chemisorb onto the surface of Tl₂Ba₂CaCu₂O₈/Tl₂Ba ₂Ca₂Cu₃O₁₀ phases, bringing into question the generality of alkanethiol adsorption onto cuprate-based HTSCs. Herein, we show that under rigorously dry conditions, 11-mercaptounde-canoylferrocene (1) adsorbs cleanly onto the surface of Tl_1.4Ba₂CaCu₂O_7.0 to form moderately stable, redox-active monolayer films. The redox activity of 1 was used to estimate adsorbate surface coverage, and it is shown that the addition of H₂O to the modifying solutions of 1 adversely affects the monolayer adsorption process. No redox activity associated with 1 could be detected for electrodes soaked in 0.1 M solutions of 1 with 5% H₂O in ethanol, which was attributed to the formation of a BaCO₃ corrosion layer that prohibited the adsorption of 1 onto the HTSC surface. The importance of sample stoichiometry on the adsorption process also is discussed.