A method to study the phase transition and desorption of self-assembled monolayers on planar gold surfaces

In-plane resistance of thin gold films (thickness similar to 1000 A) after the formation of self-assembled monolayers has been measured as a function of temperature. We attribute the observed increase in the slope of the resi stance vs temperature plot in the case of octadecanethiol and octanethiol m onolayers at characteristic temperatures to phase transitions. The structur al transition of 1,4-benzenedimethanethiol is also manifested similarly. Pr opanethiol does not show any phase transition, as expected. The observed ch anges in the alkanethiol monolayers are related to the decrease in the life time of the parallel vibrational motion of the adsorbate on the gold surfac e. The increase in slope is followed by a decrease which is attributed to t he commencement of desorption of monolayers from the gold surface.