Studies of the temperature-dependent phase behavior of long chain n-alkyl thiol monolayers on gold

The influences of temperature on the infrared spectra of a docosylthiol (C₂₂) monolayer on a gold substrate are reported. The data suggest that this adsorbate exhibits a complex phase state at 300 K in which gauche conformations concentrated at the chain termina figure prominently. The detailed temperature dependence of the spectral band intensities is found to be very similar in many regards to that of bulk hydrocarbon crystals. At low temperature, band splittings are observed which suggest the lowest energy structure for this adsorbate is one containing two chains per unit cell. A simple lattice argument, consistent with steric models and low-energy electron diffraction data, is presented to explain these observations.