THIOETHYLPYRROLE MONOLAYERS ON GOLD - A SPECTROSCOPIC STUDY IN ULTRAHIGH-VACUUM

The adsorption of 3-(2-thioethyl)pyrrole (3-TEP) and 1-(2-thioethyl)py rrole (1-TEP) on gold has been studied in ultrahigh vacuum with infrar ed reflection absorption spectroscopy, X-ray photoelectron spectroscop y, and temperature-programmed desorption mass spectroscopy. Deposition s were made from liquid phase at atmospheric pressure, from gas phase in ultrahigh vacuum: and from gas phase at atmospheric pressure. Both molecules were found to chemisorb to the gold surface regardless of th e deposition method. Most of the 3-TEP, however, broke up, losing the pyrrole ring as it adsorbed on the surface. Both monolayers were sensi tive to oxygen and oxidized quickly if stored in air. Deposition of 1- TEP from solution or vapor in air gave a higher desorption peak temper ature than deposition from gas phase in UHV. The masses of the desorbi ng fragments that were detected from the heated monolayers were smalle r than those seen upon introducing 1-TEP gas into the UHV system, reve aling that a partial decomposition of the adsorbed molecules occurred prior to or at desorption. Some samples were electrochemically cycled to positive potentials to investigate the stability of the monolayers. A large fraction of the 1-TEP and 3-TEP stayed on the surface when cy cled to 0.8 V, but some oxidation, fragmentation, and desorption were seen at higher potentials.