Hopping transport through self-assembled molecules: transport mechanism for conduction-based chemical sensors

We have fabricated a testbed for hopping transport through a self-assembled monolayer (SAM), using a back-to-back Schottky barrier structure on semi-insulating GaAs, and various molecules were self-assembled on the testbed. The leakage current of the testbed is less than 1 nA. However, it was found that some of deposited molecules induce significant increase in conductivity, compared to predeposition current. There exist two possible conduction paths that might cause this phenomenon: 1) hopping conduction through SAM 2) surface potential change due to SAM. To verify that the hopping transport is a dominant conduction mechanism, I-V characteristics of thiophenol and octadecanethiol have been compared to investigate the effects of molecular dipole moment and π-electrons on conductivity enhancement. In addition, the application of the testbed to a chemical sensor has been demonstrated by depositing redox molecules on the testbed.