KINETICS OF FORMATION OF LONG-CHAIN N-ALKANETHIOLATE MONOLAYERS ON POLYCRYSTALLINE GOLD

The effect of immersion time on the ordering properties of self-assemb led docosanethiolate (C-22) monolayers has been studied by reflection/ absorption infrared spectroscopy (RAIRS). Starting with a chemically c leaned polycrystalline gold surface, we have found that an immersion t ime of 45 s in micromolar thiol solutions is sufficient to produce ord ered ''monolayer'' films. These films have RAIR spectral features (pea k position, line width, and integrated intensity) similar to those obt ained with much longer immersion times. Decreasing the immersion time below 45 s gradually increases the disorder. The temperature dependenc e of the CH2 antisymmetric stretching (d(-)) peak position of thiol fi lms obtained with an immersion time of 120 s is identical to ones obta ined with very long immersion time (0.5 h to several days). In contras t, films obtained with a 5 s immersion time disorder at a lower temper ature. Apart from immersion time and temperature, a large solvent effe ct has been observed based on real-time RAIRS measurements of the cont inuing film ordering during aging in vacuum. Finally, a new assignment of the shoulder appearing around 2931 cm(-1) is proposed. We present arguments suggesting that the-generally accepted Fermi resonance assig nment of this shoulder should be modified to include a contribution fr om another vibrational mode.