Probing electronic properties of conjugated and saturated molecules in self-assembled monolayers

We have measured the electron transport properties of single and bundled molecules imbedded in crystalline monolayers of alkanethiols self-assembled on Au{111} surfaces. These measurements have been performed using scanning tunneling microscopy and microwave difference frequency alternating current scanning tunneling microscopy on molecules with saturated and fully conjugated chains. We have learned to separate the contributions of the molecules and of the tunneling junction. We have also found a means to determine the value of the contact conductance due to the choice of chemical connection to the substrate.