Comparative study for electrical transport characteristics of self-assembled monolayers formed by benzenethiol, cyclohexanethiol, and adamantanethiol

We investigated the effect of molecular backbone structure on the electrical transport properties of self-assembled monolayer (SAM)-based molecular devices which were made with using three different molecules; benzenethiol (denoted as BT), cyclohexanethiol (CHT), and adamantanethiol (ADT). These molecules have similar ring-shaped backbone structures but different molecular orbital systems. The molecular devices were fabricated as a vertical metal-SAM-molecule structure by a conventional optical lithography-based microscale via-hole technique with employing PEDOT:PSS (poly(3,4-ethylenedioxythiophene)) stabilized with poly(4-styrenesulfonic acid) interlayer, which leads to a high device yield. We found that the current density of BT molecular devices was one order higher than that of CHT and ADT molecular devices due to the different molecular orbital systems. Also, we observed that the current densities of CHT and ADT devices were slightly different according to the statistical analysis because of the different structural uniformity of SAMs.