The effect of permanent dipole moments of adsorbates upon I–V characteristics of a bilayer tunneling junction between self-assembled monolayers on an Au(1 1 1) substrate and a gold tip

It is important to understand an electronic property of an interface between an organic material and a metal electrode. In the present work, we measured current–voltage (I–V) curves of self-assembled monolayers (SAMs) on Au(1 1 1) using a conducting atomic force microscope (AFM) with chemically modified Au-coated AFM tips. This contact resulted in a bilayer junction between the Au(1 1 1) substrate covered with one SAM and the Au-coated tip with the other SAM. An alkanethiol (octanethiol) and benzenemethanethiols with various terminal groups (–H, –CH3, –Cl, –CF3) were used as the adsorbates. The shapes of the I–V curves depended on the terminal groups. This phenomenon was attributed to the change in the work function of gold due to different permanent dipole moments of the terminal groups.