Temperature induced reconstruction of model organic surfaces

The influences of temperature on the structure of hexadecanethiol (C₁₆) and heptadecanethiol (C₁₇) monolayers adsorbed on gold substrates are reported. Infrared Spectroscopy and molecular dynamics simulations show that defects in these layers (i.e. gauche conformations) are concentrated at the chain termini and decrease with decreasing surface temperature. Adsorption band intensity oscillations as a function of chain length show that the chain terminating group is highly oriented. Band splittings observed at low temperature establish that there must be at least two chains per unit cell. The temperature dependence of the spectral band intensities of the polymethylene chains is very similar to that found in bulk hydrocarbon crystals.